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

PURPOSE: To discuss the sensitivity of three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) for detecting aneurysms causing third cranial nerve palsy and Co propose guidelines for the use of MRA in the evaluation of patients with different clinical presentations of oculomotor nerve palsy. METHODS: From a review of the scientific literature, we determined the proportion of aneurysms of various size that cause third nerve palsy, the sensitivity of MRA in detecting aneurysms of these size classes, and the relationship of aneurysmal size to rupture. RESULTS: The data disclose that properly performed and interpreted 3D TOF MRA will overlook only 1.5% of aneurysms producing third cranial nerve palsy that will, if untreated, rupture during the subsequent 8 years. CONCLUSIONS: Magnetic resonance angiography plays an important diagnostic role in the evaluation of patients with isolated third cranial nerve palsy. However, because of the potentially drastic consequences of overlooking an aneurysm, MRA should be the definitive screening rest only among patients with a relatively low likelihood of harboring an aneurysm or a relatively high likelihood of suffering a complication from carheter angiography. (Am J Ophthalmol 1999;128:94-96. (C) 1999 by Elsevier Science Inc, All rights reserved.)