Quantitative analysis of the effects of physiologic brain motion on point-resolved spectroscopy.

BACKGROUND AND PURPOSE: Although single-voxel proton MR spectroscopy is a noninvasive method that enables measurement of brain metabolite concentrations, it has been shown that physiologic brain motion causes inaccuracies in measurement of metabolite concentrations and increases the overall SD of the measurements when the stimulated echo acquisition mode (STEAM) is used. We tested the hypothesis that the point-resolved spectroscopy (PRESS) technique is less sensitive to physiologic brain motion than the STEAM technique. METHODS: In 10 healthy subjects, spectra were obtained from a voxel located in the left basal ganglia by using the PRESS sequence with cardiac gating and without water suppression to assess global phase change as a function of physiologic brain motion. This was accomplished by acquiring data at various time delays from the R wave throughout the cardiac cycle. Subsequently, spectra were obtained in 10 healthy subjects by using PRESS both without and with cardiac gating, and with water suppression, to determine whether brain motion resulted in a statistically significant difference in mean and SD of measured metabolite concentration. RESULTS: At various time delays from the R wave throughout the cardiac cycle, no significant global phase difference was noted in water signal intensity. In addition, when PRESS data were obtained both without and with cardiac gating (by using an optimal delay obtained from previously published data by using STEAM), no significant difference was seen in measured metabolite concentrations and SDs. CONCLUSION: The PRESS technique is relatively insensitive to physiologic brain motion.

Current Applications of MRI-Guided Laser Interstitial Thermal Therapy in the Treatment of Brain Neoplasms and Epilepsy: A Radiologic and Neurosurgical Overview.

Minimally invasive stereotactic tumor ablation is a viable option for the treatment of benign and malignant intracranial lesions. Although surgical excision constitutes first-line therapy for various brain pathologies, it can cause irreversible neurologic deficits. Additionally, many patients who may benefit from surgery do not qualify as surgical candidates due to multiple comorbidities. Recent advancements in laser interstitial thermal therapy, namely the ability to monitor ablation in real-time under MR imaging, have improved the safety and efficacy of the procedure. MRI-guided laser interstitial thermal therapy is currently used as a minimally invasive treatment for brain metastases, radiation necrosis, glioma, and epilepsy. This article will discuss the principles, suggested indications, complications, and imaging characteristics of MRI-guided laser interstitial thermal therapy as they pertain to the treatment of brain pathology.

A new sign of neurofibromatosis on magnetic resonance imaging of children.

Ten pediatric patients with clinically proved neurofibromatosis underwent magnetic resonance imaging of the brain. Seven of these patients had lesions of increased signal intensity on T2-weighted images in the globus pallidus, brain stem, or cerebellar white matter. The lesions did not correlate with results of the neurologic examination or with developmental status. These abnormalities most likely represent hamartomas and should be recognized as part of the diagnostic spectrum of neurofibromatosis.

Magnetic resonance demonstration of intracranial CSF flow in children.

We determined the feasibility and value of studying intracranial CSF flow in children with potential CSF pathway problems using a cardiac gated cine magnetic resonance (MR) format. We studied 15 consecutive patients with a variety of clinical problems that suggested possible CSF pathway problems. The diagnoses included Chiari malformation, Dandy-Walker syndrome, external hydrocephalus, cerebellar tumor, CNS histoplasmosis, and tuberculous meningitis. In addition to documenting the feasibility of the technique in children (7 of 15 were less than 2 years of age), we derived significant new information relative to pathogenesis and/or therapy. The study provides preliminary evidence supporting intracranial CSF flow studies at the time of routine MR imaging of appropriate children.

MR characterization of brain and brain tumor response to radiotherapy.

