Burr Hole Endoscopic Mastoidectomy: A Morphometric Cadaveric Study.

Traditional open mastoidectomy is performed through a retro-auricular incision to expose the mastoid cortex. Few have addressed the possibility of performing an endoscopic minimally invasive mastoidectomy.  Our objective was to test the feasibility of performing an endoscopic mastoidectomy through a 1 cm incision and burr hole.  Ten cadaver heads (20 mastoids) were used for this morphometric study. We performed an endoscopic mastoidectomy through a 1 cm burr hole located over the antrum. The goals were to reach predetermined landmarks and maximize the drilling of cancellous mastoid bone. Computed tomography (CT) imaging was acquired at baseline, after endoscopic approach and after traditional open mastoidectomy. The scans were then analyzed with volumetric measurements of each mastoid.  Endoscopic mastoidectomy facilitated access to most anatomical landmarks. While open mastoidectomy enabled greater extents of mastoidectomy and tegmen exposure, the endoscopic approach exposed 76% of mastoid and 69.9% of the tegmen achievable by the open approach. Additionally, baseline mastoid volume and tegmen surface area positively correlated with the extent of mastoidectomy and tegmen exposure, respectively. Baseline mastoid volume negatively correlated with the percentage of mastoid drilled and tegmen exposed.  We demonstrated the feasibility of an endoscopic mastoidectomy through a standardized postauricular burr hole. This approach reduces the incision size and the need for soft tissue dissection. Burr hole mastoidectomy is facilitated using angled scopes which are not reliant on 0-degree line-of-sight. Although the endoscopic approach afforded slightly less exposure, the location and burr hole size can be adjusted depending on the clinical indications.