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Biomedical subjects

R W Tarr

Publications and source records attributed to R W Tarr.

At least 19 recordsLinked to original sources
PubMed1992

MR imaging features of medulloblastomas.

The preoperative MR studies of 25 patients with surgically proved medulloblastomas were retrospectively reviewed in order to characterize these neoplasms with regard to their MR signal intensity, size, location, and appearance after contrast enhancement. Gadopentetate dimeglumine--enhanced MR images were available in 11 patients. On short TR/short TE images, medulloblastomas generally had low to intermediate signal, and were predominantly slightly hyperintense relative to muscle and hypointense relative to white matter. On long TR/long TE images, medulloblastomas generally had intermediate to moderately high signal, predominantly hyperintense relative to muscle and white matter. Tumor signal relative to gray matter varied considerably on both short TR and long TR images. Signal heterogeneity on long TR/long TE images was observed in 91% of the lesions and resulted from intratumoral cystic zones, small blood vessels, and/or calcifications. In the patients who received gadopentetate dimeglumine, the fraction of tumor volume showing enhancement was found to be less than one third in two cases, between one third and two thirds in four cases, and greater than two thirds in five cases. The mean tumor size was 3.6 x 4.0 x 3.5 cm. The most frequent location of medulloblastoma was the mid and inferior vermis. We conclude that the unenhanced and enhanced MR characteristics of medulloblastomas are somewhat variable. Medulloblastomas should be included in the differential diagnosis when the MR findings described are present in the appropriate patient population.

Adolescent↗
PubMed1990

Use of acetazolamide-challenge xenon CT in the assessment of cerebral blood flow dynamics in patients with arteriovenous malformations.

Arteriovenous malformations (AVMs) may cause symptoms related to a reduction of cerebral blood flow (CBF) to surrounding brain parenchyma. To evaluate this compromise of hemodynamic reserve (commonly referred to as steal phenomenon), we used acetazolamide challenge and stable-xenon CT (Xe/CT). Baseline Xe/CT studies in 13 patients with AVMs were followed by an acetazolamide challenge to the vascular reserve. Blood flow maps were quantitated by using region-of-interest (ROI) software. ROI findings were categorized into four groups on the basis of the presence or absence of normal baseline CBF and presence or absence of normal augmentation of CBF. ROIs were designated as near site (within the vascular territory supplying the AVM) or far site (outside the vascular territory supplying the AVM). One patient had a normal baseline and normal augmentation of CBF (group 1). The other patients had a combination of one or more of the other three categories. Ten patients had parenchymal areas that exhibited either a normal or low baseline CBF with decreased augmentation; both conditions were interpreted as decreased vascular reserve (groups 2 and 3). Eleven patients had parenchymal areas that showed a low baseline CBF and normal augmentation with acetazolamide (group 4), interpreted as having a decreased demand for CBF but having a normal vascular reserve. Decreased vascular reserve was found in 27% of the nearsite areas and 17% of the far-site areas. No patients had only far-site abnormal vascular reserve. We believe that compromised vascular reserve can best be evaluated with a challenge study, such as this acetazolamide-challenge Xe/CT study.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetazolamide↗
PubMed1988

Computed tomography and magnetic resonance imaging of the acute abdomen.

CT is a noninvasive investigation that in many instances is more sensitive in elucidating intra-abdominal and retroperitoneal disease than is conventional radiography. With modern scanners, the procedure is rapid and efficient and suitable for the most severely ill and infirm. The scans are easily interpretable, and the anatomic and morphologic depiction of disease is readily understood by those with surgical training. Information regarding the state of the bowel wall, mesentery, and intraperitoneal and retroperitoneal structures is displayed in greater detail than by any other diagnostic imaging modality. The use of intravenous contrast medium is rarely essential. The concentration of iodinated contrast needed for opacification of the bowel is no greater than 2 per cent to 5 per cent and will not complicate bowel surgery, as would standard upper gastrointestinal or barium enema studies. Abscess, free air, calcium, and intraperitoneal fluid are very sensitively detected. CT is extremely useful in aiding surgical decision making in the acute abdomen and is complementary to or has replaced conventional studies.

Abdomen, Acute↗
PubMed1988

Magnetic resonance imaging of ischemic bowel in rabbit model.

