Neuroradiology

Dissection, arterial

condition in which blood penetrates through a tear in the intima, separating and dissecting it from the media. The dissection may be focal but more commonly it extends for several cm. The most common sites of arterial dissection are the internal carotid artery in the neck, after the bifurcation, and the vertebral artery in its distal extracranial portion where it penetrates the dura to become intracranial. Dissection of intracranial arteries, basilar artery and middle cerebral artery is also possible but much rarer.

Aetiology may be related to direct or indirect trauma, or to congenital structural abnormalities of the vessel wall (fibromuscular dysplasia, Marfan's syndrome).

The symptomatology may be local or at distance and flow related. Carotid dissection may be accompanied by neck pain and Horner's syndrome due to impairment of pericarotid sympathetic fibres. Vertebral dissection may be accompanied only by posterior neckpain. Major neurological deficits may result if the resulting stenosis is very severe and the intracranial collateral circulation through the circle of Willis is inefficient. From transient ischaemic attack to severe ischaemia and infarction, the full spectrum of neurological symptoms of infarction in different regions may be encountered.

The diagnosis of dissection is based on the demonstration of reduced arterial lumen and subintimal haematoma. Doppler studies may show reduced lumen, but MR and angio MR is able to demonstrate both the reduced flow in a narrowed lumen and the collection of blood between the intima and media (Fig.1). Axial T1-weighted image show a typical cresentic hyperintense collection around a reduced narrow lumen. The hyperintense collection represents methaemoglobin of the extravasated blood. Angiography better shows a characteristic progressive tapering of the lumen, with very slow flow. Not infrequently dissection resolves spontaneously with complete recanalization. Pseudoaneurysm may be a sequela that requires treatment which may be surgical, or preferably, endovascular with stenting.

GS

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Fig.1

a. Axial MR, T1-weighted image at the base of the skull. On the left side the usual flow void of the internal carotid is replaced by an hyperintense crescent with a very narrow residual lumen without signal. b. Left common carotid angiogram; the internal carotid is severely narrowed with a characteristic "radish tail" appearance due to subintimal dissection.
Dissection, arterial, Fig.1 (a)
Dissection, arterial, Fig.1 (b)