Epidemiology
Approximately 75% of lymphomas present as adenopathy and 25% present extranodally. The gastrointestinal (GI) tract is the most common site of extranodal lymphoma, followed by the head and neck region. The salivary glands serve as the site for nearly 12% of extranodal lymphoma of the head and neck region, which accounts for 2–5% of salivary gland neoplasms. About 80% of salivary gland lymphomas occur in the parotid glands, and about 20% are found in the submandibular and minor salivary glands ( Fig. 51.1 ). The median age of presentation is 50–60 years, with female predominance. Bilateral involvement is uncommon and occurs in about 10% of patients. Over 70% of salivary gland lymphoma presents at early stage (I or II). Chronic inflammatory conditions such as sialadenitis and autoimmune diseases, in particular Sjögren syndrome, are well known to be associated with the development of salivary gland lymphoma.
Histopathology
The majority of lymphomas affecting the salivary glands are non-Hodgkin lymphoma of low-grade histology, of which mucosa-associated lymphoid tissue (MALT) lymphoma is the most common (30–50%), followed by follicular lymphoma (25%). High-grade lymphoma, notably diffuse large B cell lymphoma, occurs in about 20% ( Fig. 51.2 ). Other rare subtypes (below 5%) include small lymphocytic lymphoma and Hodgkin lymphoma.
Investigations
Patients usually present with progressive painless swelling of the affected gland. There is no pathognomonic imaging finding of lymphomas affecting the salivary glands ( Fig. 51.3 ). Fine needle aspiration (FNA) is frequently inadequate, as it is associated with a high false-negative rate (32%). Excisional biopsy or parotidectomy are often performed to establish a diagnosis. Once the diagnosis of lymphoma is made, patients should be referred to oncologists for staging work-up and further management. Work-up includes blood tests for complete blood picture, liver, and renal function tests, hepatitis screening, and whole-body computed tomography (CT) or positron emission tomography (PET) CT. Bone marrow biopsy, echocardiogram, and endoscopy of the other extranodal sites are performed in selected cases.
