DOI: 10.1148/radiol.2442060394
(Radiology 2007;244:532-540.)
© RSNA, 2007
Intracranial Aneurysms: Role of Multidetector CT Angiography in Diagnosis and Endovascular Therapy Planning1
Karsten Papke, MD,
Christiane K. Kuhl, MD,
Martin Fruth, MD,
Cornel Haupt, MD,
Martin Schlunz-Hendann, MD,
Dieter Sauner, MD,
Martin Fiebich, PhD,
Alan Bani, MD, and
Friedhelm Brassel, MD
1 From the Departments of Radiology and Neuroradiology (K.P., M. Fruth, C.H., M.S., D.S., F.B.) and Neurosurgery (A.B.), Klinikum Duisburg, Zu den Rehwiesen 9, D-47055 Duisburg, Germany; Department of Radiology, Rheinische Friedrich-Wilhelms-University of Bonn, Bonn, Germany (C.K.K.); and University of Applied Sciences Giessen-Friedberg, Giessen, Germany (M. Fiebich). From the 2003 RSNA Annual Meeting. Received March 2, 2006; revision requested May 1; revision received August 2; accepted August 30; final version accepted December 15.
Address correspondence to K.P. (e-mail: karsten.papke{at}klinikum-duisburg.de).
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ABSTRACT
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Purpose: To evaluate the sensitivity of 16-detector row computed tomographic (CT) angiography in diagnosis of intracranial aneurysms and to determine whether multidetector CT angiography provides sufficient diagnostic information to guide endovascular treatment, with combined imaging and clinical data as the reference standard.
Materials and Methods: Institutional review board approval and informed consent were obtained. Eighty-seven patients clinically suspected of having subarachnoid hemorrhage underwent multidetector CT angiography and digital subtraction angiography (DSA). Aneurysm detection with multidetector CT angiography and DSA was analyzed on a per-patient and a per-aneurysm basis. For each aneurysm deemed ruptured on multidetector CT angiograms, the same multidetector CT angiography data set was used to determine whether the aneurysm was suitable for endovascular coil placement or whether a neurosurgical procedure was preferable. Criteria were based on neck width in relation to aneurysm size and the presence of vessels originating from the aneurysm. Results were compared with actual treatment that had been performed in each aneurysm after full diagnostic work-up, including DSA. Sensitivity, specificity, and positive and negative predictive values for aneurysm presence were determined.
Results: The reference standard revealed 84 aneurysms in 63 patients. Multidetector CT angiography was used to correctly identify 62 of 63 patients with 80 of 84 aneurysms and to correctly rule out aneurysms in 24 patients. DSA was used to correctly identify 62 of 63 patients with 79 of 84 aneurysms and to correctly rule out aneurysms in 23 patients. Per patient, the sensitivity, specificity, and positive and negative predictive values, respectively, for presence of aneurysm(s) were 98%, 100%, 100%, and 96% for multidetector CT angiography and 98%, 100%, 98%, and 96% for DSA. Per aneurysm, the possibility of coil embolization was correctly assessed with multidetector CT angiography in 69 (93%) of 74 target aneurysms for acute occlusive treatment.
Conclusion: Multidetector CT angiography offers high diagnostic accuracy—equivalent to that of DSA—in the detection of intracranial aneurysms. Also, the possibility of coil embolization can be reliably determined with multidetector CT angiography.
© RSNA, 2007
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INTRODUCTION
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Selective digital subtraction angiography (DSA) is considered the reference standard in the diagnosis of intracranial aneurysms (1); however, this examination carries an additional risk of morbidity and mortality (2,3). Computed tomographic (CT) angiography, however, is playing an increasing role in the evaluation of patients suspected of having intracranial aneurysms (4–10). Regarding the care of patients with subarachnoid hemorrhage, CT angiography may offer some intrinsic advantages over DSA: In the classic clinical scenario, a patient clinically suspected of having subarachnoid hemorrhage undergoes unenhanced CT of the head. CT angiography may easily be added to this initial imaging examination with little extra time needed and can provide virtually unlimited viewing angles in three-dimensional views (11), which may facilitate the assessment of morphologic details relevant to aneurysm therapy. However, on the basis of the current literature, some technical limitations exist for CT angiography, compared with selective intraarterial DSA, that seem to limit the diagnostic accuracy with which aneurysms can be detected with CT angiography (10,12–14).
