High-signal foci on MR images of the brain: observer variability in their quantification.

Foci of high signal in the cerebral white matter are common incidental findings on MR images of the brain of control subjects or patients with a variety of diseases. Although the number of foci has been reported to correlate with age and several risk factors, the degree of observer variability in quantifying foci has not been reported. We used kappa statistics to determine radiologists' agreement in counting high-signal-intensity foci on MR images obtained in healthy volunteers and in patients with hypertension. Before interpreting the images, one pair of radiologists studied 30 routine MR images and reached consensus on differentiating high-signal foci from other foci of high intensity caused by normal structures (e.g., deep gyri or Virchow-Robin spaces). These two observers than independently determined the number of foci in the study group. Using their own criteria, other radiologists independently counted the foci. Agreement between observers was determined with the kappa statistic. The results showed fair agreement between the radiologists who first reached a consensus in counting foci of hyperintensity and poor agreement between the other observers. We conclude that in order to compare the frequency of foci of hyperintensity in different groups of patients, observer variability must be controlled. Studies without proper control subjects may lead to incorrect conclusions regarding the correlation of focal hyperintensities and various risk factors.

High-intensity signals within the posterior pituitary fossa: a study with fat-suppression MR techniques.

Five different theories have been proposed to explain the high-intensity signals within the posterior pituitary fossa seen on MR: (1) a paramagnetic effect of phospholipids in the posterior lobe, (2) lipid in pituicytes in the posterior lobe of the pituitary, (3) neurosecretory granules in the posterior lobe, (4) fat within the sella but outside the pituitary gland, and (5) fat in bone marrow in the dorsum sellae. Previous reports have contained conflicting evidence on which of these structures is the cause of the high-intensity signals within the posterior sella. The purpose of this study was to examine the high-intensity signals of the normal posterior sella with fat-suppression MR techniques to reevaluate the contribution of fat to those signals. The sellae of 19 normal volunteers and two cadavers were imaged with MR with a commercially available unit and a research fat- water-suppression technique. High-intensity signals in the posterior sella were observed in all 21 subjects on conventional T1-weighted MR images. In two volunteers, the high-intensity signals in the posterior sella were suppressed with fat-suppression techniques; in 17 subjects the signals were suppressed with water-suppression techniques. In two volunteers the results were indeterminate. The high-intensity signals in the posterior sella do not behave like lipid in the majority of cases. Our study supports the conclusion that high-intensity signals in the posterior sella may have more than one source. It appears that most of these sources do not suppress with fat-suppression techniques.

Osteoporosis with vertebral compression fractures, retropulsed fragments, and neurologic compromise.

Osteoporosis frequently affects the vertebral column and causes compression fractures, biconcave ("fish-mouth") vertebrae, kyphosis, and pain. The cases are reported of three postmenopausal osteoporotic women who had neurologic symptoms of the lower extremities because of vertebral body fractures with a retropulsed fragment narrowing the spinal canal. None of the women had experienced trauma. The fractures resembled burst-type fractures that result from axial loading with major trauma. The retropulsed fragments could be seen best on computed tomographic or magnetic resonance images and were very subtle on conventional radiographs, on which an abnormal posterior vertebral body line was the only abnormality detected. This complication of osteoporosis of the spine is important to recognize so that appropriate treatment can be instituted.

Bone marrow patterns in aplastic anemia: observations with 1.5-T MR imaging.

Six patients diagnosed as having aplastic anemia underwent magnetic resonance (MR) imaging. The bone marrow in the lumbar spine, pelvis, and proximal femora was examined in each case. One patient had a normal marrow signal intensity (SI) and pattern and was considered cured of disease. The other patients had varying numbers of focal low-SI areas interspersed with high-SI areas in the marrow of the spine. The pelves and proximal femora of all patients had diffuse high-SI marrow without focal abnormalities. Biopsy of a lumbar vertebral body in one patient demonstrated that the focal low-SI areas may have been islands of active hematopoietic cells scattered in otherwise fatty marrow. MR may prove to be a valuable, noninvasive method of following the response of patients with aplastic anemia to therapy; more investigation is necessary before this can be definitely concluded.