Focal nodular hyperplasia: hepatobiliary enhancement patterns on gadoxetic-acid contrast-enhanced MRI.

OBJECTIVES: To assess the range of hepatobiliary enhancement patterns of focal nodular hyperplasia (FNH) after gadoxetic-acid injection, and to correlate these patterns to specific histological features. MATERIALS AND METHODS: FNH lesions, imaged with Gadoxetic-acid-enhanced MRI, with either typical imaging findings on T1, T2 and dynamic-enhanced sequences or histologically proven, were evaluated for hepatobiliary enhancement patterns and categorized as homogeneously hyperintense, inhomogeneously hyperintense, iso-intense, or hypo-intense-with-ring. Available histological specimens of FNHs (surgical resection or histological biopsy), were re-evaluated to correlate histological features with observed enhancement patterns. RESULTS: 26 FNHs in 20 patients were included; histology was available in six lesions (four resections, two biopsies). The following distribution of enhancement patterns was observed: 10/26 homogeneously hyperintense, 4/26 inhomogeneously hyperintense, 5/26 iso-intense, 6/26 hypointense-with-ring, and 1/26 hypointense, but without enhancing ring. The following histological features associated with gadoxetic-acid uptake were identified: number and type of bile-ducts (pre-existent bile-ducts, proliferation, and metaplasia), extent of fibrosis, the presence of inflammation and extent of vascular proliferation. CONCLUSION: FNH lesions can be categorized into different hepatobiliary enhancement patterns on Gadoxetic-acid-enhanced MRI, which appear to be associated with histological differences in number and type of bile-ducts, and varying the presence of fibrous tissue, inflammation, and vascularization.

MR liver imaging with Gd-EOB-DTPA: a delay time of 10 minutes is sufficient for lesion characterisation.

OBJECTIVES: To assess whether, in patients with normal liver function, a hepatobiliary delay time of 10 min after Gd-EOB-DTPA injection is sufficient for lesion characterisation. METHODS: In 42 consecutive patients with suspected focal liver lesions, dynamic MRI was performed after intravenous Gd-EOB-DTPA, followed by hepatobiliary phases at 5, 10 and 20 min. The following items were assessed at each hepatobiliary phase: parenchymal enhancement, contrast agent excretion in bile ducts, lesion enhancement characteristics (hypo-, iso-, or hyperintensity, rim enhancement, central non-enhancement), and contrast- and signal-to-noise ratios, separately for hypo- and hyperintense lesions. RESULTS: Following enhancement, parenchymal signal intensity increased significantly up to 10 min (86.3%, P < 0.001), and subsequently stabilised (86.5% after 20 min, P = 0.223). Biliary contrast agent excretion was first observed in 2, 32 and 5 patients after 5, 10 and 20 min respectively. Hepatobiliary lesion enhancement characteristics observed after 5 min persisted during later hepatobiliary phases. CNR and SNR ratios increased significantly (P < 0.05) up to 10 min after enhancement without further increase at 20 min, in hypo- and hyperintense lesions. CONCLUSIONS: If lesion characterisation is the primary reason for performing MRI, a hepatobiliary delay time of 10 min after Gd-EOB-DTPA injection is sufficient in patients with normal liver function. KEY POINTS : • Magnetic resonance imaging is now a first line of investigation of the liver. • Optimal CNR and SNR are achieved 10 min after Gd-EOB-DTPA injection. • Typical enhancement characteristics are observed early and do not change. • Ten-minute hepatobiliary delay is sufficient for characterisation of focal liver lesions.

Low impact of staging EUS for determining surgical resectability in esophageal cancer.

