Intracranial ependymoma and subependymoma: MR manifestations

In order to provide a detailed description of the MR appearance of intracranial ependymoma, the MR examinations of 12 patients (10 with ependymomas and two with subependymomas) were reviewed and correlated with operative and pathologic reports. Three of 10 ependymomas were intraventricular, two were intraparenchymal, and five were transependymal, extending from CSF spaces into parenchyma. Both subependymomas were intraventricular. Solid ependymomas and subependymomas were iso- to hypointense relative to normal white matter on T1-weighted images and hyperintense on proton-density- and T2-weighted images. Foci of signal heterogeneity within solid neoplasms represented methemoglobin, hemosiderin, necrosis, calcification, and encased native vessels or tumor vascularity. Gd-DTPA-enhanced images in two patients differentiated enhancing tumor from surrounding nonenhancing edema and from surrounding normal brain parenchyma. Cystic neoplasms had sharply defined, round or oval margins and uniform signal intensity equivalent to or slightly hyperintense relative to CSF. Tumor-associated calcification was not demonstrated readily by MR. Sagittal and coronal images were valuable in assessing the amount of intraventricular tumor and route of extension. We conclude that the MR differentiation of ependymomas and subependymomas from other gliomas is provided most reliably by the location and morphology of the tumor and not by differences in signal intensity. The typical ependymoma arises within the fourth ventricle as a solid mass with heterogeneous signal intensity. A propensity for spread is seen along the CSF pathways via the foramina of Magendie and Luschka and the aqueduct of Sylvius. Supratentorial ependymomas may be periventricular in location and have cystic components. The two subependymomas in our series were solid, intraventricular tumors with relatively homogeneous signal intensities.

Encephalitis caused by human immunodeficiency virus: CT and MR imaging manifestations with clinical and pathologic correlation

To determine the computed tomographic (CT) and magnetic resonance (MR) imaging manifestations of central nervous system (CNS) infection by the human immunodeficiency virus (HIV), the authors analyzed the results of imaging of the CNS in 24 patients with HIV encephalitis confirmed at autopsy. Careful pathologic correlation demonstrated that neither CT nor MR imaging enabled detection of microglial nodules with multinucleated giant cells, the hallmark of HIV encephalitis seen in all 24 affected patients. The most common abnormality observed on images of the CNS was atrophy, demonstrated in 18 patients. Demyelination and vacuolation of white matter tracts accompanying severe HIV infection caused hypoattenuation on CT scans and hyperintensity on T2-weighted MR images. These lesions had no mass effect. MR imaging was more sensitive than CT in the detection of lesions caused by HIV or other superimposed infectious agents. Although it is often difficult to attribute any radiologic appearance to a single etiologic agent in patients with acquired immunodeficiency syndrome, the combination of atrophy and symmetric, periventricular or diffuse white matter disease suggests HIV encephalitis.

The cerebellum: 3. Anatomic-MR correlation in the coronal plane

Thin (5-mm) coronal high-field (1.5-T) MR images of four human brain specimens and 14 normal volunteers were correlated with myelin-stained microtomic sections of the specimen cerebella. The primary white-matter tracts innervating several hemispheric (posterior quadrangular, superior, and inferior semilunar, gracile, biventer, tonsil) and vermian (declive, folium, tuber) lobules are oriented perpendicularly to the coronal plane of section and are shown well on proton-density-weighted (long TR/short TE) and T2-weighted (long TR/long TE) spin-echo images, which provide excellent contrast between gray and white matter. Several of the surface sulci and fissures of the cerebellar hemispheres (including the superior posterior, horizontal, secondary, and posterolateral fissures) also course perpendicular to the coronal plane and are depicted well on T1-weighted (short TR/short TE) and T2-weighted images, which maximize contrast between CSF and parenchyma. The opportunity for side-to-side comparison of the hemispheres is a distinct advantage of the coronal view. Nevertheless, more obliquely oriented surfaces (preculminate, primary, inferior posterior, inferior anterior, and intrabiventral fissures) and deep hemispheric structures (primary white-matter tracts to central, anterior quadrangular, and floccular lobules) may be obscured by volume-averaging in the coronal plane; moreover, much of the finer anatomy of the vermis is depicted poorly. The constant surface and deep anatomy of the cerebellum revealed on coronal images in normal volunteers encourages detailed mapping. MR imaging in the coronal plane should be especially useful in identifying, localizing, and quantifying normal and abnormal morphologic differences between the cerebellar hemispheres.

