Our Imaging Case of the Month is presented as a part of the Imaging Department's residency teaching program. Each month a resident collaborates with one of our attending imaging physicians to present an interesting case to the Cedars-Sinai medical community. The case is used to teach both imaging and other residents at Cedars-Sinai. Below is the current Case of the Month.
Submitted by Brian Lee, MD, and Thomas J. Learch, MD
A 25-year-old male with hypertension and Type 2 diabetes presents to the emergency department complaining of two weeks of headache and blurry vision which has been progressively worsening. In the emergency department, his initial blood pressure measurement is 238/113, and the decision is made to admit him to the hospital for hypertensive urgency. Due to his headaches and visual symptoms, a noncontrast head CT was ordered for initial work-up, showing the following:
No hemorrhage was seen, but a chronic infarct was identified in the left occipital lobe, which could account for the patient’s visual symptoms. How strange to see a chronic infarct in a 25-year-old patient.
Because of the presence of the infarct, an MRI was ordered to see if anything else could be found. The following images were obtained:
This FLAIR image shows the chronic left occipital infarct that was seen on the noncontrast CT. But also evident were numerous small hyperintense vessels (red arrows) along the cerebral convexity. Normally, these small cortical vessels are not visible on the FLAIR sequence, but given their visibility on this sequence, this is a finding that can indicate the presence of slowed vascular flow.
The following images were also obtained during the same study:
These T2-weighted images of the brain show a couple interesting findings. In the first image, at the level of the cerebral peduncles, we see an extensive and tangled network of tiny vessels (red arrows) surrounding the brainstem.
In the second image, we see a lack of blood flow in the regions where the middle cerebral arteries should be taking off (green arrows). It seems as if they are occluded.
Of note: While a non-contrast MRI brain is not the optimal study for evaluating the vasculature, due to the unique characteristics of MRI, the patency of a vessel can sometimes be assessed even without the use of contrast, as in this case.
The above findings of occluded vessels within the circle of Willis and tangled network of abnormal vessels around the brainstem are indicative of moyamoya disease. This entity is characterized by chronic occlusion of the main cerebral vessels, resulting in the formation of a network of tiny collateral vessels in an attempt to maintain perfusion to the brain.
Given this finding, a CT angiogram of the brain was performed to further assess the extent of the patient’s disease:
The above is a 3D-reconstructed angiogram of the cerebral arteries. There is diffuse irregularity of the intracranial internal carotid arteries with occluded middle cerebral arteries bilaterally, extensive abnormal tiny arteries, and overall severely diminished flow to the brain. Compare that to the following CT angiogram reconstruction performed on a normal brain:
Now that the diagnosis was made, the decision was made for the patient to undergo a potential encephaloduroarteriosynangiosis (EDAS). This is a neurosurgical procedure in which a small opening is made in the skull, and a branch of the external carotid artery supplying the scalp is surgically anastomosed to a branch of the middle cerebral artery, allowing an alternative means of collateral flow to the brain to develop. But first, to definitively characterize the arteries, a cerebral angiogram was performed:
These images show angiograms of the right and left internal carotid arteries, again showing occlusion of the distal internal carotid arteries as well as showing the extensive network of tiny collateral vessels -- a “puff of smoke” appearance, from which this condition gets its name.
Moyamoya disease was first described in 1957 as “hypoplasia of the bilateral internal carotid arteries.” While the appearance of the disease is characteristic, there are various etiologies for the disease both congenital and acquired, with approximately 10% being familial. Conditions that can predispose to moyamoya disease include sickle cell anemia, neurofibromatosis type 1, and Down’s syndrome, among others.
Symptoms can manifest in several ways, including migraine-like headache, transient ischemic attacks, and infarcts. Intracranial hemorrhage is of particular concern, as the tiny collateral vessels are fragile and can easily rupture.
Treatment for moyamoya is often surgical, as the disease is inevitably progressive as flow through the internal carotid arteries diminish. The goal of surgery is to accomplish revascularization of the brain; surgical options take advantage of the fact that moyamoya tends to affect the internal carotid arteries while sparing the external carotid arteries. Encephaloduroarteriosynangiosis (EDAS), performed for this particular patient, is an operation in which a branch of the external carotid artery (usually the superficial temporal artery) is directly anastomosed to a cortical artery.
Scott RM, Smith ER. Moyamoya disease and moyamoya syndrome. N Engl J Med 2009; 360:1226-1237.
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