Unruptured Arteriovenous Malformations in the Multidetector Computed Tomography Era: Frequency of Detection and Predictable Failures.

OBJECTIVES: While hemorrhage arising from ruptured arteriovenous malformations (AVMs) is usually evident on multidetector non-contrast computed tomography (NCCT), unruptured AVMs can be below the limits of detection. We performed a retrospective review of NCCT of patients with a proven diagnosis of unruptured AVM to determine if advances in CT technology have made them more apparent and what features predict their detection. MATERIAL AND METHODS: Twenty-five NCCTs met inclusion criteria of having angiography or MR proven AVM without hemorrhage, prior surgery, or other CNS disease. Demographic variables, clinical symptoms at presentation, abnormal CT imaging findings, attenuation of the superior sagittal sinus (SSS), and Spetzler-Martin grade of each AVM were recorded. We examined the relationship between AVM detection and SSS attenuation through Kruskal-Wallis test. Exploratory serial logistic principal components analysis was performed including demographics, symptoms, and CT features in the multivariate model. RESULTS: About 80% of the NCCTs showed an abnormality while 20% were normal. All those with an identifiable abnormality showed hyperdensity (80%). Logistic regression models indicate that clustered associations between several CT features, primarily calcifications, hyperdensity, and vascular prominence significantly predicted Spetzler-Martin grade (likelihood ratio 7.7, P = 0.006). SSS attenuation was significantly lower in subjects with occult AVMs when compared to those with CT abnormalities (median 47 vs. 55 HU, P < 0.04). CONCLUSION: Abnormal hyperdensity was evident in all detectable cases (80%) and multiple CT features were predictive of a higher Spetzler-Martin AVM grade. Moreover, SSS attenuation less than 50 HU was significantly correlated with a false-negative NCCT.

Economic impact of selective use of contrast for routine follow-up MRI of patients with multiple sclerosis.

BACKGROUND AND PURPOSE: Imaging and autopsy studies show intracranial gadolinium deposition in patients who have undergone serial contrast-enhanced MRIs. This observation has raised concerns when using contrast administration in patients who receive frequent MRIs. To address this, we implemented a contrast-conditional protocol wherein gadolinium is administered only for multiple sclerosis (MS) patients with imaging evidence of new disease activity on precontrast imaging. In this study, we explore the economic impact of our new MRI protocol. METHODS: We compared scanner time and Medicare reimbursement using our contrast-conditional methodology versus that of prior protocols where all patients received gadolinium. RESULTS: For 422 patients over 4 months, the contrast-conditional protocol amounted to 60% decrease in contrast injection and savings of approximately 20% of MRI scanner time. If the extra scanner time was used for performing MS follow-up MRIs in additional patients, the contrast-conditional protocol would amount to net revenue loss of $21,707 (∼3.7%). CONCLUSIONS: Implementation of a new protocol to limit contrast in MS follow-up MRIs led to a minimal decrease in revenue when controlled for scanner time utilized and is outweighed by other benefits, including substantial decreased gadolinium administration, increased patient comfort, and increased availability of scanner time, which depending on type of studies performed could result in additional financial benefit.

Calcifications of the Medial Choroid in the Velum Interpositum: An Unrecognized Site of Physiologic Calcifications Evident on Multidetector Computed Tomography.

