Cytological Diagnosis of an Uncommon Tumor of the Minor Salivary Gland - Basal Cell Adenoma.

Sir,

Basal cell adenoma is a rare benign epithelial tumor of the salivary gland; more than 80% arise in the major salivary glands mostly in the parotid and rarely in the upper lip and buccal mucosa.[1] It represents 1%–3% of all salivary gland neoplasms and seen predominantly in women over 50 years of age.[23]

Cytodiagnosis is challenging. The cytological differential diagnosis ranges from benign to malignant, neoplastic to non-neoplastic lesions.[3] Histopathology is a must for definitive diagnosis as these entities differ in prognosis and therapeutic aspects. Basal cell adenoma usually exhibits a monotonous, solid, tubular, trabecular, or membranous growth pattern. A mesenchymal/chondromyxoid stroma is absent.[4]

A 65-year-old lady presented with a swelling in the right buccal mucosa of 2 years duration. Clinical examination revealed a non-tender nodule in the right buccal mucosa measuring 2 × 3 cm in size. There was no history of fever, weight loss, or any other relevant clinical history. Fine-needle aspiration cytology (FNAC) was performed.

FNAC smears showed basaloid cells arranged in nests, sheets, and tubules. The cells had regular, round/oval nuclei with sparse cytoplasm and a bland nuclear chromatin. Variable amounts of pink stromal material were seen scattered. Squamous morules, hyaline globules, stromal elements, inflammatory cells, pleomorphism, mitosis, and necrosis were absent [Figure 1a and b]. Based on FNAC picture, a diagnosis of basal cell adenoma was made. Following excision, histopathology revealed a well-capsulated tumoral mass comprising mainly tubules lined by two layers of cells with inner cuboidal ductal cells surrounded by an outer layer of basaloid cells. At places, the lumina contained pink secretions. Multiple sections did not reveal chondromyxoid stroma [Figure 1c and d]. Thus, the diagnosis of basal cell adenoma (tubular type) was confirmed on histopathology.

Figure 1

:(a) FNAC smear showing cells arranged in nests, sheets and tubules (H & E stain, X40), (b) FNAC smear showing basaloid cells having regular nuclei with sparse cytoplasm (H & E stain, X100), (c) Histologic section revealing tumoral mass comprising mainly of tubules (H & E stain, X100), (d) Histologic section showing tubules lined by inner cuboidal ductal and outer basaloid cells (H & E stain, X200)

Basal cell adenoma typically presents as a solitary, slow growing, asymptomatic mass.[4] Presentation peaks in the sixth to seventh decade and there is a slight female predominance.[4] It is rarely seen in the buccal mucosa with only 3% involving minor salivary glands.[1]

Basal cell adenoma should be differentiated from basal cell adenocarcinoma, poorly differentiated adenoid cystic carcinoma, basaloid variant of squamous cell carcinoma, and morphologically similar tumors (epithelial–myoepithelial carcinoma, polymorphous low-grade adenocarcinoma).[5] Cytonuclear pleomorphism, large three-dimensional cellular clusters with glandular structures, mitotic figures, and/or evidence of necrosis suggests malignancy.[5] The present case did not have any of these features.

Surgical excision is the treatment of choice for basal cell adenoma.[4] Recurrences are rare.[4] Hence, a preoperative FNAC diagnosis would aid the surgeon in planning proper surgical treatment modality, that is simple excision.

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