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Hypoplasia of the internal carotid artery

Case contributed by Mark Hall
Diagnosis almost certain

Presentation

Sudden onset headache and vomiting. Lumbar puncture was normal but MRI brain raised the possibility of right ICA dissection or hypoplasia. A CT angiogram was carried out.

Patient Data

Age: 35 years
Gender: Female

Note: This case has been tagged as "legacy" as it no longer meets image preparation and/or other case publication guidelines.

CT Carotid Angiogram

ct

Arch:
The aortic arch is normal in appearance.  The left vertebral artery arises from the arch as an anatomical variant.

Carotid arteries:
The left common, internal and external carotid arteries are patent. The right internal and external carotid arteries arise separately from the brachiocephalic trunk, with the right internal carotid artery being extremely small in diameter, measuring only 1.5 mm, although the vessel appears patent throughout. The diameter of the carotid canal is reduced significantly (narrowing of the right foramen lacerum on axial bone window), appearances are in keeping with congenital hypoplastic right ICA.

Vertebral arteries:
Patent and normal in course and size.

Intracranial arteries:
The MCA vessels are normal in caliber bilaterally. Fetal origin of the right PCA and prominent right P1 suggesting the right MCA is being supplied primarily from the posterior circulation. Fetal origin of the left PCA, which is normal in caliber. Fenestrated ACOM.

Impression:
Hypoplastic right internal carotid. No dissection.

Case Discussion

This case demonstrates a hypoplastic right internal carotid artery. The narrow right carotid canal, fetal right PCA with prominent right P1 artery add further evidence towards this.

Agenesis, aplasia, and hypoplasia of the internal carotid artery (ICA) are rare congenital anomalies, occurring in less than 0.01% of the population.

As in this case the most common type of collateral flow is through the circle of Willis.

Although this case is an incidental finding, recognition is important as it is associated with cerebral aneurysms and has an implication during carotid endarterectomy and transsphenoidal hypophyseal surgery.

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