What are the features of a solar lentigo?
Thin rete with bulbous tips “dipped in chocolate”
Note that reticulated SKs look similar have anastomosis of the rete ridges and horn cysts
What are the features of a melanotic macule?
Where are they found?
- Common on lips and genitals
- Rete are broad and squared off with pigment at basal layer
- May have strikingly irregular pigment if on genitals, but usually light brown and evenly pigmented
What is meant by maturation of melanocytes in a benign melanocytic nevus?
What should be ABSENT at the deep component of the lesion?
- Melanocytes become progressively smaller and spindled at deeper portions of lesion
- Deep mitoses should be absent
- Melanin should NOT be present in deep melanocytic nests, which can be confirmed by HMB-45 staining → loss of staining in deep component is a surrogate marker for maturation
- EXCEPT for blue nevi, which have pigment to the base of the lesion
In benign nevi, where are the junctional nests typically located? What about in a melanoma?
- Benign nevus → tips and sides of rete
- Melanoma → tops of dermal papillae are often involved as well
How can HMB-45 and MIB-1 be used to discern between a benign nevus and melanoma?
- Benign nevus → HMB-45 stains top heavy and MIB-1 does not stain deep nuclei
- Melanoma → HMB-45 commonly stains strongly to base and MIB-1 stains deep nuclei
What are the features of a balloon cell nevus?
- Balloon change is a degenerative feature caused by swelling of cellular organelles
- Usually sharply defined
- Well nested at DEJ
- Matures
- No deep mitoses or pigment
The nevic corpuscles of a neural nevus appear similar to what other structure?
“Little corn cob in dermal papilla that feels the lightest touch. They do not detect pain.”
What are the features of a neural nevus?
- S-shaped spindle cells similar to a neurofibroma
- Nevic corpuscles resembling Meissner corpuscles
- Sharply defined
- Matures
- No deep mitoses or pigment
What are the features of a congenital nevus?
- Look for aggregates about follicles, vessel walls, and nerves
- Patchy perivascular pattern of melanocytes
- Single-file interstitial pattern of melanocytes
What type of collagen composes Kamino bodies in Spitz nevi?
Type IV collagen
What should be the staining pattern visualized for a Spitz nevus with the following stains: HMB-45, S100A6, and MIB-1?
- HMB-45 → top-heavy
- S100A6 → stains diffusely
- MIB-1 → absent in melanocyte nuclei at base of lesion
What are the features of a “special site” nevus?
- May resemble a dysplastic nevus or have large junctional nests that are poorly cohesive (white space surrounding each melanocyte)
What are the features of an acral nevus?
- Nests are elongated and follow dermatoglyphs
- Buckshot scatter is OK at center of lesion
- Well nested at DEJ
- Matures
- No deep mitoses or pigment
What are the features of an ancient nevus?
- Large, hyperchromatic nuclei
- No confluent growth or expansile growth pattern
- No mitoses
- Sharply defined
- Well nested at DEJ
- Matures
- No deep pigment
What are the features of a halo nevus?
- Bandlike lymphoid infiltrate through lesion with lymphocytes and melanocytes mingling together “like a cocktail party” (as opposed to the “riot police” [walling off] of a melanoma)
What are the features of a blue nevus?
- Wedge or bulbous outline
- Pigmented to the base of lesion
- Melanocytes do not mature
- No deep mitoses
- Typically has a distinctive sclerotic, red stroma
What type of blue nevus is associated with Carney complex?
Epithelioid blue nevus
What are the features of a combined nevus?
Two or more populations of nevus cells
What are the features of a Wiesner nevus (benign BAPoma)?
- A unique type of combined nevus with a clone of combined nevus with a clone of epithelioid nevus cells embedded in a banal nevus
- Unlike Spitz nevi, the epithelioid population lacks vesicular nuclei, does not mature/disperse at base
- Hyperchromasia and pleomorphism common
- Boomerang nuclei cells present
- HMB-45 stains strongly to base (similar to melanoma)
- Strong p16 staining, loss of BAP-1 within clone
- Low MIB-1 (Ki-67) fraction
Weisner nevus (BAPoma) is associated with what familial syndrome?
Familial uveal melanoma/renal carcinoma syndrome
What are the features of a benign Clark nevus (dysplastic nevus)?
- Fading border or fried-egg appearance clinically
- Fading macular border corresponds to “shoulder” region
- Club-shaped hyperplasia of rete
- Horizontally oriented nests with bridging of adjacent rete
- Concentric papillary dermal fibrosis
- Large oval melanocytes, especially of shoulder region
- Matures
- No deep mitoses or deep pigment in nests
What are the features of a junctional lentiginous nevus?
- Club shaped epidermal hyperplasia
- Round/oval melanocytic nests at DEJ, and tips and sides of rete
What are the features of recurrent nevus (also known as persistent nevus or pseudomelanoma)?
- Confluent, poorly/irregularly nested junctional melanocytic proliferation
- Underlying scar
- Melanocytic proliferation confined to area overlying scar
- May see residual bland nevus under scar
What are the features of a nevus of Ota/nevus of Ito?
- Dendritic melanocytes scattered between collagen bundles in upper third of dermis
- Melanocytes oriented east to west
- No sclerotic stroma
- Nevus of Ota → face
- Nevus of Ito → shoulder
