Submandibular gland aplasia

A 57-year-old female presented with anterior neck swelling for a year and occasional dryness of the mouth. The anterior neck swelling was nodular and moved with swallowing suggestive of a thyroid nodule. Clinical examination of the oral cavity, pharynx and larynx was unremarkable. Apart from a few dental procedures, there was no history of any head and neck surgery. She was referred for an ultrasound evaluation.

Ultrasonography (USG) of the neck showed a right thyroid goitre nodule and few bilateral reactive cervical lymph nodes. Incidentally, the submandibular gland (SMG) could not be identified on either side within the submandibular triangle. (Figure 1) Both parotids were normal in appearance.

Limited non-contrast computed tomography (CT) sections and magnetic resonance imaging (MRI) sequences were performed which confirmed the absence of bilateral submandibular glands. (Figures2,3) Parotid and sublingual spaces appeared unremarkable. The floor of the mouth showed symmetric soft tissues without muscle atrophy or masses. No identifiable calculi in the expected locations of the salivary ducts. No abnormal marrow signal or lucencies within the mandible.

The submandibular salivary glands are paired salivary glands located posteroinferior to the ramus of the mandible at the submandibular triangle.

Congenital agenesis (aplasia) of a major salivary gland is infrequently encountered with an incidence of about 1 in 5000 births. It was first described by Gruber in 1885 as bilateral submandibular gland aplasia. It occurs due to arrest in organogenesis. [1]

Development of salivary glands occurs during 4-8 weeks of gestation as ingrowth of the oral ectoderm into the underlying mesoderm. It further undergoes branching with the development of nerves and vessels to form glandular tissue. During development parasympathetic denervation causes a reduction in glandular weight, whereas sympathetic denervation causes atrophy of major salivary glands.  Though the exact aetiology for aplasia is unknown, sympathetic denervation may be suspected. [2]

It can be associated with first and second branchial arch defects in the Treacher-Collins syndrome (mandibulofacial dysostosis) or orbital abnormalities like lacrimal hypoplasia, canalicular atresia, and absence of the lacrimal puncta, hemifacial microsomia, ectodermal dysplasia, and lacrimo-auriculo-dento-digital (LADD) syndrome. [1-3]

Clinical presentation is variable. Over half the cases are asymptomatic while others may present with xerostomia, dysphagia, angular cheilitis, a decreased sense of taste, dental and gingival problems. Occasionally other major or minor salivary glands undergo compensatory hypertrophy of the contralateral or other major salivary glands presenting as clinical and/or radiological pseudo masses. [1-4]

A variety of imaging techniques including sialography, USG, CT, MRI, or nuclear medicine (technetium Tc99m pertechnetate) studies can be used to diagnose SMG aplasia. The characteristic radiological finding is the absence of SMG with replacement by fatty tissue. Sialography may show the inability to identify and cannulate the Wharton duct or may demonstrate only a portion of the duct with failure to show the rest of the SMG. Scintigraphy demonstrates a lack of uptake in the aplastic glands. USG being widely available, cheap and non-invasive is an important tool to diagnose aplasia. In cases with confusion, unilateral aplasia or compensatory hypertrophy CT or MRI may help to arrive at the definitive diagnosis as well as exclude other masses. [1-4]

Management is directed towards preventing complications and maintaining oral and dental hygiene. Otolaryngologists and radiologists should be familiar with this relatively rare entity which may warrant re-evaluation and search for associated deformities. Awareness of pseudo mass like presentation due to compensatory hypertrophy of other salivary glands will prevent unnecessary biopsies. [1-4]