Spectrum of fibromuscular dysplasia - acute vertebral artery occlusion, internal carotid and renal artery involvement, and renal infarct

Case contributed by Michael P Hartung


Sudden onset of dizziness and right neck pain.

Patient Data

Age: 50
Gender: Female

Asymmetric hyperattenuation of the right vertebral artery when compared to the left. 

Hounsfield unit measurement of vertebral arteries: 69 on the right, 48 on the left.

Small area of low attenuation in the right side of the medulla suggestive of an infarct.

Otherwise normal brain CT.

Right internal carotid artery: Decreased caliber of the cervical internal carotid artery at the carotid bulb with a focally increased caliber just prior to the intracranial portion, with a slightly irregular medial projecting outpouching. On the coronal reformatted images, there is slight buckling of the artery proximally.

Left internal carotid artery: No critical narrowing. Focal irregularity of the vessel wall with
narrowing just after the carotid bulb.This is followed by a focal dilation of the vessel wall measuring up to 7.4 cm, with calcification along the anterior margin. Small posterior projecting outpouching may represent a small pseudoaneurysm, which appears to lead to a small, chronic appearing dissection flap along the posterior margin.

Right vertebral artery: Relatively diminished blood flow within the right vertebral artery compared to the left. There focal segmental occlusion of the intracranial/V4 segment, leading to the vertebrobasilar junction.

Left cervical vertebral artery: Slightly dominant left vertebral artery appears patent and is without significant narrowing. No dissection.

Patent intracranial vasculature.

Multiple areas of restricted diffusion in the right cerebellar hemisphere inferiorly and the anterolateral aspect of the medulla.

Single right renal artery with multifocal beading and narrowing in keeping with a 'string of beads' appearance.

Three left renal arteries. The upper two arteries appear grossly normal. The inferior most artery has distal irregularity and beading which is best appreciated on the curved planar reformatted images.

Ectasia of the common iliac arteries on the 3D reconstructions. 

New areas of wedge-shaped peripheral cortical hypoenhancement in the upper and lower right renal poles, most consistent with development of renal infarcts. The upper pole infarct may be older or more complete than the lower pole infarct given the difference in hypoenhancement.

Case Discussion

Spectrum of imaging findings of fibromuscular dysplasia (FMD), which is a noninflammatory angiopathy of small to medium size arteries most commonly involving the renal arteries, but can also involve the internal carotid and vertebral arteries.

This patient presented with right neck pain and dizziness (no diagnosis of FMD). Noncontrast CT brain shows subtle but definite asymmetric high attenuation of the right vertebral artery indicating thrombosis (similar to the dense MCA sign). If you detected this on the noncontrast CT of the brain, great job! I thought I made a great discovery when I noticed this, however, I was called by both the technologist and the emergency room physician wondering about the same finding, so clearly suspicion was high for everyone. 

CT angiography shows segmental occlusion of the right vertebral artery, which is likely related to dissection and thrombosis. The abnormal configuration of the internal carotid arteries makes fibromuscular dysplasia the most likely cause. Acute cerebellar and lateral medullary infarct was confirmed on MR the next day.

Further workup of the renal arteries shows fibromuscular dysplasia of the renal arteries, involving the right main renal artery and one of the three accessory left renal arteries.

Subsequently, the patient developed acute abdominal pain and was reimaged with portal venous phase CT, showing segmental infarcts in the right kidney, likely related to dissection/embolism within the right renal artery. The area of hypoattenuation in the right upper pole cortex was not present on the angiogram from two days prior, and the lower pole abnormality may have been present but would be difficult to distinguish given that only arterial phase images were performed.

See the companion case.

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