Saturday, October 20, 2012

Carotid Dissection

A carotid dissection is just like a dissection in any other vessel in the body. Trauma or atherosclerosis causes a tear in the intima, blood enters into the space between intima and media, and then the blood dissects along that space causing stenosis or pseudoaneurysm.  As it's sticking out there in the neck, the carotid is probably more liable to traumatic etiologies, than, say, the SMA. Extension of an aortic dissection can also cause a carotid dissection.

The dissection can re-enter the true lumen further down the artery, resulting in a false lumen.  Thrombus can then exit out this second opening.

ICA (internal carotid artery) dissection has classically been described as irregular, originating 2-4 cm distal to the carotid bulb, and with a long tapering stenosis that usually ends before the ICA enters the petrous portion of the temporal bone.

Dissection of the carotid arteries or vertebral arteries, and the subsequent drop in cerebral flow, can be a cause of stroke, and this is a higher % etiology of stroke in young people, in whom the traditional risk factors are less likely. (Carotid dissection is the cause of 2% of ischemic strokes, but 10-20% of ischemic strokes in young or middle-aged persons).  Carotid dissection can also cause neck and face pain, headache, amaurosis fugax, and Horner's syndrome.

 Interestingly, the sympathetic nerve fibers for controlling sweat production on the face follow the external carotid artery, so ipsilateral Horner's syndrome without loss of sweat production is relatively specific for a dissection.

The modality for detection used to be catheter-based angiogram, but the initial test of choice currently is a less invasive angiogram -- CTA or MRA.(CTA may be more useful than MRA for evaluation of the vertebral arteries). CTA and MRA are also more useful for evaluation of hematoma than conventional angiography. CTA and MRA are less useful in the setting of metallic densities in the neck soft tissues (e.g. gunshot wound). In the images below, a dissection along the medial aspect of the left internal carotid artery leads to severe stenosis and fusiform aneurysmal dilatation of the downstream artery.

A more subtle case of carotid dissection, with a wispy intimal flap showing the dissection.

Not surprisingly, the same risk factors for dissection elsewhere in the body (e.g. aortic dissections) are also risk factors for carotid dissection... hypertension and the same crew of connective tissue diseases that weaken the intima: Marfan's syndrome, Ehler's-Danlos, Pseudoxanthoma elasticum, fibromuscular dysplasia, and others. The idea is that the underlying problem is a weakened or malformed arterial media (e.g. medial degeneration).  This weakened arterial media framework is unstable and cannot resist a small intimal tear.

Although dissection is the most common cause of extracranial aneurysms, 2/3 of carotid aneurysms resolve, and complications related to aneurysm are rare. Traumatic dissections show worse prognosis in all areas compared to spontaneous dissections. Cervical carotid dissections are usually treated with medical therapy. Medical therapy is primarily antiplatelet therapy or anticoagulation with the idea that infarction from dissection is partly related to embolism from dissection thrombus (the choice of which is better is controversial). Stenting could also be considered, although data is limited.

Oddly enough, spontaneous carotid dissections occur most frequently in the winter.  (people tying their scarves too tightly?)  ICA dissections have also been reported after intensive practice with Wii sports video games.

1. "Neuroradiology: The Requisites" Grossman RI,  Yousem DM. 2nd ed. (2003), 3rd ed. (2010)
2. "Abrams' Angiography" Baum ed. 2nd ed (1997)
3.  "Rutherford's Vascular Surgery" Cronenwett and Johnston. 7th ed (2010).
4. Faivre A, Chapon F, Combaz X, Nicoli F. "Internal carotid artery dissection occurring during intensive practice with Wii video sports games" Neurology. 2009 Oct 13;73(15):1242-3