Aspiration cytology in the preoperative diagnosis of granular cell tumor of thyroid region in an 11-years-old female child.

Sir,

Granular cell tumor (GCT) is a rare tumor and even rarer in children. They are neoplasms of uncertain histogenesis but neural origin is favored.[123] Here, we present a case of GCT in an 11-years-old female child who presented with well circumscribed, non tender, firm swelling of size 4 cm × 4 cm × 2 cm in the right thyroid region which was not moving with deglutination or protrusion of tongue. The swelling was present for 2 years. Ultrasonography (USG) confirmed a well encapsulated subcutaneous oval mass anterior and superior to right lobe of thyroid. Fine needle aspiration cytology (FNAC) slides stained with geimsa stain revealed polyhedral cells in syncitial clusters and in isolation with granular background. The cells showed central to eccentric round to oval nuclei, granular nuclear chromatin, small nucleoli, and abundant basophilic granular cytoplasm with ill defined fragile outlines. Cytoplasmic granules were Periodic acid-Shiff's (PAS) positive and diastase resistant. A cytological diagnosis of benign granular cell tumor was made [Figure 1a]. On biopsy, the lesion was grey white, well-circumscribed soft tissue measuring 3.5 cm × 3 cm × 1.5 cm. Microscopic examination of biopsy tissue showed characteristic picture of GCT with tumor cells arranged diffusely and separated by fibrocollagenous septae. Individual tumor cells were large polyhedral having abundant granular eosinophilic cytoplasm and ill defined cell borders. Nuclei were round to oval. Some nerve fibres were encased by the tumor. There was no necrosis or mitotic activity. Lymphoid aggregates were seen at some places. PAS stain showed granular cytoplasmic positivity which was resistant to diastase. Immunohistochemistry showed positivity for S-100 protein [Figure 1b]. The tumor was reported as benign GCT.

Figure 1

(a) Polygonal tumor cells in granular background showing fragile cytoplasmic boundaries, round nucleus, granular nuclear chromatin, and granular cytoplasm (Giemsa, ×400) Inset shows PAS positive diastase resistant granules (PAS with diastase, ×400); (b) Polygonal tumor cells with abundant granular cytoplasm, round to oval to spindle nuclei and small nucleoli (H and E, ×400). Inset tumor cells positive for S-100 protein (IHC, ×400)

Granular cell tumors are uncommon tumors that can occur at many sites although it affects most frequently head and neck, chest wall and arms.[1] Incidence among children is low and involvement of thyroid region is quite rare. In this case an USG was done which helped in the precise location of tumor and showed that the tumor had no relation with the thyroid gland. Also the tumor had peculiar cytological features and lacked pleomorphism, mitosis, atypia and necrosis differentiating it from malignant GCT.[23] Differentiation from alveolar soft part sarcoma (ASPS), rhabdomyoma, and histiocytes may at times be difficult. Alveolar soft part sarcoma cells are more epithelioid and show multinucleate giant cells, macronucleoli, cytoplasmic vacuolation, delicate threads of metachromatic staining material, and PAS positive needle like structures. Also ASPS is negative for S-100 protein.[4] Rhabdomyoma in contrast to GCT has well defined cytoplasmic borders, cytoplasmic cross striations, and clean background. Special stains and immunostains that show skeletal muscle differentiation will also help in differentiating GCT from rhabdomyoma.[5] GCT's have round nuclei as compared to bean shaped nuclei of histiocytes.[3]

In conclusion, a cytologist may encounter GCT at uncommon locations and unusual age groups but most of the times the cytological features are distinctive enough to suggest a correct diagnosis on FNAC which can help in the proper management of the patient.