Anatomy Atlas

Key Landmarks

• Galea aponeurotica. Dense fibrous layer connecting frontalis to occipitalis
• Superficial temporal artery. Palpable anterior to tragus, courses superiorly within the superficial temporal fascia
• Supratrochlear and supraorbital arteries. Supply anterior scalp, emerge at supraorbital rim
• Occipital artery. Supplies posterior scalp, courses along superior nuchal line

Danger Zones

Tumor Predilection

• BCC (Common): Scalp BCC is common especially in bald or chronically sun-exposed individuals. Often presents at advanced size due to late detection under hair-bearing skin.
• SCC (Very common): Leading site for SCC in chronically sun-exposed bald men. Higher risk for perineural invasion and regional metastasis compared to facial SCC. Actinic field damage is typical.
• Melanoma (Moderate): Scalp melanoma carries worse prognosis than other head/neck sites. Often diagnosed at greater Breslow depth due to delayed detection.

Mohs Considerations

• Tumors may extend along galea or periosteum; histologic processing must include deep en-face sections to assess these planes
• Large defects may expose calvarium. Assess periosteal integrity before choosing reconstruction
• Undermining in the subgaleal plane (above pericranium) allows wide mobilization but risks hematoma formation
• Galeal scoring can provide 1-2 cm additional advancement per parallel score incision; ensure hemostasis

Reconstruction Principles

• Primary closure with wide undermining in subgaleal plane for defects up to 3 cm; galeal scoring extends range
• Rotation flaps (O-to-Z, Orticochea) for defects 3-6 cm; design flap 4-6x defect diameter for adequate rotation
• Full-thickness skin grafts for defects with intact pericranium; bolster dressing essential for 5-7 days
• Exposed calvarium without periosteum requires outer table burring to granulation, tissue expansion, or free flap

Key Landmarks

• Frontalis muscle. Responsible for brow elevation; runs vertically, inserts into brow dermis
• Supraorbital neurovascular bundle. Exits supraorbital foramen/notch at junction of medial one-third and lateral two-thirds of superior orbital rim
• Supratrochlear neurovascular bundle. Exits supratrochlear notch approximately 1.7 cm lateral to midline
• Sentinel vein. Marks location of temporal branch of facial nerve at zygomatic arch (relevant for lateral dissection)
• Corrugator supercilii. Deep to frontalis at medial brow; supratrochlear nerve courses through this muscle

Danger Zones

Tumor Predilection

• BCC (Common): Central forehead BCC tends to be nodular subtype. Significant subclinical extension is common due to embryonic fusion planes along midline.
• SCC (Common): Actinic keratosis field damage is typical on the forehead, leading to SCC in chronically sun-exposed patients. Generally favorable prognosis unless deeply invasive.

Mohs Considerations

• Central forehead tumors may track along embryonic fusion planes (midline, brow crease). Assess margins carefully
• Forehead skin is relatively inelastic compared to cheek; tissue conservation through Mohs is especially valuable
• Consider brow symmetry when planning excision. Asymmetric brow elevation is a common functional and cosmetic concern
• Undermining is typically in the subcutaneous plane superficial to frontalis; subperiosteal plane may be used for larger flaps

Reconstruction Principles

• Primary closure oriented horizontally (within relaxed skin tension lines / forehead rhytides) for defects up to 2-3 cm
• A-to-T closure or bilateral advancement flap ideal for central defects, distributing tension evenly
• Rotation flap for lateral forehead; O-to-Z for central defects involving hairline
• Healing by secondary intention acceptable for concave surfaces near the temple or deep to brow, but avoid on convex forehead due to depressed scar

Key Landmarks

• Procerus muscle. Thin midline muscle depressing medial brow; overlies nasal bones and glabella
• Corrugator supercilii muscles. Originate from medial orbital rim, course superolaterlaly through frontalis to brow skin
• Nasion. Deepest point of nasofrontal angle; marks transition from glabellar skin to nasal dorsum
• Angular artery and vein. Course along nasofacial sulcus just lateral to the glabella

Danger Zones

Tumor Predilection

• BCC (Very common): The glabella is an embryonic fusion plane (frontonasal prominence) and a prime site for BCC with significant subclinical extension. Morpheaform and infiltrative subtypes are more common here than at other facial sites.
• SCC (Moderate): Less common than BCC at this site. May arise in the setting of chronic actinic damage.

Mohs Considerations

• Embryonic fusion plane. Tumors may show extensive subclinical spread along fascial planes, necessitating additional Mohs stages
• The glabella is a critical pedicle zone for paramedian forehead flaps. Preserve supratrochlear vessels whenever possible
• Thin skin with minimal subcutaneous fat; tumor may reach periosteum quickly, requiring careful assessment of deep margin
• Central location makes even small defects cosmetically significant. Tissue-sparing Mohs is especially important here

Reconstruction Principles

• Primary closure vertically (along vertical glabellar crease) for small defects up to 1.5 cm; recruit skin from adjacent forehead
• Glabellar V-to-Y advancement or A-to-T closure for midline defects; hides incision lines in horizontal rhytides and vertical glabellar crease
• Dorsal nasal (Rieger) rotation flap for defects extending onto the nasal dorsum
• Full-thickness skin graft from preauricular or supraclavicular donor for larger defects where local tissue is insufficient

Key Landmarks

• Temporal fusion line (conjoint tendon). Superior boundary where periosteum, temporalis fascia, and galea fuse
• Sentinel vein. Transverse branch crossing zygomatic arch, marks depth of temporal branch of CN VII
• Superficial temporal artery. Palpable anterior to tragus, bifurcates into frontal and parietal branches
• Zygomatic arch. Inferior boundary; CN VII temporal branch crosses superficial to arch periosteum

Danger Zones

Tumor Predilection

• BCC (Very common): The temple is an embryonic fusion plane between frontonasal and maxillary prominences. BCC here frequently shows aggressive histologic subtypes and extensive subclinical extension.
• SCC (Common): High chronic UV exposure area. SCC of the temple may invade the temporalis muscle or deep temporal fascia in advanced cases.

Mohs Considerations

• Embryonic fusion plane. Anticipate subclinical extension greater than clinical margins suggest, particularly in morpheaform/infiltrative BCC
• Thin skin over the temporal fossa with minimal subcutaneous fat; tumors may reach temporalis fascia relatively quickly
• Must identify and protect the temporal branch of CN VII during excision. Consider intraoperative nerve monitoring for large or deep tumors
• The concave topography of the temporal fossa makes wound assessment and tissue processing technically demanding

Reconstruction Principles

• Primary closure oriented vertically or in RSTL for defects up to 2 cm; skin is relatively inelastic in this region
• O-to-Z rotation flap or large rotation flap from adjacent forehead or scalp for defects 2-4 cm
• Full-thickness skin graft from preauricular donor matches color and texture well for this site
• Secondary intention healing may produce acceptable results in the concavity of the temporal fossa for shallow defects

Key Landmarks

• Temporal fusion line (conjoint tendon). Superior boundary where periosteum, temporalis fascia, and galea fuse
• Sentinel vein. Transverse branch crossing zygomatic arch, marks depth of temporal branch of CN VII
• Superficial temporal artery. Palpable anterior to tragus, bifurcates into frontal and parietal branches
• Zygomatic arch. Inferior boundary; CN VII temporal branch crosses superficial to arch periosteum

Danger Zones

Tumor Predilection

• BCC (Very common): The temple is an embryonic fusion plane between frontonasal and maxillary prominences. BCC here frequently shows aggressive histologic subtypes and extensive subclinical extension.
• SCC (Common): High chronic UV exposure area. SCC of the temple may invade the temporalis muscle or deep temporal fascia in advanced cases.

