The emerging role of magnetic resonance angiography in the management of patients with third nerve palsy

Abstract

The imaging guidelines Drs Lee and Brazis refer to 1 Lee AG, Onan H, Brazis PW, Prager TC. An imaging guide to the evaluation of third cranial nerve palsies. Strabismus 1999;7:153–168. Google Scholar were not published by the time of our original submission or response. Their four queries address more general issues of the clinical evaluation of patients with third cranial nerve palsy, instead of specific ones related to the role of magnetic resonance angiography, the focus of our Perspective. 1.In deriving our guidelines, we considered the clinical evaluation of the pupil separately from that of the extraocular muscles because the relative function of each is such an important tool for estimating the likelihood that the third nerve injury is the result of compression or infarction. 2 Trobe J.D. Third nerve palsy and the pupil. Footnotes to the rule. Arch Ophthalmol. 1988; 106: 601-602 Crossref PubMed Scopus (90) Google Scholar By complete extraocular muscle impairment, we imply that all extraocular muscles are totally paralyzed. By incomplete impairment, we imply that those extraocular muscles affected are not totally paralyzed, or that not all of the extraocular muscles are affected. Our rationale is similar to that articulated by Drs Lee and Brazis, and reflected in our imaging guidelines, which acknowledge that a patient with an incomplete third cranial nerve palsy, regardless of the status of the pupil, might be harboring an aneurysm. 2.The issue of initially performing computed tomography (CT) or magnetic resonance imaging (MRI) in this setting is often debated. Our imaging guidelines were designed for patients with neurologically isolated third cranial nerve palsy. We doubt that a patient with aneurysmal third cranial nerve compression and subarachnoid hemorrhage would present with ophthalmoplegia alone. 3 Jefferson G. Isolated oculomotor palsy caused by intracranial aneurysm. Proc R Soc Med. 1947; 40: 419-432 PubMed Google Scholar Moreover, although we acknowledge that obtaining CT may be more practical than obtaining MRI in some emergent situations, we caution that CT is often normal in patients with subarachnoid hemorrhage, especially after the first day of symptoms. 4 Schievink W.I. Intracranial aneurysms. New Engl J Med. 1997; 336: 28-40 Crossref PubMed Scopus (647) Google Scholar 3.Obviously, we agree with an individualized approach to these patients. 4.We also instruct the patient or the relatives of the patient to check the pupil and report immediately if it has enlarged. The reliability of this request, however, remains untested and is no substitute for serial examinations looking for delayed pupil dilation, which may occur with aneurysmal compression of the oculomotor nerve. 5 Kissel J.T. Burde R.M. Klingele T.G. Zeiger H.E. Pupil-sparing oculomotor palsies with internal carotid-posterior communicating artery aneurysms. Ann Neurol. 1983; 13: 149-154 Crossref PubMed Scopus (145) Google Scholar