Some of the specific technique-inherent disadvantages of CT angiography can be overcome with multidetector CT angiography. For instance, multidetector CT angiography enables faster imaging of larger volumes with increased spatial resolution. The almost isotropic acquisition that can be achieved with multidetector CT angiography may facilitate improved in-plane and through-plane image reconstruction, which may in turn improve the diagnostic accuracy of this technique. Hence, our objective was to evaluate the sensitivity of multidetector CT angiography in the diagnosis of intracranial aneurysms and to evaluate whether this modality provides sufficient diagnostic information to guide endovascular treatment, with combined imaging and clinical data serving as the reference standard.
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MATERIALS AND METHODS
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Patients
In a specialized tertiary care center (Klinikum Duisburg), we conducted a prospective nonrandomized clinical study to compare the utility of multidetector CT angiography and intraarterial DSA in the detection of and treatment planning for intracranial aneurysms. The institutional review board reviewed and approved the study protocol. Patients or family members (if the patient's clinical status precluded him or her from granting consent) provided informed consent for study participation after the study and radiation dose issues were explained.
From January 2003 to August 2005, 94 patients suspected of having subarachnoid hemorrhage underwent multidetector CT angiography. Inclusion criteria were as follows: Patients had to have clinical symptoms of subarachnoid hemorrhage and be able to undergo both multidetector CT angiography and DSA. The indication for multidetector CT angiography and DSA was established on the basis of clinical findings. Multidetector CT angiography demonstrated a total of 88 aneurysms in 67 patients and no aneurysm in 27 patients. Two patients in poor clinical condition (Hunt and Hess grade V) had positive multidetector CT angiography findings; however, they did not undergo DSA because they were considered unamenable to further aneurysm-specific treatment. Three patients with positive multidetector CT angiography findings underwent neurosurgical clip placement without presurgical DSA. Two patients with negative multidetector CT angiography findings did not undergo DSA because the subarachnoid hemorrhage that had been suspected clinically was ruled out with further diagnostic work-up. Accordingly, our study group consisted of the remaining 87 patients (36 men, 51 women; age range, 20–84 years; median age, 54 years) who underwent both multidetector CT angiography and DSA (Fig 1).
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Figure 1: Flowchart shows composition of the study group, which consisted of 87 patients (pts.) who underwent both multidetector CT angiography (MDCTA) and DSA. The reference standard consisted of a combined reading of multidetector CT angiography and DSA results, as well as additional clinical information. SAH = subarachnoid hemorrhage.
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After diagnostic DSA, decisions regarding the care of a patient, particularly decisions regarding endovascular or neurosurgical treatment, were made in consensus by the attending interventional neuroradiologist (K.P., C.H., M.S., or F.B.; 2–27 years of experience in endovascular aneurysm treatment) and the neurosurgeon (A.B. or one of three other neurosurgeons with 6–25 years of experience in intracranial aneurysm clip placement). First, all aneurysms that were considered potentially ruptured (on the basis of their location in relation to subarachnoid blood distribution) or otherwise symptomatic (eg, cranial nerve compression) were defined as target aneurysms for acute occlusive treatment. Second, the treatment modality was chosen for each target aneurysm in accordance with the results of the International Subarachnoid Aneurysm Trial (15,16): If endovascular coil placement was considered the best therapeutic option or if coil placement and neurosurgical clip placement were considered equally suitable, coil placement was attempted first. Otherwise, or if endovascular therapy failed, neurosurgical clips were placed. Patient care was performed at the time of initial study interpretation.
Diagnostic Imaging
Multidetector CT angiography.—A 16–detector row CT scanner was used (Somatom Sensation 16; Siemens Medical Systems, Forchheim, Germany) with 130 mAs (effective) and 120 kV. The collimation was 0.75 mm, with a 0.5-second rotation time and a table feed of 11.0 mm per rotation. Images were reconstructed with a 1.0-mm section thickness and a 0.8-mm increment with the H45f kernel.
A 50-mL dose of iodinated contrast medium ([300 mg of iodine per milliliter] Ultravist 300; Schering, Berlin, Germany) was injected at a flow rate of 4 mL/sec and followed by injection of a 20-mL bolus of NaCl 0.9%. Bolus arrival was monitored with one image per second obtained at the C4 level. Actual diagnostic spiral CT angiography was started manually with a 2-second delay as soon as the contrast material bolus arrived in the carotid arteries at the C4 level.
