<prompt> An 80 year old man has a history of progressive gait disturbance and incontinence which had been attributed to old age and prostatism. For the past 4 months he has been forgetful and confused. He has a history of head trauma 25 years ago. His head CT is shown below .The most likely diagnosisAlzheimers diseaseCreutzfeldt jakob diseaseNormal pressure hydrocephaluPelizaeus-merzbacher disease  <response>: Normal pressure hydrocephalus triad:DementiaAtaxiaIncontinenceCT or MRI brain in these patients shows enlarged frontal and temporal horns of lateral ventricles out of proportion to degree of cortical atrophy. 