Benign Enhancing Foramen Magnum Lesions.

Benign enhancing foramen magnum lesions have been previously described as T2-hyperintense small, enhancing lesions located posterior to the intradural vertebral artery. We present the first case with pathologic correlation. These lesions are fibrotic nodules adhering to the spinal accessory nerve. While they can enlarge with time on subsequent examinations, on the basis of the imaging characteristics and location, they do not necessitate surgical resection.

Evaluation of Lower-Dose Spiral Head CT for Detection of Intracranial Findings Causing Neurologic Deficits.

BACKGROUND AND PURPOSE: Despite the frequent use of unenhanced head CT for the detection of acute neurologic deficit, the radiation dose for this exam varies widely. Our aim was to evaluate the performance of lower-dose head CT for detection of intracranial findings resulting in acute neurologic deficit. MATERIALS AND METHODS: Projection data from 83 patients undergoing unenhanced spiral head CT for suspected neurologic deficits were collected. Cases positive for infarction, intra-axial hemorrhage, mass, or extra-axial hemorrhage required confirmation by histopathology, surgery, progression of findings, or corresponding neurologic deficit; cases negative for these target diagnoses required negative assessments by two neuroradiologists and a clinical neurologist. A routine dose head CT was obtained using 250 effective mAs and iterative reconstruction. Lower-dose configurations were reconstructed (25-effective mAs iterative reconstruction, 50-effective mAs filtered back-projection and iterative reconstruction, 100-effective mAs filtered back-projection and iterative reconstruction, 200-effective mAs filtered back-projection). Three neuroradiologists circled findings, indicating diagnosis, confidence (0-100), and image quality. The difference between the jackknife alternative free-response receiver operating characteristic figure of merit at routine and lower-dose configurations was estimated. A lower 95% CI estimate of the difference greater than -0.10 indicated noninferiority. RESULTS: Forty-two of 83 patients had 70 intracranial findings (29 infarcts, 25 masses, 10 extra- and 6 intra-axial hemorrhages) at routine head CT (CT dose index = 38.3 mGy). The routine-dose jackknife alternative free-response receiver operating characteristic figure of merit was 0.87 (95% CI, 0.81-0.93). Noninferiority was shown for 100-effective mAs iterative reconstruction (figure of merit difference, -0.04; 95% CI, -0.08 to 0.004) and 200-effective mAs filtered back-projection (-0.02; 95% CI, -0.06 to 0.02) but not for 100-effective mAs filtered back-projection (-0.06; 95% CI, -0.10 to -0.02) or lower-dose levels. Image quality was better at higher-dose levels and with iterative reconstruction (P < .05). CONCLUSIONS: Observer performance for dose levels using 100-200 eff mAs was noninferior to that observed at 250 effective mAs with iterative reconstruction, with iterative reconstruction preserving noninferiority at a mean CT dose index of 15.2 mGy.

Increased Curvature of the Tentorium Cerebelli in Idiopathic Intracranial Hypertension.

BACKGROUND AND PURPOSE: Transverse sinus effacement is detectable on MRV examinations in almost all patients with idiopathic intracranial hypertension. This effacement of the transverse sinus is presumed to be mediated by elevation of intracranial pressure, resulting in compression and inward collapse of the dural margins of the sinus. We sought to establish whether supratentorial broad-based downward deformity of the tentorium might explain transverse sinus effacement in idiopathic intracranial hypertension. MATERIALS AND METHODS: MRV examinations of 53 adult patients with idiopathic intracranial hypertension were reviewed retrospectively and compared with 58 contemporaneously acquired controls. The curvature of the tentorium with reference to a line connecting the transverse sinus laterally with the confluence of the tentorial leaves medially was calculated as a segment of a circle. The height and area of the segment and the angle subtended by the midpoint of the tentorium from the falx were calculated. RESULTS: The height and area of the segment described by the chord connecting the transverse sinus with the apex of the tentorial confluence and subtended midtentorial angle were greater in the idiopathic intracranial hypertension group; this finding supports the hypothesis that increased tentorial bowing is present in idiopathic intracranial hypertension. CONCLUSIONS: Increased bowing of the tentorium in patients with idiopathic intracranial hypertension compared with controls is a new observation, lending itself to new hypotheses on the nature and localization of elevated intracranial pressure in idiopathic intracranial hypertension. Bowing of the tentorium may play a part in distorting the contour of the transverse sinuses, resulting, at least in part, in the effacement of the transverse sinuses in idiopathic intracranial hypertension.

