Magnetic resonance angiography and clinical evaluation of third nerve palsies and posterior communicating artery aneurysms

Object. The authors conducted a study to determine the utility of the clinical profile and magnetic resonance (MR) angiography in evaluating patients with isolated third cranial nerve palsies or posterior communicating artery (PCoA) aneurysms. Methods. Three-dimensional time-of-flight MR angiography was performed in a consecutive series of patients with isolated acute third cranial nerve palsy not due to a ruptured aneurysm and in patients with unruptured PCoA aneurysms. A neuroradiologist, masked to the identities of the patients, interpreted reformatted maximum intensity projection (MIP) and source images of the PCoAs and aneurysms. The investigators assessed clinical features of oculomotor nerve dysfunction and focal head pain. Cases involving cranial third nerve palsy without aneurysms were classified as Group 1 (no case entailed catheter-based angiography), and cases involving PCoA aneurysms seen on MR angiography (42 cases confirmed by catheter-based angiography) were classified as Group 2. The mean age of the 73 patients in Group 1 was 60.1 years and that of the 45 patients in Group 2 was 59.1 years (p = 0.37). The pattern and severity of oculomotor (p = 0.61) and lid (p = 0.83) dysfunction and pain frequency (p = 0.2) were similar for the 73 patients with vasculopathy in Group 1 and the 15 symptomatic patients in Group 2. Abnormal pupils were observed in 38% of the patients in Group 1 and 80% of those in Group 2 (p = 0.016). In cases of complete external third nerve palsy, nine of 22 in Group 1 and none of four in Group 2 had normal pupil function. For all patients, source imaging showed 206 PCoAs (85%) and MIP imaging demonstrated 120 PCoAs (49%). Of 48 aneurysms (three bilateral), MIP imaging showed 44 (92%) and source imaging showed 47 (98%). Only a 2-mm aneurysm seen on catheter-based angiography was missed by MR angiography. Symptomatic aneurysms were equal or greater than 4 mm in size. Conclusions. Only the presence of complete external third nerve palsy and normal pupil function allowed ischemia to be clinically distinguished from a PCoA aneurysm in a patient with isolated third nerve palsy and no subarachnoid hemorrhage. When source image MR angiography demonstrates normal findings, catheter-based angiography need not be performed in these patients, even if pupil function is abnormal.