Endoscopic Mastoidectomy: A Morphometric Cadaveric Study

Introduction: Open mastoidectomy is traditionally conducted through a postauricular incision which is several centimeters long. After exposure of the mastoid cortex, drilling is performed to expose the cancellous bone and deeper structures within the mastoid. The reminder of the surgery is then directed by the requirements of the pathology. There have been few reports discussing the possibility of a minimally invasive endoscopic mastoidectomy. While some studies presented transcanal endoscopic “inside-out” techniques and others have presented a robotic guided approach to the facial recess, no studies to date have focused on an endoscopic approach through a minimal postauricular incision.

Methods: Ten cadaver heads (20 mastoids) fixed in formaldehyde were scanned using a neuronavigation protocol for the purpose of the morphometric study. The incision was located at the superior portion of the ear canal and over the antrum that had been localized with the neuronavigation. A 1 cm burr hole was done using a template for size consistency. Once the burr hole had been performed and the antrum reached, the endoscope was used to perform a cortical mastoidectomy. The goals of the surgery were to reach predetermined landmarks and to maximize the drilling of the cancellous bone. After the endoscopic drilling was performed, the heads were scanned again. The incision was then extended to and each mastoidectomy was revised via a traditional postauricular approach with the same aforementioned goals. After the open approach was completed, the heads were scanned a third time. The CT scans were then analyzed and volume of the cavity and surface area of the tegmen before and after each procedure were calculated.

Results: The EAC, sigmoid sinus, sinodural angle, tegmen, incus, facial nerve, and lateral semicircular canal were reached in all 20 mastoids via either approach. Two landmarks, the mastoid tip, and the jugular bulb where never reached with the endoscopic approach. One landmark, the facial recess was not reached in 5 of 20 mastoids. Using traditional mastoidectomy volume as the gold standard, the endoscopic approach enabled us to drill 76% of the mastoid ([Fig. 1]). Similarly, using the open approach as the gold standard, we were able to expose 69% of the tegmen ([Fig. 2]).

Discussion: Our morphometric study demonstrates the feasibility of an endoscopic mastoidectomy through a burr-hole approach. The advantages of this approach include a smaller incision, limited soft tissue manipulation, and the ability to see around corners using angled endoscopes. This new technique allows surgeons to access the majority of the anatomical landmarks of the mastoid without difficulty. It also provide increase visualization and illumination. Although there was a smaller volume and surface area exposed when trying to drill the entire mastoid, most pathologies do not require exposure of the entire mastoid for treatment. The location and size of the burr hole can be adjusted depending on the clinical indications.

Fig. 1 CT scan after the endoscopic drilling in axial and coronal view. CT, computed tomography.

Fig. 2 Postendoscopic drilling CT scan with three planes reconstruction demonstrating the exposed tegmen. CT, computed tomography.

No conflict of interest has been declared by the author(s).

Publication History

Article published online:
12 February 2021