Cytological Features of Cutaneous Granular Cell Tumor: A Brief Report.

Sir,

Granular cell tumors (GCTs) are uncommon neural origin tumors. It is most commonly found in tongue, breast, upper respiratory tract, and subcutaneous tissue of extremities.[1] As the lesions presenting on skin are located deep in the dermis, they are not aspirated very often, and reports on their cytological diagnosis at this site are few in literature.[2] The cytological diagnosis of GCT is quite challenging as it mimics many soft tissue and inflammatory lesions.

A 55-year-old female presented with a painless, deep-situated swelling in the right infraclavicular region since 6 months. The swelling was 2 × 1 cm in size, ill-defined, nontender, and firm in consistency. Fine needle aspiration was done and smears were stained by May–Grünwald–Giemsa.

Smears were moderately cellular showing clusters of cells having polygonal shape with abundant, fragile, eosinophilic, finely granular cytoplasm. The nucleus was round, with bland chromatin. Few cells showed small nucleoli and intranuclear cytoplasmic inclusions. Many stripped nuclei were also seen scattered singly. Mild nuclear pleomorphism was seen [Figure 1a and b]. Based on these features, a cytological diagnosis of benign GCT was suggested.

Figure 1

(a) Cell clusters showing abundant indistinct eosinophilic granular cytoplasm. Inset showing intranuclear inclusion (May–Grünwald–Giemsa stain, ×400). (b) Many stripped nuclei seen (May–Grünwald–Giemsa stain, ×200). (c) Nests of cells having eosinophilic granular cytoplasm. Inset showing PAS positivity (hematoxylin and eosin stain, ×400). (d) S-100 immunohistochemistry showing strong nuclear and cytoplasmic positivity

Histopathological examination showed an unencapsulated tumor comprising closely packed sheets of polygonal cells having highly eosinophilic, granular cytoplasm with central round nucleus and bland nuclear chromatin surrounding nerve fibers and skeletal muscle bundles. Features were suggestive of GCT [Figure 1c]. Special stains including periodic acid–Schiff (PAS) and PAS-D (diastase) were done, which were positive and PAS-D-resistant. Immunohistochemistry using S-100 was done which showed strong cytoplasmic and nuclear positivity which confirmed the diagnosis [Figure 1d].

GCT arises in middle-aged adults with slight female predominance. The differential diagnosis (DD) includes xanthogranuloma, alveolar soft part sarcoma (ASPS), rhabdomyoma, malignant GCT, and oncocytic lesions as all these present with cells having abundant eosinophilic cytoplasm on cytology.[3] In this case, the closest DD was apocrine carcinoma of breast as the swelling was situated close to the breast tissue. In contrast to GCT, the cells in apocrine carcinoma show a more distinct, slightly basophilic cytoplasm, significant nuclear atypia, pleomorphism, and prominent nucleoli, and hence this possibility was ruled out. Skeletal muscle neoplasms, rhabdomyoma, and ASPS are close mimickers of GCT. Whereas rhabdomyoma was excluded by the absence of cross striations and spider cells, ASPS was ruled out by the absence of nuclear atypia and intracytoplasmic rhomboid crystals.[4] Malignant GCT, although very rare, was also excluded due to the lack of nuclear atypia. Xanthogranuloma was also easily ruled out due to absence of accompanying inflammatory cells and histiocytes having vacuolated cytoplasm and indented nucleus.

Definitive cytological diagnosis of GCT is possible by sequentially excluding out its close mimickers. Presence of intranuclear cytoplasmic inclusions (described by Liu et al.,[5]) and stripped nuclei which arise due to fragility of cells[4] also provide important diagnostic clue. Since GCT is known for recurrence, its correct preoperative cytological diagnosis becomes essential to enable a wide local resection.

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