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Neuroradiology |
1 From the Departments of Radiology (T.H., K.O, Y.M.) and Neurosurgery (K.S., T.O., S.U.), Amakusa Medical Center, 854-1 Kameba, Hondo, Kumamoto 863-0046, Japan; and the Department of Radiology, Kumamoto University School of Medicine, Japan (Y.K., M.T.). Received September 5, 2000; revision requested October 18; revision received January 11, 2001; accepted February 26. Address correspondence to T.H. (e-mail: toshinor@beige.ocn.ne.jp).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Prospectively, 22 patients with or without subarachnoid hemorrhage underwent CT angiography in conjunction with DSA. Two radiologists independently evaluated DSA and CT angiographic images. Referring neurosurgeons were questioned as to how the additional information provided by CT angiography changed patient treatment.
RESULTS: Intraarterial CT angiography was superior to DSA for use in aneurysm detection in three (12%) of 26 aneurysms and for delineation of aneurysm shape, neck, and location in more than half. In 14 (64%) of 22 patients, CT angiography demonstrated 18 additional findings: a very small aneurysm (n = 2), aneurysm shape and neck (n = 6), relationship of the aneurysm to adjacent arteries or bone structure (n = 8), and branches deriving from the aneurysm (n = 2). In four (27%) of 15 patients who underwent surgery or embolization, additional information obtained at CT angiography affected the treatment. CT angiography failed to clearly demonstrate an aneurysm adjacent to bone structures and small perforators, which were derived from the parent artery.
CONCLUSION: Intraarterial CT angiography is useful for preoperative evaluation of intracranial aneurysms as a supplement to DSA.
Index terms: Aneurysm, CT, 17.1211, 17.12117 • Aneurysm, intracranial, 17.73
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The usefulness of a combined CT and angiographic unit for interventional procedures has been reported (6,7). Intraarterial CT angiography has theoretic advantages compared with contrast-enhanced CT angiography because a higher concentration of contrast material can be delivered to the intracranial artery without considering the appropriate timing of injection, and a smaller total amount of contrast material can be used. The purpose of our prospective study was to assess the usefulness of intraarterial CT angiography in conjunction with digital subtraction angiography (DSA) by using a combined CT and angiographic unit in the preoperative evaluation of intracranial aneurysms.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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There were eight ruptured aneurysms and 18 nonruptured aneurysms. In eight patients with ruptured aneurysms, intraarterial CT angiography was performed in five patients on the day of the subarachnoid hemorrhage (day 0), on day 1 in two patients, and on day 2 in one patient. Surgical treatment was performed in 14 patients, and transcatheter arterial embolization was performed with Guglielmi electrodetachable coils in one. The remaining seven patients did not undergo surgery or embolization because of advanced age, high risk, or poor condition.
DSA Acquisition
Intraarterial DSA was performed by experienced radiologists using a 1,024 x 1,024 matrix with a DSA unit (DFA-100; Hitachi). All catheterizations were performed with a transfemoral approach and the Seldinger technique. The angiographic procedure was routinely accomplished with a standard diagnostic catheter. Selective carotid angiograms were obtained bilaterally in the anteroposterior, lateral, and oblique projections. Stereoscopic technique and increased magnification were used for the aneurysm portion. Stereoscopic views were obtained at a 7° rotation with magnification images. When a patient had irregularity or stenosis of the proximal internal carotid artery, common carotid angiography was performed.
In patients with an anterior communicating artery aneurysm, DSA with manual compression of the contralateral carotid artery was performed to obtain more detailed information about the relationship between the aneurysm and parent artery. We measured the diameter of each cerebral aneurysm after correction for the magnification factor. The diameter of each aneurysm was graded as large (>13 mm), medium (5–12 mm), small (3–4 mm), or very small (<3 mm). When DSA did not clearly demonstrate an aneurysm, CT angiography was used to measure the diameter of the aneurysm.
