A 57-Year-Old Man With Hemiparesis After Coughing

Francesco Brigo, MD; Giampaolo Tomelleri, MD

Disclosures

November 27, 2017

Dissection normally occurs in the extracranial segment of the epiaortic vessels. The internal carotid artery is affected more often than the vertebral artery.[2] Dissections can be classified as traumatic or spontaneous. Traumatic dissections are linked to direct neck trauma or injury, whereas spontaneous dissections may be secondary to predisposing factors, such as fibromuscular dysplasia, Ehlers-Danlos syndrome, cystic medial necrosis, or Marfan syndrome. These conditions cause an abnormal, weakened arterial wall, thus predisposing patients to arterial dissection.[3]

Internal carotid artery dissection develops as a consequence of a tear in the intimal layer of the vessel, which allows blood to enter the wall of the artery and to split its layers; this is termed a subintimal hematoma. This means that the hematoma is located between the intimal and medial layers of the artery. Alternatively, a rupture of the vasa vasorum causes a subadventitial hematoma (ie, a hematoma between the media and the adventitial layers). Internal carotid artery dissection can lead to thrombus formation and the risk for distal embolization, whereas arterial narrowing with stroke due to inadequate blood flow is a less common mechanism of ischemia.[4] Hematoma formation and a localized inflammatory response result in compression of nearby structures, such as the sympathetic fibers of the superior cervical ganglion, which lies in the posterior wall of the carotid sheath. This can cause a postganglionic oculosympathetic palsy. Anhidrosis is not present because sweat fibers run with the uninvolved external carotid artery.

A highly suggestive constellation of signs and symptoms frequently seen with internal carotid artery dissection is Horner syndrome. Oculosympathetic palsy in the form of Horner syndrome has long been recognized as a typical manifestation of internal carotid artery dissection, although it is found in fewer than half of patients. The classic signs of Horner syndrome include ptosis of the upper lid, slight elevation of the lower lid (upside-down ptosis), and miosis reactive to light. The narrow palpebral aperture secondary to upper-lid ptosis and elevation of the lower lid give the illusion that the affected eye is smaller than the contralateral eye (illusory enophthalmos).

Horner syndrome is an expression of a disruption of oculosympathetic pathways. Ptosis (ie, upper eyelid droop) is caused by a loss of innervation to Müller smooth muscle in the upper lid. This small muscle is innervated by sympathetic fibers and is responsible for eye opening, together with the superior and levator palpebrae: striated skeletal muscle innervated by the third cranial nerve. Similarly, miosis (ie, decreased pupillary size) is caused by a loss of sympathetic innervation to the iris pupillodilator muscle. As a consequence, the pupil cannot dilate. This impaired dilation of the pupil may also be observed in a test of the ciliospinal reflex. Normally, pinching the neck causes a pupillary dilation secondary to the activation of the sympathetic pathway. In an eye with Horner syndrome, this dilation does not occur.

The most typical signs and symptoms of internal carotid artery dissection are neck pain and/or a partial Horner syndrome. This may be followed by an ischemic event ipsilateral to the ocular signs, with somatosensory and/or motor deficits contralateral to ocular signs as a consequence of distal embolization to the intracerebral arteries.

Currently, the most commonly available imaging modalities are carotid ultrasonography and CT angiography (CTA) of the head and neck. However, the best method to diagnose an internal carotid artery dissection is a combination of CTA and magnetic resonance angiography (MRA) with fat-suppressed T1 images.[1,5,6] CTA and MRA are replacing conventional angiography in the diagnosis of internal carotid and vertebral artery dissection because the resolution and accuracy of CTA and MRA are similar to that of angiography.[7,8,9] Moreover, MRI may show the intramural hematoma itself.

A review comparing MRI/MRA with CTA showed the performance characteristics to be very similar for the diagnosis of carotid artery dissection.[10] As an alternative, conventional angiography with digital subtraction may be used, although these tests are more expensive and invasive than MRI/MRA. Additionally, MRI/MRA is superior to conventional angiography in diagnosing dissections without associated luminal abnormalities.[1] Conventional angiography may reveal an abrupt narrowing of the internal carotid artery lumen (rattail-filling defect or the "string sign"). Carotid duplex ultrasonographic imaging may also be useful, especially in the younger population with less chance of severe atherosclerotic disease, which can interfere in the diagnosis.[11] Direct observation of a luminal intimal flap is diagnostic but rare; the most frequent finding is a stenosed or occluded vessel in the absence of atheromatous lesions.[12]

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