Transverse Sinus Stenosis Is the Most Sensitive MR Imaging Correlate of Idiopathic Intracranial Hypertension.

BACKGROUND AND PURPOSE: Patients with idiopathic intracranial hypertension have transverse sinus stenosis on gadolinium-bolused MRV, but other MR imaging signs are less consistently seen. Our aim was to demonstrate that transverse sinus stenosis could be identified on conventional MR imaging, and this identification would allow improved diagnostic sensitivity to this condition. MATERIALS AND METHODS: MR imaging and MRV images from 63 patients with idiopathic intracranial hypertension and 96 controls were reviewed by using 3 independent procedures. MRV images were graded for the presence and degree of stenosis of the transverse sinus. Postgadolinium coronal T1-weighted sequences were evaluated independent of MRV. The dimensions of the proximal and distal transverse sinus were measured from the MRV examinations, and the cross-sectional area of the transverse sinus was calculated. Correlation among the 3 modes of evaluation of the transverse sinus was conducted by using Wilcoxon/Kruskal-Wallis, Pearson, and Spearman ρ nonparametric statistical techniques. RESULTS: Transverse sinus stenosis was identified bilaterally on MRV in 94% of patients with idiopathic intracranial hypertension and in 3% of controls. On coronal T1 postgadolinium MR images, transverse sinus stenosis was identified in 83% of patients with idiopathic intracranial hypertension and 7% of controls. Previously described MR imaging signs of intracranial hypertension were identified in 8%-61% of patients with idiopathic intracranial hypertension. Correlation among the 3 modes of evaluation was highly significant (P < .0001). CONCLUSIONS: Even without the assistance of an MRV sequence, neuroradiologists can validly identify bilateral transverse sinus stenosis in patients with intracranial hypertension more reliably than other previously described MR imaging findings in this condition. We conclude that transverse sinus stenosis is the most useful and sensitive imaging indicator of this disease state.

Prevalence of incidental narrowing of the superior segment of the internal jugular vein in patients without multiple sclerosis.

PURPOSE: Internal jugular vein (IJV) narrowing superiorly is likely relatively frequent. IJV narrowing has been proposed as a potential pathophysiologic component for multiple sclerosis (MS). Our purpose was to investigate the prevalence of incidental superior IJV narrowing in patients imaged with neck computed tomography angiography (CTA) for reasons unrelated to IJV pathology or MS. METHODS: We retrospectively identified 164 consecutive adult patients who had undergone neck CTA in which at least one IJV superior segment was opacified (158 right, 155 left IJVs). At the narrowest point of the upper IJV, each IJV was assessed for dominance, graded (shape and narrowing), measured (diameter and area), and located (axially and craniocaudally). Associations were analyzed using Spearman rank correlations (p < 0.05 significant). Medical records were reviewed for MS. RESULTS: Among 164 patients, at least one IJV was: absent/pinpoint in 15 % (25/164), occluded/nearly occluded in 26 % (43/164). Shape, narrowing, and the three measurements all correlated with each other (all p < 0.01). Lateral location with respect to C1 transverse foramen correlated with subjectively and objectively smaller IJVs (p < 0.01). The most common craniocaudal location was at the C1 transverse process (79 % (125/158) of right and 81 % (126/155) of left IJVs). No patient had a diagnosis of MS. CONCLUSIONS: The appearance of the superior IJV is variable, with an occlusive/near-occlusive appearance present in approximately one-quarter of patients without known MS undergoing CTA. Radiologists should be aware of and cautious to report or ascribe clinical significance to this frequent anatomic variant.

Cerebral venous sinus density on noncontrast CT correlates with hematocrit.

BACKGROUND AND PURPOSE: A positive correlation between HCT and CT attenuation of intravascular blood has long been assumed but has never been established by using substantial patient numbers and modern CT equipment. The purpose of this study was to determine whether apparent increased attenuation on CT in cerebral venous sinuses can be attributed to hemoconcentration alone and to assess whether sinus thrombosis can be differentiated from hemoconcentrated blood based on attenuation values alone. MATERIALS AND METHODS: We measured HUs in a region of interest within the confluence of dural venous sinuses in 166 unenhanced head CTs and correlated these data with HCT and HGB values in male and female patients aged 2 to 100 years. We then compared these data with similar measurements in 8 patients with recent venous sinus thrombosis. Two-tailed t test and linear regression analyses were performed to evaluate HGB and HCT between groups and with measured CT attenuation of intravascular blood, respectively. RESULTS: A statistically significant relationship was noted between both HCT and HGB with CT attenuation. Seven of 8 patients with sinus thrombosis had attenuation values >70, but none of the normal subjects had HUs >70. CONCLUSIONS: Hemoconcentration correlates with CT attenuation in cerebral venous sinuses. Our findings suggest that comparing the ratio of HUs to HCT may be useful in gauging concern for sinus thrombosis.

