Jugular Foramen Syndrome in a Dog - Imaging Features

Abstract

Background: Cranial nerves IX, X, and XI share a common anatomical pathway associated with jugular foramen. Therefore, the peripheral nerve sheath tumors around the jugular foramen may lead to concurrent dysfunction of these nerves. However, peripheral nerve sheath tumors of cranial nerves IX, X, and XI are often challenging to diagnose due to their deep anatomical location and nonspecific clinical signs. This report describes a rare case of a peripheral nerve sheath tumor originating from cranial nerves IX, X, and XI, diagnosed through a combination of clinical signs and imaging findings from computed tomography (CT) and magnetic resonance imaging (MRI).

Case: A 5-year-old, intact male, Spitz was referred with chronic vomiting, left head tilt, abnormal gait and suspicion of portosystemic shunt. On CT, multiple collateral vessels were observed. However, the association between collateral vessels and the current symptoms appeared to be low. Accordingly, a central nervous system disorder was suspected, and MRI was conducted to differentiate from intracranial disease. In MRI, the mass was well-demarcated, amorphous to round shape, and was located at the left lateroventral region of the medulla oblongata, extending as a tubular lesion from the medial and caudal region of the left tympanic cavity to the jugular foramen and tympano-occipital fissure, which are the pathways for cranial nerves IX, X, and XI. The mass appeared hypointense to isointense on T1-weighted image(T1W), isointense to hyperintense on T2-weighted image(T2W), and uniformly hyperintense on fluid-attenuated inversion recovery (FLAIR) sequences, with strong peripheral rim enhancement. On retrospective CT evaluation, severe atrophy of the sternocephalic, cleidocephalic, and trapezius muscle ipsilateral to the tumor was also observed. These clinical signs and imaging findings are consistent with those typically observed in peripheral nerve sheath tumors originating from cranial nerves IX, X, and XI.

Discussion: The presumptive diagnosis of a peripheral nerve sheath tumor originating cranial nerves IX, X, and XI was supported by four key findings: characteristic morphology and location of the mass, its signal intensity on MRI, neurogenic muscle atrophy, and clinical signs consistent with jugular foramen syndrome. The tubular shape reflected the endoneurial longitudinal spread of peripheral nerve sheath tumors, with smooth widening of the jugular foramen and extension through the tympano-occipital fissure along the expected anatomical pathway of these nerves. On MRI, the lesion was isointense to hypointense on T1W, hyperintense on T2W and FLAIR, and showed peripheral rim enhancement, suggestive of malignant peripheral nerve sheath tumor. Marked neurogenic atrophy of cervical and shoulder muscles innervated by XI cranial nerve were more readily appreciated on CT than MRI, because field of view on MRI is limited. Clinically, chronic vomiting was presumed to be associated with dysfunction of cranial nerves IX and X, while muscle atrophy strongly suggested cranial nerve XI involvement. These findings are consistent with jugular foramen syndrome, in which lesions around the jugular foramen cause concurrent deficits in cranial nerves IX, X, and XI. In this dog, head tilt and abnormal gait were likely due to both direct neurologic injury and secondary neurogenic muscle atrophy. Although histopathological confirmation and laryngeal examination were not performed, the combination of imaging findings and compatible neurological signs strongly supported a presumptive diagnosis of peripheral nerve sheath tumors. When histological confirmation is not feasible, combined MRI and CT are valuable for assessing anatomical relationships and imaging features to support the presumption of tumor’s origin.

Keywords: peripheral nerve sheath tumor, PNST, jugular foramen syndrome, JFS, CT, MRI.