Magnetic resonance imaging features of presumed normal head and neck lymph nodes in dogs

To document the magnetic resonance imaging appearance of presumed normal lymph nodes of the head and neck in the dog, 91 studies of dogs with no detectable disease in the head acquired on a low-field unit were reviewed. If lymph nodes were imaged, symmetry, signal intensity, homogeneity, and size as well as the relation to the surrounding fat were noted. To improve the description of lymph node topography, we used corresponding E12 plastinated embedded sections of a dog. Compared with surrounding fat, lymph nodes were hypointense in T1 images. In T1-weighted images after intravenous contrast medium lymph nodes were isointense. In T2-weighted images, lymph nodes were slightly hypointense to surrounding fat. In T1 and T2 images, a hypointense band, created by the chemical shift artifact, could be seen at the lymph node-fat boundary along the frequency encoding gradient. In some dogs the lymph node hilus was characterized by vessels indenting the capsule of the lymph node. The facial vein is a consistent landmark to identify mandibular lymph nodes, and the mandibular salivary gland is a useful landmark to localize the medial pharyngeal lymph nodes. The parotid salivary gland or the external acoustic meatus were useful markers to identify the parotid lymph nodes, which were not consistently seen. In some dogs, nodules within the lymphoreticular tissue of the soft palate were seen.