Muesli sign for the detection of non-ishemic cerebral enhancing (NICE) lesions afte endovascular treatment.

Abstract

Introduction

Cerebral granulomatous foreign body reactions, also called delayed onset non-ischemic cerebral enhancing lesions (abbr. (NICE)) are a rare complication following endovascular procedures like aneurysm embolization (Cruz Krings AJNR 2014, Shotar Neuroimaging 2021) or mechanical thrombectomy for acute ischemic stroke (Forestier 2022, Mehta, Abbasi).

The NICE lesions described in the literature are characterized by nodular enhancement on contrast enhanced follow-up MRI scans (Shapiro 2015, Shotar Neuroradiology 2016) surrounded by vasogenic oedema. In several patients those lesions detected on MRI imaging were histologically correlated to the presence of non-caseating intracerebral foreign-body granulomas and were attributed to transarterial embolization of microscopically fragmented material during a culprit endovascular procedure (Shapiro 2015) resulting in persistent or recurrent focal inflammation. However, new MRI signs could further facilitate diagnosis and make MRI combined with the patient's history more specific regarding the diagnosic of NICE lesions. In this case series we describe the ?Muesli sign? and hypothesize that it is an imaging feature aiding in the detection of cerebral foreign body reactions (NICE lesions) in non-contrast-enhanced MRI follow up imaging of patients after endovascular procedures.

Methods

A retrospective review of all patients with endovascular neuroangiographic treatments for intracranial arterial aneurysms, AVM, acute ischemic stroke performed between from January 1, 2012 to June 30, 2023, and reported to our registry of NICE lesions was undertaken. The presence of hypointense nodules randomly distributed in a homogenously hyperintense region resembles the appearance of cereals in milk, in German language called Muesli, hence the name for the appearance on MRI T2 imaging.

Results

Overall, 57 patients were included in the analyses: 54 patients received endovascular treatment for intracranial aneurysms (93.0%), 3 patients (5.3%) were treated with mechanical thrombectomy for acute ischemic stroke, 1 patient was treated for a cerebral AVM using a EVOH liquid embolic agent (1.7%). Overall, in any kind of T2 weighted imaging (spinecho or FLAIR), the Muesli sign was identified in 42 of 57 patients by both independent reviewers (73.7% prevalence of the Muesli sign in T2 weighted imaging of NICE lesion patients) and was unanimously found absent in 16 of 57 patients (28.1% of confirmed NICE lesion patients had a negative Muesli sign). Overall, there was disagreement concerning the presence of the Muesli sign in 3 of 57 patients (5.3%).

Conclusion

Based on our observations the 'Muesli sign', which is for the first time described in this study, allows the detection of NICE lesions in non-contrast brain MRI scans, and was present in 3 of 4 patients when T2 weighted imaging was available with excellent interrater agreement for the Muesli sign detection.