Normal postnatal development of the corpus callosum as demonstrated by MR imaging.

Sixty-three patients, 3 days to 12 months old, were examined by MR imaging to evaluate the normal development of the corpus callosum in the first year of life. During the first month of life the corpus callosum is uniformly thin and of the same signal intensity as white matter throughout the brain. During the second month, a variable spurt of growth occurs in the genu, followed by a similar period of rapid growth in the splenium between 4-6 months of age. High signal intensity on T1-weighted images related to the myelination process begins to appear in the splenium by about 4 months and in the genu by about 6 months. The corpus callosum has an adult appearance on sagittal scans by about 8 months of age.

Schizencephaly: correlation of clinical findings with MR characteristics.

PURPOSE: To correlate clinical outcome with the size and location of clefts in patients with schizencephaly. PATIENTS AND METHODS: MR scans and clinical records of 20 patients with schizencephaly were retrospectively reviewed. Seven patients had bilateral clefts (10 open lip clefts, 4 closed lip clefts), eight patients had right-sided unilateral clefts (5 open lip clefts, 3 closed lip clefts), and five patients had left-sided unilateral clefts (3 open lip clefts, 2 closed lip clefts). RESULTS: Statistically significant correlations were found as follows: Patients with bilateral schizencephalies had significantly worse intellectual (P = .004) and speech (P = .03) development than those with unilateral clefts; patients with unilateral large or medium open lip schizencephalies had significantly worse motor (P = .003) and intellectual (P = .008) impairment than those with unilateral closed lip or small open-lip schizencephalies; patients with frontal lobe involvement had a significantly higher incidence of motor dysfunction than those without frontal lobe involvement (P = .01). Strong similarities were noted in the patient outcomes and the locations of cortical anomalies of patients with schizencephaly and those with nonschizencephaly focal cortical dysplasias. CONCLUSION: A common pathogenetic origin for the formation of focal cortical dysplasia in the form of polymicrogyria and schizencephalies is proposed. Patients with small unilateral schizencephalies have a good developmental prognosis, particularly when the motor cortex is not involved.

Nonlissencephalic cortical dysplasias: correlation of imaging findings with clinical deficits.

PURPOSE: To establish correlations between MR patterns and clinical outcome in patients with nonlissencephalic cortical dysplasias. PATIENTS AND METHODS: MR and clinical data from 36 patients with cerebral cortical gyral anomalies (other than classical type I or type II lissencephaly) were retrospectively reviewed. RESULT: The five patients with diffuse cortical dysplasia, including two with congenital infections, had microcephaly and severe development delay from a very early age. Infantile spasms occurred in three of the five. Focal areas of cortical dysplasia were most common in the frontal lobes, but were seen in all areas of the brain. The most common MR appearances were 1) a thickened, irregularly bumpy cortex with shallow, wide sulci, and 2) a deep infolding of thickened cortex. The twelve patients with bilateral focal dysplasia had a high incidence of bilateral motor dysfunction (67%), delayed speech (67%), and generalized developmental delay (92%). When the dysplasia was unilateral, contralateral spastic hemiplegia or monoplegia was present in 14 of 19 patients (74%), but dysphasia was uncommon, even in patients with dysplasia in the frontal lobe of the dominant hemisphere. CONCLUSION: Surgical resection of focal areas of cortical dysplasia in patients with medically refractory seizures is becoming more common, and the neuroradiologist will play an increasingly important role in the initial diagnosis and delineation of these anomalies.

Brain MR imaging in children with developmental retardation of unknown cause: results in 76 cases.

Seventy-six children with developmental retardation of unknown cause underwent MR imaging of the brain. Twenty-one (28%) had positive MR findings, including nine with atrophy, six with delayed myelination, four with multiple focal white matter lesions, three with hypoplastic white matter, and three with migration abnormalities. The frequency of abnormality was highest in nonautistic children with associated neurologic physical findings (61%) but was also significant in nonautistic children without neurologic findings (23%). We did not detect abnormalities on MR images of autistic retarded children. Delayed myelination and migration abnormalities were the predominant abnormalities in children with associated neurologic findings, whereas focal white matter lesions were more common in children without neurologic findings. Abnormalities were significantly more common in children with a small head circumference. Although MR did not have any effect on treatment or prognosis, it did aid the clinician in family counseling. MR will reveal brain abnormalities in about one third of nonautistic children with developmental retardation of unknown cause, and more often in those with neurologic deficits, seizures, or a small head size.