MR imaging in comatose survivors of cardiac resuscitation.

BACKGROUND AND PURPOSE: The prognosis of comatose survivors is determined by clinical examination. Early laboratory indicators of poor prognosis (such as evoked potentials) have low sensitivity. The role of MR imaging as a confirmatory study was investigated. METHODS: We studied fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted (DW) imaging in 10 patients comatose after cardiac arrest. RESULTS: None of the 10 comatose patients had myoclonus status epilepticus or fixed, dilated pupils on neurologic examination, and none had abnormal somatosensory-evoked potentials. Eight patients showed diffuse signal abnormalities, predominantly in the cerebellum (n = 5), the thalamus (n = 8), the frontal and parietal cortices (n = 8), and the hippocampus (n = 9). One patient showed normal MR imaging results, and one patient had abnormalities in the thalamus and cerebellum and minimal abnormality on DW images; both later awakened. None of the patients with abnormal cortical structures on FLAIR MR images recovered beyond a severely disabled state. CONCLUSION: MR imaging in comatose survivors may parallel the pathologic findings in severe anoxic-ischemic injury, and extensive abnormalities may indicate little to no prospects for recovery. If confirmed, MR imaging may have a role as a prognosticating test in anoxic-ischemic coma.

Magnetic resonance angiography at 3.0 Tesla: initial clinical experience.

Magnetic resonance (MR) angiography has undergone significant development over the past decade. It has gone from being a novelty application of MR with limited clinical use to replacing catheter angiography in some clinical applications. One of the principal limitations inherent to all MR angiographic techniques is that they remain signal limited when pushed to the limits of higher resolution and short acquisition time. Developments in magnetic gradient hardware, coil design, and pulse sequences now are well optimized for MR angiography obtained at 1.5-T main magnetic field (B-field) strength, with acquisition times and imaging matrix size near their optimal limits, respectively. Recently, the United States Food and Drug Administration (FDA) approved use of clinical magnetic resonance imaging with main magnetic field strengths of up to 4 T. Before FDA approval, use of MR with magnetic field strengths much greater than 1.5 T was essentially reserved for investigational or research applications. The main advantage of high B-field imaging is a significant improvement in the signal-to-noise ratio (SNR), which increases in an approximately linear fashion with field strength in the range of 1.5 to 3.0 T. This increased SNR is directly available when performing MR angiographic acquisitions at higher magnetic field strengths, allowing for better resolution and conspicuity of vessels with similar acquisition times. Little has been reported on the benefits of performing MR angiography at magnetic field strengths >1.5 T. The purpose of this article is to summarize our current experience with intracranial and cervical MR angiographic techniques at 3.0 T.

Imaging of hydrogel episcleral buckle fragmentation as a late complication after retinal reattachment surgery.

Hydrogel encircling bands were introduced in the early 1980s as a product that was superior to bands composed of silicone rubber or silicone sponge for the surgical treatment of retinal detachment. Late complications consisting of orbital swelling and diplopia requiring band removal began to be reported in the early 1990s. Pathologic studies of these expanded fragments of hydrogel material after removal showed in vivo hydrolysis with foreign body reaction and dystrophic calcification. We report the imaging findings in five patients in whom this late complication developed. Hydrogel fragmentation has a characteristic imaging appearance consisting of a circumferential orbital mass associated with rim enhancement. This appearance should prompt inquiries regarding previous scleral buckle procedures with hydrogel bands. Familiarity with this appearance will avoid misinterpretation and unwarranted biopsy before band removal.

Mild cognitive impairment and Alzheimer disease: regional diffusivity of water.

