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. 2021 Mar 26;34(4):363–369. doi: 10.1177/19714009211004185

Hydrophilic polymer embolization following flow diversion of cerebral aneurysms

Mohamad Abdalkader 1,, Anvitha Sathya 2, Alice Ma 1, Anna M Cervantes-Arslanian 3,4, David Y Chung 3, Glenn Barest 1, Thanh N Nguyen 1,3,4
PMCID: PMC8447820  PMID: 33765885

Abstract

Foreign body embolization is a rare and potentially under-recognized complication of neuroendovascular procedures. This complication should be considered in the differential diagnosis for clinical or radiological deterioration following neurovascular interventions. We report a case of foreign body hydrophilic coating embolization that occurred following an attempted flow diversion of an intracranial aneurysm with dramatic flare-up after repeat exposure. We also provide a literature review of all reported cases of hydrophilic polymer embolization following flow diversion procedures.

Keywords: Aneurysms, flow diversion, embolization, hydrophilic

Introduction

Hydrophilic polymer embolism has been reported as a potential complication of endovascular flow diversion in the treatment of intracranial aneurysms.13 Particulates of the hydrophilic device coatings may strip off secondary to mechanical friction/abrasion and embolize to downstream vascular territories causing a granulomatous inflammatory reaction with a wide spectrum of clinical and radiological manifestations.4,5 Commonly reported complications of flow diversion include hemorrhagic and ischemic complications.610 Recently, hydrophilic polymer embolism has been reported as an additional potential complication of flow diversion of cerebral aneurysms.13 This rare and potentially under-recognized complication should be considered in the differential diagnosis of new neurological findings following neurovascular interventions, particularly if there is a delay in the development of clinical symptoms after the procedure.

Case description

We report a woman with HIV and recurrence of a ruptured posterior communicating artery aneurysm 10 years after coiling with Micrus coils (Codman Neuro, Raynham, MA). The recurrent aneurysm was detected on imaging performed for headache. Strategies to retreat recurrent aneurysms include repeat coiling, stent assisted coiling, or endovascular flow diversion, or surgical clipping. Challenges associated with repeat coiling are the potential for coil migration in wide-neck aneurysms with shallow luminal recurrences.11,12 Given the unfavorable anatomy for repeat coiling and the difficulty of surgical treatment, a flow diverter stent was recommended. A Flexor® Shuttle® Sheath (Cook Medical, Bloomington, IN) was placed in the right internal carotid artery. An intermediate Navien™ 058 catheter was used to cannulate the petrous segment over a Marksman™ microcatheter (Medtronic, Irvine, CA) and Synchro™ 0.014-in microguidewire (Stryker, Kalamazoo, MI). Multiple attempts were made to deploy a Pipeline Flex device™ (Medtronic, Irvine, CA) (Figure 1). However, due to unfavorable positioning of the device and repetitive prolapse in the aneurysm cavity, deployment was abandoned and the device was removed. She was discharged without complications. One-month post discharge, the patient presented with partial seizures involving her left arm and leg. MRI showed multifocal micro-nodular areas of enhancement surrounded by vasogenic edema involving the right frontal and parietal regions (Figure 2). Results of an extensive work-up to identify an underlying cause were negative. The working diagnosis was delayed inflammatory reaction secondary to hydrophilic polymer embolization. Steroid treatment was considered but ultimately not prescribed due to compound risks of immunosuppression in setting of HIV. The seizures were adequately controlled with antiepileptic medications. Eighteen months later, the patient elected to have a repeated attempt of flow diversion. Using different microcatheter and guide catheters, the patient underwent successful placement of two overlapping Pipeline Flex devices™ that were delivered via Neuron Max 6 French, 088 guide catheter (Penumbra, Inc., Alameda, CA), Sofia (Microvention-Terumo, Inc.) intermediate catheter, Phenom microcatheter (Medtronic) and Synchro 0.014-in microguidewire (Stryker) (Figure 3). The procedure was uneventful without immediate complications. Two days later, the patient had focal seizures and left-sided weakness. Brain MRI exam showed worsened significant FLAIR hyperintensities and nodular enhancement in the right frontal and parietal lobes suggestive of recurrent granulomatous reaction (Figure 4). Given significant clinical worsening, treatment with corticosteroids was initiated. The patient was treated with dexamethasone (4 mg, PO, every 6 hours) for 5 days with excellent response; dexamethasone was transitioned to oral prednisone 60 mg daily with weekly decrease by 10 mg. Follow up brain MRI performed 2.5 months later showed near-complete resolution of the hyperintensities and abnormal enhancement. Repeat angiogram 6 months after successful flow diversion showed complete resolution of the recurrent aneurysm (Figure 5).

Figure 1.

Figure 1.

Angiographic images at the time of attempted flow diverter placement. Digital subtraction angiogram (right anterior oblique projection) of the right internal carotid artery (a) shows the recurrence of the previously coiled right posterior communicating aneurysm (asterisk). Unsubtracted image (b) shows the previous coil mass (white arrow) and the partially deployed flow diverter in the supraclinoid internal carotid artery (black arrow).

