The Endoscopic Relationship of the Stapedius Muscle to the Facial Nerve: Implications for Retrotympanic Surgery.

Objectives: The stapedius muscle, tendon, and pyramidal eminence are structures within the retrotympanum. In cholesteatoma surgery, the retrotympanum is a common site of residual disease. The removal of the pyramidal eminence during surgery is sometimes necessary to obtain better visualization of the superior retrotympanum during surgery. Understanding the relational anatomy of structures in the region to the facial nerve allows the surgeon to safely access regional disease. This study aims to better understand the anatomical relationship between the mastoid portion of the facial nerve, the pyramidal eminence, and the stapedius muscle. A secondary aim is to demonstrate that removal of the stapedius muscle in the cadaver model, can increase exposure to the retrotympanic space.

Study Design: Anatomical cadaveric observation study.

Methods: Endoscopic dissection of cadaveric heads was undertaken. Classification of the superior and inferior retrotympanic area was performed. The anatomy of the stapedius muscle was described including relationships, depth, course, and angle with respect to the facial nerve. The pyramidal eminence and stapedius muscle were removed in all specimens and the exposure of the retrotympanum re-evaluated to determine if exposure of the region was increased.

Results: In all cases (11 ears), the stapedius muscle was located medial and anterior to the mastoid portion of the facial nerve, with the second genu superior. The mean antero-posterior distance from the apex of the pyramidal eminence, which the stapedius tendon enters, to the stapes itself was 4.10 mm (range, 2.92-5.73 mm; standard deviation [SD] 0.90 mm). In all cases, irrespective of sinus tympani conformation, removal of the pyramidal eminence and stapedial bony crest in proximity to the facial nerve allowed exposure of the whole retrotympanic region, using a 0-degree endoscope.

Conclusions: The pyramidal eminence and stapedius muscle have a relatively constant relationship to the facial nerve. Removal of the stapedius muscle in the human cadaver model increases the exposure of the sinus tympani and subpyramidal space. Increased visualization in this region, may reduce risk of residual cholesteatoma in patients.