The Changing Landscape of Interventional Neuroradiology

Stroke is the leading cause of disability and the fifth leading cause of death in the United States. Despite the significant morbidity and costs, stroke therapy recommendations have not been well-established until recently, and radiology now plays a central role in the treatment of those patients.

Radiologists are ideally positioned to practice stroke intervention, given their acumen with image interpretation and experience with endovascular therapies. Formerly, the paradigm treatment for ischemic stroke consisted of intravenous thrombolytic therapy, which is easy to administer, typically in the setting of the emergency department. Recently, several randomized clinical trials suggested that endovascular thrombectomy provides superior outcomes.

In particular, the MR CLEAN trial, a multi-center clinical trial involving 233 stroke patients randomized to an endovascular treatment arm, revealed endovascular thrombectomy within six hours after stroke onset was effective and safe. Patients in the endovascular arm achieved improved functional outcomes in 83 percent of cases compared to 19 percent in the medical management arm. Interventional radiologists performed the majority of the thrombectomies in this trial.

Related Content: CT Predicts Stroke Patients Benefitting From Endovascular Thrombectomy​

Four other ongoing trials were terminated early, given the results of the MR CLEAN trial (1). The other four trials (ESCAPE, EXTEND-1A, SWIFT PRIME, REVASCAT), despite premature termination, also demonstrated evidence that significantly better outcomes could be achieved with thrombectomy compared to medical management. Accordingly, the American Hospital Association guidelines changed in 2015, engendering many hospitals to offer this service. The updated guidelines stated a Class 1a recommendation for the use of thrombectomy for anterior circulation large vessel occlusion strokes, up to six hours since the patient was last known well.

Unfortunately, the existing trained radiologist workforce and infrastructure of the healthcare system have not been adequate to meet the demand to deliver safe and timely treatment; high volume practitioners have been necessary to achieve the best clinical outcomes, but eligible patients have been infrequent enough to adequately sustain practice volume.

Specialized stroke care centers, thereby, have been developed for endovascular interventions as a means to funnel patients to high-volume practitioners. Similar models for cardiac ischemia, trauma, and pediatric critical care exist. Despite these efforts, disparity between thrombectomy demand and capable-physician supply still persists. Thrombectomy is currently only available to 2 percent-to-3 percdent of eligible patients in the United States. The current thrombectomy rate is 3 per 100,000 people and is expected to grow to 24 per 100,000 person-years, given the new guidelines (2).

Given these demands, accompanied by the delayed treatment time for transferring patients to designated stroke centers, alternative models have been proposed to train more radiologists to become capable of safely providing these specialized therapies. The traditional training paradigm for diagnostic radiology residents planning to specialize in interventional neuroradiology (INR) entails a neuroradiology fellowship, followed by an INR fellowship. Similarly, in order to practice INR, most interventional radiology residents are required to complete neuroradiology and INR fellowships.

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The Society of Interventional Radiology has championed a new training pathway where proctors train interventional radiologists. This pathway is suggested to be comparable to conventional neurointerventional fellowships and, therefore, serves as an alternative pathway to provide radiologists with the experience necessary to safely perform acute stroke interventions. A proctor needs to have performed 50 acute ischemic stroke cases as a primary operator, with at least two years of practice data with outcomes meeting national standards. Options for learning from a proctor could include one of the following three options (3):

• Hands-on training not limited to interventional techniques, but also including workup before and after management for thrombectomy
• Full-time training at a different institution, given the unpredictable case rate for stroke care
• Travel consultant, where the proctor travels to institution to provide hands-on training

A case study at Johns Hopkins University (JHU) demonstrated success with this model. JHU recruited an INR physician to teach four interventional radiologists how to perform cerebral thrombectomies. The trainees were available for six months, and the INR physician was flown-in by helicopter for each eligible thrombectomy case. Upon completion of training, 35 of the stroke cases were reviewed, and compared to the quality guidelines outlined in the Highly Effective Reperfusion Evaluated in Multiple Endovascular Stroke Trials (HERMES) meta-analysis published in 2016.

JHU 90-day mortality was 14 percent while HERMES was 15.3 percent. Therefore, upon being trained, the interventional radiologists had 90-day mortality ratings similar or better than the current benchmark (4). As demonstrated by the previous case study, and building upon their expertise in imaging and image-guidance, radiologists are able to acquire the skillset necessary to safely perform endovascular treatment in a short timeframe.

In summary, the morbidity and mortality of stroke is a detriment to patients and society, and, until recently, treatment attempts have often been ineffective or limited to a select group of patients. An immense opportunity now exists for radiologists to manage acute stroke patients with endovascular therapy and achieve excellent outcomes for many patients up to six hours after stroke onset.

Currently, the infrastructure of the healthcare system faces challenges in its ability to pair a capable physician and a patient in need. Radiologists are, however, ideally situated to contribute to this treatment revolution and lessen the disparity between the demand and the access for endovascular stroke therapy.

_References

1. _{Vadlamudi V. Updates on Endovascular Therapy for Acute Ischemic Stroke. SIR-RFS Webinar. June 5, 2018.}
2. _{Rai AT, Seldon AE, Boo S, et al. A population-based incidence of acute large vessel occlusions and thrombectomy eligible patients indicates significant potential for growth of endovascular stroke therapy in the USA. Journal of NeuroInterventional Surgery 2017;9:722-726.}
3. _{Sacks, D, AbuAwad, M, Ahn, S, et al. Society of Interventional Radiology Training Guidelines for Endovascular Stroke Treatment. Journal of Vascular and Interventional Radiology 2019;30(10):1523-153.}
4. _{Forrest, W. SIR: Stroke treatment training program improves outcomes. Aunt Minnie. March 22, 2019.}