MR imaging of orbital and ocular disease.

Magnetic resonance (MR) images of 27 patients with ocular and orbital pathology were reviewed retrospectively and correlated with computed tomography (CT), funduscopic examination, and tissue histology. Disease processes were classified by location into ocular, extraconal, intraconal, optic nerve, and orbital apex. The diagnostic efficacy of MR differed at each location. MR was very sensitive in detecting ocular, extraconal, and intraconal lesions larger than 5 mm but was insensitive in imaging smaller lesions and in detecting pathology of the optic nerve. The limitations of MR were related to 7 mm slice thickness and 2.6 mm interslice gap. The diagnostic accuracy is expected to improve markedly with further developments in thin-section imaging and use of surface coils.

Posterior pituitary ectopia: an MR feature of pituitary dwarfism.

Using high-field-strength, 1.5-T, high-resolution MR, we identified the following complex of neurohypophyseal abnormalities in each of five pituitary dwarfs: (1) severe hypoplasia or total absence of the infundibulum; (2) absence of the posterior pituitary bright spot in its normal location; and (3) a 3-8-mm tissue nodule at the median eminence exhibiting lipidlike signal on T1-weighted images. On the basis of its signal features and the clinical absence of diabetes insipidus in these patients, the median eminence nodule appears to represent an ectopic and functional posterior pituitary gland. We propose that this anatomic derangement is the end result of a localized defect of developmental origin, possibly ischemic in nature, and involving principally the infundibular stem. Thus, human growth hormone deficiency could result from perinatal disruption of the peri-infundibular hypophyseal portal system, which in turn impairs anterior pituitary function through deprivation of direct delivery of crucial hypothalamic-releasing factors. Finally, we suggest that the trophic influence of continued axonal neurosecretion at the median eminence engages proliferation of rest cell pituicytes; a process that induces formation of an ectopic and functional posterior pituitary gland, complete with its characteristic bright spot.

Gray matter heterotopias: MR characteristics and correlation with developmental and neurologic manifestations.

Magnetic resonance (MR) images and clinical records of 20 patients with gray matter heterotopias were retrospectively reviewed to correlate MR characteristics of the heterotopias with clinical findings. On the basis of the MR images, patients were divided into three groups: those with subependymal heterotopias (eight patients), focal subcortical gray matter heterotopias (six patients), and diffuse subcortical heterotopias (six patients). Patients with subependymal heterotopias had a significantly higher prevalence of normal development than patients in the other two groups (P = .02). When all patients with gray matter heterotopias were considered, patients with thick heterotopias and those with overlying cortical gyral anomalies, which correlated with one another, had a significantly higher prevalence of developmental delay (P = .002). Patients with thick focal gray matter heterotopias had a substantially increased prevalence of motor dysfunction. In three cases, gray matter heterotopias were associated with infoldings of dysplastic cortex containing blood vessels or cerebrospinal fluid. If not properly analyzed, these anomalies can be mistaken for vascular or cystic tumors.

Early CT findings of global central nervous system hypoperfusion.

The early computed tomographic (CT) findings of acute global central nervous system hypoperfusion were studied in 10 patients. The findings could be characterized as: (1) diffuse mass effect with effacement of the cerebral sulci and of the brainstem cisterns (nine patients); (2) global decrease in the cortical gray-matter density from edema, causing loss of the normal gray-white matter differentiation (six patients); (3) low-density lesions of the basal ganglia bilaterally (five patients); and (4) decreased gray-matter density in watershed distributions bilaterally (two patients). Subsequent contrast-enhanced scans in three of the 10 patients demonstrated selective enhancement of the cerebral cortex or the basal ganglia or both. The CT findings seen in this study predicted a poor outcome; nine of the 10 patients died from the insult. The abnormal CT findings can be ascribed to increased vulnerability of the cerebral cortex and basal ganglia to hypotensive episodes. This vulnerability is due to the large metabolic demand of these regions and their characteristic local cerebral blood flow.

Reproducibility of T1 and T2 relaxation times calculated from routine MR imaging sequences: phantom study.