Mohs Considerations

• Embryonic fusion plane. Anticipate subclinical extension greater than clinical margins suggest, particularly in morpheaform/infiltrative BCC
• Thin skin over the temporal fossa with minimal subcutaneous fat; tumors may reach temporalis fascia relatively quickly
• Must identify and protect the temporal branch of CN VII during excision. Consider intraoperative nerve monitoring for large or deep tumors
• The concave topography of the temporal fossa makes wound assessment and tissue processing technically demanding

Reconstruction Principles

• Primary closure oriented vertically or in RSTL for defects up to 2 cm; skin is relatively inelastic in this region
• O-to-Z rotation flap or large rotation flap from adjacent forehead or scalp for defects 2-4 cm
• Full-thickness skin graft from preauricular donor matches color and texture well for this site
• Secondary intention healing may produce acceptable results in the concavity of the temporal fossa for shallow defects

Key Landmarks

• Medial canthal tendon. Attaches to anterior and posterior lacrimal crests; critical anchor for eyelid position
• Lateral canthal tendon (Whitnall tubercle). Attaches inside lateral orbital rim, 2 mm posterior to orbital margin
• Orbital septum. Boundary between preseptal and postseptal (orbital) compartments; key safety landmark
• Tarsal plates. Upper tarsus 10-12 mm height, lower tarsus 4-5 mm height; provide eyelid structural support
• Lacrimal puncta. Located on medial aspect of each eyelid margin; must be preserved to prevent epiphora

Danger Zones

Tumor Predilection

• BCC (Very common): Medial canthus is a particularly common site for BCC, especially morpheaform subtypes. Tumors at the medial canthus frequently exhibit deep perineural spread along infraorbital and supraorbital nerves. The medial canthus is an embryonic fusion zone.
• SCC (Moderate): Less common than BCC in the periorbital region. May arise from actinic keratoses on the lower eyelid or lateral canthus.

Mohs Considerations

• Medial canthus tumors may invade the orbit via embryonic fusion planes. Requires meticulous deep margin assessment and possible orbital imaging for advanced cases
• Extremely thin eyelid skin (thinnest in the body at 0.5 mm) with no subcutaneous fat. Tumor reaches orbicularis quickly
• Always place a corneal shield (metal or plastic) to protect the globe during excision and cautery
• Functional outcomes (eyelid closure, tear drainage, visual axis) must take priority over cosmetic considerations in reconstruction planning

Reconstruction Principles

• Secondary intention healing is often excellent at the medial canthus (concave surface); produces results comparable to complex reconstruction in many cases
• Upper eyelid defects up to 25-33% of lid margin: direct layered closure. Larger defects require tarsoconjunctival advancement or Tenzel semicircular rotation
• Lower eyelid defects: avoid vertical tension that causes ectropion. Consider Tenzel flap, Hughes tarsoconjunctival flap (two-stage), or FTSG to anterior lamella
• Full-thickness eyelid defects require reconstruction of both anterior (skin-muscle) and posterior (tarsus-conjunctiva) lamellae. At least one lamella must contain a vascular pedicle

Key Landmarks

• Medial canthal tendon. Attaches to anterior and posterior lacrimal crests; critical anchor for eyelid position
• Lateral canthal tendon (Whitnall tubercle). Attaches inside lateral orbital rim, 2 mm posterior to orbital margin
• Orbital septum. Boundary between preseptal and postseptal (orbital) compartments; key safety landmark
• Tarsal plates. Upper tarsus 10-12 mm height, lower tarsus 4-5 mm height; provide eyelid structural support
• Lacrimal puncta. Located on medial aspect of each eyelid margin; must be preserved to prevent epiphora

Danger Zones

Tumor Predilection

• BCC (Very common): Medial canthus is a particularly common site for BCC, especially morpheaform subtypes. Tumors at the medial canthus frequently exhibit deep perineural spread along infraorbital and supraorbital nerves.
• SCC (Moderate): Less common than BCC in the periorbital region. May arise from actinic keratoses on the lower eyelid or lateral canthus.

Mohs Considerations

• Medial canthus tumors may invade the orbit via embryonic fusion planes. Requires meticulous deep margin assessment and possible orbital imaging for advanced cases
• Extremely thin eyelid skin (thinnest in the body at 0.5 mm) with no subcutaneous fat. Tumor reaches orbicularis quickly
• Always place a corneal shield (metal or plastic) to protect the globe during excision and cautery
• Functional outcomes (eyelid closure, tear drainage, visual axis) must take priority over cosmetic considerations in reconstruction planning

Reconstruction Principles

• Secondary intention healing is often excellent at the medial canthus (concave surface); produces results comparable to complex reconstruction in many cases
• Upper eyelid defects up to 25-33% of lid margin: direct layered closure. Larger defects require tarsoconjunctival advancement or Tenzel semicircular rotation
• Lower eyelid defects: avoid vertical tension that causes ectropion. Consider Tenzel flap, Hughes tarsoconjunctival flap (two-stage), or FTSG to anterior lamella
• Full-thickness eyelid defects require reconstruction of both anterior (skin-muscle) and posterior (tarsus-conjunctiva) lamellae. At least one lamella must contain a vascular pedicle

Key Landmarks

• Nasal bones. Paired bones forming the bony vault; extend approximately one-third of the nasal dorsal length
• Upper lateral cartilages. Paired, fused to dorsal septum; form the middle third of the nose
• Keystone area. Junction of nasal bones with upper lateral cartilages and septum; critical structural support
• Dorsal aesthetic lines. Paired curved lines from medial brow to tip-defining point; define dorsal width
• Nasion. Deepest point of the nasal radix at the nasofrontal angle

Danger Zones

Tumor Predilection

• BCC (Very common): The nasal dorsum is among the most common sites for BCC on the entire body. Nodular BCC predominates. Tumors may extend deeply to perichondrium or periosteum.
• SCC (Moderate): Less common than BCC on the dorsum. Usually arises in the setting of actinic damage. May be associated with SCC in situ (Bowen disease).

Mohs Considerations

• The nose is the single most common site for Mohs surgery; tissue conservation is critical given the limited skin laxity
• Tumors may extend along perichondrium of upper lateral cartilages. Examine deep margins carefully
• Consider subunit principle for reconstruction: if defect occupies >50% of the dorsal subunit, resecting to full subunit boundaries may produce superior cosmetic result
• The convex surface of the dorsum makes grafts appear depressed; local flaps generally produce better contour match

Reconstruction Principles

• Primary closure for small defects (<1 cm); orient closure along dorsal aesthetic lines or horizontally at supratip
• Dorsal nasal (Rieger) rotation flap for defects up to 2 cm. Rotates skin from glabella and lateral nose
• Bilobed flap for distal dorsal defects approaching the tip; design with 45-50 degree angles per Zitelli modification
• Paramedian forehead flap for large defects (>2 cm) or full-thickness defects requiring structural grafting beneath the flap

Key Landmarks

• Lower lateral (alar) cartilages. Paired C-shaped cartilages with medial, middle (domal), and lateral crura defining tip shape
• Tip-defining points. Light reflections at the domal apices of the lower lateral cartilages
• Soft tissue triangle (facet). Thin triangular skin between tip-defining point and nostril rim; poorly vascularized
• Alar groove. Junction between ala and cheek; important aesthetic boundary
• Alar rim. Free caudal margin of ala; must be maintained to prevent alar notching or retraction

Danger Zones

Tumor Predilection

• BCC (Very common): The nasal tip and ala are among the highest-frequency BCC sites. The alar crease and alar groove are embryonic fusion planes with associated subclinical extension risk. Nodular BCC is most common, but infiltrative subtypes are frequently encountered.
• SCC (Moderate): Less common than BCC at this site. SCC of the nasal vestibule (alar interior) warrants careful margin assessment.

