Imaging description

Most parotid masses are either benign or less likely malignant primary salivary gland tumors. The parotid glands arise from the oropharyngeal ectoderm and encapsulate late in embryologic development, entrapping lymphatic tissue within the parotid capsule and parenchyma. Anatomic studies confirm the presence of 4–7 lymph nodes in the superficial and 1–2 nodes in the deep parotid lobes [1].

It is common to see small normal intraparotid lymph nodes (IPLNs) on imaging studies, particularly on MRI (Fig. 74.1). Occasionally, reactive enlargement of IPLNs occurs, similar to reactive enlargement of neck nodes as seen in upper respiratory infections etc., mimicking parotid tumors [2]. The reactively enlarged IPLNs have a very homogeneous appearance, with attenuation values on CT and signal characteristics on MRI similar to neck lymph nodes outside the parotid, and should not be mistaken for tumor (Fig. 74.2). The reactive hyperplasia of IPLNs usually involves multiple nodes and is associated with extraparotid nodal hyperplasia. Warthin’s tumor can be multifocal and involve the extraparotid tissues, but it is more heterogeneous, showing areas of cysts, nodules, and intense enhancement in most cases that can be readily differentiated from lymph nodes.