Quantitative cine-mode magnetic resonance imaging of Chiari I malformations: an analysis of cerebrospinal fluid dynamics.

Quantitative cine-mode magnetic resonance imaging of the craniocervical junction was performed in 17 patients with a Chiari I malformation to evaluate cerebrospinal fluid (CSF) dynamics, including 8 patients who underwent surgery. The cine-mode magnetic resonance images of these patients were compared with those of 12 normal pediatric and adult subjects. The craniocervical junction was imaged by 16 cardiac-gated velocity-encoded images arranged in a cine loop. These images allowed the measurement of both the magnitude and direction of CSF velocity. Velocity measurements were made in four regions of interest--the foramen Magendie, the foramen magnum, and ventral and dorsal to the spinal cord at C2--and were plotted in relation to the cardiac cycle to produce a CSF velocity profile. All patients who underwent surgery had the same procedure: a posterior fossa craniectomy with C1 laminectomy, lysis of arachnoid adhesions, and duraplasty. Normal subjects had unobstructed flow around the craniocervical junction: a short period of cranial CSF flow was followed by a sustained period of caudal CSF flow. Patients with tonsillar herniation of more than 5 mm had obstructed CSF flow, decreased CSF velocity, and shorter periods of caudal CSF flow. These patients also had preferential cranial CSF flow as compared with the controls. Postoperatively, there was a substantial increase in both the velocity of CSF flow and in the period of caudal CSF flow in the foramen magnum. The postoperative changes mirrored the velocity profiles of the normal subjects. These changes in CSF velocity and direction correlated with a more normal-appearing foramen magnum, a reduction in syrinx size, and an improvement in symptoms.

MR imaging of CSF-like choroidal fissure and parenchymal cysts of the brain.

The purposes of this study were to delineate the MR characteristics of CSF-like parenchymal or fissural cysts of the brain and to correlate them with the clinical findings. Clinical data and MR images of 34 patients with these abnormalities were reviewed. Pathologic correlation was not available. Two types of cystic lesions were identified and separated by location: medial temporal lobe cysts arising in or near the choroidal fissure (26 patients) and parenchymal or pseudoparenchymal cysts not related to the choroidal fissure (eight patients). The choroidal fissure cysts simulated intraparenchymal cysts on axial images but their extraaxial location was well portrayed on the coronal images. Choroidal fissure cysts had a characteristic spindle shape on sagittal images. The other cysts were found in the temporal lobe (seven patients) or thalamus (one patient) and appeared parenchymal but situated close to the subarachnoid space. These lesions were round or ovoid. There was no abnormal enhancement in 10 patients studied with gadopentetate dimeglumine. Coronal images were most useful, revealing the cysts as focal CSF-intensity lesions expanding the choroidal fissure of the temporal lobe. All the cysts appeared to represent incidental findings that did not correlate with the clinical signs and/or symptoms that prompted the imaging evaluations. The MR characteristics of CSF-like cysts are important to recognize so that they are not confused with other, more serious entities, such as intraaxial cystic tumors, infarctions, or parasitic lesions.

MR imaging of CSF-like choroidal fissure and parenchymal cysts of the brain.

The purposes of this study were to delineate the MR characteristics of CSF-like parenchymal or fissural cysts of the brain and to correlate them with the clinical findings. Clinical data and MR images of 34 patients with these abnormalities were reviewed. Pathologic correlation was not available. Two types of cystic lesions were identified and separated by location: medial temporal lobe cysts arising in or near the choroidal fissure (26 patients) and parenchymal or pseudoparenchymal cysts not related to the choroidal fissure (eight patients). The choroidal fissure cysts simulated intraparenchymal cysts on axial images but their extraaxial location was well portrayed on the coronal images. Choroidal fissure cysts had a characteristic spindle shape on sagittal images. The other cysts were found in the temporal lobe (seven patients) or thalamus (one patient) and appeared parenchymal but situated close to the subarachnoid space. These lesions were round or ovoid. There was no abnormal enhancement in 10 patients studied with gadopentetate dimeglumine. Coronal images were most useful, revealing the cysts as focal CSF-intensity lesions expanding the choroidal fissure of the temporal lobe. All the cysts appeared to represent incidental findings that did not correlate with the clinical signs and/or symptoms that prompted the imaging evaluations. The MR characteristics of CSF-like cysts are important to recognize so that they are not confused with other, more serious entities, such as intraaxial cystic tumors, infarctions, or parasitic lesions.