DSA imaging.—An interventional neuroradiologist experienced in the endovascular treatment of intracranial aneurysms (K.P., C.H., M.S., or F.B.) performed DSA as soon as clinically feasible after multidetector CT angiography (interval between multidetector CT angiography and DSA varied from 1 hour to 10 days; median time, 9 hours). DSA was performed on either a biplanar digital angiography unit or a monoplanar system (Siemens Axiom Artis BA and Siemens Multistar, respectively; Siemens Medical Systems) with a 1024 x 1024-pixel matrix. Bilateral selective internal carotid artery injections and uni- or bilateral vertebral artery injections were performed and imaged in anteroposterior and lateral projections. Additional angiographic images were acquired at the discretion of the examiner on the basis of both the findings in the routine projections of DSA and the multidetector CT angiography results.
Image Analysis
All analyses were performed in consensus by two of four neuroradiologists (K.P., C.H., M.S., and F.B.) with 2–6 years of experience in reading neurovascular CT angiographic studies and 2–27 years of experience in interventional neuroradiology. To avoid reader bias, the only neuroradiologists who read the studies were those who had not been involved in the clinical care of the patient. Readers were informed of the patient's clinical symptoms at the time of CT angiography and of the unenhanced head CT findings; however, they were blinded to the patient's identity and the ultimate diagnosis, treatment, and outcome. Reading of multidetector CT angiography and DSA data sets was separated by a 6–8-week interval.
Multidetector CT angiography.—All image analyses were performed on a workstation (Leonardo 3D, version VB30B; Siemens Medical Systems). Each vascular segment was first inspected interactively by using multiplanar reformation with 1-mm section thickness and thin-slab maximum intensity projection (slab thickness, 4–8 mm depending on the vicinity of the interfering bone). For this systematic analysis, both transverse source images and reconstructions in two more orientations parallel and orthogonal to the main course of the vascular segment were reviewed. In addition, the data set was analyzed with interactive volume rendering by using the InSpace task card. Only findings that could be confirmed on the source images were rated aneurysms.
DSA imaging.—Two-dimensional DSA data sets were analyzed with the Angio evaluation tool with interactive stepwise and cine display of the complete angiographic series.
Treatment with Multidetector CT Angiography
The two readers were asked to use the multidetector CT angiography data sets to decide whether any target aneurysm was suitable for endovascular treatment. The following criteria were used to make this decision: An aneurysm was considered coilable (ie, it could be treated with coil placement) if (a) the aneurysm neck was considered narrow enough compared with the dome width to place coils within the aneurysm sack without coil protrusion into the parent vessel and (b) there were no vessel branches originating from the aneurysm above the neck level that might be occluded by the coil package. Because stent placement in wide-necked aneurysms (17–20) was not a method used in the International Subarachnoid Aneurysm Trial (15,16), only aneurysms that appeared treatable without this supportive technique were rated as coilable. Other aneurysms were rated as not coilable.
Statistical Analysis
To assess the diagnostic performance of multidetector CT angiography compared with DSA regarding the detection of intracranial aneurysms, data were analyzed on a per-patient basis to distinguish between patients with at least one aneurysm and patients with no aneurysm. Sensitivity, specificity, and positive and negative predictive values were calculated. In addition, the detectability of individual aneurysms was analyzed on a per-aneurysm basis. The diagnoses were validated with a reference standard that consisted of the combined interpretation of multidetector CT angiography, DSA, and relevant clinical data (eg, intraoperative findings and results of follow-up imaging), as rated by all four participating neuroradiologists in consensus.
The reference standard for assessment of coilability was based on the treatment performed. The treatment performed for each aneurysm was assigned to one of the following six categories: (a) coils placed without stent placement; (b) coils placed with stent placement; (c) primary clips placed; (d) clips placed after unsuccessful attempt to place coils; (e) unsuccessful attempt to place coils, no further therapy; and (f) neither coil nor clip placement attempted.
Aneurysms in which endovascular therapy was completed without coil protrusion into the parent vessel, without occlusion of branches originating from the aneurysm, without additional stent placement, and without additional neurosurgical clip placement were considered coilable; all other aneurysms were considered not coilable. On the basis of this dichotomization, sensitivity, specificity, and positive and negative predictive values were calculated.
