THE PERIHIPPOCAMPAL FISSURES - NORMAL ANATOMY AND DISEASE STATES

Understanding the three-dimensional anatomy of the perihippocampal fis sures (PHFs) can be helpful in making the correct: diagnosis of diseas es of the mesial temporal lobe. Disorders of the parenchyma and cerebr ospinal fluid spaces are reflected by specific changes in the PHFs. A marker for Alzheimer disease and mesial temporal sclerosis is atrophy of the hippocampus and associated dilatation of the PHFs, This finding is best visualized on coronal magnetic resonance images but can and s hould be appreciated on routine computed tomographic scans. Hydrocepha lus is characterized by dilatation of the temporal horn of the lateral ventricle without dilatation of the transverse fissure and its extens ions. Normal-pressure hydrocephalus can usually be distinguished from Alzheimer disease on the basis of the pattern of dilatation of the PHF s. Understanding the anatomy of the PHFs often makes it possible to be tter characterize the extents of intra- and extraaxial tumors of the m esial temporal lobe.