Olfactory Bulb Signal Abnormality in Patients with COVID-19 Who Present with Neurologic Symptoms

BACKGROUND AND PURPOSE

Unique among the acute neurologic manifestations of Severe Acute Respiratory Syndrome coronavirus 2, the virus responsible for the coronavirus disease 2019 (COVID-19) pandemic, is chemosensory dysfunction (anosmia or dysgeusia), which can be seen in patients who are otherwise oligosymptomatic or even asymptomatic. The purpose of this study was to determine if there is imaging evidence of olfactory apparatus pathology in patients with COVID-19 and neurologic symptoms.

MATERIALS AND METHODS

A retrospective case-control study compared the olfactory bulb and olfactory tract signal intensity on thin-section T2WI and postcontrast 3D T2 FLAIR images in patients with COVID-19 and neurologic symptoms, and age-matched controls imaged for olfactory dysfunction.

RESULTS

There was a significant difference in normalized olfactory bulb T2 FLAIR signal intensity between the patients with COVID-19 and the controls with anosmia (P = .003). Four of 12 patients with COVID-19 demonstrated intraneural T2 signal hyperintensity on postcontrast 3D T2 FLAIR compared with none of the 12 patients among the controls with anosmia (P = .028).

CONCLUSIONS

Olfactory bulb 3D T2 FLAIR signal intensity was greater in the patients with COVID-19 and neurologic symptoms compared with an age-matched control group with olfactory dysfunction, and this was qualitatively apparent in 4 of 12 patients with COVID-19. Analysis of these preliminary finding suggests that olfactory apparatus vulnerability to COVID-19 might be supported on conventional neuroimaging and may serve as a noninvasive biomarker of infection.

MRI Features of Histologically Diagnosed Supratentorial Primitive Neuroectodermal Tumors and Pineoblastomas in Correlation with Molecular Diagnoses and Outcomes: A Report from the Children's Oncology Group ACNS0332 Trial

BACKGROUND AND PURPOSE

Supratentorial primitive neuroectodermal tumors and pineoblastomas have traditionally been grouped together for treatment purposes. Molecular profiling of these tumors has revealed a number of distinct entities and has led to the term "CNS-primitive neuroectodermal tumors" being removed from the 2016 World Health Organization classification. The purpose of this study was to describe the MR imaging findings of histologically diagnosed primitive neuroectodermal tumors and pineoblastomas and correlate them with molecular diagnoses and outcomes.

MATERIALS AND METHODS

Histologically diagnosed primitive neuroectodermal tumors and pineoblastomas were enrolled in this Children's Oncology Group Phase III trial, and molecular classification was retrospectively completed using DNA methylation profiling. MR imaging features were systematically studied and correlated with molecular diagnoses and survival.

RESULTS

Of the 85 patients enrolled, 56 met the inclusion criteria, in whom 28 tumors were in pineal and 28 in nonpineal locations. Methylation profiling revealed a variety of diagnoses, including pineoblastomas (n = 27), high-grade gliomas (n = 17), embryonal tumors (n = 7), atypical teratoid/rhabdoid tumors (n = 3), and ependymomas (n = 2). Thus, 39% overall and 71% of nonpineal tumor diagnoses were discrepant with histopathology. Tumor location, size, margins, and edema were predictors of embryonal-versus-nonembryonal tumors. Larger size and ill-defined margins correlated with poor event-free survival, while metastatic disease by MR imaging did not.

CONCLUSIONS

In nonpineal locations, only a minority of histologically diagnosed primitive neuroectodermal tumors are embryonal tumors; therefore, high-grade glioma or ependymoma should be high on the radiographic differential. An understanding of molecularly defined tumor entities and their relative frequencies and locations will help the radiologist make more accurate predictions of the tumor types.

Brain Region-Specific Degeneration with Disease Progression in Late Infantile Neuronal Ceroid Lipofuscinosis (CLN2 Disease)

BACKGROUND AND PURPOSE

Late infantile neuronal ceroid lipofuscinosis (CLN2 disease) is a uniformly fatal lysosomal storage disease resulting from mutations in the CLN2 gene. Our hypothesis was that regional analysis of cortical brain degeneration may identify brain regions that are affected earliest and most severely by the disease.