Intraarterial CT Angiographic Acquisition
After the DSA acquisition of aneurysms was performed, the DSA unit was switched to CT mode. Intraarterial CT angiography was performed with a helical CT scanner (W3000 AD; Hitachi). According to the location of the aneurysm or suspected aneurysm determined with DSA, the scanning site was determined in each case. When the location of an aneurysm was the circle of Willis, the volume scanning usually began at the level of the sellar floor and continued cranially. Volume data were acquired in 25–30 seconds by using a section thickness of 1 mm and a table speed of 1 mm/sec (175 mAs; 120 kV); the scanning volume was 25–30 mm with a 512 x 512 matrix. Depending on the scanning time, a total of 16–24 mL of diluted contrast medium, 4.0–6.0 mL of iopamidol (Iopamiron 300; Schering, Osaka, Japan) diluted with triple the volume of saline (12–18 mL), was injected into the carotid artery at a flow rate of 0.6–0.8 mL/sec by using a power injector (Auto Enhance A-50; Nemoto Kyorindo, Tokyo, Japan). Spiral scanning was initiated 4 seconds after contrast material injection in each artery. Images were reconstructed every 0.5 mm. Image reconstruction was performed with a voxel transmission method, a kind of volume-rendering technique, to create three-dimensional CT angiograms (8). Images of the aneurysm and parent artery were reconstructed with a multiplanar reconstruction technique. Total postprocessing time was 10 minutes for each aneurysm.
The time necessary to switch between examinations was approximately 5 minutes. The intraarterial CT angiographic examination time was less than 10 minutes in all patients. In two patients with subarachnoid hemorrhage, CT angiography was repeated because of movement artifacts. Imaging data of CT angiography were successfully obtained without complications.
Image Analysis
DSA and surgical findings were used as the standard. DSA and CT angiographic images were reviewed together by two radiologists (T.H., K.O.), who performed the reviews independently. The multiplanar reconstruction and source images were always analyzed in conjunction with the corresponding three-dimensional CT angiographic images because of the potential for misinterpretation inherent in the evaluation of the three-dimensional CT angiographic images alone. The radiologists assessed whether intraarterial CT angiography was superior, equal, or inferior to DSA with regard to the depiction and delineation of the presence, shape, orientation, neck, and location of the aneurysm.
The shape indicated the aneurysm contour, which included the number of lobes of the aneurysm. The location referred to the relationship between the aneurysm and adjacent arteries. The adjacent arteries included the middle cerebral artery bifurcation or trifurcation, anterior and posterior communicating arteries, ophthalmic and anterior choroidal arteries, branches derived from the aneurysm, and fenestration. The neck referred to the size of aneurysm neck: narrow, medium, or wide. The orientation indicated the direction of the aneurysm axis.
When the detection or delineation of the aneurysm was substantially better with one modality than with the other, the former modality was defined as superior and the latter as inferior. When the detection or delineation of aneurysm was not substantially different with both modalities, the evaluation of the modalities was defined as equal. The final interpretation was obtained by consensus. 
statistics were used to assess interobserver reliability for aneurysm characteristics (9). The level of agreement was regarded as poor if the value was between 0.41 and 0.60, good if the value was between 0.61 and 0.80, and excellent if the value was between 0.81 and 1.0.
Experienced neurosurgeons (K.S., S.U.) who performed or assisted at surgery were questioned as to whether the additional information provided by intraarterial CT angiography was useful for treatment. The answers of neurosurgeons for each aneurysm were scored as follows: grade 2, CT angiography provided further information that was helpful for surgical approach; grade 1, CT angiography provided further information that was not helpful for surgery; or grade 0, CT angiography provided no further information. The judgments were obtained by consensus. When the answers of neurosurgeons were scored as grade 2, they indicated how the additional information provided by intraarterial CT angiography affected patient treatment.
In patients who underwent surgery, the surgical view of the CT angiogram was generated from the CT angiographic data set and correlated with surgical findings that were recorded on S-VHS video tapes during the entire operation. One radiologist and one neurosurgeon evaluated the surgical findings and intraarterial CT angiographic images together by consensus.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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values (presence, 0.92; shape, 0.88; orientation, 0.85; neck, 0.82; location, 0.86) for interrater variability indicated excellent agreement.
