Abstract
A transient cerebral disturbance characterized by somnolence of varying degree is described in children after cranial irradiation given as part of central nervous system (C.N.S.) prophylaxis for acute lymphoblastic leukaemia in remission.Out of 28 such children receiving cranial irradiation as part of the Medical Research Council protocol for C.N.S. prophylaxis 11 (39%) developed pronounced symptoms of somnolence, anorexia, and lethargy some six weeks after the completion of cranial irradiation, and a further 11 (39%) developed these features in mild form. In all cases the symptoms were transient, no focal neurological abnormality was detected, and all children made a spontaneous and complete recovery. E.E.G. studies on five somnolent children showed similar abnormal activity of diffuse and patchy distribution over both hemispheres. Indirect evidence is presented to support the concept that this syndrome represents a transient radiation encephalopathy, analogous to acute transient radiation myelopathy, caused by temporary disturbance of myelin synthesis.