BACKGROUND: Although studies have shown that EUS has a high sensitivity and specificity for T and N staging, the value of EUS for staging tumors as resectable or nonresectable after CT of the chest and abdomen and US neck assessment, is largely unknown. This study was designed to assess the diagnostic value of EUS for determining resectability of esophageal cancer. METHODS: A retrospective analysis of all consecutive patients with esophageal carcinoma who underwent staging EUS, CT, and US. Tumors were considered resectable when there was no evidence of metastases or ingrowth in adjacent structures. Sensitivity, specificity, positive (PPV), and negative (NPV) predictive value of CT/US neck and CT/US neck + EUS for predicting surgical resectability were calculated. PPVs of CT/US alone and CT/US + EUS together were compared for assessing the diagnostic value of EUS. RESULTS: In total, 211 patients (155 men; mean age of 64 ± 9.4 years) were included, of which 176 (83 %) underwent all three staging investigations. Based on preoperative staging, 173 (82 %) patients were considered resectable and 38 (18 %) nonresectable. Of all 173 initially resectable patients, 145 were operated on. Of these patients, five (3.4 %) tumors were found nonresectable during surgery. Postoperative sensitivity, specificity, PPV, and NPV of CT/US and CT/US + EUS for predicting surgical resectability were 88 versus 87 %, 20 versus 40 %, 97 versus 98 %, and 6 versus 10 %, respectively. CONCLUSIONS: Although EUS adds to the specificity of preoperative esophageal cancer staging after CT chest and abdomen, and US of the neck have been performed, the overall added value of EUS is limited.

Accuracy of multislice liver CT and MRI for preoperative assessment of colorectal liver metastases after neoadjuvant chemotherapy.

INTRODUCTION: To determine the best imaging modality for preoperative detection, characterization and measurement of colorectal liver metastases (CRLM) after neoadjuvant chemotherapy (NAC). METHODS: A total of 79 lesions in 15 patients with CRLM were included. Following NAC, all patients received multislice liver CT (MSCT) and magnetic resonance imaging (MRI) that were scored by two observers for lesion number, type, diameter (mm) and segmental location. Intraoperative findings, histopathology and follow-up imaging were used as reference standard for surgically treated patients; non-surgical candidates underwent follow-up imaging. RESULTS: Lesion detection rate was similar for MSCT and MRI (76 and 80%, respectively, p = 0.648). Lesion characterization was significantly superior (p = 0.021) at MRI (89%, κ 0.747, p = 0.001) compared to MSCT (77%, κ 0.235, p = 0.005). Interobserver variability for diameter measurement was not significant at MRI (p = 0.909 [95% CI -1.245 to 1.395]), but significant at MSCT (p = 0.028 [95% CI -3.349 to -2.007]). Differences in diameter measurement were independent of observer (p = 0.131), and no statistical effect from imaging modality on diameter measurement was observed (p = 0.095). CONCLUSION: MRI is superior to MSCT in preoperative characterization and measurement of CRLM after NAC. Lesion detection rates for both modalities are comparable.

Radiofrequency ablation and chemotherapy versus chemotherapy alone for locally advanced pancreatic cancer (PELICAN): study protocol for a randomized controlled trial.

BACKGROUND: Approximately 80% of patients with locally advanced pancreatic cancer (LAPC) are treated with chemotherapy, of whom approximately 10% undergo a resection. Cohort studies investigating local tumor ablation with radiofrequency ablation (RFA) have reported a promising overall survival of 26-34 months when given in a multimodal setting. However, randomized controlled trials (RCTs) investigating the effect of RFA in combination with chemotherapy in patients with LAPC are lacking. METHODS: The "Pancreatic Locally Advanced Unresectable Cancer Ablation" (PELICAN) trial is an international multicenter superiority RCT, initiated by the Dutch Pancreatic Cancer Group (DPCG). All patients with LAPC according to DPCG criteria, who start with FOLFIRINOX or (nab-paclitaxel/)gemcitabine, are screened for eligibility. Restaging is performed after completion of four cycles of FOLFIRINOX or two cycles of (nab-paclitaxel/)gemcitabine (i.e., 2 months of treatment), and the results are assessed within a nationwide online expert panel. Eligible patients with RECIST stable disease or objective response, in whom resection is not feasible, are randomized to RFA followed by chemotherapy or chemotherapy alone. In total, 228 patients will be included in 16 centers in The Netherlands and four other European centers. The primary endpoint is overall survival. Secondary endpoints include progression-free survival, RECIST response, CA 19.9 and CEA response, toxicity, quality of life, pain, costs, and immunomodulatory effects of RFA. DISCUSSION: The PELICAN RCT aims to assess whether the combination of chemotherapy and RFA improves the overall survival when compared to chemotherapy alone, in patients with LAPC with no progression of disease following 2 months of systemic treatment. TRIAL REGISTRATION: Dutch Trial Registry NL4997 . Registered on December 29, 2015. ClinicalTrials.gov NCT03690323 . Retrospectively registered on October 1, 2018.

