Promontory drilling in stapedectomy: an anatomical study.

Area of Science:

• Otolaryngology
• Surgical Anatomy
• Neurosurgery

Background:

• Anatomical variants like an overhanging facial nerve or promontory can obstruct footplate access during stapedectomy.
• Drilling the cochlear promontory or creating a 'pothole' in the oval window may be necessary but lacks detailed anatomical guidance.
• Limited published data exists on promontory anatomy relevant to these surgical maneuvers.

Purpose of the Study:

• To provide precise anatomical measurements of the bony promontory.
• To establish safe limits for bone removal inferior to the oval window during stapedectomy.
• To guide the creation of a 'pothole' for floating or depressed footplates.

Main Methods:

• Twenty human temporal bones were dissected and analyzed.
• Detailed measurements were taken to assess the thickness of the promontory bone.
• The proximity of the cochlear endosteum, spiral ligament, and stria vascularis to the oval window was quantified.

Main Results:

• The bony promontory is thickest posteriorly, with the endosteum showing minimal lateral projection.
• Bone thickness decreases anteriorly towards the oval window, with the endosteum closely following the bony contour.
• The distance from the stria vascularis/spiral ligament to the oval window inferior margin is <0.2 mm posteriorly and 0.3-0.5 mm at the footplate midpoint.

Conclusions:

• Bone removal inferior to the posterior one-third of the footplate is safe laterally to a 35-degree line from the superoinferior axis.
• For 'pothole' creation in floating/depressed footplates, the midpoint of the inferior oval window margin is recommended.
• The 'pothole' diameter should not exceed 0.3 mm to ensure safety.