MATERIALS AND METHODS

Fifty-two high-resolution 3T MR imaging datasets were prospectively acquired on 38 subjects with CLN2. A retrospective cohort of 52 disease-free children served as a control population. The FreeSurfer software suite was used for calculation of cortical thickness.

RESULTS

An increased rate of global cortical thinning in CLN2 versus control subjects was the primary finding in this study. Three distinct patterns were observed across brain regions. In the first, subjects with CLN2 exhibited differing rates of cortical thinning versus age. This was true in 22 and 26 of 34 regions in the left and right hemispheres, respectively, and was also clearly discernable when considering brain lobes as a whole and Brodmann regions. The second pattern exhibited a difference in thickness from healthy controls but with no discernable change with age (9 left hemispheres, 5 right hemispheres). In the third pattern, there was no difference in either the rate of cortical thinning or the mean cortical thickness between groups (3 left hemispheres, 3 right hemispheres).

CONCLUSIONS

This study demonstrates that CLN2 causes differential rates of degeneration across the brain. Anatomic and functional regions that degenerate sooner and more severely than others compared with those in healthy controls may offer targets for directed therapies. The information gained may also provide neurobiologic insights regarding the mechanisms underlying disease progression.

Assessment of disease severity in late infantile neuronal ceroid lipofuscinosis using multiparametric MR imaging

BACKGROUND AND PURPOSE

LINCL is a uniformly fatal lysosomal storage disease resulting from mutations in the CLN2 gene that encodes for tripeptidyl peptidase 1, a lysosomal enzyme necessary for the degradation of products of cellular metabolism. With the goal of developing quantitative noninvasive imaging biomarkers sensitive to disease progression, we evaluated a 5-component MR imaging metric and tested its correlation with a clinically derived disease-severity score.

MATERIALS AND METHODS

MR imaging parameters were measured across the brain, including quantitative measures of the ADC, FA, nuclear spin-spin relaxation times (T2), volume percentage of CSF (%CSF), and NAA/Cr ratios. Thirty MR imaging datasets were prospectively acquired from 23 subjects with LINCL (2.5-8.4 years of age; 8 male/15 female). Whole-brain histograms were created, and the mode and mean values of the histograms were used to characterize disease severity.

RESULTS

Correlation of single MR imaging parameters against the clinical disease-severity scale yielded linear regressions with R2 ranging from 0.25 to 0.70. Combinations of the 5 biomarkers were evaluated by using PCA. The best combination included ADC, %CSF, and NAA/Cr (R2=0.76, P<.001).

CONCLUSIONS

The multiparametric disease-severity score obtained from the combination of ADC, %CSF, and NAA/Cr whole-brain MR imaging techniques provided a robust measure of disease severity, which may be useful in clinical therapeutic trials of LINCL in which an objective assessment of therapeutic response is desired.

Using quantitative CT perfusion for evaluation of delayed cerebral ischemia following aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

DCI is a serious complication following aneurysmal SAH leading to permanent neurologic deficits, infarction, and death. Our aim was to prospectively evaluate the diagnostic accuracy of CTP and to determine a quantitative threshold for DCI in aneurysmal SAH.

MATERIALS AND METHODS

Patients with SAH were prospectively enrolled in a protocol approved by the institutional review board. CTP was performed during the typical time period for DCI, between days 6 and 8 following SAH. Quantitative CBF, CBV, and MTT values were obtained by using standard region-of-interest placement sampling of gray matter. The reference standard for DCI is controversial and consisted of clinical and imaging criteria in this study. In a subanalysis of vasospasm, DSA was used as the reference standard. ROC curves determined the diagnostic accuracy by using AUC. Optimal threshold values were calculated by using the patient population utility method.