OBJECTIVE: In adult patients undergoing multidetector computed tomography (CT) of the brain, we observed linear calcification along the deep venous system on thin (<3 mm) sagittal reconstructions. We found no reports of this finding in the velum interpositum (VI) in the imaging literature. We performed a focused examination of the VI on 2 autopsy cases and retrospectively reviewed sagittal, thin-section reconstructions of CT scans of 273 consecutive adult patients. METHODS: On 2 routine autopsies of the brain, sampling and histologic evaluation was performed of structures within the VI. A series of 273 unselected, sequentially acquired clinical head CT scans of patients ≥60 years old were retrospectively reviewed on a three-dimensional workstation to determine the incidence of this finding and its correlation with patient age. RESULTS: In 1 of the autopsy cases, calcified choroid plexus was identified in the region of the VI; this was also visible on the patient's premorbid CT. In the series of CT scans, linear calcification of ≥9 mm along the deep venous system was evident in 24.5% of cases. The median age of the cases without calcifications was 72 years, while the median age of the cases with calcification was 82; this difference was statistically significant (χ2, P < 0.0005). CONCLUSIONS: Evidence supports that linear midline calcification along the internal cerebral veins represents age-related, physiologic calcification of extraventricular choroid plexus within the VI. Awareness of this previously unreported finding on CT will prevent mistaking these physiologic calcifications on CT for evidence of underlying venous pathology. This finding provides additional support that the midline choroid plexus lies within the VI rather than in the third ventricle and expands our understanding of the detailed anatomy of the VI.

An Initiative to Reduce Unnecessary Gadolinium-Based Contrast in Multiple Sclerosis Patients.

OBJECTIVE: Patients with multiple sclerosis (MS) routinely undergo serial contrast-enhanced MRIs. Given concerns regarding tissue deposition of gadolinium-based contrast agents (GBCAs) and evidence that enhancement of lesions is only seen in patients with new disease activity on noncontrast imaging, we set out to implement a prospective quality improvement project whereby intravenous contrast would be reserved only for patients with evidence of new disease activity on noncontrast images. METHODS: To prospectively implement such a protocol, we leveraged our in-house computer-assisted detection (CAD) software and 3-D laboratory radiology technologists to perform real-time preliminary assessments of the CAD-processed T2 fluid attenuated inversion recovery (FLAIR) noncontrast images as a basis for deciding whether to inject contrast. Before implementation, we held multidisciplinary meetings with neurology, neuroradiology, and MR technologists and distributed surveys to objectively assess opinions and obstacles to clinical implementation. We evaluated reduction in GBCA utilization and technologist performance relative to final neuroradiologist interpretations. RESULTS: During a 2-month trial period, 153 patients were imaged under the new protocol. Technologists using the CAD software were able to identify patients with new or enlarging lesions on FLAIR images with 95% accuracy and 97% negative predictive value relative to final neuroradiologist interpretations, which allowed us to avoid the use of contrast and additional imaging sequences in 87% of patients. DISCUSSION: A multidisciplinary effort to implement a quality improvement project to limit contrast in MS patients receiving follow-up MRIs allowed for improved safety and cost by targeting patients that would benefit from the use of intravenous contrast in real-time.

Perilesional Hyperintensity on T1-Weighted Images in Intra-Axial Brain Masses other than Cavernous Malformations.

BACKGROUND AND PURPOSE: Hyperintensity on T1-weighted imaging in perilesional vasogenic edema has been reported as a useful sign for differentiating cavernous malformation from other hemorrhagic intra-axial masses. In this study, we investigated the frequency of perilesional hyperintensity on T1-weighted imaging in patients with intra-axial hemorrhagic and nonhemorrhagic brain masses. METHODS: The study was performed with the approval of the institutional review board. Magnetic resonance images of 218 patients with 282 intra-axial brain masses (129 metastases, 46 gliomas, 18 primary central nervous system lymphomas [PCNSLs], 25 intracerebral hemorrhages, 50 cavernous malformations, and 14 patients with brain abscesses) were evaluated. The signal intensity in perilesional area was qualitatively evaluated on T1-weighted sequences. In addition, signal intensity in perilesional area was quantitatively measured on T1-weighted sequences and normalized to the contralateral white matter. RESULTS: Hyperintensity on T1-weighted imaging in perilesional vasogenic edema was found in 12 (9%) of 129 metastases, 8 (16%) of 50 cavernous malformations, 1 (4%) in 25 nonneoplastic intracerebral hemorrhages, and none of the patients with high-grade glioma, PCNSL, or abscess. All of the lesions with perilesional hyperintensity showed either acute or subacute hemorrhage. Pairwise comparison of qualitative hyperintensity on T1-weighted imaging demonstrated no significant difference between the groups. Perilesional hyperintensity on T1-weighted imaging showed high specificity in both metastasis and cavernous malformation groups (94%). CONCLUSION: Perilesional hyperintensity on T1-weighted imaging is not limited to cavernous malformations and frequently evident with melanoma and other hemorrhagic metastasis to the brain. In our experience, it was not seen in high-grade glioma, PCNSL, and brain abscess.

The Many Faces of Cerebral Developmental Venous Anomaly and Its Mimicks: Spectrum of Imaging Findings.

Developmental venous anomalies (DVAs) are the most common cerebral vascular malformations and are usually found incidentally on neuroimaging studies. Despite the benign nature of DVAs, occasionally, they can be symptomatic. The objective of this article is to review the spectrum of imaging findings of DVAs on conventional and advanced imaging studies. In addition, neuroimaging findings of symptomatic DVAs as well as imaging mimicks will also be described to assist in the approach to differential diagnosis.

Absence of abnormal vessels in the subarachnoid space on conventional magnetic resonance imaging in patients with spinal dural arteriovenous fistulas.

Spinal dural arteriovenous fistula (DAVF) is an uncommon condition that can be difficult to diagnose. This often results in misdiagnosis and treatment delay. Although conventional MRI plays an important role in the initial screening for the disease, the typical MRI findings may be absent. In this article, the authors present a series of 4 cases involving patients with angiographically proven spinal DAVFs who demonstrated cord T2 prolongation on conventional MRI but without abnormal subarachnoid flow voids or enhancement. These cases suggest that spinal DAVF cannot be excluded in symptomatic patients with cord edema based on conventional MRI findings alone. Dynamic Gd-enhanced MR angiography (MRA) was successful in demonstrating abnormal spinal vasculature in all 4 cases. This limited experience provides support for the role of spinal MRA in patients with abnormal cord signal and symptoms suggestive of DAVF even when typical MRI findings of a DAVF are absent.

An approach to comparing accuracies of two FLAIR MR sequences in the detection of multiple sclerosis lesions in the brain in the absence of gold standard.

RATIONALE AND OBJECTIVES: The purpose of this study was to present a new methodology to compare accuracies of two imaging fluid attenuated inversion recovery (FLAIR) magnetic resonance sequences in detection of multiple sclerosis (MS) lesions in the brain in the absence of ground truth, and to determine whether the two sequences, which differed only in echo time (TE), have the same accuracy. MATERIALS AND METHODS: We acquired FLAIR images at TE(1) = 90 ms and TE(2) = 155 ms from 46 patients with MS (24-69 years old, mean 45.8, 15 males) and 11 healthy volunteers (23-54 years old, mean 37.1, 6 males). Seven experienced neuroradiologists segmented lesions manually on randomly presented corresponding TE(1) and TE(2) images. For every image pair, a "surrogate ground truth" for each TE was generated by applying probability thresholds, ranging from 0.3 to 0.5, to the weighted average of experts' segmentations. Jackknife alternative free-response receiver operating characteristic analysis was used to compare experts' performance on TE(1) and TE(2) images, using successively the TE(1)- and TE(2)-based ground truths. RESULTS: Supratentorially, there were significant differences in relative accuracy between the two sequences, ranging from 8.4% to 12.1%. In addition, we found a higher ratio of false positives to true positives for the TE(2) sequence using the TE(2) ground truth, compared to the TE(1) equivalent. Infratentorially, differences in the relative accuracy did not reach statistical significance. CONCLUSION: The presented methodology may be useful in assessing the value of new clinical imaging protocols or techniques in the context of replacing existing ones, when the absolute ground truth is not available, and in determining changes in disease progression in follow-up studies. Our results suggest that the sequence with shorter TE should be preferred because it generates relatively fewer false positives. The finding is consistent with results of previous computer simulation studies.

Cavernous hemangioma of the skull: surgical treatment without craniectomy.

