Our purpose was the study the magnetic resonance (MR) signal intensity of the perirolandic gyri perinatally and to correlate it with the histological findings in formalin-fixed brains, focusing on myelination. MRI of 20 neurologically normal neonates and infants, of 37-64 weeks postconception (PCA), were studied retrospectively. We reviewed four formalin-fixed brains of infants 37-46 weeks PCA microscopically. The posterior cortex of the precentral gyrus (P-PRE) and the anterior cortex of the postcentral gyrus (A-PST) had different signal intensity from the adjacent surrounding cortex. On T1-weighted images P-PRE and A-PST gave higher signal 41-44 weeks PCA; on T2-weighted images, they gave lower signal 37-51 weeks PCA. Histological examination revealed very little myelination of the nerve fibres within both the P-PRE and the A-PST, while considerable myelination was present in the internal capsule and central corona radiata. The changes in signal intensity in the perirolandic gyri may reflect not only the degree of myelination but also the more advanced development of the nerve cells, associated with rapid proliferation and formation of oligodendroglial cells, synapses and dendrites. They could be another important landmark for brain maturation.
Dynamic MRI was performed on 22 patients with extra-axial intracranial tumours. Serial images were obtained every 30 s for 3 min using a spin-echo sequence (TR 200, TE 15 ms) after rapid injection of Gd-DTPA, 0.1 mmol/kg body weight. The contrast medium enhancement ratio (CER) was correlated with the histology of the tumours. Meningiomas and extra-axial metastases showed a sharp rise, then a gradual decline. Although both had a definite early peak of CER, metastases showed a more rapid decline. Neuromas and extra-axial lymphoma showed a slow, steady increase with no peak within 180 s. This study indicates that the CER is helpful in the differentiation of extra-axial tumours.
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