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In all 14 surgically treated aneurysms, surgical findings were well correlated with surgical views generated with the CT angiographic data. Two very small aneurysms that were not clearly depicted at DSA were depicted at intraarterial CT angiography, and they were proved at surgery. In three patients, intraarterial CT angiography could not depict small perforators deriving from the parent artery of an aneurysm; these were clearly depicted at DSA. These perforators were confirmed during surgery.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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In this study, intraarterial CT angiography often provided further anatomic information about aneurysms, although a stereoscopic technique and increased magnification were used in the DSA examinations. Once CT angiographic data were obtained, they allowed us to observe aneurysms and surrounding vasculatures with various projections and sections. Some projections, such as a base view or a possible surgical view, are easy to obtain with intraarterial CT angiography but are difficult to obtain with DSA. When DSA does not provide enough information prior to surgery, intraarterial CT angiography may enable a more accurate diagnosis with a shorter examination time and use of fewer contrast agents.
Velthuis et al (3) recently studied the usefulness of CT angiography with intravenously administered contrast material for preoperative work-up in patients with subarachnoid hemorrhage. They concluded that contrast-enhanced CT angiography had some limitations in obtaining high-quality images for preoperative evaluation. First, it requires large amounts of contrast material and proper timing of the scanning. Second, patient movement due to poor patient condition causes unsatisfactory CT angiographic quality. Third, a technical error resulting in a prolonged delay between the injection of contrast material and scanning might be encountered. Also, contrast-enhanced CT angiography cannot always be repeated because of risk factors, such as renal insufficiency or heart failure. In addition, the intravenous injection site and heart function may affect CT angiographic results. Thus, contrast-enhanced CT angiography has several disadvantages in the preoperative work-up os patients with acute subarachnoid hemorrhage or risk factors.
In contrast, intraarterial CT angiography has some theoretic advantages compared with contrast-enhanced CT angiography. First, a higher concentration of contrast material in the intracranial artery is obtained with catheterization of the carotid artery. Since high-attenuating subarachnoid blood may interfere with the three-dimensional angiographic display used for the detection and delineation of aneurysms, a higher concentration of contrast material in the vessels is preferable. Second, there are no technical failures associated with inappropriate timing of the contrast material injection. Third, only small amounts of contrast material are needed, and it can easily be repeated. Approximately 4.0–6.0 mL of contrast material was required with intraarterial CT angiography; this volume is much smaller than that needed in contrast-enhanced CT angiography. In this study, intraarterial CT angiography was successfully performed in all patients, regardless of the presence of subarachnoid hemorrhage.
In two (8%) of 26 aneurysms, intraarterial CT angiography depicted very small aneurysms that were not clearly depicted with DSA. We used several techniques to obtain quality intraarterial CT angiographic images: the voxel transmission method for three-dimensional reformation (8), scanning with very thin sections, and optimized acquisition with arterial injection. These advantageous techniques probably contributed to the improved detection of very small aneurysms. Although failure to identify a very small aneurysm at DSA may simply be due to the inability to project the lesion adequately, cerebral angiography does not reveal an aneurysm in approximately 10%–20% of patients with acute spontaneous subarachnoid hemorrhage (11–14).
In the surgical treatment of aneurysms, there sometimes are blind corners in an aneurysm due to the difficulty in gaining proximal artery control and a sufficient surgical field; these may lead to unsatisfactory results (15). Therefore, a detailed understanding of aneurysm morphology and the adjacent vasculature prior to clipping the aneurysmal neck is necessary to perform a safe and successful operation. In this study, surgical views obtained with intraarterial CT angiography correlated well with the surgical findings, and the images were a useful reference for surgical clipping in some cases (Figs 3, 4). An accurate imaging study is also necessary to determine the indications for Guglielmi electrodetachable coil embolization in patients with ruptured or nonruptured intracranial aneurysms. It is sometimes difficult to evaluate the relationship between the aneurysm and parent artery with DSA alone. For one patient in this study, Guglielmi electrodetachable coil embolization was selected because intraarterial CT angiography showed a definite neck in the aneurysm that was unclear at DSA. Thus, the additional information provided with intraarterial CT angiography has the potential to affect surgical and embolization plans.
