Major Radiologic and Clinical Outcomes of Total Spine MRI Performed in the Emergency Department at a Major Academic Medical Center.

BACKGROUND AND PURPOSE: Total spine MRIs are requested by the emergency department when focused imaging can not be ordered on the basis of history or clinical findings. However, their efficacy is not known. We assessed the following: 1) major radiologic and clinical outcomes of total spine MR imaging performed by the emergency department, and 2) whether the presence of a high-risk clinical profile and/or neurologic findings impacts the clinical outcomes. MATERIALS AND METHODS: Total spine MRIs requested by the emergency department during a 28-month period were evaluated for major radiologic (cord compression, cauda equina compression, and other significant findings) and major clinical outcomes (hospital admission during the visit followed by an operation, radiation therapy, or intravenous antibiotics or steroids). Associations between a high-risk clinical profile (cancer, infection, coagulopathy) and/or the presence of neurologic findings and outcomes were assessed. RESULTS: After we excluded trauma or nondiagnostic studies, 321/2047 (15.7%) MRIs ordered during study period were total spine MR imaging; 117/321 (36.4%) had major radiologic and 60/321 (18.6%) had major clinical outcomes (34/60 in <24 hours); and 58/117(49.6%) with major radiologic outcome were treated compared with 2/205 (1.0%) without (OR = 99, P < .001). The presence of both a high-risk clinical profile and neurologic findings concurrently in a patient (142/321) increased the likelihood of major clinical outcomes during the same visit (OR = 3.1, P < .001) and in <24-hours (OR = 2.6, P = .01) compared with those with either a high-risk clinical profile or neurologic findings alone (179/321). CONCLUSIONS: Total spine MR imaging ordered by our emergency department has a high radiologic and significant clinical yield. When a high-risk clinical profile and neurologic findings are both present in a patient, they should be prioritized for emergent total spine MR imaging, given the increased likelihood of clinical impact.

Transient MRI enhancement in a patient with seizures and previously resected glioma: use of MRS.

A 35-year-old man presented with partial seizures 10 years after resection of a left-sided glioblastoma multiforme. At the old operative site MRI demonstrated extensive cortical and white matter gadolinium enhancement, and PET showed hypermetabolism. Biopsy of the area was postponed when MRS showed a normal biochemical spectrum. MRI and PET abnormalities resolved after control of the seizures. MRS is noninvasive and can provide essential information in the management of patients with seizures and previously treated cerebral neoplasms.

The value of magnetic resonance imaging in treatment planning of nasopharyngeal carcinoma.

Seven patients with AJCC Stage T4 nasopharyngeal carcinoma underwent both computed tomographic (CT) and magnetic resonance (MR) examinations prior to radiation therapy treatment planning. Lateral tumor extension into the infratemporal fossa was visualized by MR as less extensive in three cases than suggested by CT, as was inferior extension into the parapharyngeal soft tissues in three cases. MR clarified uncertainties on CT regarding involvement of the pontine cistern in three patients and of the cavernous sinus in two patients. Posterior extension of tumor was underestimated by CT in four of six cases shown by MR to involve the clivus. MR appeared superior in evaluating the presence of parenchymal brain involvement in three cases. The margins of the final boost treatment fields dictated by MR findings differed measurably from those derived from CT in six of seven cases. These findings lend support for greater utilization of MR in treatment planning of nasopharyngeal carcinoma.

MR imaging of various oxidation states of intracellular and extracellular hemoglobin.