Profiles of US and CT imaging features with a high probability of appendicitis.

OBJECTIVES: To identify and evaluate profiles of US and CT features associated with acute appendicitis. METHODS: Consecutive patients presenting with acute abdominal pain at the emergency department were invited to participate in this study. All patients underwent US and CT. Imaging features known to be associated with appendicitis, and an imaging diagnosis were prospectively recorded by two independent radiologists. A final diagnosis was assigned after 6 months. Associations between appendiceal imaging features and a final diagnosis of appendicitis were evaluated with logistic regression analysis. RESULTS: Appendicitis was assigned to 284 of 942 evaluated patients (30%). All evaluated features were associated with appendicitis. Imaging profiles were created after multivariable logistic regression analysis. Of 147 patients with a thickened appendix, local transducer tenderness and peri-appendiceal fat infiltration on US, 139 (95%) had appendicitis. On CT, 119 patients in whom the appendix was completely visualised, thickened, with peri-appendiceal fat infiltration and appendiceal enhancement, 114 had a final diagnosis of appendicitis (96%). When at least two of these essential features were present on US or CT, sensitivity was 92% (95% CI 89-96%) and 96% (95% CI 93-98%), respectively. CONCLUSION: Most patients with appendicitis can be categorised within a few imaging profiles on US and CT. When two of the essential features are present the diagnosis of appendicitis can be made accurately.

Grading of carotid artery stenosis with multidetector-row CT angiography: visual estimation or caliper measurements?

To assess the optimal method for grading carotid artery stenosis with computed tomographic angiography (CTA), we compared visual estimation to caliper measurements, and determined inter-observer variability and agreement relative to digital subtraction angiography (DSA). We included 46 patients with symptomatic carotid stenosis for whom CTA and DSA of 55 carotids was available. Stenosis quantification by CTA using visual estimation (CTA(VE)) (method 1) was compared with caliper measurements using subjectively optimized wide window settings (method 2) or predefined contrast-dependent narrow window settings (method 3). Measurements were independently performed by two radiologists and two residents. To determine accuracy and inter-observer variability, we calculated linear weighted kappa, performed a Bland-Altman analysis and calculated mean difference (bias) and standard deviation of differences (SDD). For inter-observer variability, kappa analysis was "very good" (0.85) for expert observers using CTA(VE) compared with "good" (0.61) for experts using DSA. Compared with DSA, method 1 led to overestimation (bias 5.8-8.0%, SDD 10.6-14.4), method 3 led to underestimation (bias -6.3 to -3.0%, SDD 13.0-18.1). Measurement variability between DSA and visual estimation on CTA (SDD 11.5) is close to the inter-observer variability of repeated measurements on DSA that we found in this study (SDD 11.6). For CTA of carotids, stenosis grading based on visual estimation provides better agreement to grading by DSA compared with stenosis grading based on caliper measurements.

The Atlanta Classification of acute pancreatitis revisited.

BACKGROUND: In a complex disease such as acute pancreatitis, correct terminology and clear definitions are important. The clinically based Atlanta Classification was formulated in 1992, but in recent years it has been increasingly criticized. No formal evaluation of the use of the Atlanta definitions in the literature has ever been performed. METHODS: A Medline literature search sought studies published after 1993. Guidelines, review articles and their cross-references were reviewed to assess whether the Atlanta or alternative definitions were used. RESULTS: A total of 447 articles was assessed, including 12 guidelines and 82 reviews. Alternative definitions of predicted severity of acute pancreatitis, actual severity and organ failure were used in more than half of the studies. There was a large variation in the interpretation of the Atlanta definitions of local complications, especially relating to the content of peripancreatic collections. CONCLUSION: The Atlanta definitions for acute pancreatitis are often used inappropriately, and alternative definitions are frequently applied. Such lack of consensus illustrates the need for a revision of the Atlanta Classification.

[Imaging in the diagnosis of colorectal liver metastases and extrahepatic abnormalities]. / Beeldvormende diagnostiek van colorectale levermetastasen en extrahepatische afwijkingen.

