Enhancing brain lesions after endovascular aneurysm treatment

Case contributed by Dr Michał Czerny

Presentation

Suspicion of right MCA territory infarct - left-sided unspecified neurological deficits. Endovascular treatment of right pericallosal artery aneurysm with stent implantation 6 weeks previously.

Patient Data

Age: 65 years
Gender: Female

This is a presentation of a rare entity which was initially misdiagnosed as a form of subacute ischemic stroke (RMCA territory).

Initial on- call study.

CT

There is dense embolization material that blends with stent implanted into the right pericallosal artery after endovascular treatment (EVT) of an aneurysm.

Right hemisphere, mainly in the right MCA territory, is diffusely edematous within white matter, with preserved cortex density, without signs of hemorrhage. 

Supratentorial mild/moderate positive mass effect on the right.

Mainly right-sided areas of cerebral white matter edema, mostly confluent with some cortical and basal ganglia involvement. Few foci in the left hemisphere.

After contrast administration, multiple nodular, partially confluent areas of vivid contrast enhancement are seen with cortical/subcortical and white matter angiocentric distribution. Most of the enhancing lesions show some mild peripheral diffusion restriction. 

Single foci of microhemorrhage are seen on SWI.

Impression: 

Multiple foci and regions of enhancing lesions resembling granulomas and aseptic emboli with edema and some degree of peripheral diffusion restriction, most probably due to endovascular treatment.

Follow up MR ~9 months later

MRI

Follow-up study made approximately 9 months after initial MR:

Right-sided multiple areas of white matter edema mixed with leukodegenerative changes, peripherally confluent with cortical sparing. Partial regression compared to the previous study. One such small region involving left frontal lobe.

Multiple nodular cortical/subcortical foci of gadolinium enhancement with some angiocentric areas in the white matter - moderate partial resorption.

On DWI there are areas of residual higher signal compatible with white matter lesions without any signs of true restriction diffusion on the ADC map. 

More prominent multiple foci of chronic microhemorrhages on SWI in places of contrast enhancement.

Impression: 

Moderate partial regression with complete remission of the acute changes, with higher degree of hemorrhagic component.

Case Discussion

Given the patient's history and initial findings on CT, an ischemic stroke was the primary suspicion, with confirmatory MRI that led to a false conclusion that this indeed may be an unusually looking subacute MCA territory stroke, perhaps connected to previous endovascular treatment.

The follow-up scan did not show the expected typical evolution of findings, with only a moderate partial regression. 

Unusual appearance and lack of incongruence between symptoms, laboratory workup, and initially proposed imaging diagnosis, led to literature research and retrospective analysis of the imaging studies that associated the findings with the treatment the patient had undergone - the revised diagnosis was of "enhancing brain lesions after endovascular treatment". 

This is a rare and poorly understood condition suspected to be some kind of foreign body reaction and inflammatory changes with microembolic background and lack of larger vessel infarction. One of the cases described in the literature was autopsy-proven to show trapped particles/filaments of hydrophilic coating with granulomatous foreign body reaction.

Most of these lesions show up relatively late, which excludes typical acute/subacute ischemic etiology. The laboratory workup for patients, including the one in this case, showed no findings of CNS infection, effectively ruling out septic emboli.

Based on the imaging pattern and information in the literature, this appearance is most likely caused by a foreign body reaction with components of aseptic emboli and granulomas.

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