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Granular cell tumor (GCT) is an uncommon benign neoplasm of uncertain histogenesis. Although they can occur at any site, tongue, breast, upper respiratory tract, and soft tissue of upper extremities are their common locations. As the lesions presenting on skin are located deep in the subcutis, they are not aspirated very often and so the reports of their cytological diagnosis at this site are sparse in literature. We report to the best of our knowledge the third case of cutaneous GCT diagnosed by fine-needle aspiration cytology (FNAC).
A 40-year-old man presented to the dermatology outpatient clinic with a well-defined erythematous lesion on his right forearm of 2 years’ duration that had been gradually increasing in size. Physical examination showed a 3.2 × 2.1 × 1.0 cm erythematous, firm, nontender plaque with smooth surface and subcutaneous firm mass [Figure 1]. The patient was referred for FNAC with provisional clinical diagnosis of dermatofibroma.
FNAC was done using a 22-gauge needle and a 20 cc syringe. The smear stained with Giemsa stain showed moderate cellularity and was composed of loosely dispersed groups of cells and stripped bare nuclei. The cells were large, polygonal, without appreciable cell borders containing abundant granular and fragile cytoplasm [Figure 2]. These cells showed PAS-positive diastase resistant cytoplasmic granules representing the phagolysosomes. The nuclear cytoplasmic ratio was low with round to oval central nucleus, small nucleoli, and fine chromatin pattern with occasional intranuclear inclusions [Figure 2, inset]. Some cells showed anisonucleosis; however no mitoses or pleomorphic spindle cells were noticed. The lesion was suggested to be a cutaneous GCT and excision biopsy was advised. Histopathological examination of the excised specimen showed a tumor consisting of polygonal cells with abundant granular cytoplasm [Figure 3]. They were arranged in lobules and extended deep into the subcutis. The cytoplasmic granules were PAS positive and diastase resistant [Figure 4a] and immunohistochemistry for S-100 was positive [Figure 4b]. A diagnosis of benign cutaneous GCT was confirmed.
GCT are uncommon tumors of putative neural origin and may occur at any site though they seldom involve the skin. They usually present between fourth to sixth decades of life and show a slight preponderance toward adult females. The cytological findings of cutaneous GCT seen in our case were in accordance with the previously described reports[1,2] and the presence of intranuclear inclusion in a few cells appears to be a useful cytomorphologic feature as described by Liu et al. in soft tissue and later by Mallik et al. on the skin of a forearm of a child. In most cases the cytological features are distinctive enough but differentiation from other lesions that resemble the cytological features of GCT is necessary. The foremost lesion that needs to be excluded is the alveolar soft part sarcoma that shows prominent nucleoli, multinucleated cells, and the characteristic rhomboid crystals. The absence of cross-striations and glycogen distinguishes GCT from rhabdomyoma while, the absence of lipid droplets excludes hibernoma.
To conclude, GCT may rarely present as a cutaneous lesion and both the dermatologist and the pathologist should be aware of this entity which can be diagnosed easily by FNAC.