Acute mesenteric ischemic bowel disease is a common yet complex disorder with high morbidity and mortality rates predominantly caused by delayed diagnosis. We examined the role of magnetic resonance imaging (MRI) in the early detection of small bowel ischemia using the rabbit model. Surgical ligation of the appropriate arterial vascular supply to the ileum of 10 rabbits produced the ischemic compromise. The animals were imaged at different time intervals after the arterial occlusion. Multislice, T1 and T2-weighted images were obtained in axial and coronal planes. Abnormal findings of the dearterialized segment of bowel were visualized as early as 45 minutes after vascular occlusion. The findings consisted of: (1) bowel wall thickening, (2) two- to three-fold increase in signal intensity from bowel on T2-weighted images, and (3) isointensity or slightly increased signal intensity within the bowel wall on T1-weighted images. MRI appears to be a sensitive, noninvasive technique for the early detection of bowel ischemia in the rabbit animal model.

Animals↗
PubMed1988

Insufficiency fractures of the femoral neck in association with chronic renal failure.

The femoral neck is a relatively uncommon location for stress fractures. As with other stress fractures, those occurring in the femoral neck can be divided into fatigue and insufficiency fractures. Chronic renal failure (CRF) is an underlying condition that can predispose patients to insufficiency fractures of the femoral neck. We report 12 such fractures occurring in eight patients with CRF; half had bilateral fractures. In addition, 50% of the fractures were of the tensile (transverse) type, which may progress to complete fracture.

Adult↗
PubMed1988

Primary extraosseous osteogenic sarcoma of the mediastinum: clinical, pathologic, and radiologic correlation.

We have presented a rare case of primary involvement of the anterior mediastinum by osteogenic sarcoma in which CT was useful in demonstrating calcium within the mass, and in distinguishing the mass from surrounding bony structures. Although rare, extraosseous osteogenic sarcoma should be included in the differential diagnosis of a calcified anterior mediastinal mass.

Diagnosis, Differential↗
PubMed1987

MRI of mumps encephalitis: comparison with CT evaluation.

The evaluation of a patient with mumps encephalitis by computed tomography (CT) and magnetic resonance (MR) imaging is reported. Correlation of findings on MR and CT in relation to clinical symptoms is presented. MR was found to be more sensitive in the number of lesions detected (11) as compared to CT (3). Thus, it seems that MR imaging may be a sensitive diagnostic adjunct in cases of suspected viral encephalitis.

Child, Preschool↗
PubMed1986

Magnetic resonance imaging artifacts: mechanism and clinical significance.

Many types of artifacts may occur in magnetic resonance imaging. These artifacts may be related to extrinsic factors such as patient motion or metallic artifacts; they may be due specifically to the MR system such as power gradient drop off and chemical shift artifacts; they may occur as a consequence of general image processing techniques, as in the case of truncation artifacts and aliasing. Change in patient position, pulse sequence, or other imaging variables may improve some artifacts. Although reduction of some artifacts may require a service engineer, the radiologist has the responsibility to recognize MR imaging problems. The radiologist's knowledge of MR imaging artifacts is important to the continued maintenance of high image quality and is essential if one is to avoid confusing artifactual appearances with pathology.

Diagnostic Errors↗
PubMed1985

The "aortic nipple" as a sign of impending superior vena caval syndrome.

The development of dilatation of the left superior intercostal vein ("aortic nipple") on chest radiographic studies can be used as a clue to impending superior vena caval syndrome. Two cases are described in which detection of an "aortic nipple" on chest roentgenograms predated the clinical syndrome by seven to ten weeks. Since superior vena caval syndrome is a medical emergency, recognition of signs such as this which may significantly predate the "full-blown" syndrome have far-reaching implications in the care of patients.

Adult↗
PubMedDate not supplied

Benign hemangioendothelioma involving posterior mediastinum: CT findings.

We report a case of benign hemangioendothelioma of infancy extending from the deep soft tissues of the neck to involve the entire longitudinal extent of the right posterior mediastinum. The CT findings that aid in the differential diagnosis of this and other posterior mediastinal masses are discussed.

Diagnosis, Differential↗
PubMedDate not supplied

MR imaging of recent spinal trauma.

Proper therapeutic management of acute spinal trauma depends considerably on the assessment of the condition of the underlying spinal cord and the relative stability of the surrounding bony architecture. A series of 14 patients who were examined by magnetic resonance (MR) imaging following spinal trauma is presented. Comparison of information gained by MR with that obtained by conventional CT indicates that MR is useful in assessing spinal cord compression, traumatic disk pathology, and post-traumatic intramedullary abnormalities. Computed tomography is more accurate in detecting posterior neural arch fractures and in assessing the number of displaced fragments.

Adolescent↗
PubMedDate not supplied

Use of the delayed mask for improved demonstration of aneurysms on intraarterial DSA.

