Management of the Neck With Carotid Artery Involvement Workup

Updated: Oct 26, 2018
  • Author: Devraj Basu, MD, PhD, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Workup

Imaging Studies

See the list below:

  • Angiography: The initial assessment for risk of stroke during internal carotid occlusion consists of 4-vessel angiography, which establishes the patency of the vessels and the potential availability of collateral flow through the circle of Willis if one carotid is occluded.

  • Trial balloon occlusion

    • When collateral flow is present based on angiography findings, temporary preoperative occlusion provides physiologic information on the patient's ability to tolerate transient or permanent occlusion of the carotid to be resected. The original diagnostic trials of carotid occlusion were performed intraoperatively on the common carotid artery using umbilical tape under local anesthesia. [22] Trial balloon occlusion (TBO) performed during angiography has replaced operative trial occlusion. The patient is heparinized while the balloon catheter is placed under angiographic guidance. It is inflated in the internal carotid artery for up to 15-30 minutes while the patient is monitored for development of neurologic signs and symptoms.

    • For multiple reasons, even when the patient tolerates TBO, a cerebral vascular accident (CVA) may develop if simple operative ligation is ultimately performed. First, thrombus is thought to develop in the distal carotid stump, leading to subsequent delayed embolization. Second, intraoperative blood loss and decreased systemic blood pressure under general anesthesia may decrease regional cerebral blood flow (CBF) more than balloon occlusion or ligation alone. For this reason, a hypotensive challenge during TBO may improve the predictive value of the test but is not routinely performed at most centers. [23]

  • Flow Scanning

    • Single-photon emission computed tomography scanning

      • Because of the inadequacy of predicting cerebral ischemia with TBO alone, CBF studies during carotid occlusion have been developed. Single-photon emission computed tomography (SPECT) imaging using technetium-99m hexamethylpropyleneamine oxime (Tc-99m HMPAO) provides a semiquantitative comparison of blood flow to each hemisphere. After the patient has tolerated TBO, Tc-99m is injected intravenously, with the balloon kept inflated for an additional 15-30 minutes. Tc-99m is converted to a hydrophilic form inside the brain that is retained for hours. Because the half-life of Tc-99m is 6 hours, SPECT scanning can be delayed until after completion of angiography and TBO.

      • Tc-99m SPECT scanning does not provide an exact measurement of regional CBF. Rather, it is evaluated based on differences in tracer retention between the 2 sides, and adequate CBF is defined as less than a 10% difference between hemispheres.

    • Xenon flow scanning

      • During TBO, CBF may rise or fall in either hemisphere, resulting in a significant difference in CBF between hemispheres. Thus, determination of the absolute CBF may be helpful in overcoming this ambiguity inherent in interpretation of SPECT scans. Xenon-133 scans offer a more quantitative measurement of regional CBF but are technically more difficult than SPECT when used in conjunction with TBO. [24] Although the carotid is occluded, the patient must inhale xenon gas and, unlike with SPECT, undergo simultaneous nuclear medicine scanning because xenon is rapidly absorbed and discharged.

      • The primary difficulty with this technique lies in the need to take the patient from the angiography suite to the nuclear medicine scanner with certainty that the balloon is still in place. In order to perform this procedure optimally, the nuclear medicine scanner needs to be present in the angiography suite. With this technique, adequate CBF is defined as greater than 30 mL/100g/min, although some require a threshold of as high as 40 mL/100g/min to be considered low risk. [25]

      • Regional CBF may also be measured using stable xenon as a CT contrast agent. This method requires transferring the patient to the CT scanning unit with a catheter in place and with the same considerations as in xenon flow scans. The quantitative results from this method have been shown to prevent frequent misinterpretation of flow asymmetries between hemispheres that may lead to a false-positive reading of a SPECT scan. [26]