Measurements of the normal cervical spinal cord on MR imaging.

The purpose of this study was to determine normal measurements of the C1-T3 spinal cord in anteroposterior and transverse planes from MR images and to compare these with previously published data. Seven hundred and fifty-six measurements were made from 66 randomly selected MR studies of the cervical spine. We measured the anteroposterior and transverse diameters of the cord at each vertebral level and computed the simple product of these diameters to provide a single useful numerical value, termed the approximate cord area (ACA). The cord varies in average anteroposterior and transverse diameters from 8.8 mm x 12.4 mm at C2 to 8.7 mm x 14 mm at C4 to 7.4 mm x 11.4 mm at C7. The cervical enlargement was found from C4 to C6 and was most evident by comparing the ACA values. At C2 the average ACA was 110 mm2, at C4 it was 121.9 mm2, and at C7 the average ACA was 84.6 mm2. Comparison of our data with the literature reveals disparate measurements that vary up to 6 mm from our mean values. However, our results correlated well with the postmortem studies of Nordquist (1964). A single number cannot be used as the basis for evaluating spinal cord size. Each level should be compared with the normal range specific for that level.

MR and CT evaluation of intracranial sarcoidosis.

Fourteen patients with CNS manifestations of neurosarcoidosis were evaluated by MR imaging and CT. Evaluations were done on a 0.5-T superconductive magnet with T1- and T2-weighted sequences. CT with contrast was obtained in all patients. The granulomatous lesions were classified by location into basilar, convexity, intrahemispheric, and periventricular white-matter involvement. Hydrocephalus with or without an associated lesion was also noted. MR determined the presence of disease in all patients (100%), but was less accurate than CT in depicting disease in two patients (14%). CT determined the presence of disease in 12 patients (85%) and was less accurate than MR in delineating hypothalamic involvement in two patients and periventricular white-matter disease in three patients. There was great variability in the appearance of intracranial sarcoidosis on MR. Three patients had lesions that were isointense or hypointense (relative to cerebral cortex) on both T1- and T2-weighted images while nine patients had lesions that were hyperintense on T2-weighted images. Convexity involvement and hydrocephalus were well documented by both CT and MR. These results indicate that both MR and CT are helpful in fully evaluating a patient with suspected intracranial sarcoidosis.

Adrenoleukodystrophy: correlating MR imaging with CT.

The effect on the brain of the sex-linked recessive form of adrenoleukodystrophy was studied in 40 boys, 4-18 years old. All underwent computed tomography (CT) scanning; six underwent magnetic resonance (MR) imaging. MR showed a high sensitivity in demonstrating white matter disease. Auditory pathway disease was characterized as involvement of the lateral lemniscus and medial geniculate body, and visual pathway disease was characterized by lateral geniculate body, Meyer loop, and optic radiation involvement. Contrast-enhanced CT still proved to have a greater capacity (at this time) to show the active, advancing form of the disease and concomitant calcifications. This large CT series also demonstrated the broad and variable expressions of adrenoleukodystrophy, which allowed the unification of previously described atypical forms of the disease.

MR imaging of syringobulbia.

The magnetic resonance (MR) examinations of 65 patients with syringomyelia were evaluated to determine the incidence and MR characteristics of syringobulbia. Syringobulbia was identified in 11 patients (17%), 10 of whom had communicating syringomyelia (associated with the Chiari I malformation) and one idiopathic syringomyelia. The cavities extended from 5 to 20 mm above the plane of the foramen magnum. Two types of syringobulbia were identified. The 10 patients with Chiari I malformation had thin clefts or slits extending into the medulla. These cavities were much smaller than the cervical cavities. The other patient had saccular syringobulbia in which the medullary cavity was similar to the cervical syrinx cavity. The T1-weighted images were most useful in detection of syringobulbic cavities. The theory of syringobulbia development and a brief review of the literature are included.

MR of postoperative syringomyelia.

