title: Postoperative lumbar epidural hematoma: does size really matter?
abstract: METHODS
  Prospective clinical series with comparison to retrospectively collected data.
  
  
  OBJECTIVE
  To compare direct measures of postoperative hematoma volume against a new measure of hematoma effect on the thecal sac: the critical ratio.
  
  
  BACKGROUND
  Asymptomatic epidural hematoma is common after lumbar surgery. Symptomatic patients demonstrate a typical progression from sharp peri-incisional pain to bilateral neurologic deficits. Little is known about what differentiates symptomatic and asymptomatic patients. Magnetic resonance imaging (MRI) measures of hematoma size or mass effect may correlate with postoperative symptoms.
  
  
  METHODS
  The study population consisted of 3 patient groups evaluated by MRI 2 to 5 days after lumbar decompression with or without fusion. Fifty-seven consecutive prospectively enrolled patients comprised the asymptomatic group. No patient developed severe postoperative pain or neurologic deficit. Search of our institutional database identified 4978 surgical patients within the last 24 months. Seventeen developed new postoperative symptoms. The painful group included 12 patients with severe peri-incisional pain without neurologic deficit. The cauda equina (CE) group included 5 patients with postoperative CE syndrome. Digital imaging software was used to calculate thecal sac cross sectional area on pre- and postoperative MRI at each level, hematoma volume, volume per level decompressed, and critical ratio for each patient. Critical ratio was defined as the smallest ratio of postoperative to preoperative cross sectional area within the lumbar spine. RESULTS.: The critical ratio was the only measure found to differ significantly (P < 0.05) among all 3 groups. Mean critical ratios were asymptomatic (0.8), painful (0.5), and CE (0.2).
  
  
  CONCLUSIONS
  The critical ratio correlates more closely with the presence or absence of postoperative symptoms than measures of hematoma volume, and is consistent with the clinical expectation that greater thecal sac compression may result in more severe symptoms. Few guidelines exist for postoperative lumbar MRI interpretation. The critical ratio is an important contribution.
authors.affiliation: Trinity Orthopaedics, SC, Oak Park, IL, USA.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Sokolowski
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Garvey
authors.forename: John
authors.initials: J
authors.lastname: Perl
authors.forename: Margaret S
authors.initials: MS
authors.lastname: Sokolowski
authors.forename: Burak
authors.initials: B
authors.lastname: Akesen
authors.forename: Amir A
authors.initials: AA
authors.lastname: Mehbod
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Mullaney
authors.forename: Daryll C
authors.initials: DC
authors.lastname: Dykes
authors.forename: Ensor E
authors.initials: EE
authors.lastname: Transfeldt
mesh_terms: D000368:Aged; D005260:Female; D046748:Hematoma, Epidural, Spinal / Q000209:etiology / Q000473:pathology*; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000009:adverse effects*; D011128:Polyradiculopathy; D011183:Postoperative Complications; D011446:Prospective Studies; D012189:Retrospective Studies; D013118:Spinal Cord Diseases / Q000209:etiology / Q000473:pathology*; D013131:Spine / Q000473:pathology / Q000601:surgery*; D013346:Subarachnoid Space / Q000473:pathology