Mohs Considerations

• Alar cartilage (lateral crus) must be carefully assessed during deep margin evaluation. Cartilage-invasive tumor may require cartilage resection
• The ala lacks cartilaginous structural support; reconstruction must prevent alar retraction and external nasal valve collapse
• Alar rim defects are particularly challenging. Even 1-2 mm of notching or retraction creates a visible deformity and may compromise the nasal airway
• Tumors at the alar groove (embryonic fusion plane) commonly exhibit extensive subclinical spread. Additional stages are frequent

Reconstruction Principles

• Bilobed flap (Zitelli modification) is the workhorse for tip defects 0.5-1.5 cm; pivots tissue from the lateral nose/dorsum to the tip
• Nasolabial interpolation flap for alar defects >1.5 cm or full-thickness alar defects; provides thick, well-vascularized tissue; requires second-stage division at 3 weeks
• Full-thickness alar defects require three layers: internal lining (turnover flap, septal mucoperichondrial flap, or FTSG), structural cartilage graft (septal, auricular, or rib), and external cover (interpolation flap or FTSG)
• Composite grafts from ear (helix/antihelix) for small full-thickness alar rim defects up to 1-1.5 cm in non-smokers

Key Landmarks

• Nasofacial sulcus (nasofacial groove). Natural crease between nose and cheek; ideal incision line for scar camouflage
• Upper lateral cartilage. Deep to the sidewall skin in the lower portion
• Ascending process of maxilla. Bony foundation deep to upper sidewall
• Angular artery and vein. Course along the nasofacial sulcus, superficial to the levator labii superioris alaeque nasi muscle

Danger Zones

Tumor Predilection

• BCC (Very common): The nasal sidewall is an extremely common BCC site. Tumors may extend along the nasofacial sulcus and medial cheek. Subclinical extension along the nasofacial sulcus (embryonic fusion plane) is well documented.
• SCC (Moderate): Arises in the setting of chronic actinic damage. Generally favorable prognosis at this location unless deeply invasive.

Mohs Considerations

• The nasofacial sulcus is an embryonic fusion plane. Tumors crossing or arising at this junction commonly show extensive subclinical spread requiring multiple Mohs stages
• Deep margin must assess periosteum of maxilla (upper sidewall) and perichondrium of upper lateral cartilage (lower sidewall)
• Consider potential internal nasal valve dysfunction when planning excision of lower sidewall tumors overlying the upper lateral cartilage
• The sidewall transitions between multiple aesthetic subunits. Plan Mohs stages to preserve subunit boundaries for optimal reconstruction

Reconstruction Principles

• Primary closure oriented along nasofacial sulcus for narrow defects; excellent scar camouflage
• Advancement (V-to-Y) or rotation flaps recruiting skin from cheek or dorsum for defects 1-2 cm
• Nasolabial transposition or interpolation flap for larger sidewall defects. Incision lines are hidden in the nasolabial fold
• Full-thickness skin graft from preauricular or conchal bowl for color match when local flaps are not feasible

Key Landmarks

• Nasofacial sulcus (nasofacial groove). Natural crease between nose and cheek; ideal incision line for scar camouflage
• Upper lateral cartilage. Deep to the sidewall skin in the lower portion
• Ascending process of maxilla. Bony foundation deep to upper sidewall
• Angular artery and vein. Course along the nasofacial sulcus, superficial to the levator labii superioris alaeque nasi muscle

Danger Zones

Tumor Predilection

• BCC (Very common): The nasal sidewall is an extremely common BCC site. Tumors may extend along the nasofacial sulcus and medial cheek. Subclinical extension along the nasofacial sulcus (embryonic fusion plane) is well documented.
• SCC (Moderate): Arises in the setting of chronic actinic damage. Generally favorable prognosis at this location unless deeply invasive.

Mohs Considerations

• The nasofacial sulcus is an embryonic fusion plane. Tumors crossing or arising at this junction commonly show extensive subclinical spread requiring multiple Mohs stages
• Deep margin must assess periosteum of maxilla (upper sidewall) and perichondrium of upper lateral cartilage (lower sidewall)
• Consider potential internal nasal valve dysfunction when planning excision of lower sidewall tumors overlying the upper lateral cartilage
• The sidewall transitions between multiple aesthetic subunits. Plan Mohs stages to preserve subunit boundaries for optimal reconstruction

Reconstruction Principles

• Primary closure oriented along nasofacial sulcus for narrow defects; excellent scar camouflage
• Advancement (V-to-Y) or rotation flaps recruiting skin from cheek or dorsum for defects 1-2 cm
• Nasolabial transposition or interpolation flap for larger sidewall defects. Incision lines are hidden in the nasolabial fold
• Full-thickness skin graft from preauricular or conchal bowl for color match when local flaps are not feasible

Key Landmarks

• Nasolabial fold. Deepens from alar base to oral commissure; key aesthetic landmark and incision site for flap design
• Malar eminence (zygoma). Bony prominence of the cheek; defines the midface contour
• Parotid duct (Stensen duct). Courses along a line from tragus to mid-upper lip, crosses the masseter; enters buccal mucosa opposite the upper second molar
• Facial artery. Crosses the mandible at the anterior edge of masseter, courses superomedially to become the angular artery
• Buccal fat pad. Deep to buccinator muscle; may herniate into surgical defects in the posterior cheek

Danger Zones

Tumor Predilection

• BCC (Very common): The cheek is one of the most frequent sites for BCC overall. Medial cheek (near nasolabial fold) BCC may show subclinical extension along the embryonic fusion plane. Nodular subtype predominates.
• SCC (Common): Chronic sun exposure leads to SCC, especially in the infraorbital and zygomatic subregions. SCC of the cheek generally carries a favorable prognosis with adequate margins.