This paper describes our experience in using the T1 and T2 relaxation times for quantitative evaluation of brain and brain tumor response to radiation therapy. Twenty-two computed T1 and 22 computed T2 images were obtained from 66 routine inversion-recovery and spin-echo magnetic resonance (MR) brain scans. The relaxation times of the brain tissues, determined from the computed images, were examined as a function of the absorbed dose. Statistical evaluation of the results showed no significant difference between the relaxation times of irradiated and not irradiated tissues, including tumor and normal white matter. Influence of the magnetic field strength and imaging techniques on the computed T1 and T2 values was confirmed. We conclude that the relaxation time values, as obtained today using conventional MR scanner and standard software, are not specific enough to warrant a correct assessment of the acute radiation effect on the brain tissues.

Intracranial CSF flow in pediatric hydrocephalus: evaluation with cine-MR imaging.

PURPOSE: 1) To describe the pattern of normal intracranial CSF flow in children and 2) to demonstrate altered CSF flow patterns in pediatric hydrocephalus and ventriculomegaly with flow-sensitized cine-MR examinations. METHOD: Cardiac gated, multiframe, gradient echo sequences on a 1.5-T system were displayed on a closed loop cine format and compared to standard MR images. Areas of normal flow and areas of diminished flow were determined. RESULTS: 1) In normal children, the CSF flow follows a consistent pattern with a to-and-fro movement of flow in the aqueduct, foramen of Magendie, and in the dorsal and ventral subarachnoid space at the cervicomedullary junction. 2) In patients with ventricular enlargement, the flow studies showed regional abnormalities of the CSF flow patterns: specifically, lack of flow and hyperdynamic flow. CONCLUSION: Cine-MR for CSF flow evaluation is a useful adjunct to routine MR in the evaluation of pediatric hydrocephalus because it can assist in determining the probable level of CSF obstruction.

Sonography and neurodiagnosis (neurosonography).

Sonography is a necessary part of neuroradiology. Its relative importance will increase as the sonographic images improve and the funds provided for diagnostic imaging decrease. We urge the incorporation of neurosonographic training into our neuroradiology fellowship programs and more widespread use of sonography in neurodiagnosis.

Syringomyelia associated with intradural extramedullary masses of the spinal canal.

Three cases of syringomyelia associated with intradural extramedullary tumors of the spinal canal are reported to demonstrate their radiographic feature, to postulate a mechanism for their formation, and to describe the clinical deterioration occurring in two patients immediately after metrizamide myelography. It is believed that the mechanism by which these syrinx cavities formed was similar to the mechanism of syrinx formation within chronically injured spinal cords. The cystic cavities may extend for considerable distances away from the extramedullary mass and may be present above and/or below the mass. The development of a syringomyelia in the face of an intradural extramedullary tumor may not be rare, and it is suspected that with the more frequent use of delayed metrizamide CT and now magnetic resonance imaging, syringomyelia will be found as an occasional consequence of this type of mass.

Chiari III malformation: imaging features.

PURPOSE: To analyze and discuss the MR and CT features of Chiari type III malformations. PATIENTS AND METHOD: MR and CT studies in nine neonates born at term with Chiari type III malformations were retrospectively reviewed. RESULTS: High cervical/low occipital encephaloceles were present in all cases. Hypoplasia of the low and midline aspects of the parietal bones was seen in four patients. The encephaloceles contained varying amounts of brain (cerebellum and occipital lobes, six cases; cerebellum only, three cases), ventricles (fourth, six cases; lateral, three cases), cisterns, and in one case, the medulla and pons. Associated anomalies included: petrous and clivus scalloping (five cases/nine cases), cerebellar hemisphere overgrowth (two cases/nine cases), cerebellar tonsillar herniation (three cases/seven cases), deformed midbrain (nine cases), hydrocephalus (two cases/nine cases), dysgenesis of the corpus callosum (six cases/nine cases), posterior cervical vertebral agenesis (three cases/eight cases), and spinal cord syrinxes (two cases/seven cases). In four patients who underwent surgical resection and closure, aberrant deep draining veins and ectopic venous sinuses within the encephaloceles were found. Pathology examination of the encephalocele (four cases/nine cases) showed multiple anomalies (necrosis, gliosis, heterotopias, meningeal fibrosis) that were not demonstrable by either MR or CT. The marked disorganization of the tissues contained within the cephalocele may account for the lack of MR sensitivity to these abnormalities. CONCLUSION: Preoperative determination of the position of the medulla and pons is essential and is easily accomplished by MR. To avoid surgical complications, the high incidence of venous anomalies should be kept in mind.

