title: Density measurements with computed tomography in patients with extra-axial hematoma can quantitatively estimate a degree of brain compression.
abstract: BACKGROUND
  Extra-axial hematoma can cause significant brain compression. Guidelines for surgical evacuation include imaging findings (midline shift and hematoma thickness/volume) in conjunction with Glasgow Coma Scale (GCS) scores and/or intracranial pressure (ICP) monitoring. Physiologically, overall brain density should also change with compression. In our observational study, we explored whether overall brain density, defined using computed tomography Hounsfield Units (CT HU), changes after surgical evacuation of extra-axial hematoma.
  
  
  METHODS
  Only patients with a surgical acute epidural hematoma or subacute/chronic subdural hematoma were considered. Other exclusion criteria were concurrent intraparenchymal pathology, bilateral pathology, or incomplete follow-up imaging. Between fall 2012 and spring 2015, 22 patients were included in the study. CT head imaging (preoperative, postoperative, and at ∼1- to 2-month clinic visit) were loaded into OsiriX (Pixmeo, Switzerland). All the intracranial regions were selected and all extra-axial features were removed; subsequently, software was used to calculate a global CT HU value.
  
  
  RESULTS
  A repeated-measures ANOVA found significant time effect, p < 0.01, with significance between preoperative versus postoperative CT (p = 0.03) and preoperative versus clinic visit CT (p < 0.01).
  
  
  CONCLUSIONS
  The results from this study suggest that extra-axial hematomas, which deform the brain, can cause an elevation in global CT HU value; moreover, surgical decompression is associated with lower global CT HU values. The use of global CT HU values in selected populations may serve as an adjunct for the evaluation of surgical lesions.
authors.affiliation: Department of Neurosurgery, Medical College of Wisconsin, USA hsnguyen@mcw.edu.
authors.forename: Ha Son
authors.initials: HS
authors.lastname: Nguyen
authors.affiliation: Department of Neurosurgery, Medical College of Wisconsin, USA.
authors.forename: Luyuan
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Neurosurgery, Medical College of Wisconsin, USA.
authors.forename: Mohit
authors.initials: M
authors.lastname: Patel
authors.affiliation: Department of Neurosurgery, Medical College of Wisconsin, USA.
authors.forename: Wade
authors.initials: W
authors.lastname: Mueller
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001921:Brain / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D019299:Decompression, Surgical / Q000379:methods*; D005260:Female; D015600:Glasgow Coma Scale; D006407:Hematoma, Epidural, Cranial / Q000000981:diagnostic imaging* / Q000601:surgery*; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D055815:Young Adult
keywords: CT Hounsfield Units; brain compression; epidural hematoma; subdural hematoma; traumatic brain injury