RESULTS

Ninety-seven patients were included; 41% (40/97) had DCI. Overall diagnostic accuracy was 93% for CBF, 88% for MTT, and 72% for CBV. Optimal threshold values were 35 mL/100 g/min (90% sensitivity, 68% specificity) for CBF and 5.5 seconds (73% sensitivity, 79% specificity) for MTT. In the subanalysis (n = 57), 63% (36/57) had vasospasm. Overall diagnostic accuracy was 94% for CBF, 85% for MTT, and 72% for CBV. Optimal threshold values were 36.5 mL/100 g/min (95% sensitivity, 70% specificity) for CBF and 5.4 seconds (78% sensitivity, 70% specificity) for MTT.

CONCLUSIONS

CBF and MTT have the highest overall diagnostic accuracy. Threshold values of 35 mL/100 g/min for CBF and 5.5-second MTT are suggested for DCI on the basis of the patient population utility method. Absolute threshold values may not be generalizable due to differences in scanner equipment and postprocessing methods.

Arterial spin labeling and altered cerebral blood flow patterns in the minimally conscious state

OBJECTIVE

To use arterial spin labeling (ASL) to compare cerebral blood flow (CBF) patterns in minimally conscious state (MCS) patients with those in normal controls in an observational study design.

METHODS

Subjects meeting MCS criteria and normal controls were identified. A pseudocontinuous ASL sequence was performed with subjects and controls in the resting awake state. Multiple CBF values for 10 predetermined regions of interest were sampled and average CBF was calculated and compared between controls and subjects.

RESULTS

Ten normal controls were identified, with ages ranging from 26 to 54 years. Four subjects met the MCS criteria and received an ASL study, with one patient receiving a second study at a later date. Subjects ranged in age from 19 to 58 years and had traumatic brain injury, stroke, or hypoxic-ischemic encephalopathy. Regional CBF for controls ranged from 21.6 to 57.2 mL/100 g/min, with a pattern of relatively increased blood flow posteriorly including the posterior cingulate, parietal, and occipital cortices. CBF patterns for MCS subjects showed greater variability (from 7.7 to 33.1 mL/100 g/min), demonstrating globally decreased CBF in gray matter compared with that in normal controls, especially in the medial prefrontal and midfrontal regions. In the one subject studied longitudinally, global CBF values increased over time, which correlated with clinical improvement.

CONCLUSIONS

We identified globally decreased CBF and a selective reduction of CBF within the medial prefrontal and midfrontal cortical regions as well as gray matter in MCS patients. ASL may serve as an adjunctive method to assess functional reserve in patients recovering from severe brain injuries.

Accurate localization of brain activity in presurgical FMRI by structure adaptive smoothing

An important problem of the analysis of functional magnetic resonance imaging (fMRI) experiments is to achieve some noise reduction of the data without blurring the shape of the activation areas. As a novel solution to this problem, recently the propagation-separation (PS) approach has been proposed. PS is a structure adaptive smoothing method that adapts to different shapes of activation areas. In this paper, we demonstrate how this method results in a more accurate localization of brain activity. First, it is shown in numerical simulations that PS is superior over Gaussian smoothing with respect to the accurate description of the shape of activation clusters and results in less false detections. Second, in a study of 37 presurgical planning cases we found that PS and Gaussian smoothing often yield different results, and we present examples showing aspects of the superiority of PS as applied to presurgical planning.

Assessing disease severity in late infantile neuronal ceroid lipofuscinosis using quantitative MR diffusion-weighted imaging

BACKGROUND AND PURPOSE

Late infantile neuronal ceroid lipofuscinosis (LINCL), a form of Batten disease, is a fatal neurodegenerative genetic disorder, diagnosed via DNA testing, that affects approximately 200 children in the United States at any one time. This study was conducted to evaluate whether quantitative data derived by diffusion-weighted MR imaging (DWI) techniques can supplement clinical disability scale information to provide a quantitative estimate of neurodegeneration, as well as disease progression and severity.

MATERIALS AND METHODS

This study prospectively analyzed 32 DWI examinations from 18 patients having confirmed LINCL at various stages of disease. A whole-brain apparent diffusion coefficient (ADC) histogram was fitted with a dual Gaussian function combined with a function designed to model voxels containing a partial volume fraction of brain parenchyma versus CSF. Previously published whole-brain ADC values of age-matched control subjects were compared with those of the LINCL patients. Correlations were tested between the peak ADC of the fitted histogram and patient age, disease severity, and a CNS disability scale adapted for LINCL.

