title: Perineural hematoma may result in nerve inflammation and myelin damage.
abstract: OBJECTIVE
  Perineural hematoma may occur during performance of peripheral nerve blocks. The aim of this study was to test the hypothesis that an iatrogenic hematoma in the immediate vicinity of a peripheral nerve may cause histologic evidence of nerve injury.
  
  
  METHODS
  Fifty milliliters of autologous blood was injected adjacent to the right sciatic nerve in 20 anesthetized female pigs. In order to discern between blood-related volume and immune effects, 50 mL of albumin was injected at the same location in an additional 22 pigs. Either blood or albumin was injected in random order. The left sciatic nerve served as a negative control in all animals, that is, either no needle placement or needle placement without injection. After 48 hours, the nerves were resected. The grade of nerve injury was scored from 0 (no injury) to 3 (severe injury) by histologic analysis of myelin tissue and inflammatory cells.
  
  
  RESULTS
  Eighty-two nerve specimens were examined. Injury scores were significantly (P < 0.01) higher in the blood injection (n = 20; median [interquartile range] 2 [2-2]) and albumin injection (n = 22, 1 [1-2]) conditions compared with the no needle placement (n = 22, 0 [0-1]) and "dry needle placement" (n = 20, 1 [0-1]) conditions. Widespread inflammatory changes were seen in the blood injection group, in which 15% of nerve specimens showed damage to myelin.
  
  
  CONCLUSIONS
  Our data suggest that hematoma adjacent to nerve tissue may result in structural nerve injury and inflammatory changes.
authors.affiliation: From the *Department of Anaesthesiology and Intensive Care Therapy and †Institute of Pathology, Philipps University Marburg, Marburg, Germany; ‡St Luke's and Roosevelt Hospital Center, University Hospital of Columbia University, College of Physicians and Surgeons, New York City, NY; and §Department of Anaesthesiology, University of Regensburg, Regensburg, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Steinfeldt
authors.forename: Thomas
authors.initials: T
authors.lastname: Wiesmann
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Nimphius
authors.forename: Valér
authors.initials: V
authors.lastname: Cornelius
authors.forename: Daniel
authors.initials: D
authors.lastname: Eismann
authors.forename: Thomas
authors.initials: T
authors.lastname: Kratz
authors.forename: Admir
authors.initials: A
authors.lastname: Hadzic
authors.forename: Hinnerk
authors.initials: H
authors.lastname: Wulf
authors.forename: Tilmann
authors.initials: T
authors.lastname: Werner
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D006406:Hematoma / Q000150:complications*; D009186:Myelin Sheath / Q000473:pathology*; D059348:Peripheral Nerve Injuries / Q000209:etiology / Q000473:pathology*; D012584:Sciatic Nerve / Q000473:pathology*; D020426:Sciatic Neuropathy / Q000209:etiology / Q000473:pathology*; D012720:Severity of Illness Index; D013552:Swine; D013997:Time Factors