Lack of normal MR enhancement of the pituitary gland: findings in three siblings with combined pituitary hormone deficiency.

We present the MR appearance of the sella turcica in three sibling dwarfs with combined pituitary hormone deficiency in which MR images revealed a peripheral curvilinear band of enhancement about the pituitary gland in all three patients, a normal-size pituitary gland in two siblings, a mildly enlarged pituitary gland in one sibling, and a thin infundibulum and a normal posterior pituitary bright spot in all three siblings. Possible antecedents include an abnormal vascular supply, pituitary gland replacement by a nonfunctioning adenoma, a proteinaceous cyst, or a hamartoma.

Enhancing meningeal blood vessels masquerading as leptomeningeal spread of tumor in obstructive hydrocephalus.

MR showed an enhancing mass in the pineal region and hydrocephalus and leptomeningeal enhancement, thought to indicate pinealoblastoma with leptomeningeal spread. During resection there was no evidence of spread, and repeat MR showed no residual tumor or meningeal enhancement, so the patient was not treated for metastasis. Because there were no signs of leptomeningeal tumor 4 months after surgery, the meningeal enhancement is thought to have been related to venous stasis secondary to obstructive hydrocephalus.

Somatosensory evoked potential measurements in percutaneous fluid aspiration from intraspinal cystic lesions.

Two patients were evaluated with somatosensory evoked potentials (SSEPs) before and after CT-guided fluid aspiration from cystic intraspinal lesions. Our objective was to use the information and the clinical response to this procedure to determine the suitability of the patients for surgical intervention. In both patients, one with a pseudomeningocele and the other with a subarachnoid cyst, improvement in their symptoms corresponded to significant changes in their SSEPs. We believe this technique may be useful in selected cases when it is unclear whether cystic intraspinal fluid collections are responsible for the patient's symptoms. An increase in amplitude and/or decrease in latency of SSEPs, along with clinical improvement after fluid aspiration, may indicate the potential benefit of surgical intervention.

Concurrent hydromyelia and diastematomyelia.

Hydromyelia was discovered in six of 13 patients with diastematomyelia. In one patient, hydromyelia affected only the segments of spinal cord above the diastematomyelia. In five patients, hydromyelia extended downward from the single cord into one or both hemicords. Because hydromyelia and diastematomyelia occur simultaneously, because they may produce very similar clinical changes, and because simultaneous or sequential surgical correction of both conditions may be necessary to achieve the best clinical result, the possibility of hydromyelia should be evaluated specifically in each patient demonstrated to have diastematomyelia.

Comparison of gradient-recalled-echo and T2-weighted spin-echo pulse sequences in intramedullary spinal lesions.

Nineteen consecutive patients with spinal intramedullary lesions were studied on a 1.5-T system to compare the quality of T2-weighted spin-echo and gradient-recalled-echo (GRE) pulse sequences. Direct comparisons were made in the sagittal and/or axial planes. Twenty-four studies were performed in the 19 patients. The gradient echoes were usually performed at 300/14 (TR/TE) with a flip angle of 10 degrees. Although no significant diagnostic differences were noted in the sagittal plane, there was a distinct anatomic advantage for GRE imaging over spin-echo imaging in the axial plane. This is believed to be the result of CSF time-of-flight effects in the slice-select direction, which are not compensated for by flow-compensating gradients on the spin-echo images, but which are insignificant in the GRE sequence used in this study. Pathology was seen equally well or better on GRE in 79% (19/24) of the sequences. In the other five cases, the spin-echo image showed a brighter intramedullary signal than that seen on GRE, although GRE showed the lesion in all cases. Our results indicate that properly optimized GRE imaging on a high-field-strength system can replace spin-echo imaging in the spine when intramedullary disease is suspected and that the benefits of GRE are most striking in the axial plane.

