Chapter 5: Trans-Mastoid Atticotomy

Procedure Overview

The trans-mastoid atticotomy involves dissecting anteriorly and laterally from the mastoid antrum to access and open the attic. The anatomical boundaries of the attic are as follows:

• Inferior limit: Superior wall of the external auditory canal (EAC).
• Superior limit: Tegmen tympani.
• Anterior limit: Approximates the level of the anterior canal wall.

During drilling, the direction should proceed from medial to lateral to minimize the risk of trauma to the ossicular chain. The choice of burr size is contingent upon the available surgical space. Key anatomical landmarks include the short process and body of the incus, ossicular ligaments, and the head of the malleus. To achieve complete exposure of the anterior epitympanic space, the surgeon may need to drill anterior to the malleus or, if necessary, remove the incus and head of the malleus. This approach facilitates visualization of the tympanic segment of the facial nerve (4).

Points of Caution

1. While removing bone near the medial attic and lateral to the ossicles, ensure the burr does not contact the ossicles. Accidental movement of the ossicles may result in sensorineural hearing loss, dizziness, or tinnitus.
2. In challenging cases, such as low-lying dura, forward-lying sigmoid sinus, or sclerosed mastoid, dislocating the incudo-stapedial joint may prevent vibratory transmission to the inner ear if the burr inadvertently contacts the ossicles (4).

Atticotomy Technique and Attico-Antrotomy

Microscope Orientation and Burr Use
The microscope should be positioned to provide an en face view of both the tegmen tympani and the superior aspect of the EAC. The cutting burr shaft is oriented vertically to sculpt specific anatomical areas:

• