The role of cranial computed tomography in carotid surgery

A critical analysis of cerebral computed tomography scanning before elective carotid endarterectomy and its correlation to carotid stenosis

BACKGROUND

Cerebral computed tomography (CT) scanning has been suggested to play a role in the management of patients before carotid endarterectomy (CEA). This prospective study analyzes the value of CT scanning before elective CEA and the correlation of CT findings to significant carotid stenosis.

METHODS

This study includes 131 consecutive patients considered for CEA during a 2-year period. All patients underwent carotid duplex ultrasonography, carotid arteriography, and CT scanning.

RESULTS

Eighty patients (61%) had transient ischemic attacks or prior strokes, and 51 (39%) had nonhemispheric symptoms or were asymptomatic. The CT scan was abnormal in 36 (27%) patients; however, no brain tumors or abnormalities to affect clinical management were revealed. Ninety-two CEAs were performed on 87 patients. Twenty-nine (32%) in the operative group had abnormal CT scans, but these did not influence operative decisions. On the basis of this rate of 0% of patients with CT findings to change surgical management in 92 cases, a maximum true rate of occurrence of up to 5% could be detected with alpha equals 0.05 by sampling a population of this size. Four patients (4%) had postoperative cerebral vascular accidents, and all of these had normal preoperative scans. Patients with 50% or more carotid stenosis on arteriogram were significantly more likely to have abnormal CT scans than patients with less than 50% stenosis (20% versus 7%, p = 0.0034). As carotid stenosis became more significant, the frequency of abnormal CT scans increased (p < 0.01). The cost of CT scanning was $66,089.50 in this study.

CONCLUSIONS

Significant carotid stenosis was associated with a higher frequency of abnormal CT scans; however, routine preoperative CT scanning was unnecessary before elective CEA.

Carotid endarterectomy without arteriography

Arteriography has been considered the "gold standard" for evaluation of the cerebrovascular circulation prior to carotid endarterectomy. However, arteriography is associated with a neurologic complication rate of up to 12% in certain high-risk groups. Previous studies have shown that the duplex scanner has greater sensitivity than arteriography when both are correlated to the surgical specimen. From January 1986 to December 1991 a total of 174 carotid endarterectomies were performed in 152 patients, of which 61% were symptomatic. A total of 110 carotid endarterectomies in 92 patients were performed without the use of arteriography. Of the 64 patients in whom arteriograms were obtained, 33 were made at consultation and the others for various indications. Operative findings confirmed the duplex scan findings in all cases. A total of 91% of patients had intraoperative completion arteriograms. Of the 55 patients who also had intracranial views taken, two had a 50% siphon stenosis and one patient had a small intracranial aneurysm. None of these findings would have changed our management. The overall neurologic complication rate was one (0.66%) death due to stroke and four (2.6%) patients with transient ischemic attacks. Carotid endarterectomy can be safely performed without preoperative arteriography based on a detailed history and physical examination that includes bilateral upper extremity blood pressures and a duplex scan performed by a validated laboratory.

Transcranial Doppler monitoring during carotid endarterectomy

Transcranial Doppler monitoring of the middle cerebral artery blood flow velocity was used as an adjunct to routine methods of cerebral monitoring in a prospective study of 30 consecutive patients undergoing carotid endarterectomy to investigate whether transcranial Doppler monitoring provided information influencing operative technique. Application of carotid clamps caused a significant fall in middle cerebral artery velocity and there was a linear relationship between middle cerebral artery velocity and internal carotid artery stump pressure. Assuming a stump pressure of less than 50 mmHg to be an indication for shunting, this would correspond to a systolic middle cerebral artery velocity of less than 42 cm/s and a mean velocity of less than 30 cm/s. Transcranial Doppler monitoring immediately identified problems with shunt function and demonstrated a higher frequency of intraoperative embolization than had been anticipated, particularly after shunt insertion and final restoration of flow. With revision of operative technique this phenomenon is rarely encountered now. Two of the 30 patients exhibited a minor neurological deficit on recovery of consciousness, and transcranial Doppler monitoring was able to identify the probable underlying cause in both cases. Unnecessary and potentially hazardous re-exploration was avoided. In the absence of transcranial Doppler monitoring the neurological deficit in one of the patients might have been much worse.