The in vitro behavior of various states of hemoglobin was examined over a wide range of concentrations. Solutions of increasing concentrations of oxyhemoglobin displayed significant increases in T1 and T2 relaxation rates that were insensitive to pH values between 6.0 and 6.9. Bovine serum albumin, which displayed a relaxation behavior nearly identical to that of oxyhemoglobin, was used to normalize for the protein concentration of the deoxyhemoglobin and methemoglobin samples. Concentrated protein solutions with increasing proportions of deoxyhemoglobin yielded little change in the T1 relaxation rate. In these samples, however, the T2 relaxation rate displayed a parabolic dependence on the concentration of intracellular deoxyhemoglobin paralleling the inhomogeneity of the sample; this was not observed with extracellular deoxyhemoglobin. Similar T2 relaxation behavior was observed for intracellular methemoglobin, except that the magnitude of the T2 shortening was smaller than that for deoxyhemoglobin. The magnitude of the T2 shortening was pH dependent, roughly paralleling the change in the equilibrium between the high-spin acid form of methemoglobin and the low-spin basic form of methemoglobin. Marked increase in the T1 relaxation rate is observed with increasing concentrations of methemoglobin, again with greater relaxation enhancement at lower pH. The results of our study emphasize the importance of normalizing for protein concentration when assessing the effects of paramagnetic forms of hemoglobin.

Streptokinase clot lysis in acute occlusions of the cranial circulation: study in rabbits.

An animal model of acute cerebrovascular thromboembolism was developed to evaluate the feasibility of selective fibrinolysis. In 20 Flemish Giant rabbits, autologous clot was deposited via selected catheterization of the distal end of the common carotid artery. The rates of clot lysis with streptokinase were compared in eight control rabbits and after three different dosage regimens in four rabbits each. Group A received selective infusion of 5000 U/hr; group B received 4000 U/min for 1 hr, 3000 U/min for 2 hr, and 5000 U/hr for 2 hr; and group C was treated similar to group B plus receiving an initial 20,000 U bolus of streptokinase. Lysis was evaluated by serial angiograms obtained hourly for up to 6 hr after the clot was deposited. Five proximal vessels arising from the common carotid artery were chosen for the angiographic grading system. The control group showed beginning lysis after 5-6 hr. Group A appeared to show a slight improvement about 4 hr after clotting. Group B demonstrated an early and greater improvement at 2 hr that appeared to be sustained throughout the experiment. Group C showed no difference compared with the control group. The Dunnet t procedure and the Kruskel-Wallis nonparametric analysis of variance were used for comparing the angiograms of the treatment groups with those of the control group at corresponding study times. The results of these animal experiments do not indicate a definite benefit of streptokinase treatment alone over no treatment. Further controlled studies are needed before the value of streptokinase in routine clinical practice can be determined.

High-resolution MR of the spinal cord in humans and rats.

Human and rat cervical spinal cords were imaged with high-resolution spin-echo and inversion-recovery pulse sequences in an experimental 1.9-T MR system. The gross morphology of the cord was easily discernible in fresh and fixed specimens, including the white and gray commissures, dorsal and ventral horns, and lateral and posterior funiculi. The T1, T2, and spin-density values for gray and white matter were determined from these images and were found to be 914 msec, 114 msec, and 71% for white matter other than the dorsal columns, and 946 msec, 87 msec, and 80% for gray matter in human spinal cords. These values are reduced considerably after formalin fixation: T1 to 56% (white matter) and 54% (gray matter) of prefixation values, T2 to 52% (white matter) and 70% (gray matter) of fresh values, and spin density to 90% (white matter) and 96% (gray matter) of prefixation values. Interestingly, the central gray matter demonstrates higher signal intensity than the white matter on both short and long TR/TE images. This intensity difference was observed for both human and rat spinal cords, before and after fixation, and can be explained by the relatively small T1 differences between gray matter and white matter and the gray matter-white matter spin-density ratios: 1.127 for fresh and 1.203 for fixed specimens.

MR of vascular encasement in parasellar masses: comparison with angiography and CT.

