Abnormalities of the neonatal brain: MR imaging. Part I. Intracranial hemorrhage

The authors prospectively evaluated 82 neonates, ranging in gestational age from 29 to 44 weeks postconception, with magnetic resonance (MR) imaging at 0.6 T. Twenty-two cases of hemorrhage in 15 infants were identified. Ultrasound (US) and computed tomography (CT) were superior to MR in the first few days after parenchymal hemorrhage, since at this time lesions were apparent on only T2-weighted images. After the first 3 days, MR was the single best modality because (a) hemorrhage on CT became imperceptible in the 2d week, whereas the high signal of hemorrhage on MR persisted for 2-11 weeks; (b) MR permitted rough dating of hemorrhage according to changes in signal intensity; and (c) MR was superior in identifying subdural or epidural hemorrhage. Because of the nonspecificity and restricted field of view of US and the inability of CT to depict hemorrhage after 7-10 days, the authors conclude that MR significantly improves the detection of intracranial hemorrhage in neonates.     

Selective posterior cerebral artery Amytal test for evaluating memory function before surgery for temporal lobe seizure

Selective testing for memory function with Amytal (amobarbital) in the posterior cerebral artery (PCA) is a promising modification of that test in the internal carotid artery (ICA). This new technique, performed with a Tracker catheter system, was completed successfully in 17 of 20 patients being examined before planned surgery for refractory temporal lobe seizure. The PCA test overcomes three major problems with the ICA technique. First, with the PCA technique, memory testing is begun immediately after injection, when the drug has its peak effect. Second, when the speech-dominant hemisphere is being tested with the PCA test, patients do not become aphasic. Third, injection into the PCA delivers the drug more effectively to the target, the ipsilateral hippocampal formation.     

Fetal rhombencephalon: normal US findings

Using ultrasound (US), the authors examined 25 embryos that were 8-10 menstrual weeks old for gestational age and the presence of a small cystic structure (3-4 mm) in the posterior aspect of the cranium. This structure was seen in all embryos. The US images of an in vitro embryo at 8 weeks menstrual age were also evaluated for anatomic correlation. Analysis of these US images determined that the cystic structure was the open rhombencephalon or hindbrain. Follow-up US studies or postpartum clinical examinations of the 25 in utero embryos demonstrated no abnormal posterior cranial cystic structures or neurologic deficits. This first-trimester structure should be considered a normal finding, since it develops into the normally proportioned fourth ventricle after the 11th menstrual week.     

Characterization of MR spectroscopic imaging of the human head and limb at 2.0 T

Using section-select and phase-encoding gradients, the authors obtained phosphorus chemical shift images of the human head and limb. Phosphorus spectra were acquired from planar sections divided into voxels as small as 7 cm3 in calf muscle and 27 cm3 in brain, with total examination times, including setup and proton locator imaging, of roughly 1 hour. Both spin-echo and free induction decay (FID) methods were employed; the FID gave superior results. Signal-to-noise ratios for the beta-adenosine triphosphate and phosphocreatine resonances were as high as 10:1 and 13:1 from volumes of 27 cm3 in brain.     

Screen-film mammographic technique for breast cancer screening

The values of dose and signal-to-noise ratio (SNR) for many techniques and breast thicknesses were computed and compared with a reference technique and breast thickness to provide a valid basis upon which to select a screening technique for screen-film mammography. The reference consisted of a Min-R/OM1 combination (or its equivalent) exposed through a 4.5-cm thick breast via 28 kV and a molybdenum target-beryllium window tube with a 0.03-mm Mo filter. Radiographs of an improved breast phantom were used to relate computed relative SNR values of techniques to diameters of the smallest calcific and soft-tissue objects demonstrated in mammograms. Without use of a grid, four Mo target/filtration combinations yielded similar computed dose and SNR levels, as did a tungsten target tube operated at 23 kV without a filter. Operation of the latter tube at 27.5 kV with a 0.051-mm rhodium filter should reduce dose by half but also SNR by 22%. However, such operation with a grid should greatly improve imaging moderate to large breasts without increasing dose over reference values.     

Abnormalities of the neonatal brain: MR imaging. Part II. Hypoxic- ischemic brain injury

Eighty-five infants, 82 of whom were 29-44 weeks postconceptional age, were imaged with a 0.6-T magnet. Eight infants had cerebral infarction. In premature neonates with very water, low-intensity white matter on T1-weighted images, ultrasound was better than both computed tomography and magnetic resonance (MR) imaging in depicting parenchymal changes of infarction or edema. However, after 37 weeks gestation, MR imaging was superior. Cerebral atrophy, present in seven infants, was consistent with subarachnoid space widths of 7 mm or more, or subarachnoid space widths of 5-6 mm with ventricular/brain ratios of 0.36 or greater. Delayed myelination was seen in a total of 18 infants with histories of hypoxic-ischemic insult. MR imaging shows promise in the neonatal period. It facilitates recognition of infarcts in full-term infants and may be used to predict abnormal neurologic outcome in infants who have initial delayed myelination.     

Patellar tendon autograft versus hamstring tendon autograft in arthroscopic anterior cruciate ligament reconstruction: appraisal of the evidence

Arthroscopy–assisted reconstruction of a torn anterior cruciate ligament (ACL) is a commonly performed surgical procedure. The type of graft used for ACL reconstruction has traditionally been an autograft; the more commonly used grafts are the bonepatellar tendon–bone (BPTP) and hamstring tendons, namely the gracilis and semitendinosus tendons (GST). We surveyed the evidence concerning the outcome of patients treated by arthroscopic reconstruction of the ACL with either BPTP or GST. On basis of several welldesigned studes, specifically 5 meta–analyses and one systematic review, we critically discuss the best evidence available today regarding ACL reconstruction. This evidence suggests that BPTP may be considered for patients performing high–demand activities not involving repetitive kneeling.     

Postnatal development of tyrosine hydroxylase- and dopamine transporter- immunoreactive axons in monkey rostral entorhinal cortex

Dopamine afferents from the mesencephalon appear to play a critical role in the normal development and cognitive functions of multiple areas of the primate cerebral cortex. In some regions, such as the prefrontal and motor cortices, dopamine innervation changes substantially during postnatal development. However, little is known about the postnatal maturation of dopamine afferents to the primate rostral entorhinal cortex, a periallocortical region that receives a dense dopamine innervation in adults. In this study, we used immunocytochemical techniques and antibodies against tyrosine hydroxylase and the dopamine transporter to examine the postnatal development of dopamine axons in the rostral subdivision of macaque monkey entorhinal cortex. Within animals, the axons labeled with each antibody did not differ in overall density or laminar distribution. Across development, the density of dopamine axons in layers I and VI did not change appreciably. In contrast, the density of labeled axons in layer III significantly increased by a factor of three between birth and 5-7 months of age. The timing of this change differs substantially from that observed in prefrontal cortex, where peak dopamine innervation occurs between 2 and 3 years of age. These findings, in concert with other data, suggest that developmental changes in the dopamine innervation of cortical regions may parallel the functional maturation of those areas.