Intracranial Stenosis

Intracranial stenosis is the medical term for severe narrowing of a cerebral artery that restricts blood flow to areas of the brain.  Such narrowing stems from focal, progressive atherosclerosis of the affected vessel.  Intracranial stenosis is responsible for about 10% of strokes annually, and the rate of recurrent strokes without treatment can be alarmingly high.  Current optimal medical treatment includes antiplatelet or anticoagulation medications such as aspirin or warfarin, anticholesterol agents, control of hypertension, and aggressive control of blood glucose in patients with diabetes. 

Diagnosis

Computed tomography (CT) angiography, magnetic resonance (MR) angiography, and catheter-based angiography can be used to visualize the region of vessel narrowing.  Typical areas of intracranial stenosis include the internal carotid artery, middle cerebral artery, vertebral artery, and basilar artery.  Other diagnostic tests can evaluate the adequacy of blood flow to the brain.  Computed tomography (CT) perfusion with and without acetazolamide, positron emission tomography (PET), stable xenon CT, and single photon emission CT (SPECT) are all specialized tools used to evaluate adequate blood flow to the brain. PET also has the ability to evaluate the oxygen extraction fraction, a parameter that correlates with risk of stroke.

Treatment

When patients fail optimal medical therapy and diagnostic imaging supports the benefit of treatment, neurosurgical and neuroendovascular interventions may be indicated for selected patients.  Surgical treatment can include bypass grafting to increase blood flow to the brain distal to the stenosis.  Typically, a superficial temporal artery-to-middle cerebral artery (STA-MCA) bypass is used.  Less commonly, when the demand for blood flow is high, a high-flow bypass is placed using a large caliber vein or artery for the graft.  When the arterial recipients for a direct anastomotic bypass are poor with a moyamoya-like pattern, an onlay procedure known as encephalo-duro-arterio-synangiosis (EDAS) or encephalo-duro-arterio-myo-syangiosis (EDAMS) is indicated.   The Barrow Neurological Institute is participating in the Carotid Occlusion Surgery Study, a multicenter prospective analysis of STA-to-MCA bypass for the treatment of patients with symptomatic occlusion of the ipsilateral internal carotid artery.  

Endovascular treatments include balloon angioplasty of the stenotic artery, with or without placement of an endoluminal stent.  A prospective study evaluating the effectiveness of percutaneous transluminal angioplasty and stenting for intracranial stenosis is also underway at Barrow.