Twenty-seven MR scans of 20 patients surgically treated for syringomyelia were reviewed. Thirteen patients had syringomyelia associated with the Chiari I malformation, four cases were posttraumatic, and three were idiopathic. The operations performed included syringosubarachnoid and syringoperitoneal shunts, myelotomies, and foramen magnum decompressions. Three of the foramen magnum decompressions had associated posterior fossa duroplasties, two had fourth-ventricle-to-subarachnoid shunts, and two had plugging at the obex. On 20 scans of patients in whom the syrinx cavity had been shunted, the shunt catheter was seen in 15 (75%). When adequately treated by shunting, syringes are completely collapsed and show no flow void. Nine patients were treated by foramen magnum decompression; all were well seen by MR. Three of these patients had a poor clinical result; these were the only patients in whom CSF was not seen between the foramen magnum and the neural structures of the posterior fossa on any images. The proposed mechanisms of syrinx formation and extension are discussed and related to the surgical procedures used to treat syringomyelia.

The MR appearance of syringomyelia: new observations.

Fifty-eight patients with spinal cord cavities were studied with MR imaging. Patients were separated into four groups, and the appearance of the cavities were compared. There were 24 patients (41.4%) with communicating syringomyelia (associated with the Chiari I malformation). Sixteen patients (27.6%) had posttraumatic syringomyelia, nine patients (15.5%) had associated tumors, and nine patients (15.5%) had idiopathic syringomyelia. The characteristics of each syrinx, the spinal cord, and the appearance of the cerebellar tonsils were analyzed on T2- and T1-weighted images. There is a striking similarity in the appearance of many syrinx cavities regardless of the cause. Characteristics that were found in some patients in every group included areas of increased intensity on T2-weighted images, the presence of the CSF flow-void sign (CFVS) in the syrinx cavity, eccentric cavities, "beaded" cavities, and cord enlargement. Tonsillar ectopia alone does not indicate that a syrinx is of the "communicating" type, since it was present in two of 16 patients (13%) with trauma and in two of five patients (40%) with tumors. T1-weighted images were most useful in evaluating the anatomic characteristics of the syrinx and the cerebellar tonsils. Most syrinx cavities involved the cervicothoracic junction. The average length was between five and nine vertebral segments (depending on category) but varied between one and 20 vertebral segments. T2-weighted images revealed areas of increased intensity in the spinal cord in 13 patients without tumors. Two of these cases were shown to represent gliosis on histopathologic review. The CFVS was present in the syrinx cavities of 23 patients (40%), probably reflecting pulsatile movements of the syrinx fluid. It has been proposed that such movements are a cause of syrinx propagation, and the observation of the CFVS may have prognostic significance. The development and progression of the CFVS was documented in serial MR examinations in one patient over an 18-month period. The theories of syrinx development and propagation are reviewed.

MR imaging of the mesencephalic tectum: normal and pathologic variations.

Variations of the quadrigeminal plate (mesencephalic tectum) were determined on midline sagittal MR images of the brain in 93 patients without known mesencephalic abnormalities and in 10 patients with known aqueductal stenosis or obstruction. Measurements of the thicknesses of the superior and inferior colliculi and the length of the tectum were made on the midline sagittal section. Images were obtained with a 0.5 T system with spin-echo pulse sequences using a TE of 30 or 40 msec with a TR of 500-1500 msec. The average thickness of the superior and inferior colliculi was about 5 mm, but the range was from 2-7 mm on the midline sagittal section. Abnormally thin colliculi appeared to have no clinical significance while abnormal thickness was observed in patients with neoplastic disease, sarcoidosis, and mesencephalic "beaking." While most neoplasms have abnormal signal intensity on T2-weighted images, small lesions may be difficult to perceive on transaxial images due to volume averaging or noncontiguous sections. Measurements of the tectum, on the commonly obtained midline sagittal section, may be useful for patients with small infiltrative lesions.

Magnetic resonance planned thalamotomy followed by X-ray/CT-guided thalamotomy.

Magnetic resonance imaging (MRI) is currently the optimal neuroradiologic technique for visualizing the anterior and posterior commissure for defining the AC-PC line. CT is the optimal technique for electrode and probe guidance during stereotactic thalamotomy. Various possibilities of transferring or overlying MRI and CT are outlined which in some future might result in more refined methods of CT-MRI guidance for stereotactic surgery.

