SPINDLE CELL NEVUS (SPITZ)
Originally described by Sophie Spitz as 'juvenile melanoma', this lesion has been subsequently renamed 'spindle cell nevus'. It has also been designated 'melanocytoma of Spitz'. The latter term may be preferable, but the more common term 'spindle cell nevus' is more widely used.

It has been stated that the diagnosis of a Spitz' nevus involves a decerebrate process, and it is true that experience is more valuable than knowledge of written criteria for making this diagnosis. However, there are a few points worth mentioning.

Spindle cell nevi occur most frequently in children, and there may be a history of rapid growth. These lesions are composed of plump spindle cells and/or plump epithelioid cells. These may be confined to the epidermis (junctional), confined to the dermis (intradermal), or, most commonly, found in both locations (compound).  The intradermal component usually has a fascicular component, particularly in the more superficial part of the lesion, and  the fascicles are separated from each other by connective tissue.There may be single cells or small groups of cells between native reticular dermis collagen bundles, particularly in the deep part of the lesion. The cells in the deep part of the lesion usually are smaller than the more superficial cells, and this is called maturation. Spindle cell nevi usually are symmetrical from side to side. Large epithelioid cells, when present, frequently have 'myoid' features, and these cells may fit together in a jigsaw puzzle pattern in clusters. Clefts may be formed between intraepidermal nests of cells and the adjacent epidermis.

Mitotic figures, cytologic atypia, a lymphocyte response, pagetoid cells in the epidermis, cells that appear to be in lymphatics, and perineural localization can be seen. These findings are acceptable in Spitz' nevi, particularly in young children. Such findings, if prominent, in adults may prompt a diagnosis of 'atypical spindle cell nevus' and a recommendation for conservative excision should be made.

Scan of this shave type biopsy. Click on the image to go to a larger, composite image (takes a while to download).
Low power view showing fascicular pattern and other things of interest. Note the absence of evidence of the radial growth phase of a melanoma in this example.
High power of superficial dermis of above. Note the large strap cell or myoid cell. Note the nuclear hyperchromatism.
High power of middle of dermis showing fascicular pattern.
High power of another area in the mid dermis. This cell in the center has more cytologic features of malignancy than many cells in many malignant melanomas. 
Another high power showing cytologic atypia. The distinction between benign and malignant melanocytic lesions cannot be made on the basis of a single isolated criterion.
High power of the deep part of the biopsy. The cells are smaller than those that are found in the superficial dermis. This is so-called maturation.

Another case but with less atypia:
 
Low power view of a spindle cell nevus from a child. Note the fascicles that are separated by connective tissue.
High power view of same.

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