RESULTS

ADC values assigned to brain parenchyma were higher than published ADC values for age-matched control subjects. ADC values between patients and control subjects began to differ at 5 years of age based on 95% confidence intervals. ADC values had a nearly equal correlation with patient age (R2=0.71) and disease duration (R2=0.68), whereas the correlation with the central nervous system disability scale (R2=0.27) was much weaker.

CONCLUSION

This study indicates that brain ADC values acquired using DWI may be used as an independent measure of disease severity and duration in LINCL.

Diffusion anisotropy changes in the brains of professional boxers

BACKGROUND AND PURPOSE

Professional boxing may result in brain injury. We hypothesize that quantitative MR diffusion imaging may be useful in determining early white matter changes.

METHODS

Forty-nine professional boxers (age 30 +/- 4.5 years) and 19 healthy control subjects (age 32 +/- 9.5 years) were imaged on a clinical 1.5T scanner. None of the subjects had neurologic disorder or deficit. The average diffusion constant (D(av)) and diffusion anisotropy (FA) were determined pixel by pixel. Regional diffusion measurements were done in the corpus callosum (CC) and internal capsule (IC). The whole brain diffusion constant (BD(av)) was also determined. Student t test was used to analyze the diffusion difference between boxers and the healthy control subjects. P < .05 was considered statistically significant.

RESULTS

Of the 49 professional boxers, 42 had normal conventional MRIs. The remaining 7 boxers had abnormal MR imaging findings dominated by nonspecific white matter disease. There was a significant difference in diffusion and anisotropy measurements in all the boxers compared with the healthy control subjects. In the boxer group, BD(av) increased and FA decreased significantly in the CC and posterior limb of IC. The measured FA and D(av) inversely correlated in regions of CC and IC in boxers but not in healthy control subjects. BD(av) also robustly correlated with both FA and D(av) in the splenium of CC in boxers.

CONCLUSION

Increased BD(av) and the decreased FA in the CC and IC may represent preclinical signs of subtle brain injury in professional boxers.

Internal auditory canal involvement of acoustic neuromas: surgical correlates to magnetic resonance imaging findings

OBJECTIVE

Factors that play a role in the selection of surgical approach for acoustic neuromas include patient health and age, size of tumor, hearing status, and location of tumor in the internal auditory canal (IAC) and the cerebellopontine angle. Deep extension into the IAC makes hearing preservation extremely difficult when a retrosigmoid craniotomy is used, and the best approach is a middle fossa subtemporal route. Modern gadolinium-enhanced magnetic resonance imaging (MRI) can be inaccurate in identifying the presence of tumor laterally in the IAC. This may affect the selection of a surgical approach.

STUDY DESIGN

This study was a retrospective case review.

SETTING

Patients were accrued from a tertiary referral otologic practice.

PATIENTS

From 1997 through 2000, the authors identified six patients who had undergone acoustic neuroma surgery, had adequate imaging and intraoperative data, and demonstrated a lack of correlation between MRI and intraoperative findings of the lateral IAC.

INTERVENTION

The interventions were preoperative MRI of the IAC and surgical resection of an acoustic neuroma.

MAIN OUTCOME MEASURE

Comparison of MRI and intraoperative findings of the lateral IAC were the main outcome measures.

RESULTS

Six patients demonstrated a lack of correlation between MRI and intraoperative findings of the lateral IAC.

CONCLUSIONS

Gadolinium-enhanced T1-weighted MRI findings of the depth of penetration into the lateral aspect of the IAC do not always correlate with intraoperative findings and thus may have implications in the selection of surgical approaches to acoustic neuromas.