The MR appearance of CSF flow in patients with ventriculomegaly.

The purpose of this study was to investigate the MR imaging appearance of mobile CSF in the ventricular system in patients with ventriculomegaly caused by brain atrophy and extraventricular obstructive hydrocephalus. Pulsatile CSF often has decreased intensity relative to less mobile areas of CSF, particularly on T2-weighted scans. At times, the flow-related signal dropout causes striking heterogeneity in the appearance of CSF. This has been termed the CSF flow-void sign (CFVS) and is most likely caused by spin-phase shifts and time-of-flight effects created as a result of CSF turbulence and increased velocity of CSF pulsatile flow. The effect is most pronounced in areas where a larger volume of CSF moves through a small channel or foramen, such as the aqueduct of Sylvius or foramen of Magendie. The scans of 40 patients with ventriculomegaly caused by brain atrophy or extraventricular obstructive hydrocephalus were reviewed for the presence of the CFVS. All patients had the CFVS in the aqueduct of Sylvius on T2-weighted spin-echo sequences. The sign was present in the fourth ventricle in 96%, in the third ventricle in 70%, in the foramen of Magendie in 65-77%, and in the foramina of Monro in 33%. The sign was more pronounced in patients with larger ventricles but could not be used to differentiate patients with brain atrophy from those with extraventricular obstructive hydrocephalus.

Physiology of the CSF flow-void sign: modification by cardiac gating.

Low-intensity signal seen within areas of narrowing within the ventricular system has been termed the CSF flow-void sign. This decreased signal is related to CSF flow and turbulence. Seven normal volunteers were examined, and the changes that occurred in the appearance of the CFVS were noted when data acquisition was modified by cardiac gating. Flow-void patterns within the internal cerebral veins and basilar artery were also examined. The results of this study confirm that CSF flow is related to cardiac systole and diastole. An increase in hypointensity is seen in the areas of the aqueduct of Sylvius and the foramen of Magendie during the time at which the systemic arterial pulse wave is transmitted into the brain. The physiology of this observation is related either to a direct hydraulic effect of the venous system on the CSF or to filling and expansion of the thin-walled cerebral venous system. Hypointensity or an increase in the width of the basilar artery and internal cerebral veins during systolic data acquisition was also noted. The mechanism of this phenomenon is related to propagation of the systemic arterial pulse wave.

Significance of cerebellar tonsillar position on MR.

It has been noted that a low degree of ectopia of the cerebellar tonsils on MR is of questionable significance. We measured the position of the cerebellar tonsils with respect to the inferior aspect of the foramen magnum in 200 normal patients and in 25 patients with a firm diagnosis of Chiari I malformation. In the normal group, the mean position of the tonsils was 1 mm above the foramen magnum with a range from 8 mm above the foramen magnum to 5 mm below. In the patients with Chiari I malformations, the mean position was 13 mm below the foramen magnum with a range from 3 mm below the foramen magnum to 29 mm below. Fourteen percent of normal patients had tonsils extending slightly below the foramen magnum. If 2 mm below the foramen magnum is taken as the lowest extent for tonsils in a normal patient, our sensitivity in predicting symptomatic patients is 100% and our specificity is 98.5% (three false positives). If 3 mm below the foramen magnum is taken as the lowest normal tonsillar position, our sensitivity is 96% and our specificity is 99.5%. MR demonstration of less than 2 mm of tonsillar ectopia is probably of no clinical significance in the absence of syringomyelia.

The MR appearance of CSF pulsations in the spinal canal.