Measurement of T1 and T2 relaxation times has been sought as one fundamental way to characterize tissue. Relaxation times can be calculated from routine spin-echo (SE) imaging sequences using two distinct repetition times (TRs), each with two SE samplings of signal intensity. Previous reports have quantified relaxation times without discussing the variation in their measurements. By imaging a phantom containing different samples with known T1 and T2 relaxation times on three separate occasions, the variation in relaxation time measurements inherent in different routine imaging sequences was studied. For the present study a more complete and accurate equation was used to calculate T1 values. The variation in T1 and T2 relaxation times for samples with relaxation times similar to solid tissue was 2%-4%. The amount of variability in calculated relaxation times was found to be dependent on the magnitude of the relaxation times themselves. However, the mean values were independent of the imaging sequences used to calculate the relaxation times. No significant differences were seen between left-to-right or section-to-section position within the same study or between studies performed on different occasions. The variability in the calculated T1 was dependent on the pair of TR sequences used to calculate T1. Samples with long T1 and T2 relaxation times, similar to many body fluids, had much larger variability. A computer simulation of measurement error was created to explain these results. This study indicates that properly performed routine imaging studies do yield reproducible T1 and T2 measurements.

Normal maturation of the neonatal and infant brain: MR imaging at 1.5 T.

The pattern of normal white-matter maturation as demonstrated with high-field-strength magnetic resonance (MR) imaging was investigated. Eighty-two neurologically normal infants were examined with a 1.5-T unit with use of spin-echo T1-weighted and T2-weighted pulse sequences. The infants ranged in age from 4 days to 2 years. The images were assessed for qualitative changes of white matter relative to gray matter in 14 anatomic areas of the brain and correlated with the patient's age. The MR images showed that changes of brain maturation occur in an orderly manner, commencing in the brain stem and progressing to the cerebellum and the cerebrum. Changes caused by brain myelination were seen earlier on T1-weighted images than on T2-weighted images, possibly because of T1 shortening by the components of the developing myelin sheaths. The later changes on the T2-weighted images correlated best with the development of myelination as demonstrated with histochemical methods. T1-weighted images were most useful in the monitoring of normal brain development in the first 6-8 months of life; T2-weighted images were more useful after 6 months. The milestones in the MR appearance of normal maturation of the brain are presented. Persistent areas of long T2 relaxation times are seen superior and dorsal to the ventricular trigone in all infants examined and should not be mistaken for ischemic change.

Revised classification of posterior fossa cysts and cystlike malformations based on the results of multiplanar MR imaging.

MR and clinical data on 31 patients with posterior fossa CSF collections were analyzed. A clear separation of these patients into classical categories was not possible because of new information obtained from the MR images. We present a new classification of these disorders. The Dandy-Walker malformation, Dandy-Walker variant, and mega-cisterna magna seem to represent a continuum of developmental anomalies of the posterior fossa. A possible embryologic basis for this continuum is suggested. Discrete posterior fossa CSF collections that are clearly separate from the fourth ventricle and vallecula are classified as posterior fossa cysts. Posterior fossa CSF collections that communicate with the fourth ventricle and are associated with cerebellar atrophy are classified as prominent cisterna magna. Both the Dandy-Walker complex and posterior fossa cysts can cause enlargement of the posterior fossa and scalloping of the inner table of the occipital bone. The Dandy-Walker complex presents with seizures, developmental delay, and enlarging head size; it requires CSF diversion when associated with hydrocephalus. Posterior fossa cysts present with symptoms of a posterior fossa mass; they generally require surgical resection. Prominent cisterna magna is a result of degenerative disorders and requires no surgical therapy. This new classification facilitates both diagnosis and therapy of these disorders. MR revealed that disorders previously referred to as the Dandy-Walker malformation, the Dandy-Walker variant, and the mega-cisterna magna actually are not separate entities, but appear to represent steps on a continuum of developmental anomalies of the posterior fossa. Because of this, we suggest a new term, the Dandy-Walker complex, be used to describe this continuum.

Magnetic resonance imaging of the nasopharynx.