The relationship between tumor mass and vascular involvement as seen on MR imaging was examined in 11 patients with masses in the parasellar region, and the findings were correlated with CT and angiography. In six cases, MR was superior to CT and angiography in depicting the relationship of the tumor to adjacent blood vessels. In these cases, MR demonstrated tumor surrounding the blood vessel without changing the diameter of its lumen. Angiography did not reveal encasement in these cases. In four cases, both MR and angiography showed signs of vascular encasement with narrowing of the vessel's lumen. In two cases, MR was equivocal while angiography revealed vascular encasement in one case and was negative for encasement in the other. CT was less sensitive than MR in defining vascular encasement since there is usually little contrast between an enhancing tumor and the major blood vessels. Coronal scanning appeared to be the best plane of imaging and correlated well with the anteroposterior angiogram. We propose that MR is the method of choice for evaluating arterial encasement by tumors and may obviate the need for angiography in those cases in which MR is positive for a basal lesion.

Low sensitivity of clinical MR imaging to small changes in the concentration of nonparamagnetic protein.

This study attempts to determine the magnitude of change in the concentration of a nonparamagnetic protein (human serum albumin) required to effect a detectable change in signal intensity on a clinical imaging unit. For a range of protein concentrations from 0-6100 mg/dl the concentration could not be predicted by inspecting the images. Measurement of displayed signal intensity failed to distinguish concentrations of 0.09-3700 mg/dl, while 6100 mg/dl gave slightly higher intensity signals. Although this low sensitivity represents expected behavior for low concentrations, the failure to differentiate the higher concentrations implies limitations imposed by clinical imaging techniques. Our results suggest that additional factors, such as paramagnetic material and motion as well as differences in protein concentration, may be involved in the MR signal intensities observed in pathologic CSF and cystic CNS collections.

High-field MRI of hemorrhagic cortical infarction.

High-field MRI is capable of differentiating acute, subacute, and chronic hemorrhagic cortical infarctions. In eight of nine patients, hemorrhage occurred in a vascular watershed zone. Acute hemorrhagic cortical infarction produces mild cortical low intensity on T2-weighted images outlined by subcortical edema (high intensity) and isointensity with normal cortex on T1-weighted images. Subacute hemorrhagic cortical infarction shows cortical high intensity first on T1-weighted images and later on T2-weighted images; it is also associated with subcortical edema. In the chronic stage, there is a marked persistent cortical low intensity on T2-weighted images. This is most prominent in the deeply infolded cortical gyri. The low intensity noted in acute and chronic hemorrhagic cortical infarction with T2 weighting appears to be related to two separate underlying histochemical states. The characteristic cortical low intensity observed on T2-weighted images in acute and chronic hemorrhagic cortical infarction is proportional to the square of the magnetic field strength.

Pseudoatrophy of the cervical portion of the spinal cord on MR images: a manifestation of the truncation artifact?

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.

Experimental spinal cord injury: imaging the acute lesion.

In order to obtain high resolution images of fixed excised rat spinal cords we have developed a technique using a 6-mm bore, two-turn saddle coil, with a usable imaging length of approximately 4 cm. MR imaging is performed on a prototype 31-cm bore, 1.9-T system with a 1.5-mm section thickness and 7.6-mm field of view.

Internuclear ophthalmoplegia: MR-anatomic correlation.

Internuclear ophthalmoplegia is a gaze disorder characterized by impaired adduction on the side of a lesion involving the medial longitudinal fasciculus with dissociated nystagmus of the abducting eye. Eleven patients with internuclear ophthalmoplegia (nine with clinical multiple sclerosis, two with clinical infarction) underwent MR imaging with spin-echo techniques on a 1.5-T system. Nine patients also had CT. MR showed focal or nodular areas of high signal intensity on T2-weighted images in the region of the medial longitudinal fasciculus in 10 of 11 patients. In one of four patients with internuclear ophthalmoplegia who had MR after intravenous gadolinium-DTPA, an enhancing ring lesion was seen in the region of the medial longitudinal fasciculus on short TR/TE images, indicating active blood-brain-barrier disruption, which correlated with this patient's recent-onset internuclear ophthalmoplegia. CT failed to show the lesions in all nine patients examined. This report demonstrates the superiority of MR in evaluating gaze disorders attributable to brainstem dysfunction, such as internuclear ophthalmoplegia, and correlates MR findings with the relevant neuroanatomy of the medial longitudinal fasciculus.

