The sequence of myelination in the brainstem of the rat monitored by myelin basic protein immunohistochemistry

The temporal order which is observed by nervous pathways in their myelination was investigated in the brainstem of neonatal to 16-day-old albino rats. The immunohistochemical detection of myelin basic protein in newly forming myelin sheaths provided a highly sensitive and specific criterion to judge the time of onset and the progress of myelination in its initial stages. Immunohistochemistry was performed on paraffin-embedded tissue according to the unlabeled peroxidase-antiperoxidase method. A small number of immunoreactive fibers was already present in neonate rats in the ventral funiculus of the cervical spinal cord and in the medial longitudinal fascicle of the medulla oblongata. By the 4th postnatal day myelination had commenced in many sensory tracts and in the trigeminal root, in the tectospinal tract, in the inferior cerebellar peduncle and in the roots of most cranial motor nerves. The auditory pathway up to the inferior colliculus, the gracile, spinocerebellar and rubrospinal tracts and the superior cerebellar peduncle had acquired some myelin on the 7th day. Phylogenetic late fiber systems also appeared to myelinate comparatively late: the transverse pontine fibers and the medial cerebellar peduncle started on the 10th day, and in the corticospinal tract a conspicuously synchronized myelination appeared on the 13th day. All pathways of the brainstem possessed myelinated fibers on the 16th day and some tracts had approached their relative maturity.     

Low-artifact intravascular devices: MR imaging evaluation

Flow-phantom magnetic resonance (MR) imaging, with use of both spin-echo (SE) and gradient-echo (GRE) techniques at 1.5 T, was performed on the percutaneous Greenfield (beta-III titanium alloy [TMA wire]), Amplatz (MP32-N alloy), and Simon nitinol filters and TMA wire facsimiles of the bird's nest, Gunther, new retrievable, and Amplatz vena caval filters. SE imaging allowed detection of thrombi as small as 5 X 5 mm trapped within the percutaneous Greenfield, Simon nitinol, and TMA-wire facsimile filters; with the MP32-N Amplatz filter, a larger volume of thrombus (10 X 20-mm clots) was necessary for clot detection. GRE imaging allowed detection of intraluminal tilting of the percutaneous Greenfield and facsimile Amplatz (TMA-wire) filters. GRE imaging was useful for demonstrating postfilter turbulence due to clots, which was greatest for the Amplatz filter. Imaging of facsimile vascular devices made of tantalum or TMA wire did not cause the severe "black-hole" MR artifacts typical of the stainless-steel devices. SE and GRE imaging were very useful for determining caval patency in two patients with previously placed Mobin-Uddin filters. Noninvasive MR evaluation of blood vessels in the presence of a variety of low-artifact intravascular devices appears feasible.     

Osteopetrosis: MR characteristics at 1.5 T

Four patients with proved osteopetrosis (three with the infantile malignant form and one with the benign form) were examined with magnetic resonance imaging at 1.5 T. All patients were studied in the coronal and sagittal planes using both short and long repetition time/echo time sequences. The infantile malignant form was characterized by a complete lack of signal from the marrow alternating with a signal intensity equivalent to that of the intervertebral disks, resulting in a "stepladder" appearance. In the benign form or after successful marrow transplantation in the infantile malignant form, intermediate or high signal intensity in the vertebrae was noted, suggesting the presence of some marrow elements.