Canalicular Adenoma of Parotid- A Rare Case Report

Abstract

Salivary gland canalicular adenoma is rare yet benign. It accounts for fewer than 1% of salivary tumors and is the third most common non-cancerous mass in the small salivary glands. A 45-year-old presented to the outpatient department with complaints of swelling in the left parotid region for the past 3 years. Examination revealed a firm swelling in the left parotid region. USG and MRI revealed features suggestive of pleomorphic adenoma. Superficial parotidectomy was planned but intra-operatively, the mass was seen between the two lobes of the parotid, which was removed, and on histopathological examination, it was diagnosed as canalicular adenoma. Post-operatively, the patient’s condition is excellent.

Introduction

Canalicular adenoma is a rare yet distinctive noncancerous growth that originates from the salivary gland. This tumor is the third most often occurring non-cancerous growth in the small salivary glands, accounting for less than 1% of all salivary tumors. An adenoma is a non-cancerous tumor of the salivary gland that consists of monomorphous ductal cells grouped in interconnected cords inside a vascular stroma with very few numbers of cells. It commonly occurs in the Upper lip (80%), followed by buccal mucosa, lower lip, hard and soft palate, and is extremely rare in major salivary glands (parotid).

Case Presentation

A 45-year-old female presented to outpatient department of otorhinolaryngology with swelling below her left ear for the past 3 years which was insidious in onset, initially small in size, and progressed to the current size gradually with an associated history of excessive salivation. There was no history of pain associated with swelling, increase in size of swelling while eating, dryness of mouth, discharge associated with swelling, facial weakness, difficulty in closing eyes, deviation of angle of the mouth, drooling of saliva, no dryness of eye or irritation in the eye, no dysphagia or odynophagia, no fever, ear pain, ear discharge, hard of hearing, tinnitus or giddiness. The patient is a known case of Diabetes mellitus for the past 5 years on medication. The patient is also a known case of Myasthenia gravis for 4 years and is on medication (Pyridostigmine).

Local Examination

Local examination of the left parotid region revealed on inspection a swelling of size 3 × 2 cm in the left parotid region spherical in shape, below the ear, just above the angle of the mandible extending till the ear lobule with the skin over swelling appearing as normal (Fig. 1). On Palpation, The inspectory findings were confirmed and there was no tenderness or warmth. The swelling was firm in consistency with a smooth surface and was not mobile. The skin over the swelling was pinchable. On Auscultation, no bruit was heard. The right parotid region was normal.

Fig. 1.

Swelling in the left parotid region

Management

Routine blood investigations were normal.USG of the Parotid region revealed a well-defined heterogeneously hypoechoic lesion of size 30.6 × 24.9 × 24.2 mm in the left superficial parotid gland with minimal internal vascularity. Thus, the possibility of pleomorphic adenoma was advised to be considered and FNAC correlation was suggested. MRI Neck was done which showed features suggestive of pleomorphic adenoma in the left parotid and suggested HPE correlation and it also showed non enhancing well defined cystic nodule with internal septations in the right lobe of the thyroid which is a likely benign lesion and was suggested FNAC correlation. FNAC was done which advised for excision biopsy for categorisation of the lesion The patient was thus planned for superficial parotidectomy. Under sterile aseptic precautions, and under general anesthesia, orotracheal intubation was done. The patient was placed in a supine position with the head turned to the right side and parts painted and draped. Using a marker, modified Blair incision site was marked, infiltration using 2% xylocaine and adrenaline was given and then the incision was given and deepened. The superficial muscular aponeurotic system was elevated and the flap was elevated up to the anterior margin of the parotid anteriorly and mastoid tip posteriorly. The sternocleidomastoid muscle, greater auricular nerve, the posterior belly of the digastric muscle and the facial nerve trunk were identified. On further dissection, a mass was seen between the superficial lobe and deep lobe of the parotid gland. Thus the mass was separated from the remaining parotid tissue (Fig. 2). It was then removed in toto, preserving the two lobes and the specimen was sent for histopathological examination (Figs. 3). Hemostasis was achieved throughout the procedure using diathermy. The wound was thoroughly washed with metronidazole. A Corrugator drain tube was placed and fixed in position. The wound was then approximated and sutured with 3.0 vicryl. The skin was then subsequently sutured with 4.0 ethilon and a sterile dressing was applied.

Fig. 2.

Intraoperative picture showing the mass between the two lobes of the parotid

Fig. 3.

Parotid mass after excision and cut section of the mass

Results

Biopsy sections showed benign oval cells arranged predominantly in canalicular patterns, occasionally in nests and acinar patterns. Intraluminal hyaline secretions are seen in a few foci with scant stroke. morphological features suggestive of canalicular adenoma. Thus patient was diagnosed as a case of canalicular adenoma. The corrugated drain was removed on post-operative day 3 and the patient was subsequently discharged. Sutures were removed after 8 days and the wound was healthy. The patient is on routine follow-up. There is no evidence of any recurrence and the patient’s condition is excellent.

Discussion

Canalicular adenomas are uncommon benign tumors of the salivary glands. Originally thought to be a type of monomorphic adenoma, it has now been identified as an unique identity by World Health Organization (WHO) with developments in immunohistochemistry labeling [1, 2].

Although patients sometimes report feeling pressure in the affected location, the most common presentation of canalicular adenoma is a painless nodule. Research already in existence indicates that malignant changes and recurrence are incredibly uncommon. On histopathological examination, however, it resembles malignant polymorphous low-grade adenocarcinoma or benign basal cell adenoma [3, 4]. To distinguish between comparable benign salivary gland tumors and enhance the accuracy of diagnosis, a combination of imaging, histopathological examination, and immunohistochemistry is needed.

More often diagnosed as intraoral neoplasms, canalicular adenomas account for less than 1% of all salivary tumors. They may be multifocal and can also be detected in the palate and buccal mucosa [5].

Patients over 50 years of age are usually affected by these neoplasms, which are slow-growing, migratory masses [6]. It is distinguished histologically by columns of monomorphic columnar-cuboidal cells grouped in bilayered strands that anastomose; occasionally, these strands form extensive channels with a central lumen and a loose, fibroblast-free supporting stroma with ovoid and monomorphic nuclei [7]. Histological characteristics are easily overlooked during fine-needle aspiration, making the diagnosis challenging to establish prior to surgery.

Although unclear, canalicular adenomas can recur anywhere from two months to eleven years. This is probably due to the multifocal nature of the disease which is substantiated by observing multiple microscopic foci of adenomatous growth in removed specimens [8]. Therefore, a recurrence could be the result of a microscopic focus forming near an original lesion that was previously excised with “clear margins,” suggesting that these were overlooked primary lesions.

When it comes to treating parotid canalicular adenomas, removal of the mass is advised following formal facial nerve identification.

Post-operatively, the patient can be routinely followed up to watch for recurrence but the prognosis is usually excellent with surgical removal.

Conclusion

Canalicular adenoma is an uncommon benign, slowly expanding small salivary gland tumor. The ability to distinguish canalicular adenoma from other entities is greatly aided by immunohistochemistry. The best course of treatment is surgical removal, and the recovery is very good. It has a fairly good prognosis, hence proper diagnosis facilitates better treatment management.

Funding

Not applicable.

Declarations

Research Involving Human Participants And/Or Animals

Yes, involves Human participant.

Informed Consent

Obtained.

Conflicts of Interest

Not applicable.