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266 8 Neck

therefore cannot be morphologically differentiated from pharyngeal carcinomas. The imaging characteristics are compatible with their histological grade.Carcinoma ex Pleomorphic AdenomaCarcinoma ex pleomorphic adenoma is a malignant transformation of a (resected) pleomorphic adenoma. CT MorphologySmall tumors resemble pleomorphic adenoma with benign characteristics, but larger tumors are more inhomogeneous and infiltrative with areas of necrosis. The CT morphology directly reflects this variation in macroscopy.Acinic Cell CarcinomaAcinic cell carcinoma occurs almost exclusively in the parotid gland and can be bilateral in 5% of cases. They usually occur after the 40th year but also are the second commonest salivary malignancy in children. CT MorphologyThe tumors can either be solid or cystic. The imaging characteristics are nonspecific. The tumors generally have a benign appearance.MetastasesMetastases occur almost exclusively in (the in- ttaglandular nodes of) the parotid gland. The commonest primary is melanoma of the temporal skin or other parts of the neck. Less frequent are head and neck, renal, lung, breast, and Gi carcinomas. CT MorphologyUnilateral or bilateral, enlarged intraglandular lymph nodes with a homogeneous density. After contrast administration homogeneous enhancement is seen. Necrosis can be seen occasionally, and is suggestive for malignancy. Differentiation from nodal lymphoma is often impossible.Inflammatory and Autoimmune Lesions SialadenitisAcute bacterial and viral sialadenitis are the commonest pathologies of the salivary glands, Bacterial infections usually ascend from the oral cavity when saliva flow is decreased and involve pathogens like Staphylococcus aureus. Streptococcus pyogenes, Streptococcus pneumoniae and Haemophilus influenzae. Viral infections can be caused by mumps, Coxsackie or (Parainfluenza viruses and preferentially involve the parotid glands. Intra- and periglandular lymph nodes may be involved in Lhe process. The main role for imaging is to differentiate adenitis from abscess formation. Abscesses are often formed when acute adenitis is undiagnosed or incompletely treated. These abscesses can spread quickly in rbe parapharyngeal space or other parts of the neck. CT MorphologyThe involved gland is dense and somewhat enlarged. It enhances slightly. Abscesses are demarcated regions of low attenuation,SialolithiasisStones can be located in the salivary gland ducts or the extraglandular ductal system, from 80-90% occur in the submandibular gland, 10-20% in the parotid and