Hyperintense signal abnormality in subarachnoid spaces and basal cisterns on MR images of children anesthetized with propofol: new fluid-attenuated inversion recovery finding

BACKGROUND AND PURPOSE

MR imaging is the method of choice for pediatric neuroimaging. Sedation is often needed to suppress patient motion and ensure diagnostic image quality, and propofol is rapidly becoming the preferred anesthetic. The purpose of this study was to document a new finding on fast fluid-attenuated inversion recovery (fast-FLAIR) MR images of children anesthetized with propofol that can be mistaken for subarachnoid space pathologic abnormality.

METHODS

A retrospective analysis was conducted of 55 MR images of the brain for children who ranged in age from 1 week to 12 years. Forty-two patients received chloral hydrate, and 13 received propofol anesthetic. Multiplanar MR images were studied to detect the presence or absence of hyperintense signal (artifact) in the subarachnoid spaces and basal cisterns. The T1 values and null times of chloral hydrate, propofol, and CSF were determined in vitro at room temperature by using an inversion recovery pulse sequence at 1.5 T.

RESULTS

The fast-FLAIR images of all 13 patients who received propofol had hyperintense signal abnormality. For 10 (77%) of 13 patients, this artifact was in the basal cisterns and subarachnoid spaces overlying the brain convexity. For three (23%) of 13 patients, this artifact was in the convexity region only. Two patients underwent follow-up MR imaging with a nonpropofol anesthetic agent, and the artifact resolved. None of the images of the children who received chloral hydrate had this artifact. The T1 value of chloral hydrate was 0.2 s, of propofol was 1.86 s, and of CSF was 2.32 s at room temperature.

CONCLUSION

The fast-FLAIR images of children anesthetized with propofol have artifactual hyperintense signal in the basal cisterns and subarachnoid spaces, and this artifact mimics disease of the subarachnoid space. The T1 value of propofol approaches that of CSF. Depending on the chosen null time, there may be incomplete nulling of signal coming from propofol. To account for this observation, other possible causes include increased CSF pulsation in children creating motion artifact, changes in arterial oxygen concentration intrinsic to propofol or related to the supplemental oxygen normally administered, or changes in CSF protein levels related to propofol binding to proteins for uptake into CSF.

Appearance of meningiomas on diffusion-weighted images: correlating diffusion constants with histopathologic findings

BACKGROUND AND PURPOSE

Malignant and atypical meningiomas are prone to recurrence and aggressive growth, which affects treatment planning and prognostication. Investigators have used diffusion-weighted imaging and apparent diffusion coefficient (ADC) maps to compare tumor grade and cellularity with the histopathologic findings of intraaxial primary brain neoplasms. The purpose of this study was to determine whether the signal characteristics of meningiomas on diffusion-weighted images correlate with the average diffusion constant (Dav) from ADC maps and histopathologic findings and whether the Dav can reliably distinguish benign from malignant and atypical meningiomas.

METHODS

Seventeen patients (13 women and four men; average age, 55 years) with meningiomas were prospectively studied using routine MR imaging and diffusion-weighted imaging with a single-shot gradient-echo echo-planar pulse sequence (6000/100 [TR/TE]) and b values of 0 and 1000. Signal characteristics on routine MR and diffusion-weighted images were compared with the histopathologic findings after resection by using World Health Organization criteria. Dav values were calculated within the tumor mass from ADC maps before resection.

RESULTS

Four meningiomas were malignant or atypical (World Health Organization grades II and III). Dav values were lower than normal brain values (average, 0.52 +/- 0.12 x 10(-5) cm2/s; range, 0.45-0.69 x 10(-5) cm2/s) and were hyperintense on diffusion-weighted images and hypointense on ADC maps. Thirteen meningiomas were benign. Dav values were higher than normal brain values (average, 1.03 +/- 0.29 x 10(-5) cm2/s; range, 0.62-1.8 x 10(-5) cm2/s). On diffusion-weighted images and ADC maps, most were isointense. Five benign meningiomas had very high Dav values, bright signal on ADC maps, and distinct histopathologic findings, including microcysts, necrotic infarct, and organizing intratumoral hemorrhage. The difference in Dav values between malignant and benign meningiomas was statistically significant (P < .00029).

