Answer to Image of the Month December 2015
Submitted by Gnanapriya and Suravi Mohanty
Spitz nevus
Spitz nevus most commonly occurs in children and young adults. Clinically, it presents as a single dome shaped papule or nodule. It is most commonly located on the face and extremities. Microscopically, it is symmetrical and usually involves both the epidermis and dermis although occasionally it may be junctional or intradermal. The melanocytes are spindled and/or epithelioid and arranged as nests in vertical orientation. Their nucleus is large, round to oval with small round nucleoli and there is moderate to abundant cytoplasm with sparse pigmentation. Multinucleation may occur and pseudonuclear inclusions may be prominent. Maturation in depth is noted. Occasional mitotic figures are noted and are usually seen in the epidermis or in the dermoepidermal junction. Eosinophilic Kamino bodies composed of PAS positive basement membrane components are usually located at the dermoepidermal interface. The overlying epithelium may show pseudoepitheliomatous hyperplasia, hypergranulosis or hyperkeratosis which is more prominent in lesions with a junctional component. The other variants include pigmented spindle cell nevus (Reed’s nevus), desmoplastic Spitz nevus and angiomatoid Spitz nevus. Reed’s nevus is composed exclusively of heavily pigmented spindle cells and tends to be junctional. Desmoplastic Spitz nevus is composed of chiefly epitheloid cells within a sclerotic dermal stroma. Angiomatoid Spitz nevus, considered to be a variant of desmoplastic Spitz nevus, is composed of epitheloid cells with prominent thick walled vessels and perivascular infiltrate in a sclerotic stroma.
Symmetry, absence of pushing margins, absence of significant pleomorphism, lack of maturation in depth, absence of mitotic figures at the base and pattern of staining with immunohistochemical markers (HMB-45 and Ki-67) help to differentiate it from atypical Spitz nevus and Spitzoid melanoma. Other differentials include juvenile xanthogranuloma and pyogenic granuloma.