Laboratory Studies
Vertebral artery dissection (VAD) is a disease of young, generally healthy individuals. Laboratory evaluation is directed toward establishing baseline parameters in anticipation of anticoagulant therapy.
Prothrombin time (PT), activated partial thromboplastin time (aPTT), and international normalized ratio (INR) are the usual monitoring parameters for patients on anticoagulant medication.
Erythrocyte sedimentation rate (ESR), if elevated, may suggest vasculitis involving the cerebrovascular circulation.
Procedures
Patients with suspected subarachnoid hemorrhage and a normal computed tomography (CT) scan may undergo lumbar puncture (LP) if VAD is not pursued by other imaging modalities.
CT Scanning, MRI, and MRA
Diagnosis of vertebral artery dissection (VAD) is usually made by neuroimaging, which has largely replaced conventional angiography in most centers. [32] The 2011 combined ASA/ACCF/AHA guidelines gave a class I recommendation to noninvasive computed tomography angiography (CTA) or magnetic resonance angiography (MRA) as the initial diagnostic study for suspected VAD. [33] These studies were favored over ultrasonography, but there was no specific guidance on CTA over MRA provided. If these imaging modalities are inconclusive for VAD but the clinical suspicion remains high, the guidelines gave a class IIa recommendation to either serial noninvasive imaging or invasive contrast angiography (if the patients would be candidates for revascularization). [33]
Computed tomography scanning
Data examining CTA versus magnetic resonance imaging-angiography (MRI-A)/MRA for VAD are limited, but there may be a slight preference for CTA for identifying VAD given the smaller arterial diameters compared to internal carotid dissections. [34] However, CTA is less accurate if heavy calcifications are present. CTA studies have a reported 90%-99% specificity and 40%-100% sensitivity for VAD.
CT scanning is useful in identifying patients with the complication of subarachnoid hemorrhage. [3]
Absence of hemorrhage, as demonstrated by CT scan, is a prerequisite for instituting anticoagulant therapy. Ease of access to CT scanners may provide the impetus for using CTA over MRA as the inital diagnostic study.
Magnetic resonance imaging
MRI detects both the intramural thrombus and intimal flap that are characteristic of VAD. [7]
Hyperintensity of the vessel wall seen on T1-weighted axial images is considered by some to be pathognomonic of VAD. [7, 8, 9, 10, 11]
Park et al conducted a retrospective study of 41 vertebral arteries to evaluate radiologic findings according to the stages in spontaneous and unruptured, intracranial VAD (IVAD) on 3T high-resolution MRI (HR-MRI). [35] The 3T HR-MRI revealed the vessel wall characteristics as well as provided distinguishing findings between earlier stages and the chronic stage in spontaneous and unruptured IVAD. The investigators concluded that the characterization of these radiologic findings according to stages may help with the age estimation of the dissection. [35]
In a review of VAD cases registered between April 2008 and October 2014 that compared radiologic findings between patients with extracranial VAD (EVAD) and intracranial VAD (IVAD), Kobayashi et al found that intramural hematomas were more commonly revealed by MRI in patients with EVAD. [36] By contrast, in patients with IVAD, MRI and CT scanning more frequently revealed aneurysm formation.
Magnetic resonance angiography
MRA can identify abnormalities that are characteristic of the disturbed arterial flow seen in VAD. These include the presence of a pseudolumen and aneurysmal dilation of the artery. [7]
New generation MRI and MRA appear to be as sensitive as cerebral angiography for the detection of VAD, although they probably have equivalent specificity. [8, 9, 10, 11, 12, 37]
Cerebral angiography may still have a role when clinical suspicion is high but MRI/MRA has failed to isolate the lesion. In these situations, the choice can be made between serial noninvasive imaging (if symptoms are suggestive of VAD) or invasive angiography (if the patient is a candidate for revascularization and might benefit from simultaneous diagnosis and therapy).
Four-Vessel Cerebral Angiography
Prior to the development of noninvasive techniques such as magnetic resonance imaging (MRI) and Doppler ultrasonography, cerebral angiography was the criterion standard in diagnosing vertebral artery dissection (VAD). These noninvasive techniques are supplanting angiography as the imaging techniques of choice for patients in whom VAD is suspected. [7]
A French retrospective study that evaluated clinical and imaging features with outcomes in 20 pediatric patients with extracranial VAD over 14 years indicated that the initial imaging studies should include the posterior fossa vessels and the craniocervical region with V2-V3 segments. [38] In the presence of inconclusive findings on nonivasive imaging studies, the investigators suggested use of conventional angiography for definitive diagnosis. [38]
The characteristic angiographic finding in a dissected vertebral artery is the string or "string and pearl" appearance of the stenotic vessel lumen. [10] Angiograms are shown in the images below.
A, Dissection of the left vertebral artery secondary to guidewire injury. B, Complete resolution occurred in 6 months with only aspirin and clopidogrel (Plavix) therapy.
Gunshot wound to the right side of the neck. A, The angiogram shows transections of the right vertebral artery (RVA) and the right internal maxillary artery (RIMAX), with partial transection and pseudoaneurysm formation of the midcervical right internal carotid artery (RICA). The transected segments of the RVA and RIMAX were embolized with coils. B and C, The RICA pseudoaneurysm was successfully treated with a 7 x 40-mm covered stent (Wallgraft).
Because of the high incidence (up to 40% in some series) of multiple extracranial cervical artery dissections occurring simultaneously in the same patient, 4-vessel angiography is the angiographic technique of choice in all patients with potential carotid artery dissection (CAD) or VAD. [10]
Ultrasonography
Vascular duplex scanning
Duplex ultrasonography of the vertebral arteries demonstrates abnormal flow in 95% of patients with vertebral artery dissection (VAD). [8]
Ultrasonographic signs specific to VAD (eg, segmental dilation of the vessel, eccentric channel) are detectable in only 20% of patients. Thus, ultrasonography may be useful as an initial test only if computed tomography angiography (CTA) or magnetic resonance angiography (MRA) are not readily available.
Transcranial Doppler
Transcranial Doppler is approximately 75% sensitive to the flow abnormalities seen in VAD. It is useful also in detecting high-intensity signals (HITS), which are characteristic of microemboli propagating distally as a result of the dissection. HITS are associated with symptomatic ischemic symptoms both in VAD and in other types of cerebrovascular disease.
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A, Dissection of the left vertebral artery secondary to guidewire injury. B, Complete resolution occurred in 6 months with only aspirin and clopidogrel (Plavix) therapy.
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Gunshot wound to the right side of the neck. A, The angiogram shows transections of the right vertebral artery (RVA) and the right internal maxillary artery (RIMAX), with partial transection and pseudoaneurysm formation of the midcervical right internal carotid artery (RICA). The transected segments of the RVA and RIMAX were embolized with coils. B and C, The RICA pseudoaneurysm was successfully treated with a 7 x 40-mm covered stent (Wallgraft).
