Enhancing Brain Lesions after Endovascular Treatment of Aneurysms

Discussion

It is reasonable to believe that the enhancing brain lesions we describe represent an embolic phenomenon as they were restricted in all but 1 case to the vascular territory of the catheterized arteries. In addition, lesions were predominately located in the cortico-subcortical region where small emboli are more likely to get lodged.

Clinically silent emboli are a common known occurrence of diagnostic cerebral angiograms and neuroendovascular procedures, occuring in approximately 13%–53% of cases.^12,13 Inadvertent foreign body emboli is a far less known complication, first described in 1960.¹⁴ Subsequent reports mostly focused on this phenomenon as a cause of postprocedural ischemia.¹¹ More recently, hydrophilic polymer emboli have been reported as a cause of brain infarction after EVT.^10,15 In a more recent report, intraprocedural foreign body emboli of one of the water-soluble polymers used for hydrophilic coating (polyvinylpyrrolidone or PVP) have been associated with posttreatment delayed ipsilateral intraparenchymal hemorrhage after flow diversion.¹⁶ The first reported brain parenchymal foreign body reaction presenting as MR imaging–enhancing lesions after EVT was published by Fealey et al⁸ in a 58-year-old woman with a ruptured right ICA aneurysm. This patient presented 9 months after uneventful coiling with seizures and 3 associated rim-enhancing brain lesions in the postcentral gyrus. After empiric antibitotic treatment with no change in the brain lesions, a brain biopsy was performed. The pathology specimen revealed granulomatous foreign body reaction and trapped filaments of hydrophilic coating polymer. Similar lesions were found in the arterial access site of the other 2 patients described in this case report.

It is likely that the number of diagnosed cases of brain foreign body granulomas after neuroendovascular procedures is increasing in recent years as MR and MRA widely replace the use of DSA for follow-up of aneurysms after EVT. Surprisingly, recent trials that have used MR imaging for follow-up do not comment on the presence or absence of enhancing lesions.² Specifically, the 2 recent trials that used modified platinum coils where nonvascular complications were first described made no mention regarding subacute enhancing brain lesions in their published data.^17,18

In our case series, the lesions were diagnosed on MR relatively late (after a median time of 63 days) and only a few lesions were restricted on DWI; thus, acute or subacute ischemia is not considered a plausible diagnosis. In patients for whom early postprocedure MR imaging was available, there were a few isolated DWI restricting lesions, but no early enhancing lesions were documented. All of our patients had perilesional edema, which prompted a more complete brain MR imaging protocol, and underwent extensive clinical and laboratory work-up to rule out an infectious etiology (ie, septic emboli). Moreover, the rare reports of brain abscesses after coiling, all presented with positive biochemical markers of CNS infection or isolated pathogen on CSF cultures.^19⇓–21 The 4 lesions in our series that showed diffusion restriction and rim enhancement could be in keeping with aseptic abscesses, which have been described in foreign body reaction after surgery.^22⇓–24 All these lesions evolved from a rim-enhancing pattern to a solid enhancement pattern in follow-up and the diffusion restriction disappeared (Fig 3). This appearance could represent evolution from an aseptic abscess to the more chronic form of a foreign body granuloma.

Local foreign body reaction at the puncture site was described (2.8%–5.0%) in the cardiology literature after radial access by using long hydrophilic coated sheaths.^25⇓–27 Two of our patients presented with aseptic secretion and local inflammation at the puncture site that did not respond to the initial antibiotic treatment, and eventually resolved spontaneously over a few months. Pathologic specimen was not obtained in these cases; however, the clinical picture corresponds to a foreign body skin reaction. Whether this makes the host more prone to developing a foreign body reaction to hydrophilic coating in the brain is unclear.

Our small case series is limited to EVT for aneurysms, which does not mean that this phenomenon cannot be seen in other neurovascular procedures. It is possible that all of our cases are aneurysmal due to the need to navigate distally toward the aneurysm and use coaxial catheters with friction between coaxial catheters and between the coils, stents, and the microcatheter lumen during these procedures. This might increase the risk of hydrophilic coating dislodgement. Aneurysm coiling is also the most common procedure in the institutions participating in this report and all participating institutions use MRA for follow-up, allowing depiction of asymptomatic lesions.

There are several limitations to this series. First, we report a limited series of incidental cases and not a systematic review of all cases performed, thus the exact incidence of this complication cannot be established. We can presume that it is a rare occurrence given that cases were submitted from 5 different referral neurovascular centers with an average of 95 aneurysms per center per year. One of the patients presented 5 years ago and the rest in the last 3 years with no other diagnosed cases in this time period. The timing of the initial and follow-up MR imaging varies widely from case to case and between institutions. Thus, a conclusion regarding the exact timing of lesion development is limited. In addition, none of our cases are proved by surgical biopsy, as lesion resection was not considered necessary, and the diagnosis was made on the basis of clinical and imaging features.