Primary myxoma of the posterior fossa

A rare case of primary intracranial myxoma of the posterior fossa is described in a 32-year old woman. The patient presented with a history of headaches, disequilibrium, nausea and abnormal vision for several months. Computed tomography (CT) showed a well-demarcated hypodense mass. After contrast administration the mass appeared as an inhomogeneously enhancing lesion surrounded by a small rim of edema. The mass was surgically excised with histological examination revealing a true myxoma. Echocardiography revealed no evidence of a cardiac myxoma. The CT appearance of other case reports of non-cardiac myxomas in the literature is reviewed.

Fast imaging

Gradient-echo pulse sequences are a valuable adjunct to the standard spin-echo sequences used for MR imaging of the brain and spine. Gradient-echo techniques enhance the signal of flowing fluids and increase the conspicuity of vascular lesions. They also increase the sensitivity of MR for chronic hemorrhage and calcification. Finally, steady-state techniques produce a myelographic effect to help evaluate degenerative diseases of the spine.

The cerebellum: 3. Anatomic-MR correlation in the coronal plane

Thin (5-mm) coronal high-field (1.5-T) MR images of four human brain specimens and 14 normal volunteers were correlated with myelin-stained microtomic sections of the specimen cerebella. The primary white-matter tracts innervating several hemispheric (posterior quadrangular, superior, and inferior semilunar, gracile, biventer, tonsil) and vermian (declive, folium, tuber) lobules are oriented perpendicularly to the coronal plane of section and are shown well on proton-density-weighted (long TR/short TE) and T2-weighted (long TR/long TE) spin-echo images, which provide excellent contrast between gray and white matter. Several of the surface sulci and fissures of the cerebellar hemispheres (including the superior posterior, horizontal, secondary, and posterolateral fissures) also course perpendicular to the coronal plane and are depicted well on T1-weighted (short TR/short TE) and T2-weighted images, which maximize contrast between CSF and parenchyma. The opportunity for side-to-side comparison of the hemispheres is a distinct advantage of the coronal view. Nevertheless, more obliquely oriented surfaces (preculminate, primary, inferior posterior, inferior anterior, and intrabiventral fissures) and deep hemispheric structures (primary white-matter tracts to central, anterior quadrangular, and floccular lobules) may be obscured by volume-averaging in the coronal plane; moreover, much of the finer anatomy of the vermis is depicted poorly. The constant surface and deep anatomy of the cerebellum revealed on coronal images in normal volunteers encourages detailed mapping. MR imaging in the coronal plane should be especially useful in identifying, localizing, and quantifying normal and abnormal morphologic differences between the cerebellar hemispheres.

Intracranial ependymoma and subependymoma: MR manifestations

In order to provide a detailed description of the MR appearance of intracranial ependymoma, the MR examinations of 12 patients (10 with ependymomas and two with subependymomas) were reviewed and correlated with operative and pathologic reports. Three of 10 ependymomas were intraventricular, two were intraparenchymal, and five were transependymal, extending from CSF spaces into parenchyma. Both subependymomas were intraventricular. Solid ependymomas and subependymomas were iso- to hypointense relative to normal white matter on T1-weighted images and hyperintense on proton-density- and T2-weighted images. Foci of signal heterogeneity within solid neoplasms represented methemoglobin, hemosiderin, necrosis, calcification, and encased native vessels or tumor vascularity. Gd-DTPA-enhanced images in two patients differentiated enhancing tumor from surrounding nonenhancing edema and from surrounding normal brain parenchyma. Cystic neoplasms had sharply defined, round or oval margins and uniform signal intensity equivalent to or slightly hyperintense relative to CSF. Tumor-associated calcification was not demonstrated readily by MR. Sagittal and coronal images were valuable in assessing the amount of intraventricular tumor and route of extension. We conclude that the MR differentiation of ependymomas and subependymomas from other gliomas is provided most reliably by the location and morphology of the tumor and not by differences in signal intensity. The typical ependymoma arises within the fourth ventricle as a solid mass with heterogeneous signal intensity. A propensity for spread is seen along the CSF pathways via the foramina of Magendie and Luschka and the aqueduct of Sylvius. Supratentorial ependymomas may be periventricular in location and have cystic components. The two subependymomas in our series were solid, intraventricular tumors with relatively homogeneous signal intensities.

