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Neuroradiology Case of the Week

Case 98

Xiang Liu, MD, PhD and PL Westesson, MD, PhD, DDS

Clinical Presentation: A 59-year-old female presented with right submandibular gland swelling.

Radiological Findings: Enhanced neck CT showed a 5 mm calcific density in the anterior portion of the right submandibular duct likely representing a submandibular duct stone (Fig. 1). The right submandibular duct is dilated and enlarged with stranding and reticulation of the periglandular fat (Fig. 2). There is mild enlargement of the submental, submandibular, and jugulodiagastric nodes on the right side (Fig. 2).

Diagnosis: Right submandibular stone

Clinical Discussion:  The submandibular gland duct extends from the floor of the mouth to the hyoid bone and is separated from the parotid by the stylomandibular ligament. It lies primarily below the mylohyoid muscle, but its superior portion passes up behind the mylohyoid muscle with a fingerlike projection (uncinate process) continuing over the muscle toward the sublingual space. Histologically, the submandibular gland is composed predominantly of serous acini (90%) with a mucinous acinar component (10%) [1,2].
     The submandibular duct (Wharton’s duct) is the main duct of the submandibular gland, is about 5 cm long with thinner walls, and courses from this deep portion of the gland over the mylohyoid muscle in the sublingual space along the floor of the mouth to the papilla on the side of the frenulum of the tongue.
     There are several reasons related to the formation of stone in the duct. Poorly fitting dentures, dehydration, recurrent infection, and trauma are also causes for the obstruction and dilation of the duct. Debris in the lumen of the duct due to exfoliated ductal epithelium or to mucous plugs are associated with dehydration and may serve as a nidus for the calculus. Calcium salts as calcium phosphate and hydroxyapatite are present with saliva. The thicker and more alkaline nature of the submandibular secretions predispose to precipitation of the salts.
     According to their surface structure the salivary calculi were divided into three types: the rock-like type, the granular type, and the globular type. In the salivary calculi the core structure was different from the surface structure in that the cut surface of the core was an accumulation of circular or polygonal structures forming a honey-comb pattern which was surrounded by small projections distributed radially [3].
     Intermittent swelling of the salivary gland associated with meals and lasting 2-3 hours is indicative of a stone or stricture of the duct [1].
     Sialoliths (stone, calculus) of the submandibular duct are usually (80-90%) opaque due to higher calcium salt content. Although those calculi are usually solitary, 25% of the patients may have multiple calculi, which are opaque and visible on plain films [2].
     The obstruction and stricture by stone or calculus in the submandibular duct may result in chronic infection of the duct (sialodochitis) and of the gland (chronic sialadenitis), and secondary enlargement of the spumoni gland. Complete obstruction leads to atrophy of the gland.

References:

1. Valvassori GE, Mafee MF, Carter BL. Imaging of the Head and Neck. Georg Thieme Verlag Stuttgart New York, 1975: 475-509.
2. Som PM, Brandwein MS. Salivary glands: anatomy and pathology. In: Som PM, Curtin HD. Head and Neck Imaging (4th ed.), vol. 2, Mosby:2005-2133.
3. Yamashita T, Kim DW, Takeshita H, et al. Structural analysis of phleboliths and salivary calculi. Aichi Gakuin Dent Sci. 1989; 2:39-46.