The brain of 17 asymptomatic normal adult beagles was evaluated with magnetic resonance imaging. Lateral ventricular size was quantified using computer algorithms. In beagles with large ventricles, contrast medium was introduced into the cerebellomedullary cistern to determine whether obstructive hydrocephalus was present. Total lateral ventricular volume ranged from 77 mm3 to 11,726 mm3. Based on Gd-DTPA diffusion, the CSF flow pattern was considered normal and normal neural morphology was seen using electron microscopy. Results suggest a high incidence of clinically asymptomatic ventriculomegaly in normal adult beagles.
Thirty-two patients (64 hips) in whom avascular necrosis (AVN) of the femoral heads was highly suspected clinically were studied by magnetic resonance (MR) imaging, radionuclide bone scintigraphy, and conventional radiography. MR studies were positive for AVN in 37 hips, compared with 30 positive scintigraphic studies. In all cases in which scintigraphy and radiography were positive, MR imaging demonstrated decreased signal from the affected femoral heads, indicative of bone marrow disease. Imaging results were confirmed by biopsy or subsequent imaging appearances. In patients with negative initial scintigraphic and radiographic studies, the MR imaging criterion for a positive study was a moderately decreased bone marrow signal displaying segmental patterns within an otherwise normal-appearing femoral head on relatively T1-weighted images. In this series of high-risk patients, radionuclide scintigraphy had a sensitivity of 81%, compared with 100% for MR imaging. MR imaging should be the imaging modality of choice for early evaluation of bone marrow changes indicative of AVN.
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