Laboratory Studies
If a diagnosis of spontaneous internal carotid artery dissection is under consideration, laboratory studies are largely irrelevant for diagnostic purposes. However, if contrast-enhanced computed tomography (CT) or arteriography is planned, it is appropriate to obtain a baseline creatinine concentration. If surgery is planned, the patient’s blood type, a complete blood count (CBC), and a coagulation profile (including prothrombin time [PT] and activated partial thromboplastin time [aPTT]) should be obtained.
Baseline coagulation studies may be appropriate in certain settings before the initiation of anticoagulation therapy or in cases where a patient is already taking an anticoagulant at the time that dissection is identified.
Angiography
Magnetic resonance angiography
Magnetic resonance angiography (MRA) may have already replaced conventional angiography for the diagnosis of internal carotid artery dissection. Some institutions use it as the first and only imaging modality when carotid artery dissection is suspected.
Magnetic resonance imaging (MRI) with fat saturation can show intramural blood, the pathologic hallmark of dissection, [15] and mural expansion, thus confirming the diagnosis of carotid artery dissection. [16] These findings are visualized as a semilunar hyperintensity (the mural hematoma) partially surrounding a circular hypointense signal (the residual lumen). MRA may fail to detect intramural hematoma within the first 24-48 hours after the occurrence of carotid artery dissection. [17]
Other MRA signs of dissection include irregular vessel margins, filling defects, extravasation of contrast, vascular occlusion, and caliber changes of the vessel. The last of these signs is particularly important and is well appreciated on axial views, but three-dimensional (3D) reconstructed views allow study from any angle.
Improved resolution, speed, noninvasiveness, absence of irradiation, and good negative predictive value make MRA an excellent screening and diagnostic tool, one that in most cases is superior to conventional angiography.
Helical computed tomography angiography
Helical (spiral) CT angiography (CTA) has an established role in the diagnosis of internal carotid artery dissection, and with the increased use and availability of high-resolution multidetector scanners, it is rapidly replacing conventional angiography and possibly MRA as the diagnostic modality of choice.
CTA may be the first (or even the only) modality used for screening and diagnosis in trauma patients who fit general screening criteria (based on signs, symptoms, and mechanism) for carotid artery dissection and who will already be undergoing CT for another indication. Helical CTA is fast and noninvasive, and the limitations it once exhibited in comparison with conventional angiography are steadily declining. When obtaining a CTA of the neck, the physician must specifically request for the study to rule out internal carotid artery dissection.
On noncontrast CT, dissection of the internal carotid artery may be inferred from indirect findings, which include soft-tissue swelling, hematoma adjacent to the internal carotid artery, and infiltration of perivascular fat planes. In addition, fracture or fracture-dislocation of the cervical bones should raise the index of suspicion for internal carotid artery injury. Noncontrast CT is not an adequate screening or diagnostic test for internal carotid artery dissection.
The hallmark of injury to the internal carotid artery on CTA is a change in the caliber of the vessel. Another finding that may indicate a dissection is an oval, irregular, or slitlike cross-section of the vessel lumen. In comparison with conventional angiography, helical CTA has the added benefit of imaging extravascular structures. [18] Furthermore, axial images can be reconstructed for 3D viewing and are obtained automatically in the newer CT scanners.
CTA is nearly always sufficient to confirm the diagnosis of carotid artery dissection, [16] and even early studies of CTA were able to achieve 100% sensitivity and specificity with arterial angiography. [15]
Conventional angiography
Conventional angiography was the standard modality for diagnosing internal carotid artery dissection. It has a 1% overall risk of complications; it is invasive, resource-intensive, and costly; and it should be reserved for patients in whom suspicion for internal carotid artery dissection remains high despite negative results with other imaging modalities or for patients in whom endovascular or surgical management is planned. In addition, it may miss dissections when the false lumen does not opacify with contrast medium. [15]
The pathognomonic finding for a carotid artery dissection is an intimal flap and double lumen, secondary to an intramural hematoma. This finding is rarely detected. The most common angiographic finding is termed the string sign, which is a long, tapered, narrowing column of contrast material in the distal segment of the internal carotid artery. [16, 15] The other angiographic patterns indicative of carotid artery dissection that are more commonly found include arterial stenosis, aneurysm formation, and arterial occlusion. [15]
Although conventional angiography is no longer generally considered the diagnostic modality of choice for carotid artery dissection, there remain some indications for its use, and some physicians and institutions still prefer it.
Ultrasonography
Doppler ultrasonography (DUS), or duplex scanning, is becoming an extension of the physical examination and is playing an increasingly important role in the diagnosis of a myriad of medical and surgical conditions. With its improving resolution, ready applicability, speed, and ease of use, DUS can now be used for the initial assessment of patients with suspected carotid artery dissection. [19] In trauma cases, it usually is already at the bedside for focused assessment with sonography for trauma (FAST).
Of all the imaging modalities used to diagnose carotid artery dissection, DUS has the lowest cost and the highest safety profile. Reported sensitivities are as high as 96% for diagnosing carotid artery dissections in patients who suffered stroke. [3] An abnormal blood flow pattern can be appreciated in as many as 90% of patients with carotid artery dissection, but the actual site of injury usually is not seen, because DUS has only a limited ability to evaluate past the carotid bulb.
The most common DUS finding in carotid artery dissection is a high-resistance flow pattern or the absence of signal in a totally occluded artery. [15] The pathognomonic DUS finding for carotid artery dissection is the demonstration of a membrane in the longitudinal and axial view. [15] Unlike angiography, DUS is able to demonstrate a false lumen even if it is thrombosed. [15]
A prospective review found ultrasonography to have a 31% false-negative rate in patients with carotid artery dissection who presented with Horner syndrome. [1] Whenever abnormalities are found by DUS, follow-up with another imaging modality is always indicated.
Other Tests
Supplementary tests that may be needed for evaluation of patients with a possible internal carotid artery dissection include the following:
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Electrocardiography (ECG)
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Echocardiography
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Neuroimaging (eg, contrast and noncontrast CT or MRI of the brain)
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Electroencephalography (EEG)
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Arterial dissection. (A) Tear and elevation of intima from wall of artery, resulting in luminal stenosis. Illustration shows stasis of flow in false lumen beneath elevated intima. This condition creates blind pouch that predisposes patient to thrombus formation. (B) Subadventitial dissection represents hemorrhage between media and adventitia. Artery may become dilated as result of thickening of arterial wall, with some degree of luminal narrowing. Elevation of intimal flap is not commonly associated with this type of dissection. Hemorrhage may extravasate through adventitia, resulting in pseudoaneurysm or fistula formation.