Mohs Considerations

• Medial cheek tumors near the nasolabial fold may track along embryonic fusion planes. Consider this when evaluating subclinical extension
• The SMAS provides a consistent deep plane landmark. Tumors deep to SMAS approach the facial nerve branches and parotid gland
• Large cheek defects affect multiple aesthetic subunits. Plan reconstruction considering the nasolabial fold, eyelid, and lip boundaries
• Cheek skin is relatively mobile with good laxity, especially in elderly patients. This often allows larger primary closures and flaps than other facial sites

Reconstruction Principles

• Primary closure in RSTL for defects up to 2-3 cm; cheek skin laxity is generous especially in elderly patients
• Cervicofacial advancement-rotation flap for large medial cheek defects. The workhorse flap for cheek reconstruction; incision follows preauricular crease and mandibular border
• V-to-Y advancement flap for infraorbital cheek defects; uses medial cheek skin advanced superiorly
• Full-thickness skin graft from preauricular, postauricular, or supraclavicular donor for color and texture match when flaps are contraindicated

Key Landmarks

• Nasolabial fold. Deepens from alar base to oral commissure; key aesthetic landmark and incision site for flap design
• Malar eminence (zygoma). Bony prominence of the cheek; defines the midface contour
• Parotid duct (Stensen duct). Courses along a line from tragus to mid-upper lip, crosses the masseter; enters buccal mucosa opposite the upper second molar
• Facial artery. Crosses the mandible at the anterior edge of masseter, courses superomedially to become the angular artery
• Buccal fat pad. Deep to buccinator muscle; may herniate into surgical defects in the posterior cheek

Danger Zones

Tumor Predilection

• BCC (Very common): The cheek is one of the most frequent sites for BCC overall. Medial cheek (near nasolabial fold) BCC may show subclinical extension along the embryonic fusion plane.
• SCC (Common): Chronic sun exposure leads to SCC, especially in the infraorbital and zygomatic subregions. Generally favorable prognosis with adequate margins.

Mohs Considerations

• Medial cheek tumors near the nasolabial fold may track along embryonic fusion planes. Consider this when evaluating subclinical extension
• The SMAS provides a consistent deep plane landmark. Tumors deep to SMAS approach the facial nerve branches and parotid gland
• Large cheek defects affect multiple aesthetic subunits. Plan reconstruction considering the nasolabial fold, eyelid, and lip boundaries
• Cheek skin is relatively mobile with good laxity, especially in elderly patients. This often allows larger primary closures and flaps than other facial sites

Reconstruction Principles

• Primary closure in RSTL for defects up to 2-3 cm; cheek skin laxity is generous especially in elderly patients
• Cervicofacial advancement-rotation flap for large medial cheek defects. The workhorse flap for cheek reconstruction; incision follows preauricular crease and mandibular border
• V-to-Y advancement flap for infraorbital cheek defects; uses medial cheek skin advanced superiorly
• Full-thickness skin graft from preauricular, postauricular, or supraclavicular donor for color and texture match when flaps are contraindicated

Key Landmarks

• Helix. The outer curved rim; composed of thin skin over elastic cartilage
• Antihelix and antihelical crura. Y-shaped cartilaginous ridge medial to the helix; defines the scapha
• Conchal bowl. Deepest part of the ear; overlies the external auditory canal
• Tragus. Anterior cartilaginous projection protecting the ear canal
• Lobule. Inferior, non-cartilaginous portion composed of fibrofatty tissue

Danger Zones

Tumor Predilection

• SCC (Very common): The ear (especially the helix) is a high-risk site for SCC with elevated rates of metastasis (5-9%) compared to other facial sites. Ear SCC has poorer prognosis due to thin skin, limited subcutaneous tissue, and proximity to cartilage and lymphatic drainage.
• BCC (Common): BCC of the ear most commonly involves the preauricular area, postauricular sulcus, and conchal bowl. Conchal bowl BCC may invade deeply toward the ear canal.

Mohs Considerations

• The ear has extremely thin skin overlying cartilage with minimal subcutaneous tissue. Tumors reach perichondrium and cartilage quickly, even when clinically small
• SCC of the ear is classified as high-risk per NCCN regardless of size. Mohs is strongly indicated. Sentinel lymph node biopsy should be considered for high-risk SCC
• Cartilage does not serve as a tumor barrier. Tumor may spread through cartilage and emerge on the opposite surface of the ear
• Complete circumferential margin assessment is critical given the three-dimensional auricular anatomy. Consider processing the specimen in multiple planes

Reconstruction Principles

• Helical rim defects: wedge excision with primary closure for defects up to 1.5-2 cm (up to one-quarter of helical length); Antia-Buch chondrocutaneous advancement for larger helical defects
• Conchal bowl defects: secondary intention healing produces excellent results in this concavity; alternatively, full-thickness skin graft
• Postauricular interpolation flap (two-stage) for larger anterior auricular defects; provides matching skin from the postauricular surface folded forward over a cartilage graft
• Composite graft from contralateral ear for small full-thickness helical rim defects (<1.5 cm) in non-smokers with good vascularity

Key Landmarks

• Helix. The outer curved rim; composed of thin skin over elastic cartilage
• Antihelix and antihelical crura. Y-shaped cartilaginous ridge medial to the helix; defines the scapha
• Conchal bowl. Deepest part of the ear; overlies the external auditory canal
• Tragus. Anterior cartilaginous projection protecting the ear canal
• Lobule. Inferior, non-cartilaginous portion composed of fibrofatty tissue

Danger Zones

Tumor Predilection

• SCC (Very common): The ear (especially the helix) is a high-risk site for SCC with elevated rates of metastasis (5-9%) compared to other facial sites. Ear SCC has poorer prognosis due to thin skin, limited subcutaneous tissue, and proximity to cartilage and lymphatic drainage.
• BCC (Common): BCC of the ear most commonly involves the preauricular area, postauricular sulcus, and conchal bowl. Conchal bowl BCC may invade deeply toward the ear canal.

Mohs Considerations

• The ear has extremely thin skin overlying cartilage with minimal subcutaneous tissue. Tumors reach perichondrium and cartilage quickly, even when clinically small
• SCC of the ear is classified as high-risk per NCCN regardless of size. Mohs is strongly indicated. Sentinel lymph node biopsy should be considered for high-risk SCC
• Cartilage does not serve as a tumor barrier. Tumor may spread through cartilage and emerge on the opposite surface of the ear
• Complete circumferential margin assessment is critical given the three-dimensional auricular anatomy. Consider processing the specimen in multiple planes

Reconstruction Principles

• Helical rim defects: wedge excision with primary closure for defects up to 1.5-2 cm (up to one-quarter of helical length); Antia-Buch chondrocutaneous advancement for larger helical defects
• Conchal bowl defects: secondary intention healing produces excellent results in this concavity; alternatively, full-thickness skin graft
• Postauricular interpolation flap (two-stage) for larger anterior auricular defects; provides matching skin from the postauricular surface folded forward over a cartilage graft
• Composite graft from contralateral ear for small full-thickness helical rim defects (<1.5 cm) in non-smokers with good vascularity

Key Landmarks

• Philtrum. Central concave subunit defined by two philtral columns (ridges) converging at the Cupid's bow
• Cupid's bow. The M-shaped contour of the upper vermilion border; must be meticulously aligned in reconstruction
• White roll. The pale raised ridge at the vermilion-cutaneous junction; misalignment of even 1 mm is visible
• Orbicularis oris muscle. Circular sphincter providing lip competence; deep to skin and superficial to mucosa
• Labial artery (superior). Courses within the orbicularis oris muscle approximately 5-7 mm deep to the vermilion surface

Danger Zones

Tumor Predilection

• BCC (Common): Upper lip BCC is common, particularly along the philtral columns and at the base of the columella. The philtrum represents an embryonic fusion line with associated subclinical extension risk.
• SCC (Moderate): Upper lip SCC is less common than on the lower lip (which receives more UV exposure). When present, it carries similar risk considerations to other cutaneous SCC.