Figure 2.

Figure 2.

MRI brain exam performed 1 month after aborted flow diverter placement. Axial diffusion weighted images (a) with apparent diffusion coefficient (b) showing no restricted diffusion. Axial FLAIR image (c) shows multifocal hyperintensities in the subcortical white matter of the right frontal and parietal lobes. Axial gadolinium-enhanced T1 image (d) shows multiple small enhancing lesions (white arrows).

Figure 3.

Figure 3.

Angiographic images at the time of subsequent flow diverter placement. Unsubstracted angiograms (right anterior oblique projection) of the right internal carotid artery (a) and (b) showing successful deployment of two telescoping flow diverters (white arrows) across the neck of the aneurysm with the distal end of the distal flow diverter noted in the proximal M1 segment to ensure stability.

Figure 4.

Figure 4.

MRI brain exam performed two days after successful placement of the flow diverters. Axial diffusion weighted images (a) showing no restricted diffusion. Axial FLAIR image (b) shows worsened hyperintensities in the right frontal and parietal subcortical white matter. Axial susceptibility weighted image (c) shows a few associated punctate signal voids and axial (d), coronal (e) and sagittal (f) gadolinium-enhanced T1 images show a dramatic increase in extent of multinodular enhancement.

Figure 5.

Figure 5.

Follow up MRI brain exam and angiogram performed after flow diverter placement. Axial FLAIR (a) and gadolinium-enhanced T1 (b) images 2.5 months later show near-complete resolution of the subcortical hyperintensities and enhancement in the right frontal and parietal lobes. Digital subtraction angiogram (lateral projection) of the right internal carotid artery (c) 6 months later shows occlusion of the residual aneurysm with reconstruction of the supraclinoid carotid artery.

Discussion

Recurrence after endovascular coiling of intracranial aneurysms is a known phenomenon associated with treatment of brain aneurysms and is more commonly encountered in patients who present in a ruptured state, with wide-neck aneurysms, larger sized aneurysms, or incompletely occluded aneurysms at the initial treatment.1214 Endovascular flow diversion has been shown to have high technical success in the definitive closure of intracranial aneurysms.1518 As our patient demonstrated major recurrence of her aneurysm several years after coiling of her initially ruptured aneurysm, endovascular flow diversion was selected as the preferred modality to achieve aneurysm closure.

Hydrophilic polymers (especially polyvinylpyrrolidone-PVP) are widely used as surface coatings on neurovascular medical devices including guidewires, catheters, coils, stents, stent retrievers and flow diverters to enhance biocompatibility and maneuverability, and reduce friction during vessel navigation and between the co-axial devices.19 Despite the advantages of surface coatings on neurovascular tools, particulates of these coatings may strip off the devices and embolize to downstream vascular territories causing reactive granulomatous inflammation to the foreign bodies.4,5 This complication is known as hydrophilic polymer embolization (HPE). Data about this phenomenon in neurointervention is limited to small cases series and case reports.1,3,4,7,2022

The true incidence of HPE is unknown because MRI is not systematically obtained after endovascular procedures and there may be asymptomatic cases that go unnoticed. Clinical, histopathologic and radiological manifestations of HPE are secondary to small-sized distal cerebral vessel occlusion evolving into subacute granulomatous angiitis.4,5 Symptoms vary depending on the vascular territory involved and the extent of the inflammatory reaction. HPE may be asymptomatic or may present with non-specific neurological symptoms (such as headache), fatigue, seizure or focal neurological symptoms with stroke-like symptoms corresponding to the territory involved. The time frame for clinical presentation is usually between a few weeks to a few months with most occurring within 2 weeks after the procedures. Radiologically, foreign body emboli manifest as nodular enhancing lesions in the vascular territory of the catheterized arteries at the cortico-subcortical regions where small emboli usually lodge. These lesions, also known as non-ischemic cerebral enhancing lesions (NICE), are usually surrounded by white matter edematous changes characterized by T2/FLAIR hyperintensities.21 Restricted diffusion is not typically described with these lesions, likely because of the subacute or late presentation. There may also be associated microhemorrhages characterized by blooming artifacts on gradient echo or susceptibility images as seen in our patient.4 HPE was also reported to be associated with delayed intracranial hemorrhage after flow diversion and post-procedural ischemia.7 HPE should be a consideration in patients with radiological findings in a vascular territory following endovascular procedures. It may mimic multifocal ischemic or hemorrhagic complications, meningitis or other inflammatory or malignant conditions.

