MRI ASSESSMENT OF MYELINATION OF MOTOR AND SENSORY PATHWAYS IN THE BRAIN OF PRETERM AND TERM-BORN INFANTS

A study was performed in 48 neurologically normal preterm and term-bor n infants, with a postconceptional age at MRI varying between 30 2/7 a nd 46 weeks and a mean age of 34 2/7 weeks. The purpose of the study w as to determine the normal progress of myelination on MRI in that age range. T-1-and T-2-weighted images of the brain were assessed for chan ges in signal intensity of white matter relative to gray matter. Multi ple sites in the brainstem, cerebellum and cerebral hemispheres were a ssessed separately. The findings were correlated with the ages of the infants. As judged from relative signal intensities, myelin was presen t at the postconceptional age of 30-34 weeks in the following structur es: tegmentum pontis (in particular medial lemniscus), superior and in ferior colliculi, decussation of the superior cerebellar peduncles, cr ura cerebri, ventrolateral thalamus, lateral globus pallidus, dorsolat eral putamen, dentate nucleus, middle and superior cerebellar peduncle s, vermis cerebelli, cortex bordering the central sulcus and hippocamp us. Little progress in myelination was noticed up to the postconceptio nal age of 46 weeks. Between 34 and 46 weeks, myelin appeared in the l ateral part of the posterior limb of the internal capsule and in the c entral part of the corona radiata and became more prominently visible in the cortex bordering the central sulcus.