PURPOSE: To compare the regional diffusivity of water in the brains of normally aging elderly people and patients with mild cognitive impairment (MCI) or Alzheimer disease. MATERIALS AND METHODS: Magnetic resonance images were obtained in 21 patients with Alzheimer disease, 19 patients with MCI, and 55 normally aging elderly control subjects without evidence of cognitive impairment. Regions of interest were drawn to compare the apparent diffusion coefficient (ADC) and the anisotropy index (AI) in frontal, parietal, temporal, occipital, anterior, and posterior cingulate white matter (WM), and the thalami and hippocampi. RESULTS: Hippocampal ADC was higher in MCI and Alzheimer disease patients than in control subjects. ADC of the temporal stem and posterior cingulate, occipital, and parietal WM was higher in Alzheimer disease patients than in control subjects. Except for occipital AI, which was lower in MCI patients than in control subjects, there were no differences in AI among the three groups for any of the regions. CONCLUSION: Hippocampal ADC was significantly different between control subjects and MCI patients, many of whom likely have preclinical Alzheimer disease. Elevation in hippocampal ADC may reflect early ultrastructural changes in the progression of Alzheimer disease.

Regional metabolic patterns in mild cognitive impairment and Alzheimer's disease: A 1H MRS study.

BACKGROUND: Mild cognitive impairment (MCI) is a recently described transitional clinical state between normal aging and AD. Assuming that amnestic MCI patients had pathologic changes corresponding to an early phase and probable AD patients to a later phase of the disease progression, the authors could approximate the temporal course of proton MR spectroscopic (1H MRS) alterations in AD with a cross-sectional sampling scheme. METHODS: The authors compared 1H MRS findings in the superior temporal lobe, posterior cingulate gyri, and medial occipital lobe in 21 patients with MCI, 21 patients with probable AD, and 63 elderly controls. These areas are known to be involved at different neurofibrillary pathologic stages of AD. RESULTS: The N-acetylaspartate (NAA)/creatine (Cr) ratios were significantly lower in AD patients compared to both MCI and normal control subjects in the left superior temporal and the posterior cingulate volumes of interest (VOI) and there were no between-group differences in the medial occipital VOI. Myoinositol (MI)/Cr ratios measured from the posterior cingulate VOI were significantly higher in both MCI and AD patients than controls. The choline (Cho)/Cr ratios measured from the posterior cingulate VOI were higher in AD patients compared to both MCI and control subjects. CONCLUSION: These findings suggest that the initial 1H MRS change in the pathologic progression of AD is an increase in MI/Cr. A decrease in NAA/Cr and an increase in Cho/Cr develop later in the disease course.

An evaluation of JPEG and JPEG 2000 irreversible compression algorithms applied to neurologic computed tomography and magnetic resonance images. Joint Photographic Experts Group.

We performed visual comparison of 200 head magnetic resonance (MR) and 200 head computed tomography (CT) images compressed at two levels using standard Joint Photographic Experts Group (JPEG) irreversible compression and a preliminary version of the JPEG 2000 irreversible algorithm. Blinded evaluations by neuroradiologists compared original versus either JPEG or JPEG 2000. We found that this version of JPEG 2000 did not perform as well as the current JPEG for head CTs, but for MR images, JPEG 2000 performed as well or better. Around 7:1 compression ratio seemed to be a conservative point where there was no perceptible difference.

Ultrasound appearance of synovial osteochondromatosis of the shoulder.

This case report demonstrates the ultrasound appearance of synovial osteochondromatosis of the shoulder, along with plain film radiographic, computed tomographic, and pathologic correlation. Because of recent renewed interest in the use of ultrasonography in the evaluation of musculoskeletal disease, such as rotator cuff arthropathy or suspected intra-articular loose body, opportunities to diagnose synovial osteochondromatosis with this modality have become more frequent.

Effects of a stereotactic headframe assembly on proton magnetic resonance spectroscopy.

The effects of a magnetic resonance-compatible stereotactic headframe assembly on single voxel proton magnetic resonance spectroscopy (MRS) were investigated. Multiple stimulated echo acquisition mode (STEAM) spectra were obtained within a commercially available brain metabolite phantom placed within the headframe assembly (Leksell, Model G). All acquisition parameters were kept constant, except voxel location. Maximal distortion occurred for voxels acquired in the immediate vicinity of a headframe fixation pin, manifested by spectral broadening, changes in peak area and height and distortion of the baseline, rendering these acquisitions nondiagnostic. The range of this interaction was short, and a voxel acquired with nearest edge located 2.0 cm or greater from the fixation pin tip produced NAA/Cr, Cho/Cr and mI/Cr ratios differing by less than 7.5% from a spectrum obtained at the phantom center. The feasibility of performing single voxel MRS with a stereotactic headframe in place is demonstrated.

Hippocampal transverse relaxation times in patients with Alzheimer disease.