Reversible arteriovenous malformation-induced venous hypertension as a cause of neurological deficits.

A case of a dural arteriovenous malformation with prominent localizing neurological deficits is reported. The venous drainage of the lesion and the lack of a significant pial supply implicate venous hypertension as the mechanism of neurological dysfunction. This mechanism is supported further by the angiographic changes and the prompt resolution of the deficits after endovascular treatment. This case illustrates the potential for this frequently postulated but rarely confirmed pathophysiological mechanism to cause reversible neurological dysfunction.

Postmortem magnetic resonance imaging of experimental spinal cord injury: magnetic resonance findings versus in vivo functional deficit.

The relationship between the severity of the posttraumatic functional deficit and findings on magnetic resonance imaging (MRI) was investigated in a rat model of experimental spinal cord trauma. Thirty Sprague-Dawley rats were subjected to an identical, moderate, contusion injury of the spinal cord. Control animals underwent laminectomy without cord injury. The severity of the functional deficit was assessed with the Combined Behavioral Score (CBS). Animals were killed at 3, 7, 14, 21, or 28 days after injury, and the fixed, excised spinal cords were studied with MRI at 1.9 T. The lesion length was measured on sagittal spin-echo MRI. The lesion length measured on MRI was highly correlated with the CBS functional score (r = 0.56, P = 0.002). There were significant correlations between lesion length as determined by MRI and by histological morphometry (r = 0.44, P = 0.02), between histological morphometric lesion length and CBS functional deficit (r = 0.76, P < 0.001), and between the area of residual white matter at the lesion epicenter, determined by histological techniques, and the severity of functional deficit (r = -0.59, P = 0.001). A qualitative estimate of the area of preserved white matter, derived from MRI, was significantly correlated with the severity of functional deficit (r = -0.56, P = 0.006). A multiple regression of MRI-determined lesion length and MRI estimate of residual white matter versus CBS explained more than 42% of the variability of the functional deficit among these animals subjected to the same weight drop injury. We conclude that MRI parameters are reliable predictors of the severity of neurological deficit in experimental spinal cord trauma.

Catamenial mononeuropathy and radiculopathy: a treatable neuropathic disorder.

OBJECT: The aim of this study was to investigate the indications and treatment options in patients with lower-extremity neuropathies and radiculopathies caused by endometriosis. METHODS: The authors identified five patients whose symptoms included catamenial pain, weakness, and sensory loss involving the sciatic and femoral nerves and multiple lumbosacral nerve roots. Radiographic studies supported the diagnosis of catamenial neuropathy or radiculopathy, but definitive diagnosis depended on surgical and pathological examination. Treatment of symptoms, including physical therapy and a course of antiinflammatory or analgesic medication, was not helpful. Patients responded favorably to hormonal therapy. Laparoscopy or open exploration for extrapelvic lesions was performed for diagnosis or for treatment when hormone therapy failed. Pain and sensory symptoms responded well to therapy. Weakness improved, but never recovered completely. CONCLUSIONS: Catamenial neuropathy or radiculopathy should be considered when evaluating reproductive-age women with recurring focal neuropathic leg pain, weakness, and sensory loss.

Magnetic resonance imaging of the spine. Normal anatomy.

Standard anatomy of the spine may be found in anatomy and radiology textbooks. However, there are aspects of spinal anatomy that are of particular importance to magnetic resonance imaging (MRI). The structure and orientation of the facet joints and their relationship to the neural foramina receive relatively little attention in standard anatomic works, but they are of great importance in evaluating nerve root compression syndromes. Similarly, the relationships between the cross-sectional diameters of the spinal canal, the subarachnoid space, and the spinal cord assume a great deal of significance when evaluating patients with signs or symptoms of spinal stenosis. Changes in the configurations and composition of the spinal cord will become increasingly important to the radiologists as it becomes possible to identify and distinguish spinal cord grey and white matter. Degenerative syndromes of the spinal cord may be more thoroughly evaluated once MRI permits identification of the specific regions or structures of the cord in which the tissue loss has been most severe.

