MR Imaging of Partially Thrombosed Cerebral Aneurysms: Characteristics and Evolution

Abstract

BACKGROUND AND PURPOSE A comprehensive evaluation of aneurysmal morphometry requires appreciation of both the vascular lumen and the intraluminal thrombus. MR imaging methods can both evaluate the lumen and directly image the vessel wall. We investigated the ability of T1-weighted, T2-weighted, and steady-state MR imaging techniques to delineate thrombus morphology and reveal changes with time. MATERIALS AND METHODS Nine patients with fusiform basilar or intracranial vertebral artery aneurysms that contained intraluminal thrombus were studied with MR imaging. All patients underwent at least 2 imaging sessions, which were separated by 4–22 months. Analysis of signal intensity to determine the mean signal intensity from thrombus, blood, CSF, and brain in matched regions was performed. Aneurysm maximal diameter and cross-sectional area were determined with and without thrombus. RESULTS Thrombus was identified on all image sequences, and its general appearance was consistent between imaging sessions. Thrombus produced the highest and most consistent signal intensities with T1-weighted and steady-state techniques, though the latter showed superior contrast between luminal blood and thrombus. Heterogeneity within clot was evident in 4/9 of patients, with peripheral hyperintensity being a common feature. CONCLUSIONS Steady-state imaging was found to be superior to T1- and T2-weighted imaging for delineating and characterizing intraluminal thrombus within aneurysms. The imaging characteristics of intraluminal thrombus proved to be very consistent for long periods. Assessment of overall aneurysm size, including thrombosed portions, permits more accurate evaluation of aneurysm growth and concomitantly may permit more informed clinical decision-making with regard to the timing and need for aneurysm treatment.

Pediatric Intracranial Aneurysms: New and Enlarging Aneurysms after Index Aneurysm Treatment or Observation

“…The index fusiform cervicopectoral ICA aneurysm of patient 2 (Fig 2A-C) might similarly be attributed to vascular dissection in the setting of prior significant trauma; some investigators also would consider this patient's de novo vertebrobasilar junction aneurysm to be dissecting based on its morphology and location (Fig 2D-G). 21 Given the inherent limitations of angiography, however, high-resolution MR imaging may be able to differentiate intramural from intraluminal thrombus 22 and thus may better identify the dissecting nature of aneurysms.…”

The Donut Sign: A New Angiographic Sign for Partially Thrombosed Aneurysms with Flow-Induced Intraluminal Thrombus

“…The process of growth by dissections and intramural hemorrhage from the vasa vasorum may induce perianeurysmal edema and rim enhancement of the aneurysm wall. The location of the thrombus in these aneurysms is mainly in the aneurysm wall (intramural) and not in the aneurysm lumen [1][2][3] . This same mechanism of growth is also suggested for serpentine aneurysms that develop from fusiform aneurysms 5 .…”

“…The pathogenesis of intraluminal thrombus in these aneurysms is thought to be related to subacute or chronic wall dissections and repeated intramural hematomas, proliferating vasa vasorum and triggering of inflammatory mechanisms [1][2][3][4] .…”

Pathological findings of saccular cerebral aneurysms—impact of subintimal fibrin deposition on aneurysm rupture

“…The existence of a laminar thrombus and thrombus in the aneurysm has been regarded as a risk factor of rupture in the dissecting, fusiform, or giant saccular aneurysms [18,20,21,27,28].…”