34th Annual Scientific Meeting proceedings

Objectives:

Both acquired and congenital abnormalities of the atlantooccipital joint have been described in case reports. This contrast study and case series gives a detailed description of the atlantooccipital joint and report the clinical signs associated with its pathology.

Methods:

Contrast studies were performed on post-mortem specimens to evaluate the extent of the joint and its proximity to adjacent anatomical structures. Clinical records were searched for horses which had undergone computed tomographic (CT) examination of the head and had abnormalities of the atlantooccipital joint, over an 11-year period. All CT examinations were reviewed and graded by an ECVS resident and ECVDI board-certified radiologist and relevant clinical findings were reported.

Results:

The contrast studies highlight the close proximity of the ventral joint recess to the guttural pouch, basioccipital bone, hypoglossal foramen, jugular foramen, cranial nerves (IX, X, XI and XII) and the intracanal recess of the dural sac. Eighteen horses met the inclusion criteria. Seventeen cases show distension of the joint in one or multiple joint recesses. Impingement of the dural sac was noted in 12 cases. Secondary pathology was found in the basioccipital bone (n=7), jugular foramen (n=3) and hypoglossal foramen (n=4). Osseus fragments within the joint were present in 8 cases. Cranial nerve pathology was noted in 5 cases.

Conclusions:

This report provides a comprehensive description of the atlantooccipital joint recesses, associated structures and potential pathology. Pathology of this joint should prompt a cranial nerve exam with attention paid to mobility and symmetry of the tongue (cranial nerve deficit IX, X and XII).