Imaging using ultrasonography, spiral CT, MRI and 18F-fluorodeoxyglucose positron emission tomography (FDG-PET), plays a major role at two situations during the management of patients with colorectal liver metastases: (a) at the time of the diagnosis and treatment of the primary colorectal tumour, and (b) during the follow-up for the detection of liver metastases and assessing the resectability of these metastases. At the time of the diagnosis and the treatment of the primary tumour, imaging comprising spiral CT or MRI to detect and characterize liver lesions is considered to be the modality of choice. Due to their low prevalence, imaging for the evaluation of lung metastases may be limited to conventional chest radiography. For evaluation of the extrahepatic abnormalities, abdominal and chest CT may be performed in combination with CT of the liver; alternatively a FDG-PET may be performed. During the follow-up of patients treated for colorectal carcinoma, ultrasonography is the most important imaging modality. However, if the liver cannot be adequately imaged by ultrasonography, if there is a raised level ofcarcinoembryonic antigen or irresectability cannot be determined, additional CT or MRI examination will result in more information.

Reproducibility of quantitative CT brain perfusion measurements in patients with symptomatic unilateral carotid artery stenosis.

BACKGROUND AND PURPOSE: To establish intraobserver and interobserver variability for regional measurement of CT brain perfusion (CTP) and to determine whether reproducibility can be improved by calculating perfusion ratios. MATERIALS AND METHODS: CTP images were acquired in 20 patients with unilateral symptomatic carotid artery stenosis (CAS). We manually drew regions of interest (ROIs) in the cortical flow territories of the anterior (ACA), middle (MCA), and posterior (PCA) cerebral arteries and the basal ganglia in each hemisphere; recorded cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT); and calculated ratios of perfusion values between symptomatic and asymptomatic hemisphere. We assessed intraobserver and interobserver variability by performing a Bland-Altman analysis of the relative differences between 2 observations and calculated SDs of relative differences (SDD(rel)) as a measure of reproducibility. We used an F test to assess significance of differences between SDD(rel) of absolute CTP values and CTP ratios, and the Levine test to compare the 4 perfusion territories. RESULTS: MTT was the most reproducible parameter (SDD(rel)

Evidence-base guideline on management of colorectal liver metastases in the Netherlands.

A dutch national evidence-based guideline on the diagnosis and treatment of patients with colorectal liver metastases has been developed. The most important recommendations are as follows. For synchronous liver metastases, spiral computed tomography (CT) or magnetic resonance imaging (MRI) should be used as imaging. For evaluation of lung metastases, imaging can be limited to chest radiography. For detection of metachronous liver metastases, ultrasonography could be performed as initial modality if the entire liver is adequately visualised. In doubtful cases or potential candidates for surgery, CT or MRI should be performed as additional imaging. For evaluation of extrahepatic disease, abdominal and chest CT could be performed. Fluorodeoxyglucose positron emission tomography could be valuable in patients selected for surgery based on CT (liver/abdomen/chest), for identifying additional extrahepatic disease. Surgical resection is the treatment of choice with a five-year survival of 30 to 40%. Variation in selection criteria for surgery is caused by inconclusive data in the literature concerning surgical margins.

[Ancillary diagnostic imaging is useful if there is atypical evidence of appendicitis]. / Aanvullend beeldvormend onderzoek is nuttig bij atypische aanwijzingen voor appendicitis.

Patients with an atypical presentation of acute appendicitis may benefit from ancillary diagnostic imaging, especially CT. The literature shows a decrease of the number of negative appendectomies with this approach, and other causes are diagnosed in about one third of the patients. In addition, costs were reduced. Ultrasonography is a good alternative in pregnant women and in women with suspected gynaecological pathology.

Evaluation of motion correction for clinical dynamic contrast enhanced MRI of the liver.

Motion correction of 4D dynamic contrast enhanced MRI (DCE-MRI) series is required for diagnostic evaluation of liver lesions. The registration, however, is a challenging task, owing to rapid changes in image appearance. In this study, two different registration approaches are compared; a conventional pairwise method applying mutual information as metric and a groupwise method applying a principal component analysis based metric, introduced by Huizinga et al (2016). The pairwise method transforms the individual 3D images one by one to a reference image, whereas the groupwise registration method computes the metric on all the images simultaneously, exploiting the temporal information, and transforms all 3D images to a common space. The performance of the two registration methods was evaluated using 70 clinical 4D DCE-MRI series with the focus on the liver. The evaluation was based on the smoothness of the time intensity curves in lesions, lesion volume change after deformation and the smoothness of spatial deformation. Furthermore, the visual quality of subtraction images (pre-contrast image subtracted from the post contrast images) before and after registration was rated by two observers. Both registration methods improved the alignment of the DCE-MRI images in comparison to the non-corrected series. Furthermore, the groupwise method achieved better temporal alignment with smoother spatial deformations than the pairwise method. The quality of the subtraction images was graded satisfactory in 32% of the cases without registration and in 77% and 80% of the cases after pairwise and groupwise registration, respectively. In conclusion, the groupwise registration method outperforms the pairwise registration method and achieves clinically satisfying results. Registration leads to improved subtraction images.

