Morphometric Analysis of the Transmastoid Approach

Introduction: The transmastoid approach has numerous applications and has especially gained popularity recently in the excision of encephaloceles and cerebrospinal fluid (CSF) leaks with skull base repair. It is also part of numerous neurotology cases and neurosurgery skull base approaches. Reports that advocated for the transmastoid approach have shown similar success rates compared to the middle cranial fossa (MCF) approach for encephalocele and CSF leak repairs along with decreased intraoperative time and decreased hospital stays as low as 1.6 days on average compared to 6.3 days with the MCF approach.

Despite its increasingly common use, there are no quantitative anatomical studies in the literature analyzing the transmastoid approach and its versatility. We aim to quantitatively define to the boundaries of this approach and explore the limits.

Methods: Five cadaveric specimens were used for bilateral transmastoid approach drilling in a standard fashion for a total of 10 mastoids for analysis. The anatomical structures and landmarks were measured using digital calipers (Mitutoyo Kanagawa, Japan).

Results: The average size of the outer mastoid cortex was 41.5 × 30.5 mm. The average distance from the suprameatal triangle at the surface to the antrum was 12.6 mm with a range of 12 to 14 mm. From the cortical surface of the mastoid to the center of the tegmen tympani, the average distance was 33.4 mm. Nearby critical structures were measured in relation to the center of the tegmen tympani, with the body of the incus 4.4 mm in distance and the most medial aspect of the facial nerve being 6.4 mm in distance on average.

Discussion: With increasing data showing improved outcomes after surgery, the transmastoid approach has gained popularity. There is now a further need to quantitatively define the borders of this approach, especially in the setting of encephalocele resection and skull base repair. As seen on dissection, the surgeon can gain direct visualization of the ossicles, as opposed to the middle cranial fossa approach. This allows the surgeon to safely inspect the ossicles and prevent disruption, especially if the encephalocele is in contact. We have quantitatively defined the landmarks of this approach and shown the size of the operative corridor. There is intricate anatomy and surgeons will benefit from having numerical data to define the borders ([Fig. 1]).

Fig. 1 Microscopic visualization of the right mastoid after drilling.

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Artikel online veröffentlicht:
05. Februar 2024