Search PubMed⌕ Search

Biomedical subjects

M A Norris

Publications and source records attributed to M A Norris.

32 records · Page 2Linked to original sources
PubMed1995

MR diagnosis of labral tears of the shoulder: value of T2*-weighted gradient-recalled echo images made in external rotation.

OBJECTIVE: Because several studies have shown that conventional MR imaging can fail to diagnose a significant percentage of labral tears, some authors have proposed obtaining T2*-weighted gradient-recalled echo images with the humerus in external rotation. The purpose of our study was to determine whether the diagnostic accuracy of detecting anteroinferior labral tears by MR imaging would be improved by adding a T2*-weighted gradient-recalled echo sequence with the humerus in external rotation. MATERIALS AND METHODS: The study included 24 patients for whom axial MR images of the shoulder were obtained with the humerus in both the neutral position and external rotation. Two observers interpreted the images made in the neutral position and then noted any change in their interpretations after viewing findings on the external-rotation images. MR results were correlated with surgical findings. At surgery, 14 anteroinferior labra were found to be torn and 10 were found to be intact. RESULTS: Both observers identified one patient for whom a surgically proved labral tear was seen only on the external-rotation images. The sensitivity increased from 0.43 to 0.50 (p = .35) for observer 1 and from 0.36 to 0.43 (p = .35) for observer 2. The specificity of 0.90 for both observers remained unchanged. The accuracy improved from 0.62 to 0.67 for observer 1 and from 0.55 to 0.62 for observer 2. CONCLUSION: The addition of external-rotation T2*-weighted gradient-recalled echo images to the MR examination for tears of the anteroinferior labrum leads to a small but statistically insignificant increase in diagnostic sensitivity. We conclude that the small increase in sensitivity does not justify the routine use of this sequence.

Adolescent↗
PubMed1994

MR diagnosis of meniscal tears: analysis of causes of errors.

OBJECTIVE: MR imaging of the knee is an accurate method for diagnosing meniscal tears. However, MR findings do not always agree with surgical findings. In a retrospective study, we analyzed the various causes of incorrect MR diagnoses. MATERIALS AND METHODS: We reviewed a series of 400 MR examinations for suspected meniscal tears in which the diagnostic accuracy was 90%. In this group, we found 70 patients in whom the original MR diagnosis did not agree with the surgical findings. Three musculoskeletal radiologists independently reviewed each of the 70 MR examinations without knowledge of the original interpretation or the surgical findings. Their interpretations and the MR images then were correlated with the surgical findings. The original incorrect diagnoses were categorized as being due to unavoidable errors, errors in interpretation, or errors made because of equivocal MR findings of a tear. Unavoidable errors were defined as false-positive and false-negative diagnoses that could not be avoided, even in retrospect. RESULTS: Of the 83 original diagnostic errors made in the MR evaluation of 800 menisci, 33 (40%) were unavoidable errors, 32 (39%) were due to equivocal MR findings, and 18 (21%) were due to interpretation errors. The unavoidable errors consisted of 21 missed meniscal tears and 12 false-positive MR diagnoses. In the false-positive cases, the menisci were interpreted as torn on MR images by all three observers, but no tear was found at arthroscopy. Subtle MR findings that were equivocal for a tear caused both false-positive and false-negative diagnoses. Seven of the 18 interpretation errors occurred when normal variants were mistaken for a tear. CONCLUSION: Using conventional coronal and sagittal spin-echo MR imaging, we could not identify 21 (6%) of the 333 meniscal tears, even in retrospect. In addition, subtle findings that are equivocal for a tear may still make MR diagnosis of every torn meniscus difficult even for experienced radiologists. Unavoidable false-positive diagnoses due to healed tears or tears missed at arthroscopy are an infrequent problem occurring in only 1.5% of the original 800 menisci evaluated with MR imaging.

Diagnostic Errors↗
PubMed1993

Diagnosis of meniscal tears of the knee with MR imaging: effect of observer variation and sample size on sensitivity and specificity.