We investigated the MR appearance and incidence of low-signal areas within the CSF of the spinal canal. Nonuniform areas of decreased signal intensity in intracranial CSF have been named the CSF flow-void sign (CFVS) and appear to be due to spin dephasing secondary to pulsatile CSF motion. Similar areas are seen in the spinal canal. The MR scans of 50 randomly selected patients, constituting a total of 63 spinal studies, were reviewed. There were 27 cervical, 16 thoracic, and 20 lumbar spine examinations. All patients were studied using T2-weighted and T1-weighted spin-echo pulse sequences. T2-weighted images were done with sufficiently long TE and TR to cause the CSF to appear hyperintense compared with brain and spinal cord tissue. Two patients with enlarged spinal canals and two patients with syringohydromyelia were also included to illustrate the appearance of prominent CSF pulsations. The CFVS was identified on T2-weighted scans in the cervical spinal canal in nine patients (33%), in the thoracic spinal canal in one patient (6%), and possibly in the lumbar spinal canal in two patients (10%). The CFVS was prominent in two patients with enlarged CSF spaces and was also seen in the intramedullary cavity of the patients with syringohydromyelia. The CFVS could obscure small dural lesions and, in some instances, simulate enlarged vessels. Recognition of the spinal CFVS is important to avoid the incorrect diagnosis of intraspinal lesions.

High resolution orbital computed tomography.

The latest generation CT scanners allow for spatial and contrast resolution within the orbit that has not previously been available. Utilization of these technological advances in association with appropriate techniques enables visualization of vascular and neural structures within the orbits that have not previously been emphasized in the literature. The CT scans were generated in both axial and coronal planes, using either 1 or 2 mm thick sections. All images were generated using ultrahigh resolution scanning techniques, available on the Picker 1200-SX scanner. The primary advantage of this system is the availability of secondary collimation of the X-ray beam at the detector, limiting detector aperture to only 1.3 mm. This, in association with utilization of the small focal spot and high sampling rate, aids in the visualization of divisions of the third and fifth nerves, as well as in the visualization of the sixth nerve within the orbit. Several branches of the ophthalmic artery within the orbit are also identified, including the infratrochlear and supratrochlear artery as well as the central retinal artery.

MR demonstration of altered cerebrospinal fluid flow by obstructive lesions.

We investigated the MR imaging appearance of flowing cerebrospinal fluid (CSF) in the brain in the presence of obstructive lesions of the ventricular pathways. The pulsatile movement of CSF through the ventricular system is seen as an area of low signal intensity that has been termed the CSF flow-void sign (CFVS). This is best appreciated in areas of narrowing within the ventricular system; that is, the aqueduct of Sylvius, foramen of Magendie, and interventricular foramina. MR studies of 27 patients with lesions affecting the ventricular pathways were reviewed for the presence of the CFVS. Single-echo T1-weighted and T2-weighted multisection techniques were used in all cases. The CFVS was always seen more prominently on the T2-weighted images. The presence of the CFVS indicated patency of the ventricular pathway in which it was identified. The absence of the CFVS in the presence of hydrocephalus indicated that a possible obstructive lesion was present, but it did not directly indicate the level of the obstruction. The CFVS was absent in the aqueduct of Sylvius in 13 patients with obstruction or stenosis of the aqueduct, but it was also absent in one patient with a colloid cyst of the interventricular foramina. In three patients with preoperative and postoperative MR, the CFVS was seen in the area of interest only after resection of the obstructing lesion. We concluded that the presence of the CFVS is a useful indicator of the patency of the ventricular pathway in which it is seen. The absence of the CFVS at a location in which it is normally seen may indicate the presence of an obstruction, but it must be correlated with other signs to be interpreted correctly.

Magnetic resonance demonstration of normal CSF flow.

The magnetic resonance (MR) imaging appearance and incidence of flowing cerebrospinal fluid (CSF) in the brain were investigated. The MR scans of 46 randomly selected patients with normal examinations were retrospectively reviewed. All patients were studied using both T2-weighted and T1-weighted spin-echo pulse sequences. Thirty-one patients (67%) had decreased intensity in the aqueduct of Sylvius on the T2-weighted images when compared with the intensity of CSF in the lateral ventricles. This was termed the CSF flow-void sign. The feature was present in the caudal fourth ventricle in 15 patients (32%) and in the third ventricle in two patients (4%) on T2-weighted scans. It was seen in only 13% of patients on T1-weighted scans. It is believed the CSF flow-void sign represents pulsatile CSF flow. Its recognition is important because it explains the inhomogeneity in the appearance of the CSF, which could be confused with pathologic processes. It may be valuable in the routine evaluation of MR examinations if it does reflect CSF circulatory dynamics.