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RESULTS
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According to the reference standard results, no aneurysm was present in 24 patients. Sixty-three patients had at least one intracranial aneurysm: 48 patients had one aneurysm; nine patients, two aneurysms; and six patients, three aneurysms. Of the 84 aneurysms, 74 were classified as target aneurysms for occlusive treatment.
Aneurysm Detection
In the patientwise analysis, multidetector CT angiography revealed sensitivity, specificity, and positive and negative predictive values of 98% (62 of 63 patients), 100% (24 of 24 patients), 100% (62 of 62 patients), and 96% (24 of 25 patients), respectively. With DSA, sensitivity, specificity, and positive and negative predictive values were 98% (62 of 63 patients), 100% (24 of 24 patients), 98% (62 of 63 patients), and 96% (23 of 24 patients), respectively (Table 1).
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Table 1. Comparison of Imaging Results and Combined Reference Standard for Detection of Intracranial Aneurysms on a Per-Patient Basis
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The only patient with discordant results at multidetector CT angiography and DSA was a patient with prepontine subarachnoid hemorrhage. Multidetector CT angiography findings were negative, whereas DSA depicted a small sacculation at the left A1 segment (Fig 2). Intraoperatively, this was identified as a dilated infundibulum of a small artery. Thus, this finding was listed as true-negative at CT angiography and false-positive at DSA.
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Figure 2a: False-positive (a) multidetector CT angiography and (b) DSA images in a patient with prepontine subarachnoid hemorrhage. (a) No aneurysm is visible at multidetector CT angiography. The left anterior oblique targeted maximum intensity projection image (40-mm slab thickness) shows the A1 segment of the anterior cerebral artery (arrowhead), with no evidence of an aneurysm. (b) DSA image obtained in the same projection shows a small (approximately 1 mm) sacculation arising from the proximal part of the A1 segment (arrowhead). This finding was misinterpreted as an aneurysm. At surgery, the sacculation was identified as an infundibular dilatation of a branch of the A1 segment, which was subsequently wrapped.
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Figure 2b: False-positive (a) multidetector CT angiography and (b) DSA images in a patient with prepontine subarachnoid hemorrhage. (a) No aneurysm is visible at multidetector CT angiography. The left anterior oblique targeted maximum intensity projection image (40-mm slab thickness) shows the A1 segment of the anterior cerebral artery (arrowhead), with no evidence of an aneurysm. (b) DSA image obtained in the same projection shows a small (approximately 1 mm) sacculation arising from the proximal part of the A1 segment (arrowhead). This finding was misinterpreted as an aneurysm. At surgery, the sacculation was identified as an infundibular dilatation of a branch of the A1 segment, which was subsequently wrapped.
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In another patient, both multidetector CT angiography and initial DSA were false-negative for detection of an anterior communicating artery aneurysm. This aneurysm was detected at repeat DSA and could be retrospectively identified on multidetector CT angiograms and initial DSA images (Fig 3).
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Figure 3a: Images in a patient with acute subarachnoid hemorrhage with distribution throughout all basal cisterns. At initial interpretation, anteroposterior multidetector CT angiography and DSA images were negative for aneurysms (arrowhead). (a) Initial DSA image. (b) Volume-rendering technique image. After repeat detailed interpretation of multidetector CT angiograms and DSA images, an anterior communicating artery aneurysm (arrowhead) was suspected on the basis of multidetector CT angiography data acquired with the coronal oblique volume-rendering technique of the multidetector CT angiography data. (c) DSA was repeated 3 days later in a projection similar to that of the volume-rendering technique image (b), and an anterior communicating artery aneurysm (arrowhead) was confirmed. Even retrospectively, the aneurysm could not be distinguished from overlying vessels on a.
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Figure 3b: Images in a patient with acute subarachnoid hemorrhage with distribution throughout all basal cisterns. At initial interpretation, anteroposterior multidetector CT angiography and DSA images were negative for aneurysms (arrowhead). (a) Initial DSA image. (b) Volume-rendering technique image. After repeat detailed interpretation of multidetector CT angiograms and DSA images, an anterior communicating artery aneurysm (arrowhead) was suspected on the basis of multidetector CT angiography data acquired with the coronal oblique volume-rendering technique of the multidetector CT angiography data. (c) DSA was repeated 3 days later in a projection similar to that of the volume-rendering technique image (b), and an anterior communicating artery aneurysm (arrowhead) was confirmed. Even retrospectively, the aneurysm could not be distinguished from overlying vessels on a.