Level set based cerebral vasculature segmentation and diameter quantification in CT angiography.

A level set based method is presented for cerebral vascular tree segmentation from computed tomography angiography (CTA) data. The method starts with bone masking by registering a contrast enhanced scan with a low-dose mask scan in which the bone has been segmented. Then an estimate of the background and vessel intensity distributions is made based on the intensity histogram which is used to steer the level set to capture the vessel boundaries. The relevant parameters of the level set evolution are optimized using a training set. The method is validated by a diameter quantification study which is carried out on phantom data, representing ground truth, and 10 patient data sets. The results are compared to manually obtained measurements by two expert observers. In the phantom study, the method achieves similar accuracy as the observers, but is unbiased whereas the observers are biased, i.e., the results are 0.00+/-0.23 vs. -0.32+/-0.23 mm. Also, the method's reproducibility is slightly better than the inter-and intra-observer variability. In the patient study, the method is in agreement with the observers and also, the method's reproducibility -0.04+/-0.17 mm is similar to the inter-observer variability 0.06+/-0.17 mm. Since the method achieves comparable accuracy and reproducibility as the observers, and since the method achieves better performance than the observers with respect to ground truth, we conclude that the level set based vessel segmentation is a promising method for automated and accurate CTA diameter quantification.

Imaging and treatment of patients with colorectal liver metastases in the Netherlands: a survey.

BACKGROUND: Clinical experience has highlighted the absence of a uniform approach to the management of patients with colorectal liver metastases in the Netherlands. METHODS: A written survey on the diagnosis and treatment of patients with colorectal liver metastases was sent to all 107 chairmen of oncology committees in each hospital. Questions were asked concerning: specialists involved in decision-making, availability and existence of guidelines and meetings, factors that needed to be improved, information regarding the diagnostic work-up of liver metastases, detailed techniques of ultrasonography (US), computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET), factors influencing resectability, types of surgery performed, the use of (neo)adjuvant chemotherapy, portal vein embolisation performance, considering isolated hepatic perfusion (IHP) or local ablation as treatment options, actual performance of local ablation and the use of systemic as well as regional chemotherapy. RESULTS: Response rate was 68% (73/107). Specialists involved in the management were mostly surgeons (70), medical oncologists (66) and radiologists (42). Factors that needed to be improved, as indicated by responders, were the absence of 1) guidelines; 2) registration of patients and 3) guidelines for radiofrequency ablation (RFA). Diagnostic work-up of synchronous liver metastases occurred in 71 hospitals, (by US in 69 and by CT in 2). For the work-up of metachronous liver metastases, US was used as initial modality in 14, CT in 2 hospitals, and 57 hospitals used one or the other (mainly US). As additional modality, CT was performed (71) and to a lesser extent MRI (38) or PET (22). Diagnostic laparoscopy and biopsy were performed incidentally. The choice for an imaging modality was mostly influenced by the literature, and to a lesser extent by the availability and by costs, personnel and waiting lists. Substantial variation exists in the US, CT, MRI and PET techniques. The absence of extrahepatic disease and the clinical condition were considered as the most important factors influencing resectability. Surgery was performed in 30 hospitals; hemihepatectomy in 25, segment resection in 27, multisegment resection in 23, wedge excision in 27 and combination of resection and RF A in 18 institutions. In 52 hospitals (neo)adjuvant chemotherapy was administrated to improve surgical results, partly (35%) in trials. In nine hospitals portal vein embolisation was performed, with the volume of the remnant liver as the most important factor. Local ablative techniques were considered as a treatment option in 48 hospitals and actually performed in 16 hospitals, without clearly defined indications. Experimental IHP was considered a treatment option by 45 (62%) responders, irrespective whether this treatment was available at their centre. Patients with extensive metastases received systemic chemotherapy in all 73 hospitals and regional chemotherapy in ten hospitals. CONCLUSION: This survey shows substantial variation in the diagnostic and therapeutic work-up of patients with colorectal liver metastases. This variation reflects either under- or over-utilisation of diagnosis and treatment options. Evidence-based guidelines taking into account the available evidence, experience and availability can solve this variation.

