Spindle cell melanocytic lesions: part II—an approach to intradermal proliferations and horizontally oriented lesions

Abstract

Melanocytic lesions show great morphological diversity in their architecture and the cytomorphological appearance of their composite cells. Whereas functional melanocytes show a dendritic cytomorphology and territorial isolation, lesional nevomelanocytes and melanoma cells typically show epithelioid, spindled or mixed cytomorphologies, and a range of architectural arrangements. Spindling is common to melanocytic lesions, and may either be a characteristic feature or a divergent appearance. The presence of spindle cells may mask the melanocytic nature of a lesion, and is often disconcerting, either due to its infrequent appearance in a particular lesion or its interpretation as a dedifferentiated phenotype. Spindle cell melanocytic lesions follow the full spectrum of potential biological outcomes, and difficulty may be experienced judging the nature of a lesion due to a lack of consistently reliable features to predict biological behaviour. Over time, recognition of numerous histomorphological features that may portend a more aggressive lesion have been identified; however, the translation of these features into a diagnostic entity requires a gestalt approach. Although most spindle cell melanocytic lesions may reliably be resolved through this standard approach, problem areas do exist for the surgical pathologist or dermatopathologist. With this review (part II of II), we complete our discussion of spindle cell melanocytic lesions, in order to: (1) model a systematic approach to such lesions; and (2) provide familiarity with those melanocytic lesions which either typically or occasionally display a spindled cytomorphology.

Cutaneous Clear Cell Sarcoma

“…Furthermore, all the tumors mentioned above are characterized by an intact EWS gene locus, which is inconsistent with CCCS. 15,16 Histologically, CCCS is a spindle cell tumor characterized by fascicles and nests of tumor cells surrounded by delicate fibrous connective rims or bands and scattered wreath-like giant cells. 11,12 A translocation at 22q12 is characteristically present in a subset of mesenchymal neoplasms in the so-called ''blue cell tumors category'' that includes Ewing sarcoma/peripheral primitive neuroectodermal tumors, extraskeletal myxoid chondrosarcoma, and some small cell liposarcomas.…”

Spindle cell melanocytic lesions—part I: an approach to compound naevoidal pattern lesions with spindle cell morphology and Spitzoid pattern lesions

“…Part of the appreciation of the biological diversity of melanocytic lesions has occurred as a result of the recognition that certain histopathologically disturbing melanocytic lesions may predictably behave in a benign manner (see figure 8 of Part II) 21a. Such clinicopathological correlation led to the recognition that benign naevi present in certain sites may exhibit histological features that normally connote an aggressive biological potential.…”

“…Vascular ectasia and an inflammatory component may also be seen in Spitz naevi. Spitz naevi may be present as the following histological variants: desmoplastic (refer to part II: intradermal proliferations);21a pigmented (pigmented spindle cell naevus; discussed below); angiomatoid (Spitz naevus with halo phenomenon); plexiform; hyalinised; myxoid; pagetoid; as a component of a combined naevus (refer to part II: combined lesions) 21a…”

“…However, such a phenomenon, when histologically benign, should be appreciated as satellitic Spitz naevi, akin to an agminated Spitz naevus, with no increased potential for malignant behaviour 118. Recurrent Spitz naevi119 may also be confused with a malignant process, and features of a recurrent naevus phenomenon should be appreciated (see part II: horizontally oriented lesions; naevi with disruption phenomena) 21a…”

“…The review is structured according to this approach. Part I deals with our algorithmic approach to spindle cell melanocytic lesions and includes their initial categorisation into compound naevoidal pattern lesions, Spitzoid lesions, intradermal proliferations and horizontally oriented lesions 21a. Part I further covers the compound naevoidal pattern lesions and the Spitzoid lesions.…”