Mohs Considerations

• The vermilion border (white roll and Cupid's bow) must be preserved or precisely reconstructed. Even 1 mm of misalignment is cosmetically significant
• Tumors at the philtral columns (embryonic fusion line of the medial nasal prominences) may exhibit subclinical extension along this embryonic fusion plane
• Oral competence is the primary functional goal. Assess orbicularis oris integrity after excision and plan reconstruction to restore sphincter function
• Full-thickness lip defects require three-layer reconstruction: mucosa, muscle (orbicularis oris), and skin

Reconstruction Principles

• Primary closure for defects up to one-quarter to one-third of lip width; must achieve meticulous white roll and vermilion alignment
• Perialar crescentic advancement flap for defects near the nasal sill; hides scar in the alar crease
• Abbe (cross-lip) flap from the lower lip for central upper lip and philtral defects up to two-thirds of lip width. Provides composite tissue transfer; requires second-stage pedicle division at 2-3 weeks
• Karapandzic rotation-advancement flap for large lateral upper lip defects. Preserves neurovascular bundles entering the orbicularis oris, maintaining oral competence

Key Landmarks

• Vermilion border. Must be precisely realigned during reconstruction; the lower lip vermilion is fuller centrally than the upper
• Mentolabial sulcus (labiomental crease). Transverse crease separating lower lip from chin; natural incision line
• Oral commissure. Junction of upper and lower lips; microstomia prevention is a key reconstructive goal
• Orbicularis oris muscle. Sphincter providing lip competence; runs circumferentially within both lips
• Inferior labial artery. Courses within the orbicularis oris muscle of the lower lip, providing primary blood supply

Danger Zones

Tumor Predilection

• SCC (Very common): The lower lip is the most common site for lip SCC (>90% of lip cancers). Chronic UV exposure to the lower lip vermilion (which lacks the melanin protection of cutaneous skin) is the primary risk factor. Lower lip SCC has a metastasis rate of approximately 5-10% and may require sentinel lymph node biopsy for advanced lesions.
• BCC (Uncommon): BCC rarely occurs on the lower lip vermilion. When BCC involves the lower lip, it is typically on the cutaneous (white) lip rather than the vermilion.

Mohs Considerations

• Lower lip SCC is the most common malignancy treated with Mohs at this site. Mohs is indicated for tissue conservation and complete margin control
• Perineural invasion along the mental nerve is a well-documented pattern for lower lip SCC. Numbness in the mental nerve distribution may indicate perineural spread requiring additional stages or imaging
• Oral competence is the paramount functional goal. Reconstruction must restore orbicularis oris continuity and prevent drooling
• The vermilion lacks adnexal structures and heals with minimal scarring from secondary intention. Consider this for small superficial vermilion defects

Reconstruction Principles

• Primary closure (wedge or V-excision) for defects up to one-third of lip width; ensure three-layer closure. Mucosa, orbicularis oris, and skin with meticulous vermilion border alignment
• Karapandzic rotation-advancement flap for defects one-third to two-thirds of lip width. The gold standard for large lower lip defects; preserves neurovascular supply to the orbicularis for functional oral competence
• Estlander flap (commissure-based rotation from upper lip) for lateral lower lip defects involving the commissure; results in commissure blunting
• Bernard-Burow cheek advancement for subtotal or total lower lip defects; recruits cheek tissue bilaterally but sacrifices oral competence due to denervated tissue

Key Landmarks

• Mental protuberance. Bony midline prominence of the anterior mandible
• Mental foramen. Located below the second premolar, approximately 1 cm above the mandibular inferior border; exit point of the mental nerve
• Mentalis muscle. Paired muscle originating from the mandible and inserting into chin skin; contraction elevates and protrudes the lower lip and wrinkles the chin ('chin dimpling')
• Submental crease. Natural skin crease at the inferior chin boundary; useful for incision placement

Danger Zones

Tumor Predilection

• BCC (Common): BCC of the chin is common, usually nodular subtype. The chin receives significant cumulative UV exposure.
• SCC (Common): SCC of the chin occurs in chronically sun-damaged skin. Generally favorable prognosis at this M-zone location with adequate margin control.

Mohs Considerations

• Chin skin is relatively thick with robust subcutaneous tissue. Defects may be deeper than anticipated clinically
• Mentalis muscle integrity is important for lower lip function. Disruption can lead to 'witch chin' deformity and oral incompetence with drooling
• The M-zone designation means standard excision may be appropriate for small, well-defined, low-risk tumors; Mohs is indicated for recurrent, high-risk histologic subtypes, or tissue-sparing need
• Periosteum of the mental protuberance may be involved in deeply invasive tumors. Assess with imaging if bone invasion is suspected

Reconstruction Principles

• Primary closure oriented within the mentolabial sulcus or submental crease for defects up to 2-3 cm; the chin has moderate skin laxity
• V-to-Y or A-to-T advancement flap for central chin defects; recruits tissue from the lateral chin and submental region
• Cervicofacial advancement flap extending from the neck for large chin defects; provides excellent color and texture match
• Full-thickness skin graft from submental or supraclavicular donor site for defects where local flaps produce excessive tension on the lower lip

Key Landmarks

• Nasion (bridge of nose)
• Gonion (mandibular angle)
• External auditory meatus
• Vertex of skull

Danger Zones

Tumor Predilection

• BCC (Very common): 70-80% of all BCCs arise on the head and neck. Nose, periorbital, and ear are the most common subsites. Nodular BCC predominates; aggressive subtypes (morpheaform, infiltrative) are over-represented in the H-zone.
• SCC (Very common): Head and neck account for ~60% of cutaneous SCCs. Scalp, ear, and lip have higher metastatic risk. Chronic sun exposure is the primary driver.
• Melanoma (Common): Lentigo maligna is the predominant subtype on chronically sun-damaged facial skin. Head/neck melanomas have a worse prognosis stage-for-stage compared to trunk/extremity lesions.

Mohs Considerations

• H-zone designation makes Mohs appropriate for virtually all BCCs and SCCs regardless of size per NCCN guidelines
• Tissue conservation is critical due to cosmetic and functional importance; Mohs achieves the narrowest margins with complete peripheral and deep margin assessment
• Link to the detailed face anatomy atlas for subunit-level danger zone and reconstruction data

Reconstruction Principles

• Respect aesthetic subunits of the face; place incisions along subunit boundaries and relaxed skin tension lines (RSTLs) where possible
• Prioritize function (eyelid closure, nasal airway patency, oral competence) before cosmetic outcome
• Consider staged reconstruction (interpolation flaps, tissue expansion) for large or complex defects spanning multiple subunits

Key Landmarks

• Sternocleidomastoid muscle
• Thyroid cartilage (Adam's apple)
• External jugular vein
• Spinal accessory nerve (CN XI) in the posterior triangle

Danger Zones

Tumor Predilection

• SCC (Common): The posterior and lateral neck are common sites for SCC in chronically sun-exposed patients. Risk of in-transit metastasis to cervical lymph nodes is elevated relative to trunk SCC.
• BCC (Moderate): Less common than face but occurs on the posterior neck and at the cervicomental angle. Nodular subtype predominates.
• Melanoma (Moderate): Posterior neck is a relatively common site for melanoma in men. Sentinel lymph node basins may drain to both cervical and axillary nodes, complicating staging.