Intraarterial CT angiography has several limitations in the assessment of aneurysms. First, the scanning volume of intraarterial CT angiography was limited in this study. To minimize the amount of ionizing radiation and iodinated contrast material, the scanning site was determined according to the location of a suspected aneurysm at DSA, and a small scanning volume (25–30 mm) was used. A large scanning volume may further increase the value of this technique. Second, one aneurysm adjacent to the skull base could not be depicted at intraarterial CT angiography. Several authors (1,2,16) have described that aneurysms at the skull that arise from the intracavernous or supraclinoid carotid artery may be obscured by bone, calcium, or venous blood on CT angiographic studies obtained after intravenous administration of contrast material. Although a high concentration of contrast material in the intracranial artery was obtained with intraarterial CT angiography, bone structures interfered with the evaluation of the aneurysms. Third, interpretation by using the three-dimensional CT angiograms alone may cause a false diagnosis of an aneurysm because the intravascular contrast material and mural calcifications are not completely separated. Therefore, the transverse source images or multiplanar reconstruction images, in conjunction with the three-dimensional CT angiographic images, should be used for assessing intracranial aneurysms. Fourth, intraarterial CT angiography may not always depict perforators of the parent artery, which were depicted with DSA. This could be due to the poorer spatial resolution of intraarterial CT angiography in comparison with that of DSA. Fifth, intraarterial CT angiography did not demonstrate the contralateral A1 segment of the anterior cerebral artery in the anterior communicating artery aneurysms. Careful reading of carotid angiograms, as well as intraarterial CT angiographic images, with manual compression of the carotid artery during arteriography may be used in the preoperative evaluation of the anterior communicating artery aneurysms. On the basis of these limitations, intraarterial CT angiography is considered to be a supplement to DSA.
There were two important limitations in this study. First, the results were acquired from a small group of patients, and aneurysms in the posterior fossa were not encountered in this study. However, the results warrant further study in a larger group of patients to investigate the value of intraarterial CT angiography for the assessment of intracranial aneurysms. Recently, three-dimensional rotational angiography has been evaluated (17). Perhaps a further study could be conducted to compare intraarterial CT angiography with three-dimensional rotational angiography. Second, we did not evaluate whether intraarterial CT angiography provides better image quality than does CT angiography with intravenously administered contrast material. Further investigation must be performed to determine whether intraarterial CT angiography is superior to contrast-enhanced CT angiography in the evaluation of the intracranial arteries.
In conclusion, intraarterial CT angiography is a feasible technique and was useful in our study for the preoperative evaluation of intracranial aneurysms. Although catheter-based angiography has been used as a standard, the aneurysm and surrounding vasculature may be more accurately evaluated with CT angiography than with catheter-based angiography. Intraarterial CT angiography may not clearly demonstrate perforators or very small branches of the parent artery or aneurysms adjacent to the bone structures. Therefore, we believe that intraarterial CT angiography is a supplement to DSA. When an aneurysm is found or suspected at DSA, intraarterial CT angiography may demonstrate additional information that can affect patient treatment.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, T.H.; study concepts and study design, T.H.; literature research, T.H.; clinical studies, T.H., K.O., Y.M., K.S., T.O., S.U.; data acquisition, K.O., Y.M.; data analysis/interpretation, K.S., T.O., K.O., T.H.; statistical analysis, T.H.; manuscript preparation and definition of intellectual content, T.H.; manuscript editing, T.H., Y.K., M.T.; manuscript revision/review and manuscript final version approval, Y.K., M.T.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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