Hyperperfusion syndrome after carotid endarterectomy
Cerebral hyperperfusion syndrome is a rare complication seen after treatment of long-standing severe carotid stenosis by carotid endarterectomy or carotid artery stenting. It is believed to be the result of failure of normal cerebral blood flow autoregulation.
Epidemiology
Hyperperfusion occurs in ~7.5% (range 1-14%) of patients but only a minority (~1.5%) of patients are symptomatic , with the incidence being reported slightly more frequently after endarterectomy (~2%) than after than stenting (~1%) .
Clinical presentation
Presentation is usually within the first week of surgery but has been reported up to a month after surgery . Although there is a varied clinical spectrum, common features include :
- ipsilateral headache
- hypertension
- seizures
- ipsilateral intracranial hemorrhage and associated focal neurological deficits
Pathology
The pathophysiological mechanism is unknown but thought to be secondary to increased cerebral blood flow (CBF) from a loss of cerebral autoregulation . Hyperperfusion is defined as CBF >100% above preoperative baseline but patients have been reported to be symptomatic with increases of 20-40% .
A similar syndrome can also develop after other procedures, such as angioplasty for MCA stenosis (ipsilateral syndrome) or repair of aortic stenosis (bilateral syndrome) .
Radiographic features
CT
Features are consistent with cerebral edema and/or intracerebral hemorrhage ipsilateral to the side of the carotid artery procedure . The cerebral edema is classically of the white matter and is hypodense, diffuse, and may or may not have associated mass effect . The intracerebral hemorrhages are hyperdense and may either be petechial or large in morphology .
CT perfusion
Characteristic ipsilateral features:
- increased CBF, by definition >100% increase compared with preoperative values
- increased CBV
- shortened MTT
- shortened TTP/Tmax
MRI
MRI demonstrates the same ipsilateral features as CT and often closely resembles PRES :
- T1: diffusely hypointense in affected regions
- T1 C+ (Gd): often no enhancement is seen , although leptomeningeal enhancement has been reported
- T2/FLAIR: diffusely hyperintense in affected regions
- DWI: usually normal
Regions of hemorrhage have varying MRI signal characteristics depending on age (see aging blood on MRI).
Treatment and prognosis
Management should focus on prevention, with particular attention to blood pressure management . However, if hyperfusion syndrome does manifest, antihypertensive medications such as labetalol and clonidine have been useful, and anti-epileptic medications may provide symptomatic relief to those with seizures .