PURPOSE: To determine whether hippocampal relaxation times in magnetic resonance (MR) imaging differ between patients with probable Alzheimer disease and elderly control subjects with normal cognition. MATERIALS AND METHODS: MR imaging relaxation times were measured in the head and body of the right and left hippocampi in 123 subjects: 62 patients with Alzheimer disease (44 women, 18 men; age range, 65-89 years) and 61 elderly control subjects without cognitive impairment (39 women, 22 men; age range, 65-89 years). Hippocampal relaxation times were correlated with clinical status (patient vs control subject), age, sex, laterality (right vs left), and location within the hippocampus (body vs head). The hippocampal T2 value was correlated with the severity of disease in the patients. RESULTS: No statistically significant difference in the relaxation times was found between the two clinical groups for the analysis of the right versus left hippocampi and the hippocampal head versus body. In both patients and control subjects, no correlation was found between T2 measurements and age or sex. Twenty-seven patients had a clinical dementia rating (CDR) score of 0.5 (very mild dementia), 21 patients had a CDR score of 1.0 (mild dementia), and eight patients had a CDR score of 2.0 (moderate dementia). The CDR score was not available in six patients. No statistically significant association between T2 values and severity of disease was observed. CONCLUSION: MR relaxation time measurements in the hippocampus are not useful for the detection of Alzheimer disease.

Prostatic calcifications detected on Tc-99m MDP bone scan mimicking bone metastasis.

Uptake of Tc-99m MDP tracer was noted within prostatic calcifications in a 48-year-old man with no known malignancy who underwent a three-phase bone scan for left knee and thigh pain. Routine anterior and posterior views of the pelvis demonstrated focal tracer uptake within the right pubic bone, which mimicked a metastatic lesion. Additional imaging showed the uptake to be extraosseous and localized within the prostate in a distribution similar to the extensive prostatic calcifications seen on the corresponding plain film and computed tomography examinations of the pelvis. This unusual presentation illustrates another potential artifact that may be present in scintigraphic bone imaging of the pelvis.

MR imaging of the abdomen with a phased-array multicoil: prospective clinical evaluation.

PURPOSE: To prospectively compare use of a phased-array multicoil and a conventional body coil in abdominal MR imaging. MATERIALS AND METHODS: Thirteen patients (seven men, six women; mean age, 55 years) underwent imaging with a phased-array multicoil and with a conventional body coil. Four pulse sequences were used: T2-weighted spin echo (SE), magnetization-prepared gradient-recalled echo (GRE), breath-hold fast SE, and echo planar (EP). RESULTS: Lesion detection improved the most on fast SE, multicoil-acquired images. Signal-to-noise ratio (S/N) increased 64% with fast SE (P = .0005) and EP (P < .0109) sequences. Contrast-to-noise ratio (C/N) doubled (P < .05) with T2-weighted SE sequences. Lesion conspicuity improved on multicoil-acquired images with all fast sequences (magnetization-prepared GRE, P = .015; fast SE, P = .002; EP imaging, P = .013). There was little difference in respiratory and vascular artifact. Depiction of most abdominal structures improved (P < .01). CONCLUSION: Use of the phased-array multicoil provides better MR images of the abdomen than does use of a conventional body coil.

Magnetization transfer contrast on gradient echo MR imaging of the temporomandibular joint.

Thirty-nine temporomandibular joints (TMJ) from 20 patients with suspected internal derangements were imaged by a 1.5 T MR imager. The on-resonance binomial magnetization transfer contrast (MTC) pulse was applied to gradient echo images with a dual receiver coil (9 s/section). With the use of an opening device, a series of sequential images were obtained at increments of mouth opening and closing. The tissue signal intensities with (Ms) and without (Mo) MTC were measured and subjective image analysis was performed. Compared with the standard images, MTC technique provided selective signal suppression of disks. The average of Ms/Mo ratio of the disks (0.56) was lower than that of the retrodiskal pad (0.79) and of the effusion (0.89). With MTC technique, fluid conspicuity was superior to standard image. However, no significant superiority was found in disk definition subjectivity.

Tongue displacement: visualization with rapid tagged magnetization-prepared MR imaging.

The authors describe a technique to depict tongue muscle displacement with tagged magnetization-prepared gradient-recalled echo magnetic resonance imaging. Three Japanese volunteers (three men, aged 31-36 years) were studied while they articulated specific sounds. Each image was obtained in less than 2 seconds without need for gating. Displacement and alteration of the tags within the tongue muscle during phonation were clearly visible. The technique may prove useful in the study of phoniatric pathophysiology.