[Timing and choice of intervention in necrotising pancreatitis]. / Timing en keuze van interventie bij necrotiserende pancreatitis.

Three patients, men aged 49, 62 and 33 years, were admitted with acute abdominal symptoms due to necrotising pancreatitis. They underwent multiple interventions during a hospital stay of several months, but ultimately recovered completely. In case of infected (peri-)pancreatic necrosis, intervention is required. Good clinical judgement in the differentiation between the septic inflammatory-response syndrome, sepsis and infected necrosis as the cause of the clinical condition is important. Because of the different intervention strategies, treatment by a team comprising a radiologist, gastroenterologist, intensive care specialist and gastrointestinal surgeon is required. Randomised studies on intervention in infected pancreatic necrosis are lacking. In 2002, to improve the treatment of patients with acute (necrotising) pancreatitis via a combination of research, consultation and centralisation, the Dutch Acute Pancreatitis Study Group was formed.

Planning of liver surgery using three dimensional imaging techniques.

In the simplified Couinaud classification, in which the liver is divided into eight segments, each supplied by a central vasculo-biliary sheath, little attention is given to the high prevalence of anatomical variations which occur, especially in the right hemiliver. Using volumetric acquisition techniques, such as magnetic resonance imaging or spiral computed tomography scanning, detailed insight into the individual segmental anatomy can now be obtained in a non-invasive manner. The significance of this anatomical insight lies in the planning of anatomical resections, whereby the relationship between tumour and individual segmental anatomy can be depicted in a three-dimensional format. As such, three dimensional (3D) liver imaging helps to design an individualised resection, tailored to the topographical relationship between individual segmental anatomy and tumour tissue present. Three dimensional liver imaging is of most practical value if a resection of one or more segments or sectors is considered, especially in the right hemiliver. In these cases, 3D liver imaging can demonstrate the precise location of the scissuras to the surgeon pre-operatively.

A method for sonographic counting of the lower vertebral bodies in newborns and infants.

PURPOSE: To determine whether the lumbosacral junction of the vertebral column can be identified with sonography in newborns and infants and thus serve as a method for counting the lumbar and sacral vertebral bodies. METHODS: In 32 newborns and infants, the number of ossified vertebral bodies distal to the lumbosacral junction was counted with sonography and radiography. RESULTS: Sonographic and radiographic findings agreed in 29 of 32 examinations (91%). CONCLUSIONS: The lordotic transition at the lumbosacral junction can be identified with sonography in the majority of newborns and infants, allowing intraspinal structures to be related to a specific vertebral level.

Surgical anatomy of the cerebral arteries in patients with subarachnoid hemorrhage: comparison of computerized tomography angiography and digital subtraction angiography.

OBJECT: The purpose of this study was to compare computerized tomography (CT) angiography and digital subtraction (DS) angiography studies in patients with subarachnoid hemorrhage (SAH) to assess their vascular anatomy relevant to cerebral aneurysm surgery. METHODS: From a prospective series of 100 patients with SAH, the authors selected 73 patients whose CT angiography studies were of adequate quality and in whom DS angiography of both carotid arteries had been performed. Eleven patients with no DS angiographic studies of the vertebrobasilar artery were only evaluated for the anterior half of the circle of Willis. Anterior communicating arteries (ACoAs), both precommunicating anterior cerebral arteries (A1 segments), both posterior communicating arteries (PCoAs), and both precommunicating posterior cerebral arteries (P1 segments) were assessed on CT angiography and DS angiography by two independent observers. CONCLUSIONS: Computerized tomography angiography compares well with DS angiography for visualizing normal-sized arteries, and is superior for visualizing ACoAs and hypoplastic A1 and P, segments. Important preoperative aspects such as dominant A1 segments and PCoAs are equally well seen using either modality. Neither method enabled the authors to visualize more than 50% of PCoAs. Use of CT angiography can provide the required preoperative anatomical information for aneurysm surgery in most patients with SAH.