title: Clinical Implication of Temporary Hypointense Lesion on Diffusion-Weighted Imaging After Extracranial-Intracranial Bypass Surgery.
abstract: BACKGROUND
  Postoperative hyperperfusion syndrome after extracranial-to-intracranial bypass causing temporary neurologic deterioration has been reported rarely as isosignal intensity on diffusion-weighted imaging (DWI) with hyperintense lesion on T2-weighted image and fluid-attenuated inversion recovery (FLAIR) imaging as an expression of vasogenic edema. We present a rare case of a patient suffering from temporary aphasia after an extracranial-to-intracranial bypass surgery, which was shown as a transient hypointense lesion on DWI with increased apparent diffusion coefficient value, evidence of postoperative hyperperfusion.
  
  
  METHODS
  By the preoperative single-photon emission computed tomography study analyzed retrospectively, preoperative cerebral blood flow (CBF) was compared between the lesions in which the hypointensity emerged and the lesions in which its signal remained unchanged in the hyperperfusion area. We found CBF after an acetazolamide challenge was much smaller and the percentage increase of CBF after an acetazolamide challenge was much less than zero in the temporal hypointense lesion on DWI.
  
  
  CONCLUSIONS
  An abrupt increase of CBF after bypass installation to the brain with no vascular response and complete disruption of the blood-brain barrier would cause a remarkable increase of extracellular fluid and excessive water molecule diffusion, resulting in excessive vasogenic edema. This was a plausible mechanism for the transient hypointense lesion on DWI with increased apparent diffusion coefficient value.
authors.affiliation: Department of Neurosurgery, Kobe University Graduate School of Medicine, Hyogo, Japan. Electronic address: hidekimura-nsu@umin.ac.jp.
authors.forename: Hidehito
authors.initials: H
authors.lastname: Kimura
authors.affiliation: Department of Neurosurgery, Kobe University Graduate School of Medicine, Hyogo, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Taniguchi
authors.affiliation: Department of Neurosurgery, Kobe University Graduate School of Medicine, Hyogo, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Mori
authors.affiliation: Department of Neurosurgery, Kobe University Graduate School of Medicine, Hyogo, Japan.
authors.forename: Kohkichi
authors.initials: K
authors.lastname: Hosoda
authors.affiliation: Department of Neurosurgery, Kobe University Graduate School of Medicine, Hyogo, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Kohmura
mesh_terms: D000368:Aged; D001929:Brain Edema / Q000000981:diagnostic imaging* / Q000209:etiology; D002560:Cerebrovascular Circulation / Q000502:physiology; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D008297:Male; D019635:Neurosurgical Procedures / Q000009:adverse effects*; D011183:Postoperative Complications / Q000000981:diagnostic imaging* / Q000209:etiology; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods
keywords: Diffusion-weighted image; EC-IC bypass; Hyperperfusion; Hypointense; Vasogenic edema