Cerebral hyperperfusion syndrome

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. 

Terminology

Cerebral hyperperfusion syndrome has been referred to as luxury perfusion by some authors ¹¹. Although there are some similarities (namely a failure of normal microvascular autoregulation resulting in blood flow in excess of metabolic requirements) the time course and prognostic implications are entirely different. As such reserving the term cerebral hyperperfusion syndrome for the sequelae of treatment of chronic stenosis avoids confusion.

Additionally, similar imaging features, as well as similar pathophysiological processes, are seen in a variety of conditions where there is dysregulation of cerebral perfusion (e.g. posterior reversible encephalopathy syndrome (PRES), reversible vasoconstriction syndrome (RCVS), migraine, post-seizure encephalopathy, acute hypertensive encephalopathy etc...) ¹⁰. Again, however, reserving cerebral hyperperfusion syndrome for this clinical scenario is preferred.

Epidemiology

Hyperperfusion occurs in ~7.5% (range 1-14%) of patients but only a minority (~1.5%) of patients are symptomatic ^1,2, with the incidence being reported slightly more frequently after endarterectomy (~2%) than after than stenting (~1%) ³. 

Clinical presentation

Presentation is usually within the first week of surgery but has been reported up to a month after surgery ¹. Although there is a varied clinical spectrum, common features include ^1,4:

• 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 ^1,2. Hyperperfusion is defined as CBF >100% above preoperative baseline but patients have been reported to be symptomatic with increases of 20-40% ^1,4. 

A similar syndrome can also develop after other procedures, such as angioplasty for MCA stenosis (ipsilateral syndrome) ⁵ or repair of aortic stenosis (bilateral syndrome) ⁶.

Radiographic features

CT

Features are consistent with cerebral edema and/or intracerebral hemorrhage ipsilateral to the side of the carotid artery procedure ^4,7. The cerebral edema is classically of the white matter and is hypodense, diffuse, and may or may not have associated mass effect ^4,7. The cortex, however, can be swollen and hyperattenuating due to vascular engorgement. The intracerebral hemorrhages are hyperdense and may either be petechial or large in morphology ^4,7.  

CT perfusion

Characteristic ipsilateral features:

• increased CBF, by definition >100% increase compared with preoperative values ^4,8

• increased CBV ⁸

• shortened MTT ⁸

• shortened TTP/Tmax ⁸

MRI

MRI demonstrates the same ipsilateral features as CT and often closely resembles PRES ⁴:

• T1: diffusely hypointense in affected regions ^3,4

• T1 C+ (Gd): often no enhancement is seen ⁴, although leptomeningeal enhancement has been reported ³

• T2/FLAIR: diffusely hyperintense in affected regions ^3,4

• DWI: usually normal ⁴

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 ^7,9. However, if hyperfusion syndrome does manifest, antihypertensive medications such as labetalol and clonidine have been useful, and antiseizure medications may provide symptomatic relief to those with seizures ⁹.