In our patient, although not confirmed by biopsy, a presumptive diagnosis of a foreign body reaction due to HPE was made based on the timeline of symptoms and of the imaging findings seen exclusively within the right cerebral hemisphere. Since all neuroendovascular tools used in both procedures were coated with hydrophilic materials, it is not possible to know the exact source of the embolic material. We hypothesize that the source may have been the flow diverter, since the first attempt to treat the aneurysm was technically challenging and required multiple attempts of partial unsheathing/re-sheathing, and back and forth movement of the densely coated flow diverter in the dysplastic supraclinoid internal carotid artery. This may have caused the hydrophilic coating of the flow diverter to dislodge and shower distally. The patient had uneventful coiling with hydrophilic tools 10 years previously. In addition, the only common tool between the initial attempted flow diversion and the repeated procedure 18 months later was the pipeline flow diverter. We intentionally changed the guide catheter (from Shuttle to Neuron max), the intermediate catheter (from Navien to Sofia) and the microcatheter (Marksman to Phenom) on the second deployment.

HPE has been reported after placement of flow diverter devices14,20,21,2325 (Table 1). To our knowledge, this is the first case of HPE after an aborted flow diversion. Eighteen months after the first attempt and soon after the successful deployment of the flow diverter, brain MRI showed significant worsening of the inflammatory reaction in the same territory. The rapid flare-up after the second exposure is typical of a type IV granulomatous hypersensitivity reaction when re-exposure to the foreign body reactivates specific memory T-cells triggering an accelerated reaction.26 Treatment of reactions to HPE is mainly conservative symptomatic treatment and includes corticosteroids to decrease the inflammatory reaction and the associated vasogenic edema. Our patient did not receive corticosteroids initially because of her HIV status. However, the flare-up after the successful deployment was severe enough requiring initiating steroids treatment to decrease the edema and was associated with marked clinical improvement.

Table 1.

Table showing all the reported cases of hydrophilic polymer embolization following flow diversion of cerebral aneurysms.

Author, year Study type Number of cases Aneurysm location Symptoms Symptoms onset Diagnosis Treatment Outcome
Cruz,7 2014 Case series Patient # 1 Supraclinoid aneurysm Not available 4 months MRI: NICE N/A N/A
Patient # 2 Cavernous ICA aneurysm Asymptomatic 3 months MRI: NICE  Antibiotics N/A
Hu,23 2014 Case series Patient # 1 Paraophthalmic aneurysm Parenchymal hemorrhage 3 days Autopsy: foreign body reaction None Death
Patient # 2 Paraophthalmic aneurysm Parenchymal hemorrhage 6 days Autopsy: foreign body embolic None Death
Patient # 3 Paraophthalmic aneurysm Parenchymal hemorrhage 2 weeks Foreign body embolic occlusion None Death
Shapiro,4 2015 Case series Patient # 1 Trigeminal aneurysm Fatigue, left-sided weakness and quadrantanopsia  8 weeks NICE with SWI artifacts Antibiotics and steroids  Recovery
Patient # 2 Right ICA aneurysm Fatigue, headache 8 weeks MRI: right parieto-occipital hematoma, with NICE Dexamethasone Recovered
Patient # 3 Paraophthalmic aneurysms Headache 2 weeks MRI: NICE Biopsy: giant cell granulomas  Six-week course of corticosteroids Improvement
Patient # 4 Paraophthalmic aneurysm Seizure 3 months MRI: NICE and SWI. Biopsy: granulomatous angiitis Antiepileptics and steroids Not available
Shotar,21 2016 Case report Patient # 1 Ophthalmic aneurysm Seizure at 17 months 17 months Biopsy: leukocytoclastic vasculitis Antiepileptics and steroids Recovery
Lorentzen,3 2016 Case report Patient # 1 Paraophthalmic aneurysm Headache followed by aphasia and hemiparesis 3 months MRI: NICE Biopsy: non-polarizable foreign material surrounded by giant cell granulomas  Steroids Improvement with residual headache
Sablani,1 2018 Case report Patient # 1 Supraclinoid carotid Headache, weakness and numbness 3 days MRI: NICE Steroids Recovery
Brinjikji,13 2018 Case report Patient # 1 Paraophthalmic aneurysm Headache and word-finding difficulty 2 months MRI: NICE Steroids Recovery
Daneshmand,25 2018 Case report Patient # 1 Supraclinoid carotid artery Seizure 1 year MRI: NICE Steroids Recovery
Geisbush,2 2019 Case report Patient # 1 Supraclinoid aneurysm Headache, numbness and weakness 1–2 months MRI: NICE Steroids Improvement with residual headache

Abbreviations: MRI: magnetic resonance imaging; NICE: non-ischemic contrast enhancement with surrounding edema; ICA: internal carotid artery; SWI: susceptibility weighted images; N/A: not available.

Conclusion

HPE remains a clinically and radiologically challenging and under-recognized complication of neuroendovascular procedures. We report the first case in which an aborted flow diverter deployment was associated with this complication followed by recurrence of symptoms and imaging findings following subsequent successful deployment. It is important to raise awareness of this potential complication after neuroendovascular procedures to allow for appropriate clinical management and to prevent unnecessary investigations. Also, controlling polymer coating emboli by mitigating or eliminating particulates from intravascular devices should become a focus of interest for engineers and manufacturers.

Footnotes

Conflict(s) of interest: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding: The author(s) received no financial support for the research, authorship, and/or publication of this article.

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