CONCLUSION

Albeit a small sample size, meningiomas with low Dav tended to be malignant or highly atypical (P < .00029) whereas meningiomas with the highest Dav had increased water content due to either a specific histologic subtype of meningioma or the presence of associated pathologic abnormality.

Incidental discovery of acoustic neuromas

Our objective is to report 4 cases of incidentally discovered acoustic neuromas (ANs) and to determine the incidence of asymptomatic ANs. A prospective study of 161 consecutive patients undergoing gadolinium-enhanced MRI (Gd-MRI) at a tertiary-care university-affiliated medical center was carried out from September 1994 to April 1995. The Gd-MRI scans were performed for tentative diagnoses other than AN or sensorineural hearing loss. In 161 consecutive patients examined, no ANs were found incidentally on Gd-MRI scans. Previous studies have suggested that the incidence of occult ANs is as high as 1%. On the basis of our results, we suggest that the actual incidence may be lower. However, our study is limited by its small size and the low incidence of ANs in the general population. Also reported are the clinical and MRI characteristics of 4 patients with incidentally diagnosed ANs.

Orbital CT. Current use in the MR era

The additional advantages of spiral CT have further cemented CTs role as the screening examination of choice for the orbit. The shorter scan times permit ideal enhancement yet reduce the contrast load, providing the optimal postcontrast studies that routine imaging of the orbit requires. This article is not a comprehensive study of orbital CT, but a general review emphasizing CTs strengths, especially the evaluation of childhood leukocoria (calcification), proptosis screening, and trauma.

Sensorineural hearing loss and cerebellopontine angle lesions. Not always an acoustic neuroma--a pictorial essay

While an acoustic neuroma is the most common cause of a cerebellopontine angle (CPA) mass, it accounts for only 1-10% of cases of sensorineural hearing loss (SNHL). There are many other etiologies of SNHL, with characteristic imaging features, which may or may not be confined to the CPA.

Maternal cocaine abuse: the spectrum of radiologic abnormalities in the neonatal CNS

The purpose of this study was to determine the pattern and frequency of CNS abnormalities in the offspring of cocaine-abusing mothers. The study group consisted of a retrospective review of all neonates born or admitted to our neonatal intensive care unit over a 1-year period who met criteria for maternal cocaine abuse (43 patients). A control group (62 patients) was obtained from patients seen during the same interval and the cases were matched for gestational age and race. The radiologic studies were analyzed by two independent reviewers, and CNS abnormalities were assessed by means of sonography, CT, or MR. By matching the study and control groups for gestational age, we eliminated the higher frequency of prematurity. This allowed us to determine if maternal cocaine use was associated with any intracranial abnormalities other than those seen with prematurity. The frequency of intracranial hemorrhage, ventricular enlargement, and periventricular leukomalacia was not significantly different between the study and control groups. The frequency of cortical infarction was 17% in the study group and 2% in the control group. The frequency of major congenital malformation was 12% in the study group and 0% in the control group. All five of the congenital malformations seen were midline CNS abnormalities, particularly neural tube defects. It is postulated that the higher statistically significant frequency of stroke and congenital malformations in the babies of maternal cocaine abusers is related to vasospasm caused by cocaine when used in the third and first trimesters, respectively.

Magnetic resonance imaging of arachnoid cysts

A retrospective review of magnetic resonance imaging (MRI)-computed tomography (CT) correlation was performed in 29 patients with arachnoid cysts. Short TR, short TE spin echo (SE) pulse sequences provided the best anatomic definition whereas multiple echo long TR, TE sequences allowed comparison of the signal intensity of the cyst with that of cerebrospinal fluid (CSF). Simple arachnoid cysts were isointense while neoplastic, hemorrhagic or inflammatory cysts were hyperintense relative to CSF. The CT differential diagnosis of an arachnoid cyst (depending upon its location) may include other cystic collections such as craniopharyngioma, epidermoid, astrocytoma, and chronic subdural hematoma. However, on MRI the combination of extra-axial location, morphological features, and signal intensity matching that of CSF allows one to make the diagnosis of an uncomplicated arachnoid cyst with confidence.