Radiologic evaluation of spinal cord fissures.

The clinical course and radiographic studies were reviewed of eight patients with posttraumatic spinal cord fissures (rents in the spinal cord communicating with the subarachnoid space). Five patients had spinal cord fissures associated with symptomatic intramedullary cysts that required shunting to alleviate progressive neurologic deficits and intractable pain. Their metrizamide myelograms showed contrast medium passing immediately from the subarachnoid sac into the spinal cord and their immediate metrizamide CT scans delineated the entire extent of the secondary cord cysts. Intraoperative sonography confirmed the presence of the cord fissures with sizeable cysts, detected adhesions, and guided myelotomies and the subsequent shunting and collapse of the cysts. Since neurologic improvement followed the shunting procedures in all five patients treated for progressive symptoms, it was concluded that early radiologic evaluation of posttraumatic spinal cord fissures with symptomatic cord cysts is crucial in the clinical management of these patients.

Progressive posttraumatic myelomalacic myelopathy: imaging and clinical features.

PURPOSE: To describe the imaging features, surgical management, and clinical outcome of progressive posttraumatic myelomalacic myelopathy (PPMM), a relatively unrecognized but important cause of progressive myelopathy in patients with previous spinal cord injuries. METHODS: The clinical records, imaging studies, and postoperative outcome of 10 patients with PPMM were reviewed. Fifteen preoperative and five postoperative MRs were analyzed for intramedullary signal abnormalities, the nature of these signal abnormalities, and cord tethering. All patients had intraoperative sonography. RESULTS: Neurologic signs and symptoms found in our patients included 1) progressive loss of motor function (6/10), 2) sensory level changes (4/10), 3) increased spasticity (4/10), 4) autonomic dysreflexia (4/10), 5) loss of bowel or bladder control (4/10), and 6) local and/or radicular pain (4/10). Preoperative MR in nine patients revealed intramedullary T1/T2 lengthening (9/9), extramedullary tethering/adhesions (9/9), ill-defined lesional borders (6/9), cord expansion (5/9), and increased signal intensity of the lesion on T1-weighted images compared with CSF (7/9). Proton density images in five patients demonstrated a relative increase in signal intensity over CSF. In all five postoperative MRs, there was evidence of untethering of the spinal cord and a decrease in cord size in two patients. Intraoperative sonography revealed cord tethering and abnormal cord echotexture in all cases. Postoperative clinical evaluation revealed neurologic improvement in nine patients. CONCLUSIONS: PPMM may clinically and radiographically mimic progressive posttraumatic cystic myelopathy (PPCM). MR provides clues to the diagnosis of myelomalacia preoperatively. Intraoperative sonography confirms the absence of a confluent cyst. These points are crucial in the surgical procedures in PPMM vs PPCM. In PPMM, lysis of intradural adhesions results in an improvement in symptoms in a manner similar to the shunting of PPCM.

Sequential cranial MR findings of asymptomatic and neurologically symptomatic HIV+ subjects.