PURPOSE: We retrospectively explored the use of the delayed mask technique for intraarterial digital subtraction angiography (IADSA) to demonstrate the anatomy of aneurysm necks. METHODS: The delayed mask technique was utilized in 22 patients who had craniotomies for aneurysms demonstrated at angiography. The operative notes were compared to the angiographic findings of both the traditionally masked IADSA and the delayed mask IADSA. In addition, an in vitro model was constructed to examine the relationship between the size of the aneurysm neck and the ability to indirectly define its anatomy by demonstrating the flow jet. RESULTS: In 12 of 22 cases, the delayed mask technique demonstrated a systolic jet that was not demonstrated by traditional subtraction techniques. In nine of 12 cases, the delayed mask technique gave more specific information regarding the size, location, and orientation of the aneurysm neck. CONCLUSION: The delayed mask technique can add important information regarding the anatomy of aneurysm without adding time or risk to the procedure.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Diagnosis of ruptured intracranial dermoid cyst: value MR over CT.

The CT and MR findings of seven patients with pathologically proved ruptured dermoid cysts were reviewed to analyze the MR characteristics and to see if MR evaluation had significant advantages over CT. In six cases, both CT and MR identified fatty material in the CSF spaces. Hemorrhage complicated preoperative diagnosis in one case. Patterns of extraaxial fat distribution were as follows: intraventricular fat/CSF levels (three patients), generalized subarachnoid spread (six patients), and localized subarachnoid spread with sulcal widening (one patient). There was no correlation between fat distribution and clinical symptoms. MR showed the vascular involvement better than CT did in five of seven cases, and showed extension of the cysts into the skull base in two cases. Signal intensity of the solid mass was low on T1-weighted MR images and inhomogeneously high on T2-weighted images, which correlated pathologically with the presence of crystal cholesterol, hair, sebaceous glands, and epithelial cells in all cases. On MR, brain parenchyma showed little edema or other reaction to the masses, which were typically large. The value of MR over CT in the examination of ruptured dermoid cysts is the conspicuity of the extent of subarachnoid spread, involvement of the extraaxial structures, and evidence of vascular compromise, which can obviate angiography. MR had no advantage over CT in making the initial diagnosis of ruptured dermoid, but it would be the preferred preoperative study.

Adult↗
PubMedDate not supplied

Impaired cerebral vasoreactivity after embolization of arteriovenous malformations: assessment with serial acetazolamide challenge xenon CT.

Embolization of a portion of the nidus of an arteriovenous malformation not only may alter hemodynamics within the nidus, but also may change blood flow dynamics in adjacent normal vessels. Sequential acetazolamide-challenge xenon CT cerebral blood flow studies were performed in eight patients before and after embolization of arteriovenous malformations to assess the hemodynamic effects on the major vascular territories supplying the malformation. Acetazolamide is a potent cerebral vasodilator, and its administration combined with cerebral blood flow studies allows assessment of cerebral vasoreactivity. In seven of the eight patients, one or more parenchymal areas exhibited a normal cerebral blood flow augmentation response to acetazolamide before embolization, but diminished acetazolamide flow augmentation was seen after embolization, indicating abnormal vasoreactivity. We found that the decrease in vasoreactivity peaked 6-10 days after embolization. In one of the eight patients, a temporary delayed neurologic deficit developed during a period of impaired cerebral vasoreactivity following embolization. Our results suggest that embolization of an arteriovenous malformation can induce vasoreactivity changes in adjacent normal vessels. Because these changes appear to be somewhat time-dependent, an appropriate interval should be observed between embolization stages or before surgical resection of an arteriovenous malformation following embolization to allow hemodynamic equilibration to occur. Acetazolamide challenge combined with serial cerebral blood flow studies following embolization enables determination of this hemodynamic equilibration.

Acetazolamide↗
PubMedDate not supplied

Treatment of arteriovenous malformations of the brain with combined embolization and stereotactic radiosurgery: results after 1 and 2 years.

Seven patients with large arteriovenous malformations (AVMs) of the brain were selected for combined therapy with particulate embolization, followed by radiosurgery of the residual nidus. The goal of embolization was to reduce the patient nidus to a size that facilitated successful stereotactic radiosurgery. Angiograms obtained 1 and 2 years after radiosurgery were evaluated for changes in nidus size, flow rate, and feeding and draining vessels. One year after stereotactic radiosurgery, one AVM was angiographically undetectable. Three other AVMs demonstrated a volume reduction of greater than 50%, in addition to decreased shunt speed and altered angioarchitecture at 1-year follow-up. At 2-year follow-ups, two of seven AVMs were cured, and an additional two of seven had a greater than 98% reduction in nidus volume. Although one patient experienced a transient deficit from embolotherapy, none of our patients suffered a new neurologic deficit or a hemorrhage during the follow-up period. Our data support the efficacy of combined embolotherapy and radiosurgery for definitive therapy of selected large AVMs of the brain.

Adult↗