CT in evaluation of the circle of Willis

Detection of Intracranial Aneurysms: Multi–Detector Row CT Angiography Compared with DSA

PURPOSE

To prospectively compare the effectiveness of multi-detector row computed tomographic (CT) angiography with that of conventional intraarterial digital subtraction angiography (DSA) used to detect intracranial aneurysms in patients with nontraumatic acute subarachnoid hemorrhage.

MATERIALS AND METHODS

Thirty-five consecutive adult patients with acute subarachnoid hemorrhage were recruited into the institutional review board-approved study and gave informed consent. All patients underwent both multi-detector row CT angiography and DSA no more than 12 hours apart. CT angiography was performed with a multi-detector row scanner (four detector rows) by using collimation of 1.25 mm and pitch of 3. Images were interpreted at computer workstations in a blinded fashion. Two radiologists independently reviewed the CT images, and two other radiologists independently reviewed the DSA images. The presence and location of aneurysms were rated on a five-point scale for certainty. Sensitivity and specificity were calculated independently for image interpretation performed by the two CT image readers and the second DSA image reader by using the first DSA reader's interpretation as the reference standard.

RESULTS

A total of 26 aneurysms were detected at DSA in 21 patients, and no aneurysms were detected in 14 patients. Sensitivity and specificity for CT angiography were, respectively, 90% and 93% for reader 1 and 81% and 93% for reader 2. The mean diameter of aneurysms detected on CT angiographic images was 4.4 mm, and the smallest aneurysm detected was 2.2 mm in diameter. Aneurysms that were missed at initial interpretation of CT angiographic images were identified at retrospective reading.

CONCLUSION

Multi-detector row CT angiography has high sensitivity and specificity for detection of intracranial aneurysms, including small aneurysms, in patients with nontraumatic acute subarachnoid hemorrhage.

[Cerebral aneurysms diagnosis by three-dimensional CT angiography]

Three-dimensional computerized tomography angiography is a fast diagnosis method and low invasive that passed to be used recently in the cases of intracranial aneurysms. This method presents a 100% specificity and can reach 95% of sensibility in the evaluation of the aneurysms in the circle of Willis, substituting the digital angiography but not in all of the cases. We report our experience in evaluation of the three-dimensional angiotomography exams in a period of 2 years between June of 1997 and June of 1999, were accomplished for detection of intracranial aneurysms in 136 patients, being 118 just with three-dimensional angiotomography and in 18 cases they were accomplished besides three-dimensional angiotomography also the conventional digital angiography. The exam of three-dimensional angiotomography possesses low risk being used better in the detection of the aneurysms when possess higher diameter than 3mm, with some limitations as in the very small aneurysms when smaller than 3mm, carotid intern cavarnous aneurysms, posterior circulation aneurysms as well as the non accomplishment of the dynamic exam.

Angiographic frequency of anterior circulation intracranial aneurysms

A retrospective angiographic analysis was designed to extrapolate the frequency of angiographically defined asymptomatic intracranial aneurysms in the anterior circulation from a relatively unbiased clinical series. A total of 9295 angiograms were reviewed from January, 1980, to January, 1987, and, based on these, 278 patients with minimal bias for the presence of an aneurysm were selected. Three patients were found to have incidental aneurysms; thus, the angiographic frequency of patients with asymptomatic aneurysms in this series was 1%. This patient population is skewed toward the older age groups and probably over-represents the incidence of these aneurysms in the population at large. Comparing current subarachnoid hemorrhage statistics and the low frequency of asymptomatic aneurysms suggests that a larger percentage of these aneurysms than was previously thought subsequently rupture. This study contrasts sharply with previous reports quoting a high incidence of aneurysms, and significantly alters the concept and treatment of this disease.

Magnetic resonance imaging of subarachnoid hemorrhage

Magnetic resonance (MR) imaging of subarachnoid hemorrhage (SAH) due to a ruptured aneurysm has been evaluated in relation to CT findings on 30 patients. In the acute stage, particularly less than 24 hours after the bleeding episode (25 patients), SAH appeared of high intensity relative to the surrounding brain on a T-2 weighted SE image but isointense where the corresponding CT scan showed blood clot of attenuation value over 60 H. A T-2 weighted SE image was able to reveal subtle evidence of SAH not visible on the CT scan. The T-1 weighted IR image was not as sensitive. Blood clot (HU greater than 60) appeared isointense, but mild and moderate SAH (HU less than 60) was indistinguishable from normal CSF. MR imaging was also sensitive to subacute and chronic SAH (5 patients). Three out of four SAH appearing normal on CT showed high intensity on T-2 weighted images. Thirteen out of 24 aneurysms (54%) larger than 5 mm in diameter on angiography were detected on T-2 weighted images. Smaller aneurysms less than 4 mm were not visualized. MR imaging was able to indicate the ruptured one in cases of multiple aneurysms by showing hemorrhagic lesions more clearly than CT. We conclude that MR imaging is very helpful for diagnosing SAH, particularly when CT is normal, and in indicating aneurysm location as well as rupture site.

Delineation of unruptured cerebral aneurysms by computerized angiotomography

Unruptured aneurysms were diagnosed in 15 of 86 patients with cerebral aneurysms during 2 years beginning in April, 1979. One patient with severe head injury was excluded from the series. Fifteen aneurysms in the other 14 patients were first detected by computerized angiotomography. Six aneurysms were located in the middle cerebral artery, three in the upper half of the basilar artery, two in the anterior communicating artery, two in the posterior cerebral artery, and two at the internal carotid-posterior communicating artery junction (both in the same patient). Three were smaller than 5 mm, eight were between 6 and 10 mm, and four were larger than 10 mm. The noncontrast computerized tomography (CT) findings associated with 15 aneurysms were as follows: five showed defects in the basal cistern of Sylvian fissure, four were calcified or high-density masses, and in the six instances there was no evidence of an aneurysm. Unruptured aneurysms may be suggested by a well demarcated, round, isodense mass which forms a defect in the basal cistern of Sylvian fissure on a plain CT image, and are highly and homogeneously enhanced by computerized angiotomography. A carotid artery blood iodine level of 15 mg/ml is required to obtain clear images. The authors conclude that computerized angiotomography is useful in the delineation of unruptured aneurysms.

Computed tomography in the diagnosis of subarachnoid haemorrhage and ruptured aneurysm

One hundred consecutive patients with subarachnoid haemorrhage were investigated by computed tomography (CT) within five days of the bleeding. In 19 cases CT indicated other sources than a ruptured aneurysm, most often a cerebellar haematoma. The other 81 patients did not all undergo angiography. It could be estimated by extrapolation that an aneurysm would be demonstrated in 66 of the 68 patients in whom CST showed extravasated blood in the basal cisterns, and in only five of the remaining 13 patients. In a consecutive series of 50 patients with bleeding from a verified aneurysm, CT showed some extravasated blood in all cases and a haematoma in half of these. In 74% the site of the haemorrhage correctly predicted the site of the ruptured aneurysm. Intravenous contrast medium visualized the aneurysm on CT in 15 of 25 cases; this can improve the identification of the bleeding aneurysm to 88%. Rebleeding occurred in 21 patients, and was obvious in Ct in 19. If available, CT should be the first investigation in patients with first and recurrent subarachnoid haemorrhage.