Methods for measuring brain morphologic features on magnetic resonance images. Validation and normal aging

In this article, methods for measuring brain morphologic features on magnetic resonance images are described and normative data are provided for six morphologic variables. An estimated function relating age (ranging from 8 to 79 years) to average values is given for each measure. A linear decrease over the age range is observed in the volume of the cerebrum. Linear increases are observed in measures of ventricular and sulcal fluid. A curvilinear decrease in cortical volume is found and is demonstrable even in young adults. Highly nonlinear increases in the volume of signal hyperintensities are observed in cortical and subcortical regions. The methods described may be used to provide an age-adjusted index of morphologic abnormality for each subject on any of the measures. They are currently in use in ongoing neurobehavioral studies of patients with nonfocal brain abnormalities and primary disorders of affect and cognition.

Abnormalities of the brain in AIDS patients: correlation of postmortem MR findings with neuropathology

The ability of MR to detect CNS lesions in AIDS patients was evaluated by postmortem scanning of 10 formalin-fixed brains. Nine patients had premortem mental status changes and five had focal neurologic deficits. The brains were imaged and sectioned in corresponding planes. MR images showed atrophy in eight of the 10. All grossly identified lesions and areas of MR abnormality were histologically evaluated. Areas of infarction and necrosis associated with cytomegalovirus (CMV) or Toxoplasma gondii were seen as foci of increased signal intensity. Severe ventriculitis and focal gliosis were also visible by MR. Neither CT nor MR was able to detect diffuse CMV- or HIV-associated microglial nodules. Dementia without focal neurologic signs correlated best with the presence of diffuse microglial nodules at pathology. Our results demonstrate the usefulness of correlating postmortem MR imaging with neuropathology, and the relevance of postmortem findings to the interpretation of MR images in living patients.

Clinical experience with routine Gd-DTPA administration for MR imaging of the brain

A retrospective analysis of intracranial magnetic resonance (MR scans of 514 patients who underwent nonselective Gd-DTPA enhanced MR imaging was performed to determine the efficacy of this protocol for Gd-DTPA administration. This report reviews the frequency and clinical significance of abnormally enhancing areas that were entirely undetectable on precontrast images or would have been missed without the retrospective knowledge of enhancement. Fifty-seven patients (11% of the 514 patients studied) showed enhancing lesions, with 16 (3.1% of the total) of these patients demonstrating one or more lesions identifiable only on postcontrast images. Of those 16 patients, 8 had other focal abnormalities on precontrast studies, whereas the remaining 8 (1.6% of the total) had negative precontrast studies. The new diagnoses affected clinical management directly in five patients and in another nine contributed potentially significant information. Considerations regarding a selective versus nonselective protocol for Gd-DTPA administration for intracranial MR imaging and the use of clinical information to augment these protocols are discussed.

Subcortical abnormalities detected in bipolar affective disorder using magnetic resonance imaging. Clinical and neuropsychological significance

Magnetic resonance imaging was utilized to determine the nature and rate of subcortical abnormalities in bipolar affective disorder. Nine of 19 bipolar patients and no controls demonstrated subcortical signal hyperintensities on blind evaluation of the images. There was no apparent change in the appearance of the hyperintensities in 7 of 7 subjects with abnormal magnetic resonance images who underwent repeated imaging at 1 year. Bipolar patients with abnormalities had a history of more hospitalizations and appeared more impaired on tests of fluency and recall when compared with bipolar patients without abnormalities or with controls. The possible etiology and significance of signal hyperintensities in bipolar affective disorder is discussed.

