Bilateral ICA block: MRI

Case Report 

76 yrs old female pt. presets for MR brain angio with c/o giddiness of long duration.

MRA shows – marked narrowing & grossly reduced flow signal of both ICA in carotid canal with complete absence of cavernous ICA with  source images suggesting right PCOM feeding ipsilateral MCA &  left MCA possibly filling from right side. Both MCA are grossly reduced in caliber with origins not identified along with poorly visualized both ACA & ACOM.

Dominant grossly tortuous & atheromatous vertebral system with basilar artery suggesting tortuosity/atheromatous looping / redundancy with both PCA normal for the age.

Multiple tiny possible collaterals identified in the basal ganglia (right > left) along with external carotid branches possibly feeding Circle of Willis branches predominantly MCA.   

Brain parenchyma shows possible gliosis post infarction in right frontal lobe & multiple ill defined irregular T2/FLAIR hyperintensities in both gangliocapsular & periventricular whitematter suggesting old infarctions with rest of brain & CP angles unremarkable for the age. Submitted by Dr MGK Murthy, Dr GA Prasad

Clinical features of ICA occlusion range from asymptomatic to acute stroke or death, transient monocular blindness (  amourosis fugax), orthostatic TIA  / post prandial hypotension, exercise induced ischemic symptoms ( cerebral claudication), involuntary limb shaking, headache ( due to collateral circulation) , syncope , dementia.

Pathogenesis -  In chronic ICA occlusion, collateral circulation may maintain cerebral perfusion. ICA occlusion is frequently associated with borderzone infarcts.Compensatory mechanisms like collateral vessels can prevent ischaemia in ICA occlusion. The most important source of collateral flow are contralateral ICA via the circle of Willis. The blood flows in an anterograde manner up the contralateral ICA and then across the circle of Willis to the anterior communicating artery. From here, it goes in an anterograde manner along the cortical branches of the anterior cerebral artery and in a retrograde manner along the anterior cerebral artery to the middle cerebral artery (MCA), and then distally into the MCA territory in the usual anterograde manner.

-          Orbital branches of the ipsilateral ECA. Anterograde flow up in the ECA to the orbit (mainly via its maxillary branches &  via facial, frontal branches or leptomeningeal branches) allows links with the ophthalmic branch  of the ICA. Blood flows in a retrograde manner in the ophthalmic branch to join the supraophthalmic part of the ICA.

It is important to differentiate total extracranial ICA occlusion from a near-total occlusion (also termed preocclusive stenosis). The patients with symptomatic near-occlusion are considered to be at a high risk of future embolisation and can derive benefit from carotid endarterectomy. However, carotid endarterectomy is not an option in complete ICA occlusion.

it is technically difficult to open a chronically occluded ICA, the management of a chronic ICA occlusion mainly includes strategies to reduce the risk of future strokes and other cardiovascular events, reducing  embolic risk, modifications of risk factors  -for example, hypertension, diabetes, hyperlipidaemia and smoking & use of antithrombotic  & anticoagulant agents.