Outflow angle measurement: a simple approach for the differential diagnosis of intracranial protrusion with a branch artery arising from its top

Abstract

Purpose: Magnetic resonance angiography (MRA) is an important diagnosis method for the detection of intracranial aneurysms (IAs), but it is not useful for differentiating between IA and infundibular dilatation (ID) in patients in whom imaging shows an intracranial protrusion with a branch artery at its top. The objective of this study was to introduce a new approach-measurement of the outflow angle (OA)-for differentiating between IA and ID in such cases.

Methods: The study included 7 patients with a total of 9 protrusions. The protrusions were separately reviewed on MRA and DSA images. We first diagnosed the protrusions using OA approach. An OA ≥90° was considered indicative of an IA and an OA <90° was considered indicative of an ID. The diagnosis by the OA method was compared with diagnosis by the gold standard-DSA.

Results: Among the 9 intracranial protrusions, 5 were IAs and 4 were IDs. The OAs of 5 IAs were all ≥90°; the average OA of the 5 IAs was 115.20°. The OAs of the 4 IDs were all <90°; the average OA of the 4 IDs was 59.50°. The diagnosis results by the OA method were in agreement with DSA diagnosis in all cases.

Conclusion: The OA method can discriminate between IA and ID in patients in whom imaging shows an intracranial protrusion with a branch artery at its top. The method is simple and convenient, and can be easily applied in clinical practice. It can be especially useful for novice neuroradiologists.

Keywords: Angle; Artery branch; Infundibular dilation (ID); Intracranial aneurysm (IA); Magnetic resonance angiography (MRA); Protrusion.