system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Facial recess or the posterior sinus is bounded by -
assistant
The correct answer is  Facial recess or Posterior sinus – It is a depression in the posterior wall of the middle ear.
It is bounded by:
Medially – Vertical part of VIII nerve
Laterally – Chorda tympani
Above – Fossa incudis
Importance – This recess is important surgically, as direct access can be made through this into the middle ear without disturbing posterior canal wall. (Posterior tympanotomy approach)