Mohs Considerations

• Anterior neck and midline structures are NCCN M-zone; Mohs is appropriate for recurrent tumors, aggressive histologic subtypes, and where tissue conservation is needed
• The thin skin of the neck can allow deep tumor extension along fascial planes; careful deep margin evaluation is essential
• Poorly differentiated SCC on the neck warrants consideration of adjuvant radiation and nodal imaging given regional metastatic risk

Reconstruction Principles

• Cervical skin has excellent laxity in most patients; primary closure oriented along horizontal RSTLs is often achievable for moderate defects
• Avoid vertical scars on the anterior neck that can lead to scar contracture and restricted neck extension
• Full-thickness skin grafts from the supraclavicular or preauricular area provide good color and texture match for larger defects

Key Landmarks

• Acromion process
• Deltoid muscle bulk
• Clavicle (lateral third)

Danger Zones

Tumor Predilection

• Melanoma (Common): The upper back and shoulder are among the most common melanoma sites in men, related to intermittent intense UV exposure. Superficial spreading melanoma predominates.
• BCC (Moderate): Superficial BCC is more common on the trunk and shoulders than nodular BCC, which predominates on the face.
• SCC (Uncommon): Less common on the shoulder than on the head/neck or distal extremities. When present, typically occurs in chronically sun-damaged skin.

Mohs Considerations

• Shoulder is M-zone per NCCN; Mohs is appropriate for recurrent tumors, aggressive histology, or when tissue conservation is important around the joint
• Melanoma in situ/lentigo maligna on the shoulder may be treated with Mohs using immunohistochemistry (MART-1/MelanA) for margin assessment at specialized centers
• Wide local excision remains the standard for invasive melanoma; Mohs with rush permanent sections (slow Mohs) is an evolving approach

Reconstruction Principles

• Skin tension is high over the deltoid; primary closure along Langer's lines minimizes wound tension but wide excisions may require grafting
• Shoulder mobility must be preserved; avoid closures that restrict abduction
• This is a high-tension site prone to hypertrophic scarring; consider delayed primary closure or grafting for larger defects

Key Landmarks

• Biceps muscle (anterior)
• Medial and lateral epicondyles
• Bicipital groove

Danger Zones

Tumor Predilection

• Melanoma (Moderate): The upper arm (especially lateral aspect) is a moderate-risk site for melanoma, particularly in women. Superficial spreading melanoma is the most common subtype.
• SCC (Uncommon): Uncommon on the upper arm in the absence of chronic sun damage or immunosuppression. SCC in situ (Bowen's disease) may occur.
• BCC (Uncommon): Superficial BCC is the most common subtype on the extremities. L-zone designation means standard excision is usually preferred over Mohs.

Mohs Considerations

• L-zone per NCCN; standard excision is usually adequate. Mohs is reserved for recurrent tumors, aggressive histology, or incompletely excised lesions
• Consider Mohs for DFSP on the upper arm, where wide subclinical extension is typical and tissue-sparing excision has functional benefit
• Perineural invasion along cutaneous nerve branches of the medial/lateral antebrachial cutaneous nerves may require expanded margin assessment

Reconstruction Principles

• Good skin laxity on the medial upper arm allows primary closure for most Mohs-sized defects oriented along the long axis of the arm
• Lateral upper arm skin is tighter; larger defects may require split-thickness or full-thickness skin grafts
• Undermining should stay superficial to the muscular fascia to avoid neurovascular structures in the bicipital groove

Key Landmarks

• Extensor tendons (dorsal hand)
• Anatomical snuffbox (radial artery branch)
• Carpal tunnel (volar wrist)
• Dorsal venous network of the hand

Danger Zones

Tumor Predilection

• SCC (Very common): Dorsal hand and forearm are among the most common SCC sites due to chronic cumulative UV exposure. Actinic keratoses are often confluent. SCC on the hand is NCCN H-zone and warrants Mohs.
• BCC (Uncommon): BCC is relatively uncommon distal to the elbow. When present, superficial BCC predominates on the forearm.
• Melanoma (Moderate): Acral lentiginous melanoma involves the subungual and palmar/plantar areas. Non-acral melanoma on the dorsal forearm occurs in chronically sun-damaged skin.

Mohs Considerations

• Dorsal hand, digits, and nail unit are NCCN H-zone; Mohs is appropriate for all BCC and SCC at these sites due to tissue-conservation needs and high recurrence risk with standard excision
• Forearm is L-zone; Mohs is reserved for recurrent, aggressive, or incompletely excised tumors
• Subungual SCC and melanoma may require Mohs with careful coordination; nail matrix biopsy and possible digit amputation should be discussed preoperatively

Reconstruction Principles

• Dorsal hand has minimal subcutaneous tissue; full-thickness skin grafts (from hypothenar eminence, medial arm, or groin) are often needed for larger defects
• Second-intention healing works well for fingertip and distal phalanx defects that do not expose bone or tendon
• Preserve extensor paratenon to support graft take; flap reconstruction (reverse radial forearm flap, cross-finger flap) may be needed for tendon or bone exposure

Key Landmarks

• Sternum and xiphoid process
• Umbilicus
• Costal margins
• Nipple-areolar complex

Danger Zones

Tumor Predilection

• BCC (Common): Superficial BCC is the most common subtype on the trunk, accounting for up to 40-50% of trunk BCCs. Multifocal superficial BCC can mimic eczema or psoriasis. Nodular BCC is less common on the trunk.
• Melanoma (Common): The trunk is the most common melanoma site in men. Superficial spreading melanoma predominates. The presternal and interscapular areas are highest risk, correlated with intermittent UV exposure.
• SCC (Uncommon): SCC is uncommon on the trunk in the absence of immunosuppression, chronic wounds, or radiation history. SCC in situ (Bowen's disease) is more common than invasive SCC on the trunk.

Mohs Considerations

• L-zone per NCCN; standard excision is the primary treatment. Mohs is appropriate for recurrent tumors, aggressive histology (morpheaform/infiltrative BCC), DFSP, or incompletely excised lesions
• Superficial BCC on the trunk may be managed with topical therapies (imiquimod, 5-FU) or curettage and electrodesiccation for low-risk lesions in appropriate candidates
• DFSP has a strong predilection for the trunk and has wide subclinical spread; Mohs achieves significantly lower recurrence than standard wide excision

Reconstruction Principles

• Primary closure along RSTLs is usually feasible; the trunk has good skin laxity, especially inferiorly and laterally
• Presternal and upper chest wounds are prone to hypertrophic and keloidal scarring; minimize tension and consider delayed closure or steroid injection for at-risk patients
• Large trunk defects can be managed with split-thickness skin grafts or healing by secondary intention, which produces acceptable cosmetic results on the trunk

Key Landmarks

• Spinous processes (midline)
• Scapulae (medial borders)
• Iliac crests
• Posterior superior iliac spines

Danger Zones

Tumor Predilection

• Melanoma (Very common): The upper back (interscapular region) is the single most common melanoma site in men. Associated with intermittent intense UV (blistering sunburns). Superficial spreading melanoma predominates.
• BCC (Moderate): Superficial BCC is common on the upper and mid-back. Large superficial BCCs may be present for years before diagnosis due to the difficulty of self-examination.
• SCC (Uncommon): SCC is uncommon on the back unless there is a history of radiation therapy, chronic scarring, or immunosuppression.