Thirty subjects with normal nasopharyngeal anatomy and 12 patients with a variety of abnormalities were examined with computed tomography (CT) and magnetic resonance imaging (MR), using a prototype 0.35-T superconducting system. A spin-echo technique, a repetition time (TR) of 2.0 sec., and echo times (TE) of 28 and 56 msec. were optimal for depiction of both normal and abnormal anatomy. MR was superior to CT for display of both superficial and deep nasopharyngeal soft tissues in all 30 normal subjects and 10 of the 12 abnormal patients, clearly differentiating mucosal and lymphoid tissue (adenoids, lingual and palatine tonsils) from the surrounding musculature. MR was also superior to CT in distinguishing tumor from soft tissues and more sensitive to carotid sheath adenopathy, permitting a more detailed evaluation of retropharyngeal and deep cervical nodal metastases in 2 cases. Bones, calcification, and subtle abnormalities at the base of the skull were shown better by CT. The specificity of MR and its ability to differentiate nodal metastases from reactive lymphadenopathy require further evaluation.

Magnetic resonance scanning in orbital tumor diagnosis.

We have compared the accuracy of magnetic resonance scanning (MRI) versus computed tomography (CT) in the differentiation of lateral orbital masses. The MRI results did not improve our ability to accurately diagnose malignant epithelial and lymphoid tumors.

Relative intensity of abdominal organs in MR images.

Knowledge of the normal relative intensity of organs and tissues is a valuable aid to clinical interpretation of magnetic resonance images. In this study the in vivo spin echo image intensities of normal parenchymal organs and other structures in the upper abdomen were evaluated for eight parameter combinations. The examinations of 40 patients were used. Image intensity and calculated T1, T2, and spin density values were obtained for liver, spleen, pancreas, renal cortex, renal medulla, bone marrow, skeletal muscle, and fat. Repetition times (TR) of 500, 1,000, 1,500, and 2,000 ms and echo times of 28 and 56 ms were used. The T1 and T2 values and relative spin density were calculated using a new algorithm. Liver had the smallest relative standard deviation of T1 of all the tissues studied. For comparison purposes, relative image intensities were calculated by normalizing them to the intensity of liver in the same image. The resulting compiled data show the normal ranks and ranges for relative intensity for the tissues in each of eight types of spin echo images. Although images with short TR and echo time (TE) are known to display the greatest T1 contrast, the mean relative intensities of all tissues except muscle and fat in the TR = 500 and TE = 28 ms images were within 20% of liver. A much larger spread in the normal relative intensities was observed with longer TE and TR.

Brain abscess following marrow transplantation: experience at the Fred Hutchinson Cancer Research Center, 1984-1992.

The etiology of brain abscess in patients undergoing marrow transplantation at the Fred Hutchinson Cancer Research Center in Seattle was assessed in a retrospective review. Fifty-eight patients with histology- or culture-proven brain abscess diagnosed between January 1984 and March 1992 were identified. A fungus was isolated in 92% of cases. Aspergillus species were the most prevalent fungi (58% of cases), and Candida species were second in frequency (33%); sporadic cases were caused by Rhizopus, Absidia, Scopulariopsis, and Pseudallescheria species. Bacteria were involved in fewer than 10% of cases. There was no appreciable variation from year to year in the incidence of brain abscess over this period. Aspergillus brain abscess was associated with concomitant pulmonary disease (87% of cases), whereas candida brain abscess often occurred in association with fungemia (63% of cases) or neutropenia (63%). Mortality was high (97%); the risk of death was unrelated to etiology or therapeutic regimen. Since the etiology of brain abscess in patients undergoing marrow transplantation is primarily fungal, the development of better antifungal therapeutic and/or prophylactic modalities is warranted.

Neurofibromatosis types 1 and 2: cranial MR findings.

Neurofibromatosis 1 (NF-1) (von Rekhlinghausen disease) and neurofibromatosis 2 (NF-2) (bilateral acoustic neurofibromatosis) have been recently recognized to be distinct disorders through genetic linkages. The authors compared the cranial magnetic resonance (MR) images of 53 patients with NF-1 and 11 with NF-2. In the NF-1 group, MR imaging revealed 19 patients with optic gliomas and eight with parenchymal gliomas. In 32 patients, foci of prolonged T2, similar to those reported previously as hamartomas, were identified in the cerebellar peduncles, globus pallidus, midbrain, and other locations. The frequency of these foci was related to both age and the presence of optic gliomas. In the NF-2 group, MR imaging revealed eight patients with cranial nerve schwannomas and six with meningiomas (in addition to acoustic schwannomas in all 11). These findings demonstrate that NF-1 and NF-2 are different diseases requiring different imaging protocols. NF-1 seems to be associated with tumors of astrocytes and neurons and NF-2 with tumors of meninges and Schwann cells.

