eRadiograph Volume 7: Imaging of Oral Cavity | Page 224

Lymphoepithelial cysts: These nearly always are seen in relation to HIV. They are usually bilateral and multi cystic occuring due to obstruction of the parotid lymph nodes and associated cystic changes. The appearances depend on the contents which can range from fluid to mucoid or caseous. Due to their hyperintensity on T2 WI they are difficult to distinguish from true branchial cyst, cystic Warthin tumor or low grade mucoepidermoid carcinoma. Branchial cleft cyst: Within the parotid gland is very rare ,these may be intraparotid in location or preauricular. The preauricular are more commonly and seen as a well defined fluid filled mass with peripheral enhancement. Intraparotid are seen as well defined cystic masses. Polycystic dysgenic disease: This is similar to as seen as polycystic disease of the kidney. The entire gland is replaced by cysts usually bilaterally. Acquired cysts: Sialocysts these occur due to duct obstruction which may be due to a calculus, trauma, post inflammatory stricture, or post surgical – These appear as well defined fluid density lesions with or without enhancing margins. Pneumatoceles are air filled cysts which occur in trumpet players, glass blowers as air coll ects in the ducts due to increased intrabuccal pressure. Sialadenitis Infection of the salivary gland is known as sialadenitis. This may be caused by viruses, bacteria, mycobacteria, fungi, parasites, though most commonly due to bacterial/viral infections. Mumps which is caused by paramyxovious is the most common viral injection affecting the salivary glands with the parotid gland being most commonly affected. The clinical presentation and disease progression is sufficient for a definitive diagnosis – imaging findings are nonspecific and further not required. Chronic sialadenitis This may be due to infectious or noninfectious process like sarcoidosis, post radiation or autoimmune disease. On imaging in chronic sialadenitis the gland is shrunken, there may be duct ectasia, imaging is also required to differentiate between obstructive and non obstructive causes of chronic sialedenitis. Sarcoidosis involves the parotid glands in 10 – 30 % cases. They may present as parotid masses which are solitary or multinodular with or without associated adenopathy. These should not be confused with malignancy – presence of unilateral facial palsy, mediastinal adenopathy, pulmonary granulomas helps establish the diagnosis. Radiation causes 224 Parotid Space Bacterial infections are retrograde via oral cavity through the salivary ducts. These occur more commonly in the parotid gland as the orifice of stensons duct is wide. Clinically they present with acute sialadenitis. On imaging the gland is enlarged with enlarged intraparotid lymph nodes. There is dilatation of the ducts with enhancement of the ductal wall. Subsequently an intraparotid abscesses may develop as a focal peripherally enhancing hypodense lesion on CT scan and a T2 hyperintense lesion with peripheral enhancement on MRI.