Long-term MRI findings of muslin-induced foreign body granulomas after aneurysm wrapping. A report of two cases and literature review

Abstract

Muslin-induced foreign body granulomas are rare delayed complications after wrapping of intracranial aneurysms. Few small case series have been reported, with a paucity of documented MRI findings. In addition, there are no reports on long-term radiological appearances or temporal evolution of conservatively managed patients. We thus report on the long-term radiological and clinical follow-up of two patients with asymptomatic muslin-induced foreign body granulomas after wrapping of recurrent middle cerebral arterial aneurysms. Both patients were successfully managed conservatively and remain asymptomatic three and six years after diagnosis of their granulomas. A literature review confirms that MRI features of muslin-induced foreign body granuloma are typical. Features include focal areas of elevated T2 signal with increased diffusion-weighted signal and thin rim enhancement. To the best of our knowledge, this is the first report to confirm that there is a corresponding reduction in apparent diffusion coefficient, as typical in an intracranial abscess. Thus a history of aneurysm wrapping is critical for diagnosis. Accurate clinical recognition of this exuberant inflammatory response will avoid misdiagnosis as pyogenic abscess or tumor and prevent unnecessary or invasive treatment.

Keywords: granuloma; intracranial aneurysm; magnetic resonance imaging; wrapping.

Figure 1

MRI imaging course of the granuloma in patient 1. A) Axial fluid attenuated inversion recovery (FLAIR) and coronal contrast enhanced T1-weighted MRI. At diagnosis, 7 months post muslin wrapping, there is edema in the right temporal operculum adjacent to the wrapped aneurysm (arrow in top image), and a ring-enhancing mass centered on the wrapped aneurysm (arrow in bottom image). B) Axial FLAIR MRI and right internal carotid artery (ICA) DSA. Six months after diagnosis, there is increased peri-aneurysmal brain parenchymal edema (arrow in top image) and by the second year after diagnosis, there is prominent peri-aneurysmal vascular narrowing in the M1 and M2 branches of the MCA (bottom image). C) Axial FLAIR, right ICA MRA and coronal contrast-enhanced T1 MRI. Six years after diagnosis, there is a reduced but persistent peri-aneurysmal T2 signal (arrow in top left), peri-aneurysmal vascular narrowing (bottom left) and a ring-enhancing mass (arrow in bottom right).

Figure 2

MRI imaging course of the granuloma in patient 2. A) Axial FLAIR MRI. Twelve months after muslin wrapping, there is new edema in the right temporal operculum and external capsule (arrow in top image) adjacent to the wrapped aneurysm (arrow in bottom image). B) DW, ADC map, axial FLAIR and contrast enhanced axial T1-weighted MRI 28 months after muslin wrapping. There is now marked abnormal peri-aneurysmal brain parenchymal T2 signal with mass effect (arrow in top right) with a large lobulated enhancing mass around the wrapped aneurysm. There are focal round areas of elevated T2 signal with elevated DW signal (arrow in top left) and ADC reduction (arrow in bottom left) with ring enhancement (arrow in bottom right). These are imaging features typically seen with intracranial abscess formation. C) Axial FLAIR and contrast-enhanced axial T1-weighted MRI. During 3 years of follow-up after diagnosis, there is improvement, but persistent abnormal peri-aneurysmal T2 signal and a ring-enhancing mass.