Biomedical subjects
Publications and source records attributed to S W Atlas.
The recent advent and implementation of rapid spin-echo techniques has allowed increased imaging speed while maintaining spin-echo-like contrast. This review explains the basis of fast spin-echo imaging and attempts to elucidate the etiology of the differences between it and spin-echo imaging. Clinical applications and limitations of fast spin-echo imaging in the brain and spine will also be addressed.
We report on a patient with spontaneous remission of a third-nerve palsy who was subsequently found to have meningeal lymphoma. Initial magnetic resonance images (MRI) showed bilateral enhancement of the third nerves. Follow-up MRI 7 months later, without treatment, showed complete resolution. One year after initial presentation, the patient developed multiple lumbosacral radiculopathies and examination of a nerve root biopsy specimen disclosed a B-cell lymphoma. Serial cerebrospinal fluid analyses over the previous year showed occasional atypical cells, later found to resemble closely the biopsy cell type. We conclude that meningeal lymphoma may have a protracted course, with spontaneous remission of both clinical and neuroimaging findings.
The authors evaluated a three-dimensional Fourier transform implementation of a very short repetition time (TR) (24 msec), steady-state free precession (SSFP) pulse sequence for clinical imaging of the brain and compared it with a conventional two-dimensional Fourier transform long TR/echo time (TE) spin-echo sequence. First, the optimal flip angle of 10 degrees for generating images with contrast similar to that of long TR/TE spin-echo images was determined. Then, 29 patients with suspected brain lesions were studied with both techniques. Although the SSFP images did not exhibit the magnetic susceptibility artifacts that plague other rapid-imaging techniques, the conspicuity of most parenchymal lesions was often less than that on the spin-echo images. Also, the visibility of paramagnetic effects, such as the low signal intensity of brain iron, was less obvious at SSFP imaging. These substantial limitations may relegate the SSFP sequence to an adjunctive role, perhaps mainly demonstration of the cystic nature of mass lesions, because of its extreme sensitivity to slow flow.
We report a patient who rapidly developed unilateral proptosis and complete ophthalmoplegia following blunt trauma to the orbit. Computed tomography (CT) scan revealed a mass involving the sinuses and orbit with erosion of the cribriform plate. Biopsy of this suspected neoplasm revealed features consistent with allergic Aspergillus sinusitis, but cultures later grew a Bipolaris species. Our review of the literature suggests that when allergic fungal sinusitis involves the orbit, Bipolaris is a more commonly isolated organism than Aspergillus. Additionally, extraocular motility impairment and proptosis occur more frequently than visual loss. Treatment is controversial, but surgical drainage followed by corticosteroids is the most often recommended therapy.
We report a biopsy-diagnosed patient with Creutzfeldt-Jacob disease showing on magnetic resonance images bilateral increased signal intensity in the basal ganglia on long repetition time images. Creutzfeldt-Jacob disease (CJD) is a degenerative process of the brain, induced by a novel infectious agent, and is usually characterized by a rapidly progressive dementia. We report a biopsy-diagnosed patient with CJD with a distinctive magnetic resonance (MR) appearance.
A modified fat-suppression pulse sequence (consisting of combined frequency-selective fat presaturation followed by a spin-echo acquisition when fat and water magnetization vectors have opposite phase) was used to optimize the conspicuity of intravenous enhancement by gadopentetate dimeglumine on magnetic resonance images in 10 patients previously operated on for lumbar discogenic disease as well as in two patients with herniated disks who had not previously undergone surgery. This technique produced the greatest degree of fat suppression in the phantom study. In six of the patients who had previously undergone surgery, epidural enhancement was more obvious on the fat-suppressed images than on conventional spin-echo images, while in four patients, enhancement was equivalent. The herniated disks in two patients not previously operated on were not enhanced with either technique. Contrast enhancement was universally distinguishable from fat signal and from nonenhancing water-containing tissue on the fat-suppressed images obtained after contrast material administration. This technique may reduce the need for precontrast imaging. Furthermore, postoperative enhancement of nerve roots was more obvious on fat-suppressed images in seven of eight patients. This finding might represent previously undiagnosed degrees of arachnoidal inflammation, which may be a factor in the failed back syndrome.
The authors studied a carefully screened pool of healthy adult volunteers aged 20-80 years, so that a normal brain deep gray matter hypointensity map, as detectable on routine spin-echo magnetic resonance (MR) images, could be formulated. Previous MR imaging studies about brain iron reported findings either in children only or in adults, all of whom had suspected central nervous system disease. The results showed that (a) areas of hypointensity in the red nucleus, substantia nigra, and dentate nucleus were relatively unchanged throughout all age groups; (b) the globus pallidus showed an increased volume of hypointensity in the middle-aged and elderly population compared with that in the young adult; (c) the putamen was hypointense only in the elderly age group; and (d) hypointensity was never seen in the thalamus or caudate nucleus in any subject, regardless of age. In cases in which these patterns are not observed in patients suspected to have central nervous system disease, the presence of such disease should be considered.