Subdural and epidural empyemas: MR imaging

The MR images of six patients with extraaxial empyemas (five subdural and four epidural) were reviewed and compared with CT scans. MR demonstrated convexity and interhemispheric collections, which were mildly hyperintense relative to CSF and hypointense relative to white matter on short TR pulse sequences and hyperintense relative to CSF and white matter on long TR pulse sequences, allowing distinction from sterile effusions and most chronic hematomas. A hypointense rim, representing displaced dura, was depicted at the interface between the lesion and brain in epidural empyemas, a feature absent in subdural empyemas. Inflammation-induced parenchymal abnormalities, including edema, mass effect, and reversible cortical hyperintensity, were well depicted on MR imaging. MR was superior to CT in demonstrating the presence, nature, and extent of these lesions in all cases. Because early and accurate diagnosis will significantly improve the prognosis of these serious infections, MR is preferred to CT for patients in whom an acute intracranial infection is suspected.

Differentiation between meningeal fibrosis and chronic subdural hematoma after ventricular shunting: value of enhanced CT and MR scans

Unenhanced CT in four patients with long-standing ventricular shunts demonstrated bilateral low-density extraaxial collections that were indistinguishable from chronic subdural hematomas. After administration of contrast material, however, there was marked enhancement of the collections as well as prominent paratentorial and parafalcial enhancement. MR imaging, performed in three patients, demonstrated the extent and paradural location of the collections better than CT did, but, as with unenhanced CT, the collections could not be distinguished from chronic subdural hematomas. On follow-up CT and MR, there was no change in the size, enhancement, or intensity of the collections. Histologic examination of biopsies from two patients demonstrated fibrosis of the meninges characterized by granulation tissue and collagen deposition. Meningeal fibrosis is a rare postshunt phenomenon that may mimic chronic subdural hematoma on unenhanced CT and MR. Recognition of this entity is important, particularly if therapeutic intervention is being considered. Therefore, an enhanced CT or enhanced MR scan should be obtained in chronically shunted patients to differentiate between a drainable chronic subdural hematoma and meningeal fibrosis.

Large Virchow-Robin spaces: MR-clinical correlation

High-field MR scans frequently show Virchow-Robin spaces, which conform to the path of the penetrating arteries as they enter either the basal ganglia or the cortical gray matter over the high convexities. A retrospective review of 816 MR scans was undertaken to determine the clinical significance and associations (if any) of this finding. The Virchow-Robin spaces were graded, as were the nonspecific white-matter lesions. The presence of atrophy, infarction, hydrocephalus, and miscellaneous disease was noted. Large Virchow-Robin spaces were identified in 314 cases. A study sample was created consisting of a positive group containing all the larger grade 2 and 3 Virchow-Robin spaces (67 patients) and a negative or control group of 109 randomly selected patients from the original 502 who did not have large Virchow-Robin spaces. The charts of this study sample were reviewed and the following patient variables were noted: age, gender, incidental white-matter lesions, infarction, dementia, hypertension, and atrophy. For each variable, the proportion of patients who were positive for that variable was calculated for each of the two groups and compared across groups by using a Fisher exact test. Multiple logistic regression analysis was used to determine whether any of these variables were jointly associated with being "positive" or "negative" for large Virchow-Robin spaces. Some variables were strongly associated with being positive for large Virchow-Robin spaces: age, hypertension, dementia, and incidental white-matter lesions. Logistic regression analysis revealed that when all of these variables are considered jointly, only age remains significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute intracranial hemorrhage: intensity changes on sequential MR scans at 0.5 T

