A Rare Presentation of Canalicular Adenoma of the Parotid Gland
Canalicular adenoma is an uncommon benign neoplasm of the salivary glands. It occurs almost exclusively in the upper lips, next common site being the buccal mucosa. Parotid gland is a rare site for its occurrence. It is most likely to occur in the elderly. Here we report a case of a 43-year-old male, who presented with a history of a swelling below the right ear.
Canalicular adenoma occurs most commonly in the elderly, with a mean age of 65 years, and a slight female predilection. It is primarily an oral lesion. The upper lip is the site of predilection, which accounts for 74% of the cases, followed by the buccal mucosa (12%), palate, and, rarely major salivary glands. Patients present with a non-ulcerated, painless mass that grows slowly. Infrequently, multifocal nodules, ulceration, necrosis, and bone destruction may be seen.
Here, we present a case of a 43-year-old male with a history of swelling below the right ear for the past 3 months. The patient was subjected to a fine needle aspiration cytology (FNAC) and the diagnosis of pleomorphic adenoma was made. The lesion was subsequently excised and sent for histopathology.
A 43-year-old male presents with a chief complaint of noticing a swelling below his right ear for the past 3 months, which had gradually increased in size over this duration. This patient had no other specific disease or any history of trauma to the area.
On examination, it was a single swelling measuring 3 x 3 centimetres (cm), just above the angle of mandible on the right side of firm consistency, mobile, and non-tender. FNAC was done and the diagnosis of pleomorphic adenoma was made. The lesion was subsequently excised and sent for histopathology.
Gross examination showed a brownish-white irregular shaped specimen measuring 4 x 3 x 2 cm. Cut-section showed a well circumscribed nodule measuring 2 cm.
Microscopically, there was a well circumscribed tumoral mass comprising of bilayered strands/ribbons of columnar epithelial cells separated by a loose, well-vascularised stroma. In places they were arranged in sheets. Cells had moderate amount of cytoplasm and vesicular nuclei with prominent nucleoli. No mitosis seen.
A final histopathological diagnosis of canalicular adenoma was made.
Salivary gland tumors are unusual and less than 3% of all head and neck neoplasms. Canalicular adenoma represents less than 1% of all salivary gland tumors. Most salivary gland tumors of the head and neck involve the major salivary glands, with benign minor salivary gland tumors often involving the hard palate, buccal mucosa and tongue. Canalicular adenoma, however, has a significant predilection for occurrence in the minor salivary glands, with highest occurrence observed in the upper lip followed by the buccal mucosa. Canalicular adenomas are sometimes multifocal. Despite this predilection for the upper lip, there are reports of canalicular adenomas occurring in the lower lip. There have been no reports of canalicular adenomas of the submandibular gland or sublingual gland, and canalicular adenoma is rarely found in the parotid gland.
Monomorphic adenomas are benign epithelial tumors of salivary glands without any evidence of mesenchyme-like tissue. The term monomorphic adenoma was originally proposed for any benign epithelial salivary gland tumor other than benign mixed tumors (pleomorphic adenoma) and it therefore includes tumors such as oxyphillic adenoma, Warthin tumor, sebaceous lymphadenoma, and basal cell adenoma.
The term monomorphic adenoma is no longer used (it does not appear in the new WHO classification of salivary gland tumors) and tumors in this category are named according to their composition and appearances. According to Batsakis et al. the histological classification of monomorphic adenoma is as follows:
(i) Tumors of terminal duct origin: basal cell adenoma, canalicular adenoma.
(ii) Tumors of terminal or striated duct origin: sebaceous adenoma, sebaceous lymph adenoma.
(iii) Tumors of striated duct origin: oncocytoma, papillary cystadenoma lymphomatosum also called Warthin’s tumor.
(iv) Tumors of excretory duct origin: sialadenoma papilliferum or inverted ductal papilloma.
Canalicular adenomas are usually small (< 3 cm) and well-circumscribed, with or without a capsule. Multifocal lesions are not uncommon. It is composed of bilayered strands of cells that abut and diverge haphazardly, giving rise to single files, beads, canaliculi, and pseudopapillae. The epithelial cells that form the strands are cuboidal or columnar, with a moderate amount of amphophilic cytoplasm and regular oval nuclei. Cellular pleomorphism and mitoses are not seen. The stroma is characteristically edematous with many capillaries and sinusoids; it can be so loose that tumour strands may appear to be ‘floating in the air’.
Immunohistochemistry and Electron Microscopy Findings:
The tumor cells are positive for cytokeratin, vimentin, S100 protein, and infrequently epithelial membrane antigen (EMA). A distinctive pattern of linear GFAP immunoreactivity is seen at the interface between tumor cells and connective tissue.
Although canalicular adenoma is a rare entity, especially when it is not located on the upper lip, it is important to consider this tumor type when differentiating between pleomorphic adenoma, basal cell adenoma, Warthin’s tumor, and especially adenoid cystic carcinoma, when this occurs in the parotid gland. Histopathological biopsy is required for accurate diagnosis, because it may be difficult to differentiate canalicular adenomas from other diseases using FNACs alone.
- Ellis GL, Auclair PL. Tumors of the salivary glands. Atlas of tumor pathology. Armed Forces Institute of Pathology, Washington, D.C. 1996. Series 3, fascicle 17.
- Rousseau A, Mock D, Dover DG, et al. Multiple canalicular adenomas: a case report and review of the literature. Oral Surg Oral Med Oral Pathol. 1999; 57:181-188.
- Bansal AK, Bindal R, Kapoor C, Vaidya S, Singh HP. Current concepts in diagnosis of unusual salivary gland tumors. Dent Res J (Isfahan). 2012; 9: S9-S19.
- Barnes L. Pathology and genetics of head and neck tumours. IARC. 2005; 267.
- Vaidya AD, Pantvaidya GH, Metgudmath R, Kane SV, D’Cruz AK. (2012) Minor salivary gland tumors of the oral cavity: A case series with review of literature. J Cancer Res Ther. 2012; 8 (1): 111-115.
- Kratochvil FJ. Canalicular adenoma and basal cell adenoma. Surgical pathology of the salivary glands. Saunders, Philadelphia, USA. 1991. 202-224.
- Gardner DG, Daley TD. The use of the terms monomorphic adenoma, basal cell adenoma, and canalicular adenoma as applied to salivary gland tumors. Oral Surg Oral Med Oral Pathol. 1983; 56:608-615.
- Batsakis JG, Brannon RB, Sciubba JJ. Monomorphic adenomas of major salivary glands: a histologic study of 96 tumors. Clin Otolaryngol Allied Sci. 1981; 6(2):129-43.
- Edwards PC, Bhuiya T, Kelsch RD. Assessment of p63 expression in the salivary gland neoplasms adenoid cystic carcinoma, polymorphous low-grade adenocarcinoma, and basal cell and canalicular adenomas. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2004; 97:613-619.
- Curran AE, Allen CM, Beck FM, et al. Distinctive pattern of glial fibrillary acidic protein immunoreactivity useful in distinguishing fragmented pleomorphic adenoma, canalicular adenoma and polymorphous low-grade adenocarcinoma of minor salivary glands. Head Neck Pathol. 2007; 1:27-32.