Magnetic resonance imaging features of bilateral multiloculated extraneural ganglion cysts of the occipito-atlanto-axial joint causing hypoglossal nerve paralysis in a dog.

A 14-year-old spayed female Miniature Pinscher presented with tongue curling, dysphagia, hypersalivation, and sublingual gland swelling. Comprehensive evaluation, including neurologic and musculoskeletal examinations, blood work, and urinalysis, revealed no abnormalities other than tongue-related signs. Magnetic resonance imaging (MRI) revealed a multilobed cystic structure in the occipito-atlanto-axial joint, compressing the right hypoglossal canal. The lesion appeared cerebrospinal fluid (CSF)-like on T1-weighted and T2-weighted images, and hyperintense compared with CSF on fluid-attenuated inversion recovery T2-weighted images. The scans suggested mucinous content with enhanced peripheral areas on contrast-enhanced images. Surgical removal and drainage of this cyst were performed, and clinical signs improved markedly. The dorsal cyst was tentatively diagnosed as a ganglion cyst based on histopathologic and imaging findings. Ganglion cysts should be considered in the differential diagnosis for dogs with similar MRI findings and neurologic signs.