Diagnostic Imaging and Fine-Needle Aspiration of the Salivary Glands

Although some disorders of the salivary glands can be diagnosed and treated without the use of radiographic studies, imaging of the salivary glands can be useful in the workup of patients with a broad spectrum of salivary pathology. Imaging is used to localize the lesion, define its appearance to limit the differential diagnosis, evaluate it for staging, describe its size and extent for operative planning, and guide fine-needle aspiration (FNA) for pathologic diagnosis. Some modalities—including magnetic resonance imaging (MRI), magnetic resonance (MR) sialography, ultrasound (US), and computed tomography (CT)—have improved to a point where invasive imaging techniques, such as conventional sialography, are used much less frequently. Percutaneous tissue sampling of the salivary glands is routinely performed, often under US guidance, for diagnosis and/or presurgical workup of salivary lesions. The role of nuclear medicine imaging in the evaluation of salivary lesions is limited.

Cross-sectional imaging is useful not only for the characterization of the major salivary glands and their various pathologies but also for the evaluation of the surrounding planes and structures; it can reveal possible extension of salivary neoplasms into adjacent spaces, perineural or vascular spread, nonpalpable lesions, and lymphadenopathy or infiltration of the bone marrow. Lesions can also be more clearly defined as extraglandular, as would be seen with a lymph node, schwannoma, developmental cyst, or lipoma.

The clinical presentation of the patient is important in the choice of imaging modality. Patients may present with a painless palpable mass, acute or chronic pain and swelling, or xerostomia in the setting of collagen vascular disease or radiation therapy. The correct choice of primary imaging modality will assist diagnosis in each instance ( Box 82.1 ).

Sialolithiasis ( Fig. 82.1 ) can be seen in any salivary gland but is most commonly associated with the submandibular gland secondary to the more mucinous saliva and the horizontal trajectory of the submandibular duct. Symptoms of acute pain and swelling in the region of a salivary gland would raise suspicion for sialolithiasis, and a CT scan should be ordered because CT is the modality with the greatest sensitivity for calcification in an obstructive stone.

Open full size image

Multiple stones within the right submandibular duct (Wharton duct) with enlargement of the right submandibular gland and periglandular inflammatory fat stranding.

Neoplasms can occur in any salivary gland tissue. The likelihood of malignancy increases as the size of the gland decreases. Lesions of the minor salivary glands, for example, have a 50% to 80% chance of being malignant. In the parotid gland, only 20% to 30% of lesions will be malignant, whereas 40% to 60% of submandibular gland lesions will be malignant. In the parotid, therefore, 70% to 80% of lesions will be benign. Of these benign lesions, 80% will be pleomorphic adenomas ( Fig. 82.2 ). Although imaging can give clues as to the pathologic diagnosis—that is, smooth borders are more likely benign and infiltration of adjacent structures is a sign of malignancy—the role of imaging is primarily to localize the lesion, describe its association with adjacent structures to aid in operative planning, and assess for tumor spread beyond the salivary gland.

Open full size image

(A) T1-weighted fat-saturated postcontrast magnetic resonance image of a pleomorphic adenoma that appears as a well-defined enhancing mass in the left parotid gland. (B) On T2-weighted imaging with fat saturation, the pleomorphic adenoma is hyperintense, a characteristic appearance for this lesion.