The authors report the case of a large cranial cavernous hemangioma that was treated using embolization and craniotomy with preservation of the outer cranial table. A 3-year follow-up demonstrated no recurrence. Results in this case suggest that cavernous hemangiomas of the cranium may be safely and effectively treated without craniectomy in some cases.

Internal structure in pineal cysts on high-resolution magnetic resonance imaging: not a sign of malignancy.

OBJECT: In this paper, the authors' goal was to determine whether benign pineal cysts have smooth walls or internal structure on high-resolution MR imaging and to evaluate their imaging characteristics on FLAIR images. METHODS: The authors retrospectively reviewed the MR imaging findings in 60 consecutive patients who were reported to have pineal cysts over a 19-month period. Patients were identified retrospectively using a word search of radiology reports. Of these 60 patients, 24 with stable follow-up imaging or pathological proof of a pineal cyst were included in this study. In all cases, axial or sagittal FLAIR images were available, and in 10 of 24 patients the authors obtained sagittal images using fast imaging employing steady-state acquisition (FIESTA). For those cases in which FIESTA studies were obtained, the authors classified the cysts into 1 of 4 categories based on their appearance. Eighteen of 24 cases were performed with intravenous contrast. RESULTS: Of the 24 cases, 21 had signal intensity on FLAIR images that differed from that of CSF. Of the 10 cases with FIESTA, 6 had evidence of internal structure within the pineal cyst. The authors found it of interest that 20 of the 24 patients were female. CONCLUSIONS: Although the presence of a thin wall supports the diagnosis of a benign pineal cyst, fine internal septations or small internal cysts are common on high-resolution MR imaging and this finding should not be considered evidence of an underlying tumor. It is typical for pineal cysts to have relaxation times that differ from CSF as determined by FLAIR imaging.

Computed tomographic angiography as an adjunct to digital subtraction angiography for the pre-operative assessment of cerebral aneurysms.

OBJECTIVES: Computerized tomographic angiography (CTA) has emerged as a valuable diagnostic tool for the management of patients with cerebrovascular disease. The use of CTA in lieu of, or as an adjunct to, conventional cerebral angiography in the management of cerebral aneurysms awaits further experience. In this study, we evaluated the role of CTA specifically for the pre-operative assessment and planning of cerebral aneurysm surgery. PATIENTS AND METHODS: We reviewed the relevant neuroimaging of all patients treated at Dartmouth Hitchcock Medical Center between January, 2001 and December, 2004 with a diagnosis of cerebral aneurysm and diagnostic evaluation with both CTA and conventional digital subtraction angiography (DSA) using standard imaging protocols. 32 patients underwent both CTA and DSA during the study period for a total of 36 aneurysms. Images were independently re-assesed by two neurosurgeons for information valuable for pre-operative surgical planning. RESULTS: In 26 of 36 aneurysms (72%), the CTA was felt to provide the best image quality in defining the morphology of the aneurysm. In 14 aneurysms (39%), CTA provided clinically valuable anatomic detail not demonstrated on DSA, largely due to better visualization of parent and perforating vessel relationships at the aneurysm neck. There were no instances where a lesion was seen on DSA but missed on CTA. The DSA was of most clinical value in determining flow dynamics, such as the arterial supply of an anterior communicating artery aneurysm and distal anterior cerebral branches via the two A1 segments. CONCLUSION: CTA with three-dimensional reconstructions is a valuable adjunct to the preoperative evaluation of cerebral aneurysms. We advocate routine use of CTA in all patients in whom surgical aneurysm repair is planned, even when DSA has already been performed.

Computerized tomographic angiography for preoperative assessment of the superficial temporal artery for external carotid artery to internal carotid artery bypass: Case illustration.

