Introduction: Wide variation has been reported for symptomatic hydrocephalus following traumatic brain injury (TBI), largely due to differences in definition. However, the incidence of post traumatic hydrocephalus (PTH) reported in TBI patients in general (0.7-29%) is considerably less than patients treated with craniectomy (10-40%). Additional data has shown that there is a lower rate of symptomatic hydrocephalus in patients requiring decompressive craniectomy if the superior medial aspect of the bone flap is greater than 25mm off midline. We sought to provide additional data supporting both removal of a bone flap via craniectomy and distance from the midline in the most superior medial aspect of the bone flap are independent and modifiable iatrogenic risk factors in developing PTH.

Methods: 380 patients were retrospectively identified as status post craniectomy for TBI from a single, level-one trauma center from 2005-2014. We defined "symptomatic PTH" as those cases requiring ventriculoperitoneal shunt (VPS) placement. 24 patients (6.3%) met crieteria for symptomatic PTH, 354 (93.7%) did not. Craniectomy distance from midline was calculated for each patient. Mean distance for each group was compared using an unpaired two-tailed t test.

Results: The mean axial distance from midline in the PTH group was 12.8mm and 16.6mm in the non-PTH group. This difference was significant (p = 0.037). Only 6.3% of patients met criteria for symptomatic PTH.

Conclusions: These data reinforce previously published data that correlate craniectomies approaching midline with a higher incidence of TBI-related hydrocephalus. This supports the concept that both craniectomy and the proximity of the craniectomy to midline are both independent, modifiable risk factors in the development of PTH. Furthermore, when symptomatic PTH is defined as requiring VPS placement, the incidence may be lower than previously reported.

Patient Care: We hope this research will help guide bone flap planning for decompressive hemicraniectomy operations following traumatic brain injury. Allowing a greater distance from the midline may reduce the incidence of ventriculoperitoneal shunt dependent hydrocephalus after traumatic brain injury without compromising the surgeon's ability to decompress the middle fossa and brainstem adequately. Although we do not examine it in this study, greater distance from the midline during craniectomies could also help reduce complications related to superior sagittal sinus injury.

Learning Objectives: By the end of this session, participants should be able to 1) understand craniectomy and craniectomy distance from midline as modifiable risk factors for PTH and 2) discuss proposed theories for the contribution of bone flap removal in the development of PTH.

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