title: Diagnostic method for differentiating external hydrocephalus from simple subdural hygroma.
abstract: OBJECTIVE
  The various terms used to describe subdural fluid collection--"external hydrocephalus", "subdural hygroma", "subdural effusion", "benign subdural collection", and "extraventricular obstructive hydrocephalus"-reflect the confusion surrounding the diagnoses of these diseases. Differentiating external hydrocephalus from simple subdural hygroma may be difficult, but the former appears to be a distinct clinical entity separate from the latter. In this report, the authors present a diagnostic method for differentiating external hydrocephalus from simple subdural hygroma, based on their clinical experience in treating subdural fluid collection after mild head trauma.
  
  
  METHODS
  Twenty patients with subdural fluid collection after mild head trauma were included in this study. Ventricle size was measured using a modified frontal horn index (mFHI); that is, the largest width of the frontal horns divided by the bicortical distance in the same plane, instead of the inner table distance. Bur hole trephination was performed on the appearance of a subdural fluid collection thicker than 15 mm on computed tomography (CT), persistent (longer than 4 weeks) or increasing in size, and accompanied by neurological symptoms (confusion or memory impairment). During the procedure, subdural pressure was measured using a manometer before opening the dura mater. Subdural pressure varied among the patients, ranging from 3 to 27.5 cm H2O. Four patients with a subdural pressure greater than 15 cm H2O had hydrocephalus after surgery (p < 0.05). Hydrocephalus developed in a pediatric patient (2 years old) with a subdural pressure of 12 cm H2O. All of the patients in whom hydrocephalus developed after bur hole trephination had had enlarged ventricles (mFHI > 33%) on preoperative CT scans.
  
  
  CONCLUSIONS
  Monitoring subdural pressure may be a valuable tool for differentiating subdural hygroma from external hydrocephalus in patients with mild head trauma. Additionally, the mFHI reflects the nature of the subdural collection more accurately than the standard frontal horn index.
authors.affiliation: Department of Neurosurgery, Uijeongbu St. Mary's Hospital, The Catholic University of Korea, College of Medicine, Uijeongbu-City, Gyeonggi-do, Korea.
authors.forename: Pil-Woo
authors.initials: PW
authors.lastname: Huh
authors.forename: Do-Sung
authors.initials: DS
authors.lastname: Yoo
authors.forename: Kyung-Suok
authors.initials: KS
authors.lastname: Cho
authors.forename: Chun-Kun
authors.initials: CK
authors.lastname: Park
authors.forename: Seok-Gu
authors.initials: SG
authors.lastname: Kang
authors.forename: Young-Sup
authors.initials: YS
authors.lastname: Park
authors.forename: Dal-Soo
authors.initials: DS
authors.lastname: Kim
authors.forename: Moon-Chan
authors.initials: MC
authors.lastname: Kim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D006259:Craniocerebral Trauma / Q000150:complications; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D006849:Hydrocephalus / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D007427:Intracranial Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013353:Subdural Effusion / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D013355:Subdural Space; D014057:Tomography, X-Ray Computed