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Granular cell ameloblastoma‐diagnosis on aspiration cytology

To the Editor, Ameloblastoma is the most common odontogenic neoplasm arising in the mandible. However, granular cell variant of ameloblastoma (GCVA) constitutes only 4% to 5% of the ameloblastoma and poses a diagnostic dilemma by the presence of granular eosinophilic cells. A few cases of GCVA had been described in literature till date. We present a case of GCVA with its detailed cytological features and correlation with radiological and histological findings. A 55-year-old male presented with swelling in the left-sided lower jaw for duration of 1 year associated with pus like discharge in the oral cavity. On examination, a firm swelling was identified in the left mandibular region. No enlarged lymph nodes were identified. Contrast enhanced computer tomography revealed expansile lytic lesion in the lower mandible extending anteriorly up to mandibular symphysis and posteriorly up to the angle of mandible (Figure 1). Soft tissue enhancement measuring 2.6 cm in maximum dimension was also noted associated with the lesion. Overlying cortex was thinned out and appeared deficient at multiple sites. Superiorly alveolar aspect of the mandible was also involved. The patient was subjected to standard fine-needle aspiration cytology (FNAC) under ultrasound guidance from the mandibular lesion, followed by a biopsy from the same lesion. Cytological features: FNAC performed was of moderate cellularity and showed multiple cell clusters with peripheral palisading of the nuclei. The cells showed abundant granular cytoplasm with hyperchromatic nuclei polarized away from the basement membrane (Figure 2). This is in contrast to the other ameloblastoma variants, where the cells show basaloid cells morphology with scant cytoplasm. The stromal component included showed presence of few metaplastic squamous like cells with elongated cytoplasm and tapered ends. These cells resemble the stellate cells of the tooth germ. Background showed presence of few neutrophils. FNAC was predominantly composed of the granular eosinophilic cell component making the diagnosis a challenging one. The possibility of warthin cell tumor, oncocytoma, and oncocytic variant of mucoepidermoid carcinoma were also considered in the differential diagnoses. However, the lack of lymphocytic background and the absence of mucous cells with cytoplasmic vacuolation favored the diagnosis of ameloblastoma, granular cell variant. Histological features: Biopsy performed later showed predominantly multiple follicles lined by granular odontogenic neoplastic epithelial cells with peripheral palisading. Granular cells were present predominantly in luminal aspect of the follicles (Figure 3). Focally presence of plexiform type of ameloblastoma with stellate reticulum cells were also identified. These neoplastic odontogenic cells and granular cells showed diffuse immunopositivity for cytokeratin 5/6 and cytokeratin 19. GCVA is characterized by the presence of granular cells in the center of follicles. The granular cells represent a transitional or matured phase in ameloblastoma lifecycle which begins from stellate cell, leading to granular cell with granules production, and later cyst formation. In the index case, there were multiple cell clusters with peripheral palisading of the nuclei. The cells showed abundant granular cytoplasm with hyperchromatic nuclei polarized away from the basement membrane. This was in contrast to the other ameloblastoma variants, where the cells show basaloid cells morphology with scant cytoplasm. Similar to the previous cytological descriptions of granular cell ameloblastoma by Deshpande et al, the smears were predominantly composed of the granular eosinophilic cells but with the lack of basaloid cells, the possibility of salivary gland tumor like warthin cell tumor, oncocytoma, and oncocytic variant of mucoepidermoid carcinoma were also considered in the differential diagnoses. However, the lack of lymphocytic background and the absence of mucous cells