Mohs Considerations

• L-zone per NCCN; standard excision is generally preferred. Mohs is indicated for DFSP, recurrent tumors, morpheaform/infiltrative BCC, or incompletely excised tumors
• DFSP is one of the most common Mohs indications on the trunk; subclinical extension can be extensive (several centimeters beyond the clinical margin)
• The back has thick dermis that can harbor deep tumor extension; ensure adequate deep margin assessment during Mohs processing

Reconstruction Principles

• Primary closure is usually achievable with wide undermining in the subcutaneous plane; orient closures along horizontal RSTLs on the upper back
• The upper back/interscapular area is a high-tension zone prone to wound dehiscence and hypertrophic scarring; consider deep dermal sutures with prolonged support (e.g., barbed sutures)
• Secondary intention healing is well-tolerated on the back for concave defects; split-thickness grafts are an option for very large defects

Key Landmarks

• Greater trochanter
• Femoral triangle (inguinal ligament, sartorius, adductor longus)
• Patella (inferior boundary)

Danger Zones

Tumor Predilection

• Melanoma (Moderate): Melanoma occurs on the thigh with a female predominance (lower extremity is the most common melanoma site in women). Superficial spreading subtype predominates.
• SCC (Uncommon): SCC is uncommon on the thigh in immunocompetent patients. Occurs more frequently in immunosuppressed patients or at sites of chronic inflammation.
• BCC (Uncommon): BCC is rare on the thigh. When present, superficial BCC is the most common subtype.

Mohs Considerations

• L-zone per NCCN; standard excision is the primary approach. Mohs is reserved for DFSP, recurrent tumors, or aggressive histology
• DFSP has a predilection for the proximal extremities and trunk; Mohs achieves lower recurrence rates (1-2%) compared to wide excision (up to 20%)
• Groin and inguinal crease tumors can have complex deep extension along fascial planes; careful preoperative imaging may be warranted for large or recurrent tumors

Reconstruction Principles

• The thigh has abundant skin laxity; primary closure is feasible for most defects, oriented along oblique or longitudinal RSTLs
• Medial thigh defects near the groin crease heal well by secondary intention but can be closed primarily along the crease for optimal cosmesis
• Full-thickness or split-thickness skin grafts are rarely needed; reserve for very large defects over the lateral thigh where skin is tighter

Key Landmarks

• Tibial crest (shin, subcutaneous)
• Medial and lateral malleoli
• Achilles tendon (posterior)

Danger Zones

Tumor Predilection

• SCC (Common): The pretibial lower leg is a common SCC site, especially in older women with chronic actinic damage. Pretibial SCC can be aggressive with higher local recurrence due to poor blood supply and thin tissue.
• Melanoma (Common): The lower leg is a high-risk melanoma site in women. Superficial spreading melanoma predominates. Sentinel lymph node drainage is to the inguinal (popliteal less commonly) basins.
• BCC (Uncommon): BCC is uncommon on the lower leg. Superficial BCC is the predominant subtype when it occurs.

Mohs Considerations

• The pretibial area is classified as M-zone by some NCCN-based references due to notoriously poor wound healing; Mohs tissue conservation is particularly valuable here to reduce defect size
• Lower leg wounds heal slowly due to dependent edema, reduced blood supply, and thin subcutaneous tissue; surgical planning must account for prolonged recovery
• Compression therapy and leg elevation are essential postoperative adjuncts to promote wound healing and reduce dehiscence risk

Reconstruction Principles

• Primary closure is often difficult on the pretibial surface due to thin, inelastic skin; avoid excessive tension that can lead to dehiscence and chronic wounds
• Full-thickness skin grafts from the thigh or groin are frequently used for pretibial defects; bolster dressings and strict postoperative immobilization improve graft take
• Secondary intention healing is a viable option for small pretibial defects but requires prolonged wound care (weeks to months); negative-pressure wound therapy can accelerate healing

Key Landmarks

• Medial and lateral malleoli
• Metatarsal heads (weight-bearing surface)
• Dorsalis pedis artery (dorsal foot)
• Calcaneus (heel)

Danger Zones

Tumor Predilection

• Melanoma (Moderate): Acral lentiginous melanoma (ALM) is the most important melanoma subtype on the foot, particularly on the plantar surface, heel, and subungual areas. ALM is the most common melanoma in non-White populations and often presents at an advanced stage.
• SCC (Moderate): SCC occurs on the dorsal foot and periungual areas. Verrucous carcinoma (epithelioma cuniculatum) has a predilection for the plantar surface. HPV-related SCC can occur periungually.
• BCC (Uncommon): BCC is rare on the foot. Reports exist but it should always raise suspicion for an alternative diagnosis when encountered below the ankle.

Mohs Considerations

• Nail units and digits are NCCN H-zone; Mohs is appropriate for SCC and melanoma in situ of the nail unit and periungual skin, where tissue conservation can preserve digit function
• Plantar melanoma (acral lentiginous) is often treated with wide excision; Mohs with immunohistochemistry (MART-1/HMB-45) is used at specialized centers for in situ disease to preserve weight-bearing surface
• Verrucous carcinoma of the plantar surface is a Mohs indication given its locally aggressive nature and the importance of preserving plantar tissue for ambulation

Reconstruction Principles

• Weight-bearing plantar defects require durable reconstruction; full-thickness skin grafts or local flaps that preserve plantar padding are preferred over thin grafts that break down
• Dorsal foot defects can be managed with full-thickness skin grafts from the instep or groin; avoid tight closures over extensor tendons that may restrict dorsiflexion
• Heal and plantar defects may require muscle or fasciocutaneous flaps for coverage of exposed bone; free-tissue transfer may be needed for large plantar defects

Key Landmarks

• Inguinal creases
• Perineal body
• Pubic symphysis

Danger Zones

Tumor Predilection

• SCC (Common): Genital SCC includes penile SCC (glans, foreskin), vulvar SCC, and perianal SCC. HPV-related SCC (types 16, 18) is common in this region. Erythroplasia of Queyrat (SCC in situ of the glans) and Bowen's disease of the genital skin are important precursor lesions.
• Extramammary Paget disease (Moderate): EMPD has a strong predilection for apocrine-rich genital skin. Subclinical extension is often extensive, making Mohs the treatment of choice. Must rule out underlying internal malignancy (especially colorectal or genitourinary).
• BCC (Uncommon): BCC is rare in the genital area but does occur. Genital BCC should prompt evaluation for Gorlin syndrome in younger patients.

Mohs Considerations

• NCCN H-zone; Mohs is the treatment of choice for genital SCC, EMPD, and BCC due to tissue conservation in this functionally and cosmetically sensitive area
• EMPD frequently requires multiple Mohs stages due to wide subclinical extension with skip areas; cytokeratin 7 (CK7) immunostaining is essential for margin assessment
• Penile and vulvar SCC may require multidisciplinary management with urology/gynecology for deeply invasive tumors; sentinel lymph node biopsy should be considered for invasive disease

Reconstruction Principles

• Genital skin has excellent elasticity and blood supply; primary closure is often achievable even for moderate defects
• Full-thickness skin grafts from the inguinal crease or inner thigh provide excellent color and texture match for genital reconstruction
• Functional preservation (urethral meatus patency, vaginal introitus, anal sphincter competence) takes priority over cosmetic outcome

Key Landmarks

• Gluteal folds
• Intergluteal cleft
• Sacral prominence
• Greater trochanters (lateral boundaries)

Danger Zones

Tumor Predilection

• SCC (Moderate): Perianal and gluteal SCC may arise in the setting of chronic inflammation, prior radiation, or HPV infection. Marjolin's ulcer (SCC arising in chronic wounds/scars) can occur in the sacral/gluteal region in patients with chronic pressure ulcers.
• BCC (Uncommon): BCC is uncommon on the buttocks. Superficial BCC is the most likely subtype if encountered.
• Melanoma (Uncommon): Melanoma is uncommon on the buttocks but may occur. The gluteal region is considered a sun-protected site; melanomas here may have different molecular profiles (higher NRAS mutation rates).