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Figure 3c: Images in a patient with acute subarachnoid hemorrhage with distribution throughout all basal cisterns. At initial interpretation, anteroposterior multidetector CT angiography and DSA images were negative for aneurysms (arrowhead). (a) Initial DSA image. (b) Volume-rendering technique image. After repeat detailed interpretation of multidetector CT angiograms and DSA images, an anterior communicating artery aneurysm (arrowhead) was suspected on the basis of multidetector CT angiography data acquired with the coronal oblique volume-rendering technique of the multidetector CT angiography data. (c) DSA was repeated 3 days later in a projection similar to that of the volume-rendering technique image (b), and an anterior communicating artery aneurysm (arrowhead) was confirmed. Even retrospectively, the aneurysm could not be distinguished from overlying vessels on a.
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In the analysis of individual aneurysms, of the 84 aneurysms that were present in our patient cohort, as determined with the reference standard, three aneurysms were missed with both DSA and multidetector CT angiography, and one aneurysm was missed with DSA but was diagnosed with multidetector CT angiography. These diagnostic errors were as follows:
Both multidetector CT angiography and initial DSA failed to depict a second aneurysm of the right posterior communicating artery in a patient with a ruptured aneurysm of the anterior communicating artery (Fig 4). One day after successful coil embolization of the anterior communicating artery aneurysm, a posterior communicating artery aneurysm was suspected after careful review of multidetector CT angiography and DSA findings, confirmed at repeat DSA, and successfully treated. In another patient with successful embolization of a posterior communicating artery aneurysm, two additional aneurysms (one at the right proximal medial cerebral artery and one at the right middle cerebral artery trifurcation) were not identified with multidetector CT angiography or initial DSA. These aneurysms were detected at follow-up DSA 6 months later and could be identified retrospectively on the original multidetector CT angiograms and DSA images.
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Figure 4a: Patient with a ruptured aneurysm of the anterior communicating artery and an additional aneurysm of the posterior communicating artery. The aneurysm of the right posterior communicating artery was initially missed with both multidetector CT angiography and DSA. (a) The paracoronal volume-rendering technique image shown here had the strongest conspicuity. After successful embolization of the anterior communicating artery aneurysm (arrowhead), review of the multidetector CT angiography data the next day raised suspicion of an additional posterior communicating artery aneurysm (arrow). With the aneurysm parallel to the course of the posterior communicating artery, the aneurysm appeared broad based and not coilable. (b) At repeat DSA, a projection angle similar to that of the volume-rendering technique image is used, and the posterior communicating artery aneurysm (arrow) is confirmed. At DSA, the same projection angle used for volume-rendering technique multidetector CT angiography was used and the relatively narrow neck could be appreciated. The aneurysm was successfully treated with coil placement, and stent placement was not necessary. Note the coil package after embolization of the anterior communicating artery aneurysm (arrowhead).
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Figure 4b: Patient with a ruptured aneurysm of the anterior communicating artery and an additional aneurysm of the posterior communicating artery. The aneurysm of the right posterior communicating artery was initially missed with both multidetector CT angiography and DSA. (a) The paracoronal volume-rendering technique image shown here had the strongest conspicuity. After successful embolization of the anterior communicating artery aneurysm (arrowhead), review of the multidetector CT angiography data the next day raised suspicion of an additional posterior communicating artery aneurysm (arrow). With the aneurysm parallel to the course of the posterior communicating artery, the aneurysm appeared broad based and not coilable. (b) At repeat DSA, a projection angle similar to that of the volume-rendering technique image is used, and the posterior communicating artery aneurysm (arrow) is confirmed. At DSA, the same projection angle used for volume-rendering technique multidetector CT angiography was used and the relatively narrow neck could be appreciated. The aneurysm was successfully treated with coil placement, and stent placement was not necessary. Note the coil package after embolization of the anterior communicating artery aneurysm (arrowhead).
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One aneurysm was missed with DSA but detected with multidetector CT angiography in a patient with two adjacent aneurysms of the anterior communicating artery (both pointing downward, one directed anteriorly and the other directed posteriorly). Only one of these aneurysms was visible on the DSA image. The second aneurysm, which had been depicted with multidetector CT angiography, could only be verified at superselective DSA with the microcatheter after coil embolization of the first aneurysm. This procedure was initiated because of the suspicious multidetector CT angiography findings. Thus, the second aneurysm would have been missed at diagnostic DSA without prior knowledge of the multidetector CT angiography findings.