Thirty-seven patients underwent MR imaging at 0.5 T within 7 days of a CT-documented intracranial hemorrhage. A total of 57 hematomas were evaluated. Twelve patients underwent serial scanning and 12 patients had multiple hemorrhages into different intracranial compartments. The appearances of the hematomas on spin-echo (SE) images with a short repetition time (TR) of 500 msec and short echo time (TE) of 32 msec (SE 500/32), long TR/intermediate TE (SE 2000/60), and long TR/long TE (SE 2000/120) were carefully evaluated with specific attention to the precise time after ictus. Hematomas showed heterogeneous, complex, rapidly changing intensities. There was a significant amount of variation among patients, especially between the third and seventh days. Hematomas studied between 12 and 24 hr after hemorrhage were mildly hyperintense on short TR scans and markedly hyperintense on long TR (intermediate and long TE) scans (stage I). These findings in acute hemorrhage have received little prior attention. Over the next 1-2 days, hematomas became iso- to mildly hypointense on short TR scans and markedly hypointense on long TR scans (stage II). Hypointensity on long TR scans has previously been described at high field strengths; our communication demonstrates that this phenomenon is seen routinely at intermediate field strengths as well. Hematomas became markedly hyperintense on short TR scans beginning on approximately the fourth day postictus and redeveloped hyperintensity on long TR scans approximately 5-6 days after ictus (stage III). By the end of the first week they were hyperintense on all pulse sequences (stage IV). MR findings on the first day after intracranial hemorrhage (in particular, subtle hyperintensity on short TR scans) probably allow for a specific diagnosis, while the variable, hetergeneous, and rapidly changing intensities noted between days 2 and 7 are often less specific.

Head trauma: comparison of MR and CT--experience in 100 patients

The results of CT and MR imaging were reviewed retrospectively and compared in 100 patients who experienced clinically significant head trauma. The findings were analyzed on the basis of several parameters in an attempt to establish objective clinical guidelines for the use of each diagnostic technique. CT remains the screening method of choice in evaluating acute severe head trauma; however, MR revealed additional clinically relevant findings in all four cases in which the patient's clinical symptoms were disproportionate to the CT findings. MR was equal or superior to CT in the evaluation of all patients with acute minor head trauma and in 94 of 95 patients examined in the subacute, chronic, or remote phase of injury, irrespective of the severity or pathologic nature of their injuries. All subacute contusions (21 lesions) and white-matter shearing lesions (18 cases) were demonstrated to particular advantage on MR compared with CT, as were all subdural hematomas (of 52 small subdural collections, 58% were detected only by MR). Although surgical management was not altered by the additional information provided by MR, the implications regarding the medical management and disposition of the patients with head trauma were significant.

Hemorrhagic neoplasms: MR mimics of occult vascular malformations

The MR scans of 24 patients who had findings previously reported to be characteristic of occult cerebral vascular malformations were reviewed to demonstrate that such findings may also occur in primary or secondary neoplasms. Eighteen of the 24 patients were found to have hemorrhagic neoplasms. Additional criteria, such as multiplicity of lesions and the presence of edema, were of some help in differentiating between occult vascular malformation and hemorrhagic neoplasm. In certain cases, CT was necessary to provide further information, such as the presence of calcification; however, an absolute and accurate diagnosis was impossible in several cases. The striking similarity on MR between cryptic vascular malformation and some hemorrhagic neoplasms is most likely due to the unifying mechanisms that underlie the evolution of extravascular intracerebral blood. Although the preponderance of neoplastic etiologies in our series may be partly due to the strong bias in our sample population toward patients with tumors, it seems clear that when an MR scan discloses findings "typical" of an occult vascular malformation, consideration must also be given to the generally more serious possibility of underlying neoplasm.

Clinical and magnetic resonance features of primary intracranial arachnoid cysts

The clinical features of 33 patients with primary intracranial arachnoid cysts are reviewed. Magnetic resonance imaging was performed in 9 patients and was particularly useful in the multiplanar definition of complex cysts and in differentiating arachnoid cysts from other lesions that are hypodense on computed tomographic scans. Hydrocephalus, cranial nerve palsies, or symptomatic brain compression was considered an indication for surgical intervention in 21 patients. Outcome was uniformly good: mild focal weakness and seizure disorders constituted the sequelae.

Angiographic demonstration of an aorto-left renal vein fistula

The unusual complication of an atherosclerotic abdominal aneurysm rupturing into a retro-aortic left renal vein is presented. Angiographic findings and the anatomic variations of the left renal vein are discussed.