INTRODUCTION: While catheter angiography has traditionally been used to assess the caliber and course of the superficial temporal artery prior to its use as a conduit for external carotid artery to internal carotid artery (EC-IC) bypass, computed tomographic angiography (CTA) has become increasingly used in the diagnostic assessment of cerebral vasculature. We demonstrate the application of CTA for evaluation of the superficial temporal artery as a vascular conduit for EC-IC bypass. CASE PRESENTATION: A female in the fourth decade of life presented with the chief complaint of headache. CTA of the Circle of Willis revealed an unruptured fusiform aneurysm of the M1 segment of the right middle cerebral artery (MCA). We performed CTA for the preoperative assessment of the STA for a putative EC-IC bypass procedure, and correlated this to conventional external carotid angiography. Reformatted CTA provided excellent surface visualization of the STA and its course in relationship to the cranial and zygomatic surfaces, and correlated well with findings on the conventional angiogram. CONCLUSION: CTA may eventually prove sufficient for use in assessing the STA in preparation for EC-IC bypass.

Utility of multislice computed tomography and reformatted images: identification of migratory intraventricular clot exacerbating obstructive hydrocephalus.

Multidetector CT has become widely available and with it the ability to rapidly create detailed reformatted images. Multiplanar images can be created depicting the anatomy in planes other than the traditional axial plane, using isotropic to near-isotropic data. It is important for both clinicians and radiologists to be aware of this capability in order to take advantage of such images. To illustrate the value of this type of imaging, the authors present a case of a third ventricular clot that migrated into the cerebral aqueduct exacerbating hydrocephalus.

Prototypical metal/polymer hybrid cerebral aneurysm clip: in vitro testing for closing force, slippage, and computed tomography artifact. Laboratory investigation.

OBJECT: The aim of this study was to explore the possibility that a hybrid aneurysm clip with polymeric jaws bonded to a metal spring could provide mechanical properties comparable to those of an all-metal clip as well as diminished artifacts on computed tomography (CT) scanning. METHODS: Three clips were created, and Clips I and 2 were tested for mechanical properties. Clip 1 consisted of an Elgiloy spring (a cobalt-chromium-nickel alloy) bonded to carbon fiber limbs; Clip 2 consisted of an Elgiloy spring with polymethylmethacrylate (PMMA) jaws; and Clip 3 consisted of PMMA limbs identical to those in Clip 2 but bonded to a titanium spring. Custom testing equipment was set up to measure the aneurysm clip clamping forces and slippage. Clips 2 and 3 were visualized in vivo using a 64-slice CT unit, and the slices were reformatted into 3D images. RESULTS: According to the testing apparatus, Clip 2 had a similar closing force but less slippage than three similar commercial aneurysm clips. The artifact from the cobalt alloy spring on CT scanning largely offset the advantage of the nonmetal PMMA limbs, which created no artifact. The hybrid titanium/PMMA clip (Clip 3) created very little artifact on CT and allowed visualization of the phantom through the limbs. CONCLUSIONS: It is feasible to build a potentially biocompatible hybrid cerebral aneurysm clip with mechanical properties that closely resemble those of conventional metallic clips. Further testing should be directed toward establishing the reliability and biocompatibility of such a clip and optimizing the contour and surface treatments of the polymer

Optimizing computed tomography to reduce artifacts from titanium aneurysm clips: an in vitro study. Technical note.

OBJECT: At many institutions digital subtraction angiography remains the standard imaging procedure for the postoperative evaluation of patients following placement of a cerebral aneurysm clip largely because of the artifacts produced by the clip on computed tomography (CT). The authors evaluated the effect of various imaging parameters on the quality of 3D reconstructions from CT scans while imaging a phantom to optimize the CT angiograms. METHODS: Using multidetector CT scanners with submillimeter detector collimation (0.625 mm), the authors scanned a silicone phantom with attached commercial aneurysm clips. Slice thickness, reconstruction overlap, kilovolt level, milliampere level, and pitch were varied. Neuroradiologists, who were blinded to the scanning parameters, rated the reconstructions for image quality and artifact reduction. RESULTS: Images of the titanium clip using 140 kV and 380 mA with 0.625-mm overlapping reconstructed slices provided excellent 3D visualization of both the clip and the aneurysm model, even when using two adjacent clips. CONCLUSIONS: Overlapping reconstructions combined with thin-section acquisition can provide detailed images of titanium clips and surrounding tissues without the use of low-pitch values.