CASE 17263 Published on 29.04.2021

A case of bilateral internal carotid artery hypoplasia with ectasia of vertebrobasilar system and flow related aneurysms presenting with subarachnoid haemorrhage.



Case Type

Clinical Cases




48 years, male

Area of Interest Neuroradiology brain, Neuroradiology peripheral nerve, Neuroradiology spine ; No Imaging Technique
Clinical History

A 48 years old gentleman presented with complaints of headache for the past 3 days. The patient did not have any other symptoms.

On clinical examination, the patient was conscious and oriented. No focal neurological deficit was found. His laboratory parameters were within normal limits.

Since the patient has worsening of headache, He was referred for MRI brain by the neurologist.

Imaging Findings

The MRI brain revealed subarachnoid haemorrhage along the bilateral parietal, inferior temporal and bilateral occipital regions (FIG 1: B)

There was subacute bleed noted within the bilateral lateral ventricles, 3rd and 4th ventricles. (FIG 1: A)


Non contrast MR angiogram revealed diffusely thin calibre of bilateral internal carotid arteries with ectasia of the vertebrobasilar system with flow related aneurysms in basilar artery and left PCOM. (FIG 2: A& B)

The patient was further evaluated with CT angiogram (FIG4:A&B) which revealed diffuse hypoplasia of the bilateral cervical and intracranial internal carotid arteries. 

Enlarged and ectatic bilateral vertebral arteries and left PCOM with saccular aneurysm in left PCOM (FIG 3: A) and fusiform aneurysms in the basilar top (FIG 3: B) - likely flow related aneurysms due to compensatory flow. 

Due to the risk of rebleed from the aneurysm, our patient was advised for endovascular management however our patient deferred the treatment and hence he was treated symptomatically & conservatively.


Congenital anomalies of the internal carotid artery are extremely rare involving < 0.01 % of the population. The varies anomalies include aplasia, hypoplasia and agenesis [1].

The presence of hypoplasia of the ICA was first described by Hyrtle in the year 1836 in a postmortem series [2].

Most of the patients are asymptomatic due to the rich collateral supply and incidentally diagnosed when imaging was done for some other reasons.

Symptomatic patients usually present with various symptoms like transient ischemic attacks, infarct, seizures, aneurysmal subarachnoid hemorrhage or parenchymal bleeds [3].

Due to the presence of rich collateral supply, increased blood flow and velocity with haemodynamic alternation, these patients are more prone to develop intracranial aneurysms as compared with the general population.

Zink et al discovered that in patient with congenital ICA hypoplasia, the incidence rate of intracranial aneurysm was about 27.8% [4].  These aneurysms are more common along the basilar artery and the posterior cerebral artery (PCA) [5].

Various syndromes like horner syndrome, congential hypopituitarism are seen in relation with congenital carotid hypoplasia especially in the pediatric population [6]. 

Our patient also presented with complaints of severe headache due to the subarachnoid haemorrhage.


Cross sectional imaging modalities like computed tomography, Magnetic resonance imaging can help us suggest the diagnosis. Non contrast MR angiogram reveals the small caliber of the bilateral internal carotid arteries and the presence of aneurysms and the collateral vessels.

3D CT angiogram is a non-invasive technique, with the volume rendered and surface shaded images provide pre- operative road map for the management of the aneurysms.

Non contrast CT in bone window helps in differentiating absence of internal carotid artery from hypoplasia.

In congenital absence of ICA, the osseous carotid canals are usually absent and in hypoplasia the carotid canals are also hypoplastic [7].

However Digital subtraction angiography is the gold standard method for the confirmation of diagnosis and for the detection of complications like flow related aneuryms and collaterals [6].

FINAL DIAGNOSIS: Congenital hypoplasia of bilateral internal carotid arteries with ectasia of the vertebrobasilar system.


There is no protocol for the management of asymptomatic patients with bilateral internal carotid artery and follow up with imaging will suffice to look for aneurysms.

However symptomatic patients and those with aneurysms need intervention in order to prevent intracranial bleed.

Differential Diagnosis List
Congenital hypoplasia of bilateral internal carotid arteries with ectasia of the vertebrobasilar system
Congenital bilateral ICA agenesis.
Final Diagnosis
Congenital hypoplasia of bilateral internal carotid arteries with ectasia of the vertebrobasilar system
Case information
DOI: 10.35100/eurorad/case.17263
ISSN: 1563-4086