Multidetector computed tomographic angiography in isolated third nerve palsy

Objective: To evaluate whether multidetector computed tomographic angiography (CTA) scanners can detect a clinically significant intracranial aneurysm in the circle of Willis causing an isolated third nerve palsy (ITNP). Design: Retrospective cross-sectional study. Participants: One hundred thirty-seven patients who presented with an ITNP were examined by multidetector CTA scanners. Methods: All patients whose symptoms were caused by a compressive cerebral aneurysm were identified. The remaining patients were observed clinically to exclude the possibility of a missed cerebral aneurysm causing the ITNP. No patient underwent diagnostic conventional cerebral angiography (CCA), but all patients who underwent treatment underwent CCA at the time of the treatment. Main Outcome Measures: Accurate identification of a cerebral aneurysm that may cause an ITNP. Results: A cerebral aneurysm causing an ITNP was detected in 27 patients (19.7%). The smallest maximal diameter of a clinically significant aneurysm was 5.7 mm. Of the 27 patients, 25 underwent endovascular coiling at which time CCA confirmed the aneurysm. In no case was another lesion found by CCA. Of the patients without an aneurysm, 81 of 110 (74%) made a complete spontaneous recovery. In no patient was there clinical evidence to suggest that a compressive cerebral aneurysm had been missed on CTA. Conclusions: Multidetector CTA is a safe and effective diagnostic imaging tool in detecting clinically significant aneurysms when a patient presents with an acute ITNP. We no longer perform CCA to detect a causative aneurysm or determine the type of treatment offered in these patients.