Intermittent Occlusion of Internal Carotid Artery by Hypoglossal Nerve

The case reported here demonstrates intermittent, total occlusion of the internal carotid artery and oCcipital artery with head and neck rotation and extension. We believe the close proximity of the crossing hypoglossal nerve was the major cause. Case Report A 51-year-old man experienced the onset of positionally dependent neurologic changes. When he turned his head to the left and extended his neck for longer than 3 sec he became dizzy and experienced a sensation of "numbness" over his right body, including his face. This was accompanied by loss of motor control of the right body. He had some blurring of vision during these episodes but no loss of con­ sciousness and no associated headache. A CT scan demonstrated an area of infarction in the left parietooc­ cipital region. A conventional cerebral arteriogram performed with the head in a neutral position (Fig. 1) was unremarkable except for the presence of an incomplete circle of Willis. The horizontal segment of the right anterior cerebral artery never opacified, and both peri callosal arteries opacified on the left common carotid artery injection. Sub­ sequently, several left carotid injections were repeated with the patient performing the head maneuver that provoked his symptoms (head turned toward the left with extension of the neck; Fig . 2). Depending on the degree of rotation of the head and extension of the neCk, there was partial or total occlusion of the left internal carotid artery about 4 cm above the common carotid bifurcation. This oc­ curred at approximately the level of the adjacent occipital artery coursing posteriorly, and seemed to be caused by an extrinsic pressure effect. On one of the injections (not shown), occlusion of the OCCipital artery also occurred. There was no abnormal course or elongation of the internal carotid artery, which could have been responsible for this finding. At surgery the hypoglossal nerve and the occipital branch of the external carotid artery were found to be intertwined in such fashion that the hypoglossal nerve was pulled taut and stretched against the adjacent internal carotid artery when the head was hyperextended and turned to the ipsilateral side. The internal carotid artery was also noted to bear a small indentation at this level where chronic compres­ sion by the hypoglossal nerve had occurred (Fig. 3) . Consequently, external compression by the hypoglossal nerve was believed to be responsible for the intermittent occlusive changes in the internal carotid artery.