Cardiac function, substrate utilization, and myocardial energy metabolism studied with 31-P NMR spectroscopy during acute hypoglycemia and hyperketonemia

Whether severe hypoglycemia alone or in combination with hyperketonemia might cause deterioration of cardiac function has been controversial. Therefore, the influence of acute hypoglycemia (mean 33 mg/dL) with and without hyperketonemia (mean 1.3 and 3.3 mM) on cardiac function, substrate utilization, and myocardial high energy phosphate levels was studied in 10 mongrel dogs. After 45 min of hypoglycemia, mean aortic pressure, total peripheral resistance, and myocardial oxygen consumption had increased significantly, but other hemodynamic parameters and regional myocardial function had not changed. Additional infusion of 3-hydroxybutyrate did not affect hemodynamic variables significantly. During both metabolic interventions in vivo phosphorus-31 nuclear magnetic resonance spectroscopy showed stable levels of myocardial phosphocreatinine, ATP, as well as the phosphocreatinine/ATP (3.0-3.2) ratio. Biochemical measurements revealed that hyperketonemia led to significant alterations in arterial concentrations and arteriocoronary venous differences of selected citric acid cycle intermediates, thus confirming previous reports which suggested a blockade of the 2-oxoglutarate-dehydrogenase reaction induced by ketone body oxidation. However, despite this blockade, the energy supply to the heart was not impaired as shown by normal nuclear magnetic resonance spectroscopy and cardiac performance. It is speculated, that the blockade might be due to an enhanced NADH/NAD ratio.

Heterotopic brain in the middle ear: CT findings

A soft tissue mass was found by CT in the mesotympanum of the left middle ear of a 4-year-old boy. This lesion was without radiologic or surgical evidence of associated bony defect or communication with the intracranial cavity. Pathological examination revealed heterotopic brain tissue. Although heterotopic brain tissue in the middle ear is rare, it should be considered in the differential diagnosis of soft tissue middle ear masses.

The cerebellum in sagittal plane--anatomic-MR correlation: 2. The cerebellar hemispheres

Thin (5-mm) sagittal high-field (1.5-T) MR images of the cerebellar hemispheres display (1) the superior, middle, and inferior cerebellar peduncles; (2) the primary white-matter branches to the hemispheric lobules including the central, anterior, and posterior quadrangular, superior and inferior semilunar, gracile, biventer, tonsil, and flocculus; and (3) several finer secondary white-matter branches to individual folia within the lobules. Surface features of the hemispheres including the deeper fissures (e.g., horizontal, posterolateral, inferior posterior, and inferior anterior) and shallower sulci are best delineated on T1-weighted (short TR/short TE) and T2-weighted (long TR/long TE) sequences, which provide greatest contrast between CSF and parenchyma. Correlations of MR studies of three brain specimens and 11 normal volunteers with microtone sections of the anatomic specimens provides criteria for identifying confidently these structures on routine clinical MR. MR should be useful in identifying, localizing, and quantifying cerebellar disease in patients with clinical deficits.

The cerebellum in sagittal plane--anatomic-MR correlation: 1. The vermis

Correlation of thin (5-mm) sagittal high-field (1.5-T) MR images of three brain specimens and 11 normal volunteers with microtome sections of the human cerebellar vermis and hemispheres demonstrates that proton-density-weighted (long TR/short TE) and T2-weighted (long TR/long TE) spin-echo pulse sequences provide the greatest contrast between gray and white matter. These images also can display (1) the corpus medullare and primary white-matter branches to the vermian lobules, including the lingula, centralis, culmen, declive, folium, tuber, pyramis, uvula, and nodulus; and (2) several finer secondary branches to individual folia within the lobules. Surface features of the vermis including the deeper fissures (e.g., preculminate, primary, horizontal, and prepyramidal) and shallower sulci are best delineated by T1-weighted (short TR/short TE) and T2-weighted images, which provide greatest contrast between CSF and parenchyma. Given that the width of the normal vermis varied from 6 to 12 mm in our volunteers, the acquisition of thin slices (less than or equal to 5 mm) was required to minimize volume averaging of the cerebellar hemispheres with the vermis on a midline sagittal MR section. Knowledge of the detailed normal anatomy of the cerebellar vermis on sagittal MR images can assist in the identification of various pathologic alterations.

Ketone bodies maintain normal cardiac function and myocardial high energy phosphates during insulin-induced hypoglycemia in vivo