PURPOSE: To compare results of a prospective MR and clinical reevaluation of HIV+ asymptomatic and neurologically symptomatic subjects who had had initially abnormal cranial studies to determine what cranial MR changes occur and how these changes correlate with serial neurologic and neuropsychologic findings. PATIENTS AND METHODS: Thirty-one asymptomatic (n = 20) and neurologically symptomatic (n = 11) subjects seropositive for the human immunodeficiency virus (HIV+) were prospectively reevaluated by cranial magnetic resonance (MR) one to two years following an initially abnormal MR of the brain. RESULTS: All 31 HIV+ subjects with initial abnormal MR had abnormal follow-up scans (showing atrophy and/or white matter lesions). Twenty-seven showed no progression of MR abnormalities (among whom were 18 with minimally abnormal scans who remained asymptomatic with improved or static neuropsychologic performance). Of the four subjects with scan changes (all with clinically suspected HIV encephalopathy), one showed MR, clinical, and neuropsychologic test improvement; the remaining three showed MR (n = 3), neurologic (n = 3), neuropsychologic (n = 1) worsening and autopsy (n = 1) confirmed the presence of HIV-1 containing multinucleated giant cells in the brain. CONCLUSIONS: This study suggests that: 1) Progression of intracranial MR abnormalities due to HIV-1 is seen only in a minority of HIV+ subjects over a 1- to 2-year time period, only in those neurologically symptomatic, and correlates with clinical deterioration. 2) Minor cerebral MR abnormalities seen in HIV+ subjects who remain neurologically asymptomatic do not change over a 1- to 2-year period. 3) Although HIV is known to infect the brain early, it may, nevertheless, not routinely do significant anatomical damage early on in the disease, as based on MR criteria.

Creutzfeldt-Jakob disease: focal symmetrical cortical involvement demonstrated by MR imaging.

The authors present two biopsy-proved cases of Creutzfeldt-Jakob disease. MR appears to be more sensitive than CT in detecting pathologic changes; signal abnormalities, when found, are predominantly within gray matter and may involve only peripheral cortex.

Acquired spinal subarachnoid cysts: evaluation with MR, CT myelography, and intraoperative sonography.

Fifteen patients with acquired spinal subarachnoid cysts (14 surgically proved, one presumed) were evaluated preoperatively with immediate and/or delayed CT myelography (seven patients), MR (11 patients), or both (three patients). CT myelography separated subarachnoid cyst from myelomalacia and/or intramedullary cysts in four cases but failed to diagnose them in three, while MR accurately diagnosed subarachnoid cyst in all 10 cases that were also surgically proved. The results of these preoperative examinations were evaluated to determine the efficacy of each study in diagnosing subarachnoid cysts, ascertaining their extent and internal architecture, and detecting associated abnormalities of the spinal cord. In addition, during surgery these cysts were studied with sonography to gain an understanding of the pathophysiological mechanisms involved in their formation and propagation and to guide the surgeon in their decompression. On the basis of our experience, MR appears to be the most efficient preoperative study in diagnosing and characterizing acquired subarachnoid cyst and associated abnormalities. Intraoperative sonography provides a reliable means of ensuring adequate decompression of these cysts.

MR angiography of normal intradural vessels of the thoracolumbar spine.

PURPOSE: To identify and describe the normal intradural vessels detected on MR angiograms of the thoracolumbar spine. METHODS: Six adult subjects who had clinical evidence of myelopathy, yet normal findings at spinal digital subtraction angiography (DSA), were also studied without and with contrast-enhanced MR imaging and three-dimensional time-of-flight, single-slab MR angiography. Sagittal and coronal subvolume (targeted) maximum intensity projection images were compared with arterial and venous phase DSA images. Angiographic images were then compared with postmortem, formalin-fixed cord specimens. RESULTS: Recognizable intradural vessels were detected only on contrast-enhanced MR angiograms. These vessels corresponded to the posterior and/or anterior median (midline) veins and the great medullary veins. The median veins had variable but mild tortuosity. The medullary veins, which extended from the median veins and coronal venous plexus on the cord surface to the epidural venous plexus, were relatively straight and usually located at T-12 or L-1. The anterior spinal artery could partially contribute to the anterior midline vascular signal. CONCLUSION: The intradural vessels identified on contrast-enhanced MR angiograms are primarily veins, and these are usually the largest vessels on or near the cord surface. The limited number and minimal tortuosity of these veins may serve as a baseline for the examination of patients with clinically suspected arteriovenous malformation or fistula.