Canalicular Adenoma - An Overview

Introduction:

Canalicular adenoma is known to be a unique tumor of a benign (noncancerous) nature that affects the salivary glands and is distinctly separated from other adenomas or tumors according to the classification by the World Health Organization (WHO). Read the article to know the unique and multifocal nature, characteristics or clinical features, histology, and the management of canalicular adenoma.

What Is Canalicular Adenoma?

A canalicular adenoma is a rare but diagnostically challenging benign tumor that affects the minor salivary glands. Usually, this tumor is mostly prevalent in older adults and affects individuals at the mean age around the sixth decade of life, according to oral pathology research. The upper lip remains the most commonly affected site for the development of these benign tumors followed by the buccal mucosa and palate which are the other locations that the tumor would possibly affect. These tumors present as nodular lesions without any tendency for recurrence once they are treated by a dentist or a maxillofacial surgeon (doctors specialized in treating conditions related to teeth, jaws, and face).

Canalicular adenoma (CA) is unusual in many characteristics in comparison to other oral tumors because the tumor does not arise in the minor salivary glands it affects, but rather from the ductal tissues that form the glands with a canalicular structure histologically and hence the name. It is representative of the third most common minor salivary gland tumor that impacts the oral cavity. This is after the first and most common benign tumor of the salivary gland, that is, pleomorphic adenoma, and the second common tumor is the mucoepidermoid carcinoma.

What Is the Unique Nature of Lesions and the Challenges Faced in the Diagnosis of Canalicular Adenoma?

• Patients who are affected are usually older individuals, as elaborated earlier, and it affects individuals most commonly in the sixth decade, according to documented case reports across the world. However, it could also possibly manifest in the age group anywhere between 33 to 91 years, as per medical literature reports of canalicular adenoma tumors. Also, this tumor is seldom reported in pediatric patients and is an extremely rare occurrence in children. While some patients in the affected age groups (from 33 to 91 years) would not have any symptomatic features of these tumors in the mouth, most of the patients affected usually are known to present with painless, non-ulcerated masses that have slow or steady growth in the mouth (when lesions are left untreated or due to fear of visiting a dentist or an oral surgeon) with an average time duration that spans two to three years after which the tumors or non-ulcerated masses in the intraoral sites affected are visible.
• The tumor lesions seem to extensively occur again uniquely unlike the other salivary gland tumors (such as in pleomorphic adenoma or acinic cell carcinoma), specifically in regions of The upper lip remains the most commonly affected site for the development of these benign tumors, followed by the buccal mucosa and palate, which are the other locations that the tumor would possibly affect.
• The tumor is known to be more prevalent in women than men in comparison, according to case reports from medical literature (with a female-to-male prevalence ratio of 1.7:1).
• The challenging diagnosis for the dental physician or dentist would be to detect these tumors in their initial stages. As they only manifest as flat asymptomatic nodules initially and are slow-growing over a period of two to three years, they are unique in this perspective compared to other benign oral tumors. They may exhibit mobility on clinical examination by the dentist. Over a while past a year, usually, these tumors can present with oral manifestations of ulceration, hemorrhage, extravasation of mucus, inflammation locally in the affected region of the lip or palate, and even regional oral pigmentation might occur.
• However, if most of the salivary gland tumors are taken into account or considered in terms of the intraoral sites that are affected (for both benign and malignant tumors), canalicular adenoma represents less than one percent of the tumors in the salivary glands, but it is a challenging clinical presentation that can lead to a misdiagnosis. Hence, these lesions would require thorough histological examination and differential diagnosis establishment to come to a confirmative diagnosis by a dentist, oral pathologist, or maxillofacial surgeon.

What Is the Differential Diagnosis of Canalicular Adenoma?

The canalicular architecture observed upon microscopic or histological examination is a characteristic feature of this disease, with the phenomenon of "beading" of cells that is certainly diagnostic and confirmative of this rare tumor. The beading of cells is rather by the joining of parallel epithelial or superficial cell rows, which is quite unique in this lesion of canalicular adenoma.

The lesional cells are usually columnar and have very limited to absent pleomorphic features with focally noted nucleoli. The lesions further appear always to be encapsulated with a characteristic proliferation of columnar epithelial cells as they are arranged in islands and cords alongside their ductal structures. Immunohistochemically, the detection of canalicular adenomas is their strong expressivity to CK7 and CK13 markers or marker positivity.

Histologically, the differential diagnosis of canalicular adenoma lesions is as follows:

• Primary salivary gland neoplasms.

• Basal cell adenoma.

• Pleomorphic adenoma (PA).

• Adenoid cystic carcinoma (ACC).

• Ductal adenoma.

• Reticulated myoepithelioma.

• Ameloblastoma.

• Adenomatoid odontogenic tumor (AOT).

• Paraganglioma.

• Basal cell carcinoma of the skin.

What Is the Treatment for Canalicular Adenoma?

As any other minor salivary gland tumors (MSGTs) would be frequently sampled by biopsy first (which is the common procedure employed to establish a differential diagnosis with other similar tumors or lesions like oral cysts), the final diagnosis should always be confirmed with a dentist, or it would be quite incorrectly interpreted leading to inappropriate management. Also, as the occurrence of multifocal tumors is uncommon in the oral cavity, especially the benign or malignant tumors of the minor salivary glands, this multifocal benign tumor remains unique and should prompt an investigation for confirming canalicular adenoma (after histological examination).

• The point to primarily note during the diagnosis should depend on the location of this tumor, such as the upper lip (the most affected site in nearly 70 % of canalicular adenoma cases).

• The treatment of choice for these benign tumors is by enucleation (removal of the tumor like a nut from its shell) surgical procedure, with the recurrence rates being extremely rare once they are treated.

Conclusion:

Canalicular adenomas are unique and rare minor benign salivary gland tumors that may not present typically as single slow-growing nodules but have an unusual multifocal pattern and occur more commonly on the upper lip. According to medical and dental research and case reports, malignant transformation of these benign tumors is uncommon, and they have an excellent prognosis post-oral surgical treatment procedures.