Sean O. Casey

High-field strength interventional magnetic resonance imaging for pediatric neurosurgery.

Background: Interventional magnetic resonance (MR) imaging allows neurosurgeons to interactively perform surgery using MR guidance. High-field (1.5-Tesla) strength imaging provides exceptional visualization of intracranial and spinal pathology. The full capabilities of this technology for pediatric neurosurgery have not been defined or determined. Materials and Methods: From January 1997 through June 1998, 10 of 85 cases performed in the interventional MR unit were in the pediatric population (mean age 8.3, median 8, range 2–15 years). Procedures included 2 brain biopsies, 5 craniotomies for tumor, 2 thoracic laminectomies for syringomyelia, and placement of a reservoir into a cystic brainstem tumor. The biopsies and reservoir placement were performed using MR-compatible equipment. Craniotomies and spinal surgery were performed with conventional instrumentation outside the 5-Gauss magnetic footprint. Interactive and intraoperative imaging was performed to assess the goals of surgery. Results: Both brain biopsies were diagnostic for cerebral infarct and anaplastic astrocytoma and the reservoir was optimally placed within the tumor cyst. Of the 5 tumor resections, all were considered radiographically complete. One biopsy patient and 1 tumor resection patient experienced transient neurological deficits after surgery. The patient with the thoracic syrinx required reoperation when the syringosubarachnoid shunt migrated into the syrinx 3 months after initial placement. No patient sustained a postoperative hemorrhage. Tumor histologies found at craniotomy were craniopharyngioma, ganglioglioma, and 3 low-grade gliomas. No evidence of tumor progression has been seen in any of these patients at a mean follow-up of 5.3 (range 4–8) months. The goals of the procedure were achieved in all 10 cases. There were no untoward events experienced related to MR-compatible instrumentation or intraoperative patient monitoring, despite the present inability to monitor core body temperature. Conclusions: 1.5-Tesla interventional MR is a safe and effective technology for assisting neurosurgeons to achieve the goals of pediatric neurosurgery. Preliminary results suggest that surgical resection of histologically benign tumors is enhanced in the interventional MR unit. The incidence of surgically related morbidity is low.

Diffusion-weighted MR imaging findings in carbon monoxide poisoning

Abstract. Diffusion-weighted MR imaging (DWI) of two patients with carbon monoxide (CO) poisoning demonstrated white matter and cortical hyperintensities. In one patient, the changes on the FLAIR sequence were more subtle than those on DWI. The DWI abnormality in this patient represented true restriction. In the second patient, repeated exposure to CO caused restricted diffusion. DWI may be helpful for earlier identification of the changes of acute CO poisoning.

Intraspinal epidermoid cyst: diffusion-weighted MRI.

Abstract We report a 7-year-old boy who presented with two-month history of worsening low back and right leg pain. Conventional MR images demonstrated a poorly outlined intradural mass recognized by the displacement of the conus medullaris and the nerve roots of the cauda equina at the L2–3 level. The signal intensity of the lesion was similar to CSF. There was no contrast enhancement of the lesion. Diffusion-weighted images and ADC values revealed restricted diffusion within the mass. Myelography confirmed the mass as an intradural filling defect with myelographic block at the L2–3 level. The patient underwent total surgical excision of the mass. Pathologic examination revealed the diagnosis of epidermoid cyst.

Intracranial metastasis via transplacental (vertical) transmission of maternal small cell lung cancer to fetus: CT and MRI findings

We present the computed tomography (CT) and magnetic resonance imaging (MRI) findings of brain metastases in an unusual case of a premature, 33‐week gestational age neonate who was emergently delivered from a mother suspected of having lung cancer according to imaging performed during the third trimester of pregnancy. Owing to the presence of placental metastases noted after delivery, the fetus had initial screening with brain MRI and chest/abdomen CT as well as serial screening imaging studies during the first 5 months of life, all of which were apparently normal. However, serial examinations eventually revealed a cerebellar lesion that significantly improved after chemotherapy but recurred and enlarged within a few months. This lesion was later confirmed to be metastasis by subsequent biopsy and resection. More metastatic lesions were identified in the frontal and temporal lobes on follow‐up MRI. In the setting of aggressive maternal malignancy (without known fetal primary malignancy) an intracranial mass can, on the exceedingly rare occasion, result from maternal high‐grade malignancy and the neuroradiologist should be alerted to this phenomenon.

Subarachnoid hemorrhage associated with cyclosporine A neurotoxicity in a bone-marrow transplant recipient

Abstract We report subarachnoid hemorrhage associated with cyclosporine A (CSA) neurotoxicity after bone-marrow transplantation for chronic myelogenous leukemia. CT showed occipital subarachnoid hemorrhage. MRI confirmed this, and demonstrated cortical and subcortical edema in the posterior temporal, occipital, and posterior frontal lobes bilaterally, which was typical of CSA neurotoxicity. Recognition of CSA neurotoxicity as the cause of the subarachnoid hemorrhage obviated angiographic investigation. After cessation of cyclosporine therapy, the cortical and subcortical edema resolved on follow-up MRI with some residual blood products in the subarachnoid space.

Reversal of increased intracranial pressure with removal of a torcular epidermoid: Case report

OBJECTIVE AND IMPORTANCE Venous obstruction has been postulated as a cause of increased intracranial pressure, but it has been documented rarely. We present a case of obstruction of the torcula by a slow-growing epidermoid. The tumor caused increased intracranial pressure, which was relieved when it was excised. In addition, the torcular epidermoid is associated with a bifid straight sinus. CLINICAL PRESENTATION A 35-year-old man presented with a headache and a lump on the back of the head. Physical examination revealed a firm, bony lesion approximately 4 × 4 cm in size. Lumbar puncture demonstrated an intraspinal pressure of 39 cm H2O. Neuroradiological studies revealed an epidermoid that compressed and almost completely occluded the torcula. INTERVENTIONAfter the tumor was resected, the intraspinal pressure decreased to 19 cm H2O and remained stable 6 months later. CONCLUSIONPure venous obstruction causes increased intracranial pressure. Removal of the obstruction relieves the intracranial hypertension. In addition, computed tomographic venography is a safe and easy method of documenting torcular anatomy, and it was useful in the follow-up of this patient. Computed tomographic venography can demonstrate a double straight sinus, which is a congenital variant that may be associated with the epidermoid.

Gadolinium enhancement of spinal subdural collection on magnetic resonance imaging after lumbar puncture

We report a 35-year-old male with an unusual contrast-enhancing sterile spinal subdural collection on magnetic resonance imaging (MRI), apparently occurring as a complication of lumbar puncture. Follow-up MRI after 4 weeks demonstrated spontaneous resolution of the collection without intervening treatment.

Macroscopic static field inhomogeneity in the human brain during MRI examination

The macroscopic static field inhomogeneity is not only the source of MR signal loss in gradient echo based imaging techniques, but also the source of geometrical image distortion as well as a limitation of spectral resolution. This piece of information is useful for both active shimming coil design and clinical imaging application. In order to further understand the spatial variation of the macroscopic background static field in human brain during MRI examination, this static field inhomogeneity was measured from the adult human volunteers with a volumetric imaging scheme, which was based on a 3D gradient echo technique with two consecutive gradient echoes. All the human volunteers were scanned in supine position using a birdcage headcoil on a 1.5 T clinical whole body scanner. We have constructed a high resolution 3D static field map over the brain volume. All experimental results have shown consistently that there are mainly two spots in the brain tissue volume exhibiting relatively severe static magnetic field inhomogeneity . They are normally located in the brain areas in the inferior frontal lobe immediately anterior to the nasal cavity and in the inferior temporal lobe above the ear canals, where air spaces exist in the vicinity. At those locations, the observed offset frequency in the proton resonance reached about 50 Hz over 5 mm distance along the z direction at 1.5 Tesla, corresponding to 1.5 ppm/cm locally.

Actual imaging slice profile of 2D MRI

It has been known that the actual slice profile of 2D MRI is often far form that of a perfect rectangular shape especially when the flip angle is large. This can be the source of error and image artifact in many MRI experiments. To carefully study this imperfection in RF excitation for various numerically optimized RF pulses, we have implemented an efficient numerical algorithm for simulating the evolution of the magnetization during a MR experiment. The scheme solves the Bloch equation via a numerical procedure that involves only the successive matrix multiplications, which are initialized by the values of RF amplitude and the frequency offset due to the companioning magnetic gradient field. It permits the consideration of the magnetization relaxation processes. The actual slice profile was numerically simulated by solving the Bloch equation for a given RF pulse shape and slice selection field gradient. The simulation results shows that the slice profile is often far from perfect for many commonly used frequency selective RF pulses. As a result of this, the apparent image intensity is an integrated signal over the slice envelope for the transverse magnetization for each pixel, which is an averaged contribution over the entire slice thickness, and can be significantly different than that predicted by the ideal case. As expected, this discrepancy worsens when the flip angle exceeds the flip angle for which the RF pulse was optimized. Furthermore, in the routine diagnostic imaging, because of the non-uniform excitation angle along the slice profile, it generates non-uniform steady state profile and can even alter the resulting image contrast.

More information can be mined from the routine PCA data

Phase contrast angiography (PCA) delineates the vasculature morphology based on the fact that the blood is flowing inside the vessels. And the source images of PCA have significantly less background signals than that of the time of flight (TOF) MRA. Although the PCA scan requires a slightly longer acquisition time than that of the TOF, it contains a lot more information regarding to the flow direction and velocity of the blood. Unfortunately, all these are discarded except the signal enhancement due to flow when the resulting angiogram is reconstructed and displayed on a clinical MR machine. To reveal more information contained in the PCA a presentation scheme was developed, in which each pixel after the angiographic projection has assigned a color in addition to the intensity. Employing the concept similar to the three elemental color mixing, the directional information of flow can be conveyed in an easy to comprehend format. Using the maximum intensity projection (MIP) algorithm along the viewing trace, the pixel intensity value was obtained and signed to the corresponding pixel on the PP. The final pixel color is determined by the flow direction. To demonstrate the effectiveness of the method, we obtained a PC angiography data set (TR/TE/Flip equals 20ms/3.9ms/20 degree) of the circle of Willis in transverse orientation from both normal volunteers and patient heads at 1.5T using Venc of 60 cm/sec. Results showed additional information can be gained from the PCA data, which may be useful for selected patients and sometimes crucial in the routine clinical diagnosis.