title: Hippocampal malrotation is an anatomic variant and has no clinical significance in MRI-negative temporal lobe epilepsy.
abstract: OBJECTIVE
  There is considerable difficulty in diagnosing hippocampal malrotation (HIMAL), with different criteria of variable reliability. Here we assess qualitative and quantitative criteria in HIMAL diagnosis and explore the role of HIMAL in magnetic resonance imaging (MRI)-negative temporal lobe epilepsy (TLE).
  
  
  METHODS
  We studied the MRI of 155 adult patients with MRI-negative TLE and 103 healthy volunteers, and we asked (1) what are the qualitative and quantitative features that allow a reliable diagnosis of HIMAL, (2) how common is HIMAL in a normal control population, and (3) is HIMAL congruent with the epileptogenic side in MRI-negative TLE.
  
  
  RESULTS
  We found that the features that are most correlated with the expert diagnosis of HIMAL are hippocampal shape change with hippocampal diameter ratio > 0.8, lack of normal lateral convex margin, and a deep dominant inferior temporal sulcus (DITS) with DITS height ratio > 0.6. In a blinded analysis, a consensus diagnosis of unilateral or bilateral HIMAL was made in 25 of 103 controls (24.3% of people, 14.6% of hippocampi-14 left, six right, 10 bilateral) that did not differ from 155 lesion-negative TLE patients where 25 had HIMAL (16.1% of patients, 11.6% of hippocampi-12 left, two right, 11 bilateral). Of the 12 with left HIMAL only, 9 had seizures arising from the left temporal lobe, whereas 3 had right-sided seizures. Of the two with right HIMAL only, both had seizures arising from the left temporal lobe.
  
  
  CONCLUSIONS
  HIMAL is an anatomic variant commonly found in controls. HIMAL is also an incidental nonpathologic finding in adult MRI-negative TLE and should not influence surgical decision making.
authors: Department of Medicine, Epilepsy Research Centre, Austin Health, University of Melbourne, Heidelberg, Victoria, Australia.|Department of Neurology, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung, Taiwan.|Department of Nursing, Meiho University, Pingtung, Taiwan.
authors: Meng-Han
authors: MH
authors: Tsai
authors: Department of Neurology, Austin Health, Florey Institute of Neuroscience and Mental Health, Melbourne, Victoria, Australia.
authors: David N
authors: DN
authors: Vaughan
authors: Department of Radiology, Austin Hospital, Melbourne, Victoria, Australia.
authors: Yuliya
authors: Y
authors: Perchyonok
authors: Department of Radiology, Austin Hospital, Melbourne, Victoria, Australia.
authors: Greg J
authors: GJ
authors: Fitt
authors: Department of Medicine, Epilepsy Research Centre, Austin Health, University of Melbourne, Heidelberg, Victoria, Australia.|Department of Neurology, Austin Health, Florey Institute of Neuroscience and Mental Health, Melbourne, Victoria, Australia.|Department of Paediatrics, Royal Children's Hospital, University of Melbourne, Melbourne, Victoria, Australia.
authors: Ingrid E
authors: IE
authors: Scheffer
authors: Department of Medicine, Epilepsy Research Centre, Austin Health, University of Melbourne, Heidelberg, Victoria, Australia.|Department of Radiology, Austin Hospital, Melbourne, Victoria, Australia.
authors: Samuel F
authors: SF
authors: Berkovic
authors: Department of Neurology, Austin Health, Florey Institute of Neuroscience and Mental Health, Melbourne, Victoria, Australia. gjackson@brain.org.au.
authors: Graeme D
authors: GD
authors: Jackson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004569:Electroencephalography; D004833:Epilepsy, Temporal Lobe / Q000000981:diagnostic imaging*; D005260:Female; D007839:Functional Laterality; D006624:Hippocampus / Q000000981:diagnostic imaging* / Q000473:pathology*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007223:Infant; D016015:Logistic Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D014741:Video Recording; D055815:Young Adult
keywords: Hippocampal sclerosis; Incomplete hippocampal infolding; Lesion-negative epilepsy; Neuroimaging