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Atypical benign melanocytic lesions

Definition of atypia

· Any nevus which departs from it's normal counterpart e.g. banal nevus, acral nevus, genital nevus, Spitz nevus, Reed nevus · Atypia may be architectural when it is often of less or little significance · Cytological atypia is also of variable significance depending upon the context and site of the nevus · Stromal changes are probably of little importance

What is the pathologist's role in patient management?

· To recognize melanoma · To not over diagnose nevi as melanoma · To not under diagnose melanoma when at low power it looks like a nevus · To assess adequacy of excision · To recommend reexcision when necessary · To review previous biopsy specimens when pertinent · · · · ·

Melanocytic lesions which may show architectural & cytological atypia

Dysplastic nevus (always does by definition)* Banal nevus Recurrent nevus Neonatal nevus & proliferation nodule(s) Nevi at special sites genital and "milkline nevi", acral, ear & scalp · Common & cellular blue nevus · Spitz and Reed nevus

Problems with the use of the term atypical

· Implies diagnostic uncertainty · By definition must contain both completely benign and malignant lesions · Doesn't help the clinician or the patient · Leads to many consultations (which may be a good thing!) · May lead to loss of confidence in your diagnostic ability by the clinician


· Asymmetry · Border irregularity · Color variegation · Diameter > 6.0 mm · Evolution · Family history

Atypical nevi: histological parameters

Atypical nevi Junctional architecture Nest cohesion Nevus cell pigmentation Presence and size of nucleoli Maturation Lymphocytic infiltration Pagetoid spread Symmetry Circumscription Histological features Nest size Nest retraction artifact Cytological atypia Degree of atypia Pigmentary incontinence Mitotic activity Dermal mitoses Edge of lesion

Recurrent or traumatized nevus (pseudomelanoma)

· Follows incomplete removal after punch or shave biopsy or trauma · Presents within months as an irregular area of pigmentation in a scar · Dysplastic nevi may recur in addition to banal, blue, Spitz nevi & melanoma

Recurrent or traumatized nevus (pseudomelanoma)

· Dermal scarring · Junctional or compound · Asymmetrical lentiginous and/or nested population limited to scar · Variable atypia · Pagetoid spread

Recurrent nevus in a child aged 8 years

Spitz nevus

· · · · · · White population Generally children Pink, red or brown papule or nodule Face, trunk & extremities Agminated variant May be mistaken for PG or XG

Spitz nevus Histological variants

· · · · · · · · · Pagetoid intraepidermal Pagetoid and junctional Junctional Compound Dermal Desmoplastic Pigmented Combined "Atypical"

Spitz nevus Histological features

· Circumscribed · Symmetrical · Dyscohesive junctional nests · Retraction artifact · Epithelioid or spindled · Uniform pleomorphism · Prominent nucleoli · Kamino bodies

Spitz nevus Histological features

· Central pagetoid spread · Matures with depth · Infiltrating lower border · Occasional superficial dermal mitoses · No deep or atypical forms, necrosis or vascular invasion

The problem of "atypical Spitz nevus"

· · · · · · ·


Evolved as a consequence of partial biopsy Lack of confidence Litigation Never ending literature Atypical Spitz nevus does not exist Atypical Spitz never did exist Examples are either Spitz nevus or melanoma showing varying degrees of spitzoid morphology

Spitzoid melanoma (melanoma with variable spitzoid morphology)

· A melanoma which to a varying degree mimics a Spitz nevus

Atypical Spitz nevus

· A diagnosis to be avoided at all costs · Represents a convenient waste basket for any Spitz nevus which departs from the normal even if such departure is trivial in the extreme · When in doubt use immunohistochemistry e.g. S100 protein, cyclinD1, MIB1 and p53 · Show to colleagues and seek a consultation opinion

Congenital nevus

· · · · · · · 1% population Present at birth or soon after Small (up to 1.5 cm) Medium (1.520 cm) Large (>20 cm) Melanoma may arise in large variants Frequency : 3.818%

Atypical neonatal nevus

· Most neonatal nevi show features identical to any congenital nevus · Rarely, they may show severe cytological atypia, pagetoid spread & dermal mitoses such that a diagnosis of melanoma may be considered

Atypical neonatal nevus

· Large abnormally situated junctional nests with appendageal involvement · Lack of maturation · Cytological atypia of junctional & dermal components · Pagetoid spread · Dermal mitoses

4 month old child

7 months

Proliferation nodule

· Smooth surfaced brown to black papule/nodule arising in a congenital nevus · Typically solitary; satellite lesions may occur · Large epithelioid melanocytes, abundant cytoplasm and mildly pleomorphic nuclei which may blend at the margin of the adjacent nevus or more often present as a distinct, circumscribed lesion · Mitoses are "said" to be rare and necrosis is not a feature · May show metaplastic features

Nevi at special sites

· Vulva · Groin · Umbilicus · Breast · Axilla · Scalp · Ear · Acral · · · ·

Atypical genital (milk line) nevus

Children & young women Pigmented, irregular macules or papules =/< 1.0 cm Labium majus, mons pubis, labium minus & clitoris · Also umbilicus, axilla, breast & inguinal folds

Atypical genital nevus

· Asymmetrical · Large junctional nests of dyscohesive, atypical melanocytes · Pigmentation ++ · Bridging · Pagetoid spread · Dermal mitoses · Banal deep component · Maturation with depth

Nevus of Nipple & Breast

· Lentiginous & nested · Enlarged nests · Retraction artifact · Often dyscohesive · Focal pagetoid spread · Mild cytological atypia · Often dendritic forms · Pigment incontinence · Lymphocytic infiltrate

Nevus of the ear

· Asymmetrical & poorly circumscribed · Shoulder formation · Architectural disorder · Focal pagetoid spread · Moderate to severe cytological atypia · Large vesicular nuclei · Prominent nucleoli · Absence of mitoses & apoptosis

Scalp nevus

· · · · · · · · Symmetrical Circumscribed Large dyscohesive nests Architectural disorder Follicular involvement Mild cytological atypia Focal pagetoid spread Limited impaired maturation

Acral nevi Clinical features

Acral nevi Histological features

· Circumscribed & symmetrical · Lentiginous & nested proliferation · Variable nest size · Retraction artifact · Vertical nest orientation · Nest elimination

Small, usually 23mm diameter brown or black macules on fingers, toes, elbows, knees and nails predominantly affecting children or young adults

"Maniac" Histological features

· Poor circumscription · Lentiginous & nested · Basal melanocytes with dendrites · Cytological atypia · Pagetoid spread · No mitoses or apoptosis

Differential diagnosis

Features favoring a diagnosis of melanoma include: Size >56mm Irregular acanthosis More widespread cytological atypia Disordered pagetoid spread in evolved lesions Mitoses/apoptosis Dendritic processes reaching granular layer Inflammatory cell infiltrate in dermis

Pagetoid (lentiginous) Spitz nevus

· Lentiginous growth pattern · Uniform enlarged melanocytes with even distribution · Abundant cytoplasm, retraction artifact, vesicular nuclei · Multinucleate forms · Pagetoid spread

Atypical benign melanocytic lesions

· Diagnosis depends upon careful clinicopathological correlation · Never make a diagnosis on a melanocytic lesion without knowing the site and age of the patient · When in doubt, show the case to a colleague or send it out for a consultation


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