title: Membrane Surface Area to Volume Ratio in Chronic Subdural Hematomas: Critical Size and Potential Postoperative Target.
abstract: It is unknown why some chronic subdural hematomas (CSDHs) grow and require surgery, whereas others spontaneously resolve. Although a relatively small CSDH volume (V) reduction may induce resolution, V percent reduction is often unreliable in predicting resolution. Although CSDHs evolve distinctive inner neomembranes and outer neomembranes (OMs), the OM likely dominates the dynamic growth-resorption equilibrium. If other factors remain constant, one previous hypothesis is that resorption could fail as the surface area (SA) to V ratio decreases when CSDHs exceed a critical size. We aimed to identify a critical size and an ideal target, which implies resolution without recurrence.
  
  
  
  Three-dimensional computed tomography CSDH SA to V ratios were obtained using computer software to compare CSDH SA to V between cases requiring surgery (surgical) and cases managed conservatively with spontaneous resolution (nonsurgical).
  
  
  
  Data were obtained in 45 patients (surgical: n = 28; nonsurgical: n = 17). CSDH risk factors did not significantly differ between surgical and nonsurgical cases. Surgical V was 2.5× the nonsurgical V (119.9 ± 33.1 mL vs. 48.4 ± 27.4 mL, respectively; P < 0.0001). Surgical total SA was 1.4× nonsurgical SA (256.63 ± 70.65 cm2vs. 187.67 ± 77.72 cm2, respectively; P = 0.004). Surgical total SA to V ratio was approximately one half that of nonsurgical SA to V ratio (2.14 ± 0.90 mL-1vs. 3.88±1.22 mL-1, respectively; P < 0.0001). Surgical OM SA (SAOM) was 120.63 ± 52 cm2, and nonsurgical SAOMwas 94.10 ± 41 cm2(P < 0.0001). Nonsurgical SAOMto V ratio was 1.94 mL-1, whereas surgical SAOMto V ratio was 1.005 mL-1(i.e., surgical SAOM≈ V).
  
  
  
  Because surgical total SA to V ratio was ≈2:1, one neomembrane may indeed dominate the dynamic growth-resorption equilibrium. CSDH critical size therefore appears to be when SAOM≈ V, which is intuitive. Practically, subtotal CSDH evacuation which approximately doubles total SA to V ratio or SAOMto V ratio implies CSDH resolution without recurrence. This could guide subdural drain removal timing, discharge, or transfer. Prospective validation studies are required.
authors.affiliation: Department of Neurosurgery, The Townsville Hospital, Douglas, Townsville, Queensland, Australia.
authors.forename: Appukutty
authors.initials: A
authors.lastname: Manickam
authors.affiliation: Department of Neurosurgery, The Townsville Hospital, Douglas, Townsville, Queensland, Australia; School of Medicine, James Cook University, Douglas, Townsville, Queensland, Australia. Electronic address: l.a.g.marshman@btinternet.com.
authors.forename: Laurence A G
authors.initials: LAG
authors.lastname: Marshman
authors.affiliation: Department of Marine & Tropical Biology, James Cook University, Douglas, Townsville, Queensland, Australia.
authors.forename: Ross
authors.initials: R
authors.lastname: Johnston
mesh_terms: D000368:Aged; D004388:Dura Mater / Q000000981:diagnostic imaging*; D005260:Female; D020200:Hematoma, Subdural, Chronic / Q000000981:diagnostic imaging* / Q000601:surgery*; D046648:Hematoma, Subdural, Intracranial / Q000000981:diagnostic imaging* / Q000601:surgery*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D009929:Organ Size; D018579:Patient Selection; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome
keywords: Membrane; Subdural hematoma; Surface area; Volume