Inferior Frontal Lobe Position after Endoscopic Anterior Skull Base Resection and Repair with Acellular Allograft

Background: Reconstruction methods for large anterior skull base defects vary without consensus on the optimal reconstruction to achieve a water-tight seal and anatomic frontal lobe position. Many have described the use of multilayer closure utilizing a septal flap with excellent results. Unfortunately, a septal flap may not always be available in extensive resections. High success has been reported with single layer reconstruction using acellular allograft. However, it is unclear if there is sufficient support with a single layer reconstruction to achieve anatomic frontal lobe positioning.

Objectives: 1. Determine the position of the frontal lobe after tumor resection and large anterior skull base defect reconstruction with a single layer of acellular allograft. 2. Compare with frontal lobe position in nonsurgical patients. 3. Determine if frontal lobe position after reconstruction changes in the short-term as compared with the long-term. 4. Determine the rate of post-operative cerebrospinal fluid (CSF) leak.

Study Design: Retrospective cohort study.

Methods: We reviewed all patients who underwent endoscopic anterior skull base resection and reconstruction with acellular allograft between 1/2007–2/2014. Patients with at least 5 cm of skull base defect and post-operative imaging were included. The imaging study at the furthest post-operative time point was utilized. A random sample of nonsurgical patients receiving cranial imaging for unrelated reasons were collected for measurement comparison. The position of the inferior frontal lobe was measured in reference to a line from the nasion to the planum sphenoidale. Analysis was performed using a 2-sample t-test assuming unequal variance. The frontal lobe position of patients with post-op imaging at less than and greater than 3 months post-op was compared by paired t-test.

Results: 29 surgical patients met inclusion criteria. 20 nonsurgical patient measurements were collected. The surgical cohort was significantly older than the nonsurgical cohort (mean: 60 and 45 years of age, respectively) with similar proportion of women (48% verses 40%, respectively). Frontal lobe position was not statistically different between the two groups; surgical cohort 0.5mm above the line (standard deviation (SD) 4, range 14 to -16mm) compared with nonsurgical cohort 1mm below the line (SD 2, range 3.6 to -1.7mm), p = 0.54. The average length of time from reconstruction to imaging was 429 days (SD 484, median 280 days). This study has >90% power to detect a one centimeter change in frontal lobe position. In the 7 surgical patients who had imaging assessment prior to and after 3 months postoperatively, there was no statistically significant change in frontal lobes position between time-points (p = 0.12); mean 3mm below the line (SD 5mm) verses 1.3mm below the line (SD 3mm), respectively. No surgical patients had a CSF leak.

Conclusions: Reconstruction of large skull base defects using a single layer of acellular allograft without the use of a ridged layer (e.g., bone, cartilage) does not significantly change frontal lobe position as compared with nonsurgical patients. This is a viable method for reconstruction of large anterior skull base defect that restores anatomic frontal lobe position and has a low incidence of CSF leaks requiring re-operation.