Chapter 6: Facial Recess Approach (Posterior Tympanotomy)

The facial recess approach (posterior tympanotomy) is an  essential surgical technique in otologic procedures. This method enable access to critical anatomical structures in the middle ear and mastoid while ensuring preservation of vital elements such as the facial nerve and chorda tympani.

Facial Recess Approach

Anatomy and Topography

The facial recess is a collection of air cells situated lateral to the external genu of the facial nerve. It occasionally acts as a pathway for middle ear infections to spread into the mastoid, bypassing the antrum. Cholesteatomas frequently invade these cells, necessitating meticulous surgical intervention as transcanal approaches often fail to provide adequate access (1).

Opening the facial recess is beneficial in chronic ear disease, as it promotes mastoid aeration and improves visualization of the middle ear cavity, especially during facial nerve decompression. It is also the primary route for accessing the round window during cochlear implantation (1).

Key Landmarks (1):

• Horizontal semicircular canal
• Fossa incudis
• Posterior canal wall
• External genu of the facial nerve

Surgical Procedure

The dissection begins by identifying the external genu or descending portion of the facial nerve in the mastoid cavity. Using a cutting burr, the bone is thinned until the facial nerve sheath becomes visible as a pearly white structure. Diamond burrs are used for finer dissection to ensure preservation of the nerve and its surrounding structures. Adequate irrigation and magnification are critical for maintaining clear visualization (1).

The chorda tympani, which branches from the facial nerve, is preserved by thinning the adjacent bone while carefully following its course to the tympanic annulus. Bone overlying the incudal buttress is thinned to access the recess without disturbing the incus (5).

Objective and Clinical Applications

The posterior tympanotomy provides access to the posterior middle ear cavity and is commonly performed for:

• Cholesteatoma excision (combined approach by Jansen)
• Facial nerve decompression
• Cochlear implantation for electrode insertion
• Implantable hearing aid placement (2, 4).

Anatomy and Boundaries

The facial recess is bounded by the following structures:

• Posteriorly: Facial nerve
• Antero-inferiorly: Chorda tympani
• Superiorly: Fossa incudis
• Laterally: Posterior canal wall (4, 5).

Landmarks used to guide the dissection include the horizontal semicircular canal, incus, and chorda tympani. The facial nerve typically lies medial to the lateral semicircular canal, with a median distance of 1.77 mm, as reported by Anson and Donaldson (2).

Surgical Techniques

1. Thinning the Posterior Canal Wall:
   Bone is carefully thinned to expose the horizontal segment of the facial nerve and the chorda tympani. Adequate thinning enhances visibility while preserving a protective bony layer over these structures (4, 12).
2. Chorda Tympani and Facial Nerve Identification:
   The chorda tympani is identified by tracing it from the main nerve trunk. The facial nerve is skeletonized distally along its descending mastoid portion and medially into the middle ear (5, 11).
3. Exposure of Middle Ear Structures:
   The surgical field is expanded to visualize critical components such as the long process of the incus, pyramidal eminence, stapes, and round window niche. Special attention is required to avoid damaging ossicles or the tympanic membrane during dissection (11, 12).
4. Cochleostomy for Cochlear Implantation:
   A cochleostomy is created by drilling into the scala tympani just anterior and inferior to the round window niche. This ensures atraumatic insertion of the implant electrode (12).

Points to Remember

1. Always drill parallel to the fallopian canal to avoid nerve injury.
2. Use high-intensity illumination and magnification for precise visualization.
3. Preserve a thin bony layer over the facial nerve to protect it from injury.
4. Avoid contact between the rotating burr and delicate structures such as the ossicles and sigmoid sinus (4, 11).

Clinical Pearls

• The chorda tympani is often mistaken for the annulus; careful tracing of its origin from the facial nerve is essential to prevent disruption (5).
• Preserved bone over the facial nerve acts as a safeguard during deeper dissections and minimizes the risk of nerve injury (5).

The facial recess approach and posterior tympanotomy are versatile techniques that enable precise surgical intervention in otologic procedures. These methods, when performed with meticulous attention to anatomical landmarks and careful instrumentation, offer significant advantages in achieving desired clinical outcomes while preserving critical structures.