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23 March 2023 - Case of the Month #525

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Case of the Month #525

Clinical history:
A 25 year old man presented with a 1 cm, well demarcated, dome shaped, blue-black lesion on his finger, which was excised.

Histopathology images:

What is your diagnosis?

Click here for diagnosis, test question and discussion:

Diagnosis: Common blue nevus

Test question (answer at the end):
Which statement is usually true about common blue nevus?

A. It typically affects the elderly
B. A junctional component is commonly present
C. Close follow up is typically required because it is associated with malignant disease
D. Its melanocytes commonly express S100, HMB45 and MelanA (MART1)

Common blue nevus generally occurs on the skin, with predilection to the dorsal aspect of the hands and feet, buttocks, scalp and face. Rare examples have been reported in extracutaneous sites, including oral mucosa, vagina, cervix, prostate, spermatic cord and pulmonary hilus. It most commonly arises in children and young adults, commonly females, but can occur at any age or as a congenital lesion.

Blue nevus presents as a solitary, blue to black dome shaped lesion, usually about 1.0 cm in diameter. It may be due to arrested melanocytic migration from the neural crest. It is characterized by a dermal or submucosal proliferation of elongated, wavy spindle cells within the connective tissue or dense collagenous stroma. Cells can be arranged in nests and admixed with heavily pigmented melanophages. The pigmented bipolar dendritic cells do not display significant cytological atypia or mitotic figures. The overlying epidermis / mucosa lacks a junctional component.

Immunohistochemically, the melanocytes of blue nevus express S100, HMB45 and MelanA (MART1).

Nonneoplastic and inflammatory conditions resulting in cellular or extracellular pigment or post-hemorrhagic hemosiderin depositions can enter in differential diagnosis with blue nevus. Iron staining can be helpful in distinguish hemosiderin from Fontana-Masson positive melanin pigment.

Treatment: excision is adequate treatment because this lesion is benign with a low risk of malignant transformation. For atypical cellular blue nevi, excision with 1 cm margins and close follow up are recommended.

Am J Dermatopathol 1988;10:289, Adv Anat Pathol 2009;16:365, J Oral Pathol Med 1990;19:197, Urology 1974;4:617, Histopathology 2004;45:433

Test question answer:
D. Its melanocytes commonly express S100, HMB45 and MelanA (MART1). Answer A is wrong because it most commonly arises in children and young adults, not the elderly. Answer B is wrong because the overlying epidermis / mucosa lacks a junctional component. Answer C is wrong because excision is adequate treatment. Close follow up is needed only for atypical lesions.

Image 01 Image 02