Cranial bone marrow in children: assessment of normal development with MR imaging.

Magnetic resonance images of cranial bone marrow in 238 patients (246 examinations) less than 25 years old were reviewed to establish normal age-related standards. Bone marrow in the clivus and calvaria had uniformly low signal intensity (grade 1) on T1-weighted images in most infants less than 1 year old. The number of patients with grade 1 marrow decreased rapidly in early childhood, while the number of patients with marrow of low and high signal intensity (grade 2) and uniformly high signal intensity (grade 3) gradually increased with age. A grade 1 marrow was no longer observed in either the clivus or calvaria after age 7. Most patients had a grade 3 marrow by age 15. Because bone marrow in certain pathologic conditions has decreased signal on T1-weighted images and therefore resembles grade 1 or 2 appearances of normal marrow in children, these results may be useful for differentiating normal and abnormal bone marrow signal intensities in infants and children.

MR technology: effect of even-echo rephasing on calculated T2 values and T2 images.

In multiple spin-echo image sequences of blood flow, the "even-echo" phenomenon produces an absolute increase in signal magnitude from first- to second-echo images of normal vessels harboring slow flow. Distinguishing this from the apparent relatively high signal intensity seen on second-echo images in pathologic foci of stationary tissue is important to the diagnostician. Selected case material containing two tissue types was reviewed retrospectively: tissues known to harbor slow flow, such as normal veins and venous sinuses and vascular malformations, and tissues that have long transverse (T2) relaxation times and appear as intense structures on second-echo images, such as neoplasms, infarcts, and regions of demyelination. Calculations of T2 parameters were made by computer for defined regions of interest. T2 images were also generated. Visual inspection of the acquired images did not reliably distinguish increased intensity due to even-echo rephasing from the relative changes between adjacent tissues seen on second-echo images. More definitive differentiation of the even-echo phenomenon was provided by calculated values of T2 and computer-synthesized T2 images representing acquired intensity data of two-echo sequences. The synthesized images were especially useful when stationary tissue with lengthened T2 values was adjacent to or in proximity to vessels or vascular lesions. A five spin-echo image sequence was valuable for separating slow flow from stationary tissue by a technique of synthesizing T2-difference images using three consecutive echoes.

Reproducibility of relaxation times and spin density calculated from routine MR imaging sequences: clinical study of the CNS.

This study was undertaken to determine if routine clinical magnetic resonance imaging sequences using only two different repetition times (TRs) and with only two sequential spin echoes (SEs) can be used to calculate reproducible relaxation time and spin density values for normal central nervous system tissue using a 0.35 T production-model instrument. In 43 patients 650 regions of interest of 11 different anatomic sites were measured. T1 and T2 relaxation times and spin density were measured. For each anatomic location, the mean and standard deviation of these values were determined. In most solid regions of brain, the standard deviation of both T1 and T2 was 4%-8%. Relaxation times of cortical gray matter varied more, with a standard deviation of 10%, probably because of volume-averaging with adjacent cerebrospinal fluid (CSF). CSF and ocular vitreous humor were neither reproducibly nor accurately measured because of the short TR and TE settings of the imaging sequences relative to the long T1 and T2 relaxation times of these substances. Significant and reproducible differences were found between the spin densities of gray matter and white matter, as well as between different regions of white matter. These differences are of major importance in contrast discrimination of gray and white matter on the long TR images. Knowing that relaxation values and spin densities calculated from routine imaging sequences are in fact reproducible, these normal ranges can now be used to investigate changes occurring in disease states.

Magnetic resonance imaging and characterization of normal and abnormal intracranial cerebrospinal fluid (CSF) spaces.

A retrospective review of twenty-five normal MRI brain studies performed with the spin-echo technique focused special attention on the ventricular and extraventricular cerebrospinal fluid (CSF) and revealed unique signal intensity characteristics in the two locations. In addition, MRI studies of ten patients with abnormal extraaxial fluid collections either missed with CT or indistinguishable from CSF on CT images were also analyzed. MRI is more sensitive when compared to CT in evaluating the composition of CSF. Unique signal intensity characterizes the two major CSF compartments and presumably reflects their known but subtle difference in protein concentration (10-15 mg%). Normal variant or abnormal developmental fluid collections can be better characterized with MRI than with CT. These preliminary observations are offered in view of their implications for patient management and suggest further investigation.