Degenerative disk disease.

Evaluation of degenerative disk disease is, by far, the most common indication for spinal magnetic resonance imaging (MRI). It is rare to identify a patient over the age of 40 whose spine does not demonstrate at least some of the imaging features of degenerative disease. In spite of the ubiquitous nature of degenerative changes in the spine and decades of intensive study of degenerative processes, many questions concerning degenerative disease, including its immediate etiology, remain unanswered. Radiologic evaluation of degenerative spine disease focuses on the anatomic relationships between the disk, vertebral endplates and facet joints with the subarachnoid space, nerve roots, and spinal cord. Although MRI lacks the detail of high resolution computed tomography for defining the anatomy of osteophytes, MRI appears to be the primary modality for evaluating degenerative spine disease, and in most cases, MRI may be definitive.

Neoplasms and related disorders.

Spinal neoplasms may be primary or metastatic, benign or malignant. In adults, metastatic involvement of the spine will represent the most important neoplastic disease of this region. However, hemangiomas are the most common spinal neoplasms. The vast majority of intradural, extramedullary neoplasms that will be identified in the spine are meningiomas and neurofibromas. Both lesions may be sporadic or associated with phakomatoses. Intramedullary spinal cord and filum terminale tumors are relatively rare and are far less common than intramedullary brain tumors. As is the case in the brain, these are overwhelmingly glial neoplasms, with ependymomas and low-grade astrocytomas representing the majority of the lesions. Hemangioblastoma deserves mention because of its often characteristic imaging findings and its association with von Hippel-Lindau disease.

Inflammation, infection, cavitary disorders, and ischemia.

Demyclinating lesions of the spinal cord, including multiple sclerosis as well as other less common diseases, probably represent the etiology of a substantial proportion of all idiopathic myelopathies. Magnetic resonance imaging (MRI) has made major advances in the diagnosis and characterization of demyclinating disease. Infections of the spine may have severe consequences and, if detected early, are usually treatable processes. Osteomyelitis and epidural abscesses have characteristic imaging findings. Poor outcomes are more often due to delays in clinical presentation or the debilitated condition of the patients than to limitations in the accuracy of MRI diagnosis. Cavitary lesions of the spinal cord were among the first applications in which MRI proved its superiority to previously available techniques. Accurate diagnosis of these lesions involves detecting characteristics findings and relating these observations to the clinical history. Spinal cord infarction is relatively rare due to the extensively collateralized blood supply to the spinal canal. However, aortic aneurysms and the surgery for these lesions places the blood supply of the distal spinal cord and conus at risk. The syndrome of postoperative spinal cord infarction has characteristic clinical findings. However, MRI may contribute to distinguishing transient ischemia from true infarction and to predicting the severity of the final deficit.

Magnetic resonance imaging of the spine. Technology and technique.

Perhaps in no other area of radiology is the appearance of the images as dependent on the technique used to obtain them as is the case in magnetic resonance imaging (MRI). In some instances, such as decreasing signal-to-noise ratios at the periphery of surface coils or obvious difficulties in localizing the level of an abnormality detected in spinal images, the technical dependence is obvious. There are many instances, however, in which the influence of technology may be more subtle, although no less important. It is far less of a problem to have difficulty localizing a level when this difficulty is recognized than it is when ambiguity concerning the level of an abnormality goes undetected. Obsessive attention to accurate localization of levels is necessary to avoid potentially dangerous mistakes. Terms such as "T1-weighted" rarely provide an accurate description of the contrast characteristics of an MRI image. Careful use of terminology, or at a minimum clear thinking concerning the determinants of image contrast will avoid confusion in image interpretation. The "weighting" of an image usually cannot be defined in terms of a single parameter, and attempts to do so often obfuscate more than they clarify. As technology evolves, a variety of different "T1-weighted" pulse sequences may be introduced. Each of these may display different contrast characteristics. It will be important to identify the specific pulse sequence, rather than "weighting" to understand the signal intensities observed on images.