In addition to these false-negative findings, two false-positive diagnoses were made with multidetector CT angiography. In one patient with a ruptured lobulated aneurysm of the left internal carotid artery, a 2.5-mm-diameter sacculation noted at the right internal carotid artery was mistaken for a mirror aneurysm on the basis of multidetector CT angiography findings; however, DSA depicted an infundibular dilatation of the right posterior communicating artery (Fig 5). In another patient, a kinked course of the anterior communicating artery was misdiagnosed as an aneurysm.
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Figure 5a: False-positive multidetector CT angiograms of an aneurysm of the right internal carotid artery. (a) Transverse volume-rendering technique image of a lobulated aneurysm at the left internal carotid artery (arrow) and a broad-based sacculation with a diameter of 2.5 mm directed dorsomedially from the right internal carotid artery (arrowhead). These findings were misinterpreted as a mirror aneurysm. However, DSA revealed an infundibular dilatation of the right posterior communicating artery. (b) Targeted thin-slab maximum intensity projection multidetector CT angiograms obtained at different transverse oblique projections show that the posterior communicating artery (arrowheads) originates from the dilatation and does not run parallel to it. These findings represent an enlarged infundibulum and not an aneurysm.
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Figure 5b: False-positive multidetector CT angiograms of an aneurysm of the right internal carotid artery. (a) Transverse volume-rendering technique image of a lobulated aneurysm at the left internal carotid artery (arrow) and a broad-based sacculation with a diameter of 2.5 mm directed dorsomedially from the right internal carotid artery (arrowhead). These findings were misinterpreted as a mirror aneurysm. However, DSA revealed an infundibular dilatation of the right posterior communicating artery. (b) Targeted thin-slab maximum intensity projection multidetector CT angiograms obtained at different transverse oblique projections show that the posterior communicating artery (arrowheads) originates from the dilatation and does not run parallel to it. These findings represent an enlarged infundibulum and not an aneurysm.
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Assessment of Endovascular Treatment Possibility
Coilability was assessed correctly in 93% (69 of 74) of target aneurysms (Table 2, Fig 6). The sensitivity, specificity, and positive and negative predictive values of multidetector CT angiography in predicting coilability were 94% (47 of 50 aneurysms), 92% (22 of 24 aneurysms), 96% (47 of 49 aneurysms), and 88% (22 of 25 aneurysms), respectively.
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Table 2. Assessment of Endovascular Treatment Options with Multidetector CT Angiography in the Target Aneurysms for Occlusive Treatment
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Figure 6a: Images in a patient with two potentially ruptured aneurysms, one situated at the posterior communicating artery and one originating from the carotid artery at its bifurcation into the anterior and medial cerebral arteries. (a) The sagittal volume-rendering technique image demonstrates a well-defined neck of the posterior communicating artery aneurysm (white arrow), which was considered coilable. The carotid aneurysm (black arrow) was considered not coilable because of the apparently absent neck. (b) Coronal road map DSA image. Coil placement was attempted in the carotid aneurysm, with the coil protruding into the vessel lumen (arrow). The coil was withdrawn, and a stent was placed across the wide neck of the aneurysm. (c) Coronal unsubtracted DSA image obtained after successful stent (arrowheads) placement and coil (white arrow) embolization of the carotid aneurysm. The posterior communicating artery aneurysm (black arrow) was successfully treated with coil placement; stent placement was not required.
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Figure 6b: Images in a patient with two potentially ruptured aneurysms, one situated at the posterior communicating artery and one originating from the carotid artery at its bifurcation into the anterior and medial cerebral arteries. (a) The sagittal volume-rendering technique image demonstrates a well-defined neck of the posterior communicating artery aneurysm (white arrow), which was considered coilable. The carotid aneurysm (black arrow) was considered not coilable because of the apparently absent neck. (b) Coronal road map DSA image. Coil placement was attempted in the carotid aneurysm, with the coil protruding into the vessel lumen (arrow). The coil was withdrawn, and a stent was placed across the wide neck of the aneurysm. (c) Coronal unsubtracted DSA image obtained after successful stent (arrowheads) placement and coil (white arrow) embolization of the carotid aneurysm. The posterior communicating artery aneurysm (black arrow) was successfully treated with coil placement; stent placement was not required.