We report a patient with meningovascular syphilis who had a dorsal midbrain syndrome, cognitive dysfunction, and a left peripheral seventh nerve palsy. Magnetic resonance imaging (MRI) disclosed a large lesion of the midbrain and thalamus with intense enhancement of the interpeduncular cistern, both of which resolved after treatment with intravenous penicillin. The clinical features, radiographic appearance, and response to therapy suggest that this lesion was a focal syphilitic inflammatory process, or gumma. We conclude that MRI with intravenous contrast may reveal the full spectrum of pathologic involvement in neurosyphilis and, in certain situations, may obviate the need for biopsy of an associated mass lesion.
MR imaging has represented a significant advance in the diagnosis and management of adult supratentorial neoplasms, and indeed MR has become the modality of choice for the initial diagnosis and follow-up in these cases. It is clear that the overall sensitivity has increased significantly, due to both the use of MR itself and to the implementation of IV contrast agents. It appears that some inroads have been made with regard to specificity, but significant overlap still exists in the imaging appearance of many of these entities. A thorough knowledge of neuroanatomy, pathophysiology, and neuropathology aid markedly in the imaging diagnosis of these processes.
The Tolosa-Hunt syndrome consists of painful ophthalmoplegia caused by cavernous sinus inflammation, which is responsive to steroid therapy. The MR features of 11 patients with the clinical diagnosis of Tolosa-Hunt syndrome were studied. Two patients had normal MR studies of the orbit and cavernous sinuses. In nine patients, abnormal signal and/or mass lesions were seen in the cavernous sinuses; in eight cases, the abnormality was hypointense relative to fat and isointense with muscle on short TR/TE images and isointense with fat on long TR/TE scans. Extension into the orbital apex was seen in eight cases. In six of nine cases the affected cavernous sinus was enlarged; in five of nine it had a convex outer margin. One patient had a thrombosed cavernous sinus and superior ophthalmic vein in addition to a cavernous sinus soft-tissue mass. The signal intensity of Tolosa-Hunt syndrome in this limited series was similar to that of orbital pseudotumor and is confined to a limited differential diagnosis, which includes meningioma, lymphoma, and sarcoidosis.
Routine evaluation of axial MR images of the cervical spine with high-intensity CSF (long TR/TE spin-echo or gradient-echo images) revealed apparent narrowing of the cord's anteroposterior diameter when these images were compared with corresponding postmyelography CT scans. This discrepancy was believed to be due to the truncation artifact at the CSF-cord boundary. To examine the truncation effect, we compared cord diameters in 12 patients on postmyelography CT scans and MR images and then compared these with MR scans of normal volunteers and of an agar-saline spine phantom. There was an artifactual diminution of the cord diameter in the 128-step phase-encoding axis of the 128 x 256-matrix MR scan as compared with the diameter of the cord in the patients' postiohexol CT scans and in the 256 phase-encoded axis MR scan in the volunteer study. A similar discrepancy was noted in the spine phantom study, in which the cord diameter in the 256-step phase-encoded MR scan, the CT scan, and direct measurement exceeded that in the 128-step phase-encoded axis MR scan. The range of differences between the measurements was as large as 2.3 mm (patients), 1.7 mm (volunteers), and 1.8 mm (phantom) for the three studies. In all three studies, varying the photographic window width and level produced variation in the apparent cord diameter of up to 1.5 mm. To eliminate this effect, the cord diameters in the phantom and the normal control subjects were measured at identical window levels. The truncation artifact, coupled with standard window settings used in photography, may lead to inaccurate display of the diameter of the cervical spinal cord.
Explore the source record for details and available documents.
Juxtaarticular intraspinal synovial cysts are unusual lesions of the spine associated with facet arthropathy. These lesions can cause radicular symptoms and may masquerade clinically as other, more common entities. Synovial cysts have been detected at myelography and have been well characterized at computed tomography as posterolateral epidural masses, typically at L4-5. Six synovial cysts of the lumbar spine were demonstrated on magnetic resonance (MR) images. The signal-intensity patterns of these lesions are variable. MR imaging can be used to document the presence of hemorrhage within the cyst, which may relate to the exacerbation of symptoms. Air-filled synovial cysts may be difficult to detect and distinguish from facet arthropathy.
