gms | German Medical Science

Objective: The aim of this study was to characterize unruptured giant intracranial aneurysms using 7 Tesla (7T) magnetic resonance imaging (MRI) with special focus on the aneurysm wall.

Method: Six patients with giant intracranial aneurysms were prospectively evaluated using an ultra-high-field 7T whole-body MR system (Siemens Healthcare Sector, Germany) equipped with a 32-channelradiofrequency head coil between April 2011 and October 2014. Three patients were male and three were female, with an average age of 65.2 years (range 50-80 years). The applied sequences included time-of-flight (TOF), magnetization-prepared rapid acquisition gradient-echo (MPRAGE) and susceptibility weighted imaging (SWI). The regions of interest were placed in the wall of the dome farthest away from the aneurysm base. Two raters assessed the parameters including aneurysm and parent artery diameters, wall thickness and the signal intensity in the aneurysm wall, intraluminal thrombus, intraluminal flow and surrounding brain tissue in consensus reading. In addition, contrast ratios were calculated between the aneurysm wall and adjacent brain tissues. Two surgically resected aneurysms were suitable for histological examination, and correlation between MRI and histopathology was evaluated.

Results: Five out of six aneurysms showed partial to complete thrombosis. Mean diameters of aneurysms and parent arteries were 30.1 mm (range 25.1-37.9) and 3.0 mm (range 1.7-3.9). The wall was depicted as hypointense on TOF and SWI in all patients, showing heterogeneous intensity in MPRAGE. Mean (range) thickness of aneurysm wall was: TOF 0.94 mm (0.73-1.39), MPRAGE 1.08 mm (0.79-1.55), magnitude SWI 1.36 mm (1.22-1.67), and SWI 1.50 mm (1.28-1.86). Mean (range) of contrast ratio to adjacent brain tissue was: TOF -0.42 (0.00 - -0.60), magnitude SWI -0.69 (-0.59 - -0.77) and SWI -0.87 (-0.75 - -0.96). In TOF and SWI, the aneurysm wall was depicted as a triple layered structure, corresponding to iron deposition in both histopathological specimens. The measured wall thickness in TOF corresponded best with the histological findings.

Conclusions: The wall of giant intracranial aneurysms was well depicted as hypointense in 7T TOF and SWI compared to adjacent tissues, precisely revealing the aneurysm wall microstructure. Ultra-high-field MRI of this rare intracranial vascular pathology might contribute to a better understanding of the complex pathophysiology of aneurysm growth and rupture.