OBJECTIVE: A wide range in the efficacy of MR imaging for the diagnosis of meniscal tears of the knee has been reported. To evaluate two possible causes for this variation, we studied how sensitivity and specificity are affected when different observers and sample sizes are used. MATERIALS AND METHODS: Two hundred MR examinations of the knee in patients for whom the results of arthroscopy were available were used for the study. One hundred eight medial meniscal tears and 58 lateral meniscal tears were found at arthroscopy. The sensitivity and specificity for detection of meniscal tears were determined for the original interpretations and retrospective evaluations by three observers. Comparisons were also made between sample sizes of 25 and 100. chi 2 analysis was used for unmatched data sets and McNemar's statistic was used for matched sets. RESULTS: For the 200 examinations, the sensitivity was 0.89-0.93 for medial meniscal tears and 0.79-0.83 for lateral meniscal tears. The specificity was 0.86 for medial meniscal tears and 0.90-0.92 for lateral meniscal tears. Sensitivity and specificity varied widely among different observers and different sample sizes. However, we found no significant difference between any of the comparisons at the p < .05 level. The largest interobserver variation occurred in the detection of lateral meniscal tears, with a sensitivity of 0.71 for one observer and 0.88 for another observer (p = .16). The largest variation between sets of 100 examinations was a change in sensitivity for detection of lateral meniscal tears from 0.74 to 0.88 for the original interpretations (p = .10). For the sample sets of 25 cases, the variation was even larger, with the sensitivity for detection of lateral meniscal tears varying from 0.5 for one set to 1.0 for another. CONCLUSION: We conclude that chance variation related to sample size can cause large but not statistically significant variations in sensitivity and specificity in this setting. These variations are of sufficient magnitude to explain many of the differences in reported sensitivity and specificity for MR imaging in the diagnosis of meniscal tears. We found no significant difference in observer performance.

Adolescent↗
PubMed1993

MR diagnosis of meniscal tears of the knee: importance of high signal in the meniscus that extends to the surface.

OBJECTIVE: The presence of intrameniscal signal in contact with the surface is a commonly used criterion for the diagnosis of meniscal tear. This signal presumably represents the actual tear in the meniscus. However, some menisci with signal that contacts the surface are noted to be intact at arthroscopy whereas other menisci that have no signal in contact with the surface are found to be torn. We investigated the relationship between the presence of a meniscal tear at arthroscopy and the location within the menisci of signal that contacted the surface. We hypothesized that patterns were present that would improve the accuracy of MR diagnosis of a meniscal tear. MATERIALS AND METHODS: We reviewed the MR and arthroscopic findings from 200 consecutive patients who had both knee MR examinations and knee arthroscopy. There were 108 medial and 58 lateral meniscal tears on arthroscopy. Each MR examination was reviewed for three aspects of intrameniscal signal: the number of images showing signal possibly or definitely contacting the surface, the specific surfaces involved, and the signal location. The coronal and sagittal images were evaluated separately. We correlated each of these features with the presence of a meniscal tear at arthroscopy. RESULTS: Menisci with signal possibly contacting the surface had the same frequency of tears (three tears in 33 menisci) as menisci without signal contacting the surface (15 tears in 194 menisci). More than 90% of menisci with signal contacting the surface on more than one image were torn, but only 55% of medial and 30% of lateral menisci with such signal on only one image were torn. In the torn menisci with signal contacting the surface, such signal was seen only on sagittal MR images in 31% of the medial menisci and 45% of the lateral menisci. Sixteen percent of the torn lateral menisci had signal contacting the meniscal surface in only the anterior two thirds of the meniscus, whereas this was true in only 2% of the torn medial menisci. Distinct patterns were not seen in the association between tears and signal contacting either the superior or the inferior surface. CONCLUSION: We found definite patterns in the location of intrameniscal signal that comes in contact with the meniscal surface. These patterns vary in the frequency of associated meniscal tears. Although menisci with internal signal in contact with the surface are usually torn, a tear is less likely if such signal is present on only one image. Tears may be identifiable on only one image plane. Tears in the anterior horn of the lateral meniscus are not uncommon. Knowledge of these patterns should help in the MR diagnosis of meniscal tears.

Adolescent↗
PubMed1992

Magnetic resonance imaging of myositis ossificans: analysis of seven cases.

Myositis ossificans typically presents as soft tissue swelling with progressive ossification on radiographs. Since magnetic resonance imaging (MRI) is commonly used to evaluate soft tissue masses, we analyzed eight MR examinations in seven patients with myositis ossificans to determine if typical patterns were present. One acute lesion had homogeneous intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Two subacute lesions had low signal intensity margins with slightly increased signal intensity centers on T1-weighted images and very high signal intensity on T2-weighted images. Five chronic lesions had two different patterns. All five were well-defined with low signal intensity borders. Three had signal intensity patterns characteristic of fat on T1-weighted and T2-weighted images. The other two lesions had intermediate signal intensity on T1-weighted images and slightly increased signal intensity on T2-weighted images. We conclude that typical MR appearances of myositis ossificans do exist. A low signal intensity rim is a common finding. However, these patterns are not unique to myositis ossificans and resemble those that have been reported in other lesions. It is important to be aware of the spectrum of MR findings of myositis ossificans when considering the differential diagnosis of a soft tissue mass.

