title: Hypersomnia due to injury of the ventral ascending reticular activating system following cerebellar herniation: A case report.
abstract: BACKGROUND
  We report on a patient with hypersomnia who showed injury of the lower ascending reticular activating system (ARAS) following cerebellar herniation due to a cerebellar infarct, detected on diffusion tensor tractography (DTT).
  
  
  METHODS
  A 53-year-old male patient was diagnosed as a left cerebellar infarct, and underwent decompressive suboccipital craniectomy due to brain edema at 2 days after the onset of a cerebellar infarct. Three weeks after onset when the patient started rehabilitation, he showed hypersomnia without impairment of consciousness; he fell asleep most of daytime without external stimulation and showed an abnormal score on the Epworth Sleepiness Scale: 15 (full score: 24, cut off for hypersomnia: 10).
  
  
  METHODS
  On 3-week DTT, narrowing of the upper portion of the lower ventral ARAS between the pontine reticular formation and the hypothalamus was observed on both sides. In addition, partial tearing was observed in the middle portion of the right lower ventral ARAS.
  
  
  CONCLUSIONS
  In conclusion, we found injury of the lower ventral ARAS in a patient with hypersomnia following cerebellar herniation due to a cerebellar infarct.
authors.affiliation: Department of Physical Medicine and Rehabilitation Department of Neurosurgery, College of Medicine, Yeungnam University, Daegu, Republic of Korea.
authors.forename: Sung Ho
authors.initials: SH
authors.lastname: Jang
authors.forename: Chul Hoon
authors.initials: CH
authors.lastname: Chang
authors.forename: Young Jin
authors.initials: YJ
authors.lastname: Jung
authors.forename: Hyeok Gyu
authors.initials: HG
authors.lastname: Kwon
mesh_terms: D056324:Diffusion Tensor Imaging; D006970:Disorders of Excessive Somnolence / Q000209:etiology*; D004677:Encephalocele / Q000150:complications*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012154:Reticular Formation / Q000000981:diagnostic imaging* / Q000473:pathology