Mohs Considerations

• L-zone per NCCN; standard excision is usually adequate. Mohs may be indicated for perianal SCC (tissue conservation near the anal sphincter), recurrent tumors, or DFSP
• Perianal SCC requires careful coordination with colorectal surgery; high-resolution anoscopy may identify additional intra-anal disease
• DFSP can occur on the buttock/sacral area with extensive subclinical spread; Mohs achieves superior local control compared to wide excision

Reconstruction Principles

• Gluteal skin has good laxity; primary closure oriented along gluteal creases is usually feasible for moderate defects
• Large sacral/gluteal defects may require gluteal rotation or V-Y advancement flaps
• Weight-bearing and pressure considerations are important for sacral defects, especially in patients with limited mobility; durable closures are essential to prevent wound breakdown

Key Landmarks

• Extensor tendons and dorsal expansion
• Metacarpophalangeal joints (knuckles)
• Dorsal venous arch
• Anatomical snuffbox (radial wrist)
• Nail units (including eponychium and hyponychium)

Danger Zones

Tumor Predilection

• SCC (Very common): Dorsal hand is one of the most common SCC sites due to chronic cumulative UV exposure. Actinic keratoses are often confluent. Field cancerization is common. SCC on the hand is NCCN H-zone.
• SCC (subungual) (Moderate): Subungual SCC can present as chronic nail dystrophy or periungual wart-like lesion. HPV-related SCC (especially HPV-16) is common periungually. Biopsy of persistent nail lesions is essential.
• Melanoma (Moderate): Subungual melanoma (acral lentiginous melanoma) presents as longitudinal melanonychia. Hutchinson's sign (periungual pigmentation) suggests nail matrix melanoma.

Mohs Considerations

• NCCN H-zone; Mohs is the treatment of choice for all SCC and BCC on the dorsal hand and digits due to tissue-conservation needs
• Nail unit tumors require specialized Mohs technique; en face sections of the nail matrix may be needed
• Subungual melanoma in situ may be treated with Mohs using immunohistochemistry (MART-1/MelanA) at specialized centers to preserve digit length

Reconstruction Principles

• Full-thickness skin grafts from the hypothenar eminence, medial arm, or groin provide the best functional and cosmetic results for dorsal hand defects
• Second-intention healing is excellent for fingertip defects not exposing bone or tendon
• Flap options include cross-finger flaps, reverse dorsal metacarpal artery flaps, and thenar flaps for digit defects with exposed structures

Key Landmarks

• Thenar eminence (thumb base)
• Hypothenar eminence (ulnar side)
• Palmar creases (distal, proximal, thenar)
• Carpal tunnel (deep to transverse carpal ligament)
• Digital flexor tendon sheaths

Danger Zones

Tumor Predilection

• Melanoma (Moderate): Acral lentiginous melanoma (ALM) involves the palmar surface. ALM is the most common melanoma subtype in non-White populations and often presents at an advanced stage. Dermoscopy of pigmented palmar lesions (parallel ridge pattern) is essential for early detection.
• SCC (Uncommon): SCC is uncommon on the palm but can occur in the setting of chronic arsenicosis, HPV infection, or at sites of prior radiation therapy.

Mohs Considerations

• NCCN H-zone; Mohs is appropriate for SCC and melanoma in situ of the palm to conserve tissue and preserve grip function
• Palmar melanoma (ALM) in situ may be treated with Mohs using MART-1/HMB-45 immunostaining at specialized centers
• Deep margin assessment is critical as ALM can extend along eccrine ducts and dermal ridges

Reconstruction Principles

• Palmar defects require durable, sensate reconstruction; full-thickness skin grafts from the instep (plantar non-weight-bearing area) provide the best match for glabrous skin
• Local advancement or rotation flaps preserve palmar padding and sensation better than grafts for small defects
• Larger defects may require regional pedicled flaps (radial forearm flap, ulnar artery perforator flap) or free-tissue transfer

Key Landmarks

• Extensor tendons (extensor hallucis longus, extensor digitorum longus)
• Dorsalis pedis artery (palpable between first and second metatarsals)
• Medial and lateral malleoli (ankle boundaries)
• Toenail units

Danger Zones

Tumor Predilection

• SCC (Moderate): SCC occurs on the dorsal foot, especially in chronically sun-exposed individuals. Periungual SCC of the toenails (often HPV-related) can mimic fungal infection and should be biopsied.
• Melanoma (Moderate): Subungual melanoma of the great toenail is one of the most common presentations of acral melanoma. Longitudinal melanonychia of the toenail warrants biopsy.
• BCC (Uncommon): BCC is rare below the ankle. When encountered, it should raise suspicion for an alternative diagnosis.

Mohs Considerations

• Toenail units are NCCN H-zone; Mohs is appropriate for SCC and melanoma in situ of the nail unit to preserve digit function and length
• Dorsal foot skin is M-zone; Mohs is valuable for tissue conservation over extensor tendons where primary closure is difficult
• Thin dorsal foot skin allows rapid tumor penetration to tendon/periosteum; early and complete margin assessment is important

Reconstruction Principles

• Full-thickness skin grafts from the instep or groin are commonly used for dorsal foot defects
• Avoid tight primary closures over extensor tendons that may restrict dorsiflexion
• Second-intention healing is an option for small defects with intact paratenon; bolster dressings and postoperative immobilization improve graft take

Key Landmarks

• Heel pad (calcaneal fat pad)
• Metatarsal heads (weight-bearing surface)
• Medial longitudinal arch
• Plantar aponeurosis

Danger Zones

Tumor Predilection

• Melanoma (Common): The plantar surface is the most common site for acral lentiginous melanoma (ALM). ALM is the most common melanoma in non-White populations. Dermoscopy showing parallel ridge pattern is pathognomonic. Any new or changing pigmented lesion on the sole should be biopsied.
• SCC (verrucous) (Moderate): Verrucous carcinoma (epithelioma cuniculatum) has a predilection for the plantar surface. Presents as a slowly enlarging, well-differentiated verrucous mass that can mimic a plantar wart.

Mohs Considerations

• NCCN H-zone due to functional importance; Mohs is the treatment of choice for plantar SCC and verrucous carcinoma to preserve weight-bearing tissue
• Plantar melanoma in situ may be treated with Mohs using immunohistochemistry (MART-1/HMB-45) at specialized centers to maximize tissue preservation for ambulation
• Deep margin assessment must account for the compartmentalized anatomy of the plantar fat pad; tumor may extend along fibrous septa

Reconstruction Principles

• Weight-bearing plantar defects require durable, padded reconstruction; full-thickness grafts from the non-weight-bearing instep provide the best glabrous skin match
• Local plantar flaps (V-Y advancement, rotation flaps) preserve native plantar padding and sensation, which are irreplaceable by grafts
• Large plantar defects may require free-tissue transfer (medial plantar artery flap, free fasciocutaneous flaps) for durable weight-bearing coverage