It has been suggested that myocardial utilization of ketone bodies might cause deterioration of cardiac function. Therefore, the influence of ketonemia (mean: 1.3 and 3.3 mM) in the presence of hypoglycemia (mean: 33 mg/dl) on cardiac function, substrate utilization and myocardial high energy phosphate levels was studied in 10 mongrel dogs. Hypoglycemia alone led to a significant increase of mean aortic pressure, total peripheral resistance and myocardial oxygen consumption, but other hemodynamic parameters and regional myocardial function were not changed. Additional infusion of 3-hydroxybutyrate did not affect hemodynamic variables significantly. During both metabolic interventions in vivo phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy showed stable levels of myocardial Pi, PCr, ATP, as well as PCr/Pi (3.2-3.4) and PCr/ATP (3.0-3.2) ratios. Biochemical measurements revealed that ketonemia led to significant alterations in arterial concentrations and arterio-coronary venous differences of selected citric acid cycle intermediates, thus confirming previous reports which suggested a blockade of the 2-oxoglutarate-dehydrogenase reaction induced by ketone body oxidation. However, despite this blockade, the energy supply to the heart was not impaired as shown by normal NMR spectroscopy and cardiac performance. It is speculated that the blockade might be due to an enhanced NADH/NAD ratio.

Reduced cerebellar hemisphere size and its relationship to vermal hypoplasia in autism

Cerebellar hemisphere size was calculated in 10 autistic and 8 normal control subjects by summing the cross-sectional areas of cerebellar hemisphere tissue measured on paramidline sagittal magnetic resonance images. The areas of two cerebellar vermal regions (lobules I through V and lobules VI through VII) were also measured using the midsagittal image. Our cumulative slice area measure of cerebellar hemisphere size was significantly smaller in the autistic subjects than in the control group. The cumulative slice area correlated positively with the area of vermal lobules VI through VII only in the autistic subjects. Our results indicated that the decreased size of the cerebellar hemispheres and vermal lobules VI through VII was associated with autism.

Optic neuropathy associated with cryptococcal arachnoiditis in AIDS patients

We studied two cases of bilateral visual loss secondary to an optic neuropathy in patients with cryptococcal meningitis. In both cases a history of visual loss after the onset of an episode of cryptococcal meningitis was elicited. Visual fields were consistent with optic nerve disease. The patients' visual loss appeared to be the result of perineuritic adhesive arachnoiditis. Although no surgical interventions were carried out in our patients, medical or surgical intervention may be useful to prevent or relieve constrictive arachnoiditis and preserve vision in selected patients.

Mucocele of the anterior clinoid process: CT and MR findings

A patient with biopsy-proven primary mucocele of the anterior clinoid process is presented. Gadolinium-DTPA enhanced magnetic resonance imaging revealed a nonenhancing lesion isointense to gray matter. Computed tomography revealed well corticated bony margins without direct involvement of the sphenoid sinus.

MR demonstration of reversible brain abnormalities in eclampsia

A 24-year-old woman with eclamptic convulsions during her 25th week of gestation is presented. Magnetic resonance imaging revealed multiple hyperintense foci within the cerebral cortex, most likely related to cerebral ischemia and edema. The MR abnormalities resolved completely within 1 week.

MR imaging and CT in three cases of Sturge-Weber syndrome: prospective comparison

Three patients with Sturge-Weber syndrome (5 months, 6 years, and 17 years old) were studied prospectively with MR imaging and CT of the brain. Both techniques demonstrated parenchymal volume loss, choroid plexus enlargement, calvarial hemiatrophy, and proptosis. In regions of parenchymal volume loss, MR alone demonstrated thickened cortex with decreased convolutions and abnormal white matter. A focal thalamic lesion and prominent medullary and subependymal veins were also shown better by MR. However, CT definitively demonstrated the characteristic cortical calcification, while T2-weighted MR images detected only smaller, nonspecific foci of hypointense signal. MR and CT are complementary in the evaluation of Sturge-Weber syndrome.

Abnormalities of the brain in nonketotic hyperglycinemia: MR manifestations

MR imaging in seven patients (4 days to 38 months old) with nonketotic hyperglycinemia showed age-related findings of progressive atrophy and delayed myelination. Parenchymal volume loss was found as early as 4 days after birth and increased in severity with increasing age to 27 months. Both supratentorial and infratentorial volume loss were present in the most severely affected patients. The corpus callosum was abnormally thin in all patients. The state of myelination of the CNS was assessed on T2-weighted images. Decreased or absent myelination within supratentorial white-matter tracts was detected in all four patients 10 months of age or older. Myelination of the brainstem and cerebellum progressed normally. No correlation was found between the degree of volume loss or abnormality of myelination demonstrated by MR and the concentration of glycine in the CSF or plasma. Abnormalities shown by MR correlate well with known pathologic findings in patients with nonketotic hyperglycinemia.