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Figure 6c: Images in a patient with two potentially ruptured aneurysms, one situated at the posterior communicating artery and one originating from the carotid artery at its bifurcation into the anterior and medial cerebral arteries. (a) The sagittal volume-rendering technique image demonstrates a well-defined neck of the posterior communicating artery aneurysm (white arrow), which was considered coilable. The carotid aneurysm (black arrow) was considered not coilable because of the apparently absent neck. (b) Coronal road map DSA image. Coil placement was attempted in the carotid aneurysm, with the coil protruding into the vessel lumen (arrow). The coil was withdrawn, and a stent was placed across the wide neck of the aneurysm. (c) Coronal unsubtracted DSA image obtained after successful stent (arrowheads) placement and coil (white arrow) embolization of the carotid aneurysm. The posterior communicating artery aneurysm (black arrow) was successfully treated with coil placement; stent placement was not required.
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There were two false-positive findings (ie, aneurysms were considered coilable but were not amenable to endovascular therapy at preinterventional DSA). In one posterior communicating artery aneurysm that was rated coilable with multidetector CT angiography, microcatheter placement in the aneurysm was impossible because of a tortuous internal carotid artery below the volume imaged at multidetector CT angiography. Furthermore, one aneurysm of the pericallosal artery was rated as coilable with multidetector CT angiography, but a clip was placed because DSA demonstrated a relatively wide neck.
There were three false-negative ratings (ie, aneurysms were not considered coilable; however, successful endovascular treatment was finally completed). One posterior communicating artery aneurysm had a long and narrow configuration and was parallel to the course of the parent vessel (Fig 4). Thus, the aneurysm appeared to be broad based at multidetector CT angiography, but a narrow neck was seen at DSA. An aneurysm of the middle cerebral artery trifurcation appeared to have a vessel branch originating from the base of the aneurysm at multidetector CT angiography, but the branch originated below the neck level at DSA. Both aneurysms were successfully treated with coils. The third false-negative rating was assigned to a broad-based aneurysm of the posterior communicating artery. Despite the relatively wide neck, coils could be placed without stent placement.
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DISCUSSION
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Our results demonstrate that the diagnostic performance of multidetector CT angiography is comparable to that of DSA.
Furthermore, morphologic changes in aneurysms can be depicted precisely enough to enable identification of aneurysms that can be treated with coil embolization.
Compared with the results of previous studies in which single-section helical CT angiography and four–detector row CT angiography were used, our data suggest that use of 16–detector row CT angiography has better diagnostic performance in the detection of intracranial aneurysms. In a systematic review, a diagnostic accuracy of 89% per aneurysm was calculated for single-section CT angiography (21). In another meta-analysis, weighted sensitivity and specificity of 92.7% and 77.2%, respectively, were reported (11). The better diagnostic performance of multidetector CT angiography compared with that of single-section CT angiography in our cohort was in line with the findings of previous studies with smaller series of patients (22,23) and is likely related to a number of factors.
For single-section CT angiography, it has been shown that detection rates correlate with aneurysm size (21,24). Thus, spatial resolution is a limiting factor in aneurysm detection, and improved detection sensitivity may be expected with a reconstructed section thickness of 1.0 mm, as in our study.
Another advantage of 16–detector row CT angiography is the increased imaging speed. The arteriovenous transition time within the cerebral circulation is only a few seconds; therefore, in both single-section CT angiography and four–detector row CT angiography, arterial and venous structures have nearly equivalent attenuation (23). Aneurysms within the cavernous sinus or close to other venous structures may therefore be obscured by venous enhancement. In contrast, with 16–detector row CT angiography and bolus triggering, as used in our study, arterial and venous structures can be distinguished by their different attenuations.
Furthermore, with single-section CT angiography, the limited acquisition volume in the z direction has been responsible for radiologists missing aneurysms outside the imaged volume (11,12). The results obtained with a 16–detector row CT scanner suggest that this limitation may be overcome effectively.
The improved detection of intracranial aneurysms in our study compared with that in previous studies, including one in which four–detector row CT angiography was used (23), may also be due in part to improved data postprocessing. It has already been demonstrated for magnetic resonance angiography that the volume-rendering technique enables better visualization of intracranial aneurysms than does the maximum intensity projection algorithm (25). Thus, we included interactive volume-rendering technique display in addition to transverse source images, multiplanar reformations, and maximum intensity projection reconstructions.