Acute Disease↗
PubMed1991

Evaluating painful osteopenia in the elderly.

Osteopenia is a frequent finding on radiographs of elderly patients. When the exam is performed for skeletal pain, this finding may be significant. The differential diagnosis for osteopenia is extensive, but individualizing the patient work-up begins with a careful clinical history and laboratory studies. Appropriate radiographic exams can then be requested. A plain radiograph is always the starting point, followed by--as indicated--a nuclear bone scan, computed tomography, and magnetic resonance imaging.

Aged↗
PubMed1990

Fibrous dysplasia: magnetic resonance imaging appearance at 1.5 tesla.

Fibrous dysplasia has been described in a small number of cases in the literature as showing low signal intensity on T1- and T2-weighted magnetic resonance images. We reviewed magnetic resonance scans of 13 patients with fibrous dysplasia to determine if there might be a characteristic appearance. All lesions had sharply defined borders and were of intermediate signal intensity on T1-weighted images. With T2 weighting, six lesions (46%) showed high signal intensity, four (31%) showed persistent intermediate signal intensity, and three (23%) showed mixed intermediate and high signal intensity. Ten lesions (77%) had inhomogeneous signal intensity and three (23%) had homogeneous signal intensity. We concluded that fibrous dysplasia does not have a characteristic appearance on magnetic resonance imaging. However, magnetic resonance may be helpful in establishing the diagnosis of fibrous dysplasia if low to intermediate signal intensity is seen on both T1- and T2-weighted images. This situation occurred in 54% of our cases, whereas the other 46% had nonspecific signal characteristics indistinguishable from many other bone lesions.

Adult↗
PubMed1989

Experimental pancreatic cancer in the Syrian hamster: effect of cholecystectomy.

Because cholecystectomy stimulates hypertrophy and hyperplasia in the hamster pancreas, its effect on experimental pancreatic carcinogenesis was studied in this animal model. Forty female Syrian hamsters underwent cholecystectomy, while 40 others underwent sham operations. Two weeks later, 30 hamsters undergoing cholecystectomy and 30 hamsters undergoing sham operations received 4 weekly subcutaneous injections of N-nitroso-bis (2-oxopropyl) amine (BOP) (10 mg/kg). Remaining hamsters (n = 20) received equal volumes of 0.9% saline solution. A further 10 hamsters (controls) underwent no surgery and received no injections. Thirty weeks after the first BOP or saline injection the pancreas of hamsters that had undergone cholecystectomy was only 3% heavier than that of sham-operated animals, and there was no difference in the incidence of pancreatic cancer between BOP-treated hamsters that had undergone cholecystectomy and those that had undergone sham operations. In this study, cholecystectomy had no influence on BOP-induced pancreatic carcinogenesis in the Syrian hamster.

Animals↗
PubMed1989

Ultrasonography of post-traumatic soft-tissue lesions.

This article highlights the varied uses of ultrasound for detection of trauma to soft tissues. The emphasis is on the diagnosis of tendon and muscle disruptions. Detection of soft-tissue foreign bodies by ultrasound, an important recent innovation, is also reviewed. Miscellaneous potential applications of ultrasound for diagnosing meniscal injuries, cartilage integrity, epidermoid cysts, and traumatic vascular malformations are discussed briefly. Ultrasound is efficacious because of its low cost, noninvasiveness, wide availability, and accuracy.

Achilles Tendon↗
PubMed1982

Bladder reconstruction in rabbits with glutaraldehyde-stabilized amniotic membranes.

Glutaraldehyde-treated human amniotic membranes were used to repair rabbit bladders after supratrigonal cystectomies. The membranes maintained the integrity of the bladders until healing and reepithelialization occurred. There was no significant loss of bladder capacity or decreased renal function postoperatively. Calcification did not occur on the membranes but was noted on chromic sutures retaining the membranes in 7 of 27 bladders. These findings suggest that glutaraldehyde-stabilized amnion is well tolerated by the urothelium and may serve as a suitable material for replacement of genitourinary tissues.

Amnion↗