title: Postoperative intraspinal subdural collections after pediatric posterior fossa tumor resection: incidence, imaging, and clinical features.
abstract: OBJECTIVE
  Postoperative intraspinal subdural collections in children after posterior fossa tumor resection may temporarily hinder metastasis detection by MR imaging or CSF analysis, potentially impacting therapy. We investigated the incidence, imaging and clinical features, predisposing factors, and time course of these collections after posterior fossa tumor resection.
  
  
  METHODS
  Retrospective review of postoperative spine MRI in 243 children (5.5 ± 4.6 years of age) from our clinical data base postresection of posterior fossa tumors from October 1994 to August 2010 yielded 37 (6.0 ± 4.8 years of age) subjects positive for postoperative intraspinal subdural collections. Their extent and signal properties were recorded for postoperative (37/37), preoperative (15/37), and follow-up spine (35/37) MRI. Risk factors were compared with age-matched internal controls (n = 37, 5.9 ± 4.5 years of age). Associations of histology, hydrocephalus and cerebellar tonsillar herniation, and postoperative intracranial subdural collections with postoperative intraspinal subdural collections were assessed by the Fisher exact test or χ(2) test. The association between preoperative tumor volume and postoperative intraspinal subdural collections was assessed by the Wilcoxon rank sum test.
  
  
  RESULTS
  The overall incidence of postoperative intraspinal subdural collections was 37/243 (15.2%), greatest ≤7 days postoperatively (36%); 97% were seen 0-41 days postoperatively (12.9 ± 11.0 days). They were T2 hyperintense and isointense to CSF on T1WI, homogeneously enhanced, and resolved on follow-up MR imaging (35/35). None were symptomatic. They were associated with intracranial subdural collections (P = .0011) and preoperative tonsillar herniation (P = .0228).
  
  
  CONCLUSIONS
  Postoperative intraspinal subdural collections are infrequent and clinically silent, resolve spontaneously, and have a distinctive appearance. Preoperative tonsillar herniation appears to be a predisposing factor. In this series, repeat MR imaging by 4 weeks documented improvement or resolution of these collections in 88%.
authors.affiliation: From the Departments of Radiological Sciences (J.H.H., Z.P.).
authors.forename: J H
authors.initials: JH
authors.lastname: Harreld
authors.affiliation: Department of Imaging Diagnostic (N.M.), Institute of Paediatric, Kuala Lumpur Hospital, Kuala Lumpur, Malaysia.
authors.forename: N
authors.initials: N
authors.lastname: Mohammed
authors.affiliation: Department of Radiology (G.G.), McFarland Clinic, Ames, Iowa.
authors.forename: G
authors.initials: G
authors.lastname: Goldsberry
authors.affiliation: Biostatistics (X.L., Y.L.).
authors.forename: X
authors.initials: X
authors.lastname: Li
authors.affiliation: Biostatistics (X.L., Y.L.).
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.affiliation: Surgery (F.B.), St. Jude Children's Research Hospital, Memphis, Tennessee.
authors.forename: F
authors.initials: F
authors.lastname: Boop
authors.affiliation: From the Departments of Radiological Sciences (J.H.H., Z.P.) zoltan.patay@stjude.org.
authors.forename: Z
authors.initials: Z
authors.lastname: Patay
mesh_terms: D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D015994:Incidence; D015192:Infratentorial Neoplasms / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D019635:Neurosurgical Procedures / Q000009:adverse effects*; D011184:Postoperative Period; D012189:Retrospective Studies; D013116:Spinal Cord / Q000473:pathology*; D013118:Spinal Cord Diseases / Q000453:epidemiology* / Q000209:etiology* / Q000473:pathology