When comparing multidetector CT angiography with DSA in the clinical scenario of subarachnoid hemorrhage, an important advantage of multidetector CT angiography is that information on the presence of aneurysms and their morphologic characteristics is available at the earliest possible time. The capability to view three-dimensional data sets obtained with multidetector CT angiography with different techniques (multiplanar reformation, maximum intensity projection, and volume-rendering technique) and unlimited angulations yields additional anatomic information that is difficult or time consuming to achieve with DSA.
If multidetector CT angiography is performed before DSA, it may also improve the diagnostic performance of DSA because additional DSA views may be targeted to questionable aneurysm locations determined from multidetector CT angiography findings. Thus, both methods may complement each other in diagnostic performance.
As 16–detector row CT angiography becomes more widely available, intracranial aneurysms will increasingly be diagnosed at institutions where aneurysm treatment is unavailable. Thus, it is important to determine whether multidetector CT angiography can be used to identify aneurysms that can be treated with endovascular coil placement so that patients can be directed to an institution where aneurysms can be treated endovascularly. In our study, coilability was correctly assessed on the basis of multidetector CT angiography findings in 69 (93%) of 74 aneurysms. We believe that multidetector CT angiography data sets can be used to select aneurysm treatment and thus avoid performing purely diagnostic DSA. Instead, multidetector CT angiography data sets can be transferred to specialized centers where physicians may decide on the further care of the patient.
Concerning the comparison between multidetector CT angiography and DSA with respect to aneurysm detection, a limitation of our study was that DSA was performed with knowledge of the multidetector CT angiography results. Thus, the DSA results reflect the combination of both modalities in most cases, and the diagnostic performance of DSA compared with that of multidetector CT angiography subsequently may have been overestimated in our study. On the other hand, incorporation of multidetector CT angiography into the combined reference standard biased the results in favor of multidetector CT angiography.
Because of the small number of aneurysms that were treated with neurosurgical clip placement, our findings cannot contribute to the question of whether diagnostic DSA is necessary prior to neurosurgical clip placement. However, this has been addressed in previous studies (26–28); meanwhile, large series of aneurysms have been treated with clips without preoperative DSA.
The definition of coilability used in our study may appear somewhat arbitrary. However, this judgment must incorporate both personal and institutional experience in the treatment of intracranial aneurysms. Thus, we did not use a fixed threshold of the neck-to-dome ratio; instead, we left the decision (based on this criterion) to the readers, taking into account their personal and institutional experience in aneurysm treatment. This means that our results cannot be generalized, and as a consequence, it appears important that treatment decisions be made by the interventional neuroradiologist on the basis of his or her individual postprocessing of source images.
With 16–detector row CT angiography, intracranial aneurysms can be diagnosed with a performance that is comparable to that of DSA and can be assessed with respect to endovascular treatment options.
We conclude that multidetector CT angiography, if available, can be used as the first step in the diagnostic work-up of patients with subarachnoid hemorrhage. If multidetector CT angiography depicts the ruptured aneurysm, a diagnostic-only DSA examination without the possibility to initiate endovascular treatment in the same session can be avoided, especially in patients with aneurysms that appear to be good candidates for coil placement at multidetector CT angiography. If multidetector CT angiography findings are negative, however, diagnostic DSA remains necessary, in our opinion, to rule out aneurysms not depicted by multidetector CT angiography or to depict alternative bleeding sources.
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ADVANCES IN KNOWLEDGE
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- The diagnostic performance of 16–detector row CT angiography in the detection of intracranial aneurysms was good, with sensitivity, specificity, and positive and negative predictive values of 98%, 100%, 100%, and 96%, respectively, on a per-patient basis; these values were equivalent to those obtained with digital subtraction angiography.
- With 16–detector row CT angiography, the possibility of using endovascular coils to treat intracranial aneurysms can be predicted with sensitivity, specificity, and positive and negative predictive values of 94%, 92%, 96%, and 88%, respectively.
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FOOTNOTES
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Abbreviations: DSA = digital subtraction angiography
Authors stated no financial relationship to disclose.
Author contributions:Guarantors of integrity of entire study, K.P., C.K.K., F.B.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, K.P., D.S., M. Fiebich; clinical studies, K.P., M. Fruth, C.H., M.S., A.B., F.B.; statistical analysis, K.P., C.K.K., D.S., M. Fiebich; and manuscript editing, K.P., C.K.K., D.S.
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ABSTRACT
INTRODUCTION
