Rate of Submandibular Gland Atrophy Secondary to Chronic Sialolithiasis

Abstract

The rate of salivary gland atrophy secondary to chronic obstructive sialolithiasis has not been well-documented. The combination of 5 imaging studies over 12 years in a patient with repeat imaging for an unrelated pathology provides a unique opportunity to assess glandular atrophy over time. We hope that this case will support previous literature with an in vivo representation of the rate of glandular atrophy.

Clinical Report

A 65-year-old female was referred to the otolaryngology clinic by her dentist for a large left submandibular gland (SMG) stone seen on recent panoramic radiograph. She reported a multiple year history of left SMG swelling, pain, and tenderness to palpation. On physical examination, there was no palpable stone intraorally; however, the neck exam revealed firmness along the left submandibular area, with the left SMG noticeably smaller than the right. There was no salivary flow from the left Wharton duct.

The patient’s past medical history is notable for a right hemispheric ischemic stroke in 1994 with bilateral carotid artery dissections after a cerebral arteriogram. Since then, she has been routinely evaluated with a computed tomography angiogram (CTA) of the head and neck by her neurologist. With multiple serial imaging examinations available for this patient, the SMG stone was noted to be present on imaging as early as 12 years prior to presentation. Representative imaging of the stone and surrounding glandular tissue demonstrate the progression of SMG atrophy in a novel context over a 12-year interval (Figure 1).

Figure 1.

Axial computerized tomography (CT) imaging study of the left SMG from (A) 2009 with an estimated SMG of or 1570 mm³, (B) 2014 with an estimated SMG of 495 mm³, (C) 2016 with an estimated SMG of 345 mm³, (D) 2019 with an estimated SMG of 178 mm³, and (E) 2020 with an estimated SMG of 6.32 mm³. SMG indicates submandibular gland.

Volumetric analysis of the left SMG was conducted at each imaging date to quantify the extent of SMG atrophy. Axial CTA images were selected for review. A volumetric measurement tool in Sectra IDS7 Imaging Software (Sectra AB, Sweden) was utilized to calculate approximate residual glandular volume. Images showing the largest SMG volume in the axial plane were included in this report to most clearly demonstrate the progression of atrophy. The dates of each available CTA imaging study (from earliest to most recent) are as follows: 2009, 2014, 2016, 2019, and 2020.

Sialolithiasis, or salivary stones, is the result of calcium phosphate crystals mechanically obstructing salivary glandular outflow. The pathophysiology of sialolithiasis has been demonstrated to involve positive feedback loops whereby tissue damage and crystallization reinforce one another. Inflammatory cytokines lead to augmentation of calcification in ectopic tissue ¹ with calcium crystals, then stimulating macrophage-mediated pro-inflammatory effects. ² Furthermore, long-standing obstruction and buildup of secretory fluid in the gland proximal to the ductal blockage can lead to epithelial damage to acinar cells and eventual apoptosis. ³ Reinforcing this, homologous studies conducted with kidney stones demonstrate that apoptotic epithelial cells can serve as substrates for crystal formation. ⁴

Studies investigating the histopathology of excised SMGs from human subjects due to irretrievable sialoliths showed progressive atrophy with varying levels of inflammation, calcification, fibrosis, and acinar atrophy thereby supporting previous literature. ^5,6 Finally, it has been well-established that CT imaging of patients with a suspected SMG calculus has demonstrated glandular atrophy secondary to obstructive sialolithiasis. ^7,8

The earliest imaging study available for our patient was in 2009, and even at that stage, the gland showed evidence of early fatty replacement with an estimated volume of 1570 mm³. By comparison, the volume of the healthy right SMG from the same imaging study was found to be 5898 mm³. In 2014, the gland had decreased to 495 mm³ and further to 345 mm³ in 2016. In 2019, the gland had diminished to 178 mm³. By 2020, the left SMG volume had reduced dramatically to 6 mm³. Over the same period of time, the salivary stone reached a maximum size of 327 mm³ in 2020 with minimal change since 2014. The salivary stone grew 77 mm³ since 2009.

The rate of salivary gland atrophy secondary to obstructive sialolithiasis has not been well-documented. The present clinical report provides a unique opportunity to estimate this rate of glandular atrophy as the patient has serial CTA studies performed for a nonrelated medical condition. Using volumetric analysis, we were able to calculate the rate of salivary gland atrophy secondary to sialolithiasis to be approximately 130 mm³ annually, assuming a linear atrophy.