Basal cell adenoma of the deep lobe of the parotid gland misdiagnosed as mucoepidermoid carcinoma - A case report

Abstract

Introduction: Basal cell adenoma is a rare, benign epithelial tumour of the salivary gland, comprising only 1-2 % of all salivary gland tumours. Predominantly found in the parotid gland, basal cell adenoma can also occur in minor salivary glands and are often confused with other benign and malignant salivary gland tumours. A thorough histopathological examination can provide a definitive diagnosis.

Presentation of case: A 65-year-old woman presented with a painless mass in the right infra-auricular region. Imaging revealed a well-defined hypodense lesion in the deep lobe of the right parotid gland, initially suspected as mucoepidermoid carcinoma. Fine needle aspiration was inconclusive, leading to the decision to perform a total conservative parotidectomy. Histopathology confirmed basal cell adenoma, characterized by cystic areas filled with mucoid material and basaloid cells arranged in trabecular and tubular patterns.

Discussion: Basal cell adenoma was classified as a distinct entity by the WHO in 1991. Cytologically, they imitate both benign and malignant salivary as well as non-salivary gland tumours. The histological hallmark of basal cell adenoma involves basaloid cells with small round nuclei showing no atypia, scant pale cytoplasm, and distinct peripheral palisading. Treatment involves surgical removal, with a more radical approach for certain variants such as the membranous type.

Conclusion: This case highlights the clinical, radiological, and histopathological features of basal cell adenoma, emphasizing the importance of accurate diagnosis and appropriate surgical management. Early detection and appropriate treatment are crucial for optimizing patient outcomes in basal cell adenoma management.

Keywords: Basal cell adenoma; Case report; Parotid gland; Parotid neoplasm; Salivary gland neoplasm.

Fig. 1

Contrast enhanced computed tomography showing a well-defined hypodense lesion (red arrow) arising from both superficial and deep lobes of right parotid gland with enhancement and an area of cystic/necrotic component on its lateral aspect. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

(A) Facial nerve exposed after superficial parotidectomy. (B) Total conservative parotidectomy with all the branches of the facial nerve preserved.

Fig. 3

(A) The Cut section of the superficial parotidectomy specimen shows a well-circumscribed solid and cystic lesion. (B) Microscopically, the neoplasm is well-capsulated and distinct from normal parotid tissue. (C) The solid portion comprises cuboidal cells in trabeculae, tubules, nests and sheets. (D) The tubular-trabecular pattern of cuboidal cells shows minimal nuclear atypia and variable cellular stroma. (B and C are magnified at 100×, and D is at 400×.)

Fig. 4

(A) Postoperative transient marginal mandibular nerve paresis (B) Normal facial nerve function on 1 month follow up.