Progressive multifocal leukoencephalopathy (PML) is an uncommon demyelinating disease that occurs in immunocompromised patients. The authors evaluated magnetic resonance (MR) images of 10 patients with pathologically proved PML and clinically diagnosed acquired immunodeficiency syndrome (AIDS) to determine the MR characteristics of this disorder. All patients had asymmetric cerebral involvement. Lesions were distributed throughout the brain, including the brain stem and basal ganglia. White matter was affected in all 10 patients; gray matter was also involved in five. In one patient the lesion enlarged and crossed the corpus callosum and contained focal hemorrhage. The authors conclude that, contrary to reported findings on computed tomographic scans, PML in patients with AIDS has a variable appearance on MR images and has many characteristics that differ from those previously thought to be typical on imaging studies.
MR images of 24 patients with 33 subdural collections were retrospectively reviewed to determine the spectrum of MR findings associated with such lesions. The lesions were dated by history, when available. Hematomas were grouped as follows: acute, four; early subacute, four; late subacute, four; chronic, 13. Six collections were classified as rehemorrhage; and two patients had CSF hygromas. Subdural hematomas evolved in a pattern similar to intracerebral hemorrhage with the exception of chronic subdural hematomas, in which isointensity of hypointensity relative to gray matter was observed on short TR/TE images compared with the persistent very high signal intensity noted in chronic parenchymal hematomas. Hemosiderin was rarely seen in chronic hematomas. These findings are most likely the result of the absence of a blood-brain barrier, which allowed clearance and dilution of blood products. Subdural hematomas with repeat hemorrhage demonstrated multiple phases of bleeding with layering phenomenon and more frequent hemosiderin deposition. It is possible that the clearance of blood products, as observed in chronic subdural hematomas, is impaired or poorly functional when rehemorrhage occurs. The persistence of high signal from methemoglobin in a hematoma that is expected to be in the chronic phase also suggests repeated hemorrhage. Acute CSF subdural hygromas had signal intensities identical to CSF without MR evidence of blood products. At surgery, clear fluid under pressure was found. MR imaging, with its unique ability to delineate the various phases of hemorrhage, is well suited to the evaluation of subdural hemorrhage.
Explore the source record for details and available documents.
1. There is a constant sequence of signal intensity patterns that characterize 1.5 T, spin echo MR images of hemorrhagic lesions. 2. The MRI appearance of intraparenchymal hemorrhage is determined by the sequential chemical degradation of Hb, by the paramagnetic properties of the degradation products and by certain biologic factors including pO2, edema formation, hematocrit and BBB. 3. Acute intraparenchymal hemorrhage is characterized by markedly diminished signal intensity centrally relative to surrounding white matter (hypointensity) on T2 weighted images and often by a moderately increased signal intensity (hyperintensity) of the adjacent white matter produced by surrounding edema on proton density and T2 weighted images. 4. Early subacute intraparenchymal hemorrhage is characterized centrally by moderate hypointensity on T2 weighted images, and peripherally, by moderate hyperintensity on T1 weighted and marked hypointensity on T2 weighted images. Hyperintensity on proton density and T2 weighted images of nearby white matter owing to edema may again be seen. 5. Late subacute intraparenchymal hemorrhage is characterized by marked peripheral and central hyperintensity on both T1 and T2 weighted images. Also, marked hypointensity of the adjacent brain rim on T2 weighted images owing to hemosiderin deposition may be seen. 6. Chronic intraparenchymal hemorrhage is characterized by marked hyperintensity both centrally and peripherally on both T1 and T2 weighted images and by marked hypointensity of the adjacent brain rim on T2 weighted images owing to hemosiderin deposition. Surrounding edema is no longer present. 7. The integrity of the blood-brain barrier appears to be important in determining whether or not hemosiderin accumulations consistently occur in subacute and chronic hemorrhage. 8. Hemorrhagic conditions in which the defined sequence of signal intensity patterns may be seen include: venous thrombosis, hemorrhagic infarction, occult vascular malformation and intracranial aneurysm.
Fifty-seven patients with hemorrhagic intracranial lesions were examined with magnetic resonance (MR) imaging at 1.5 T with use of both spin-echo (SE) and gradient-echo-acquisition (GEA) techniques to assess the clinical applications and limitations of GEA in evaluation of intracranial hemorrhage at high field strength. All GEA images were obtained with a long echo time and short flip angle to emphasize T2*-based contrast. In 30 of 61 cases, GEA images demonstrated more hemorrhagic lesions than SE images. In 14 of 61 cases, GEA images failed to depict the lesion or obscured the specific diagnosis (as depicted by SE MR imaging). The authors believe that GEA imaging in its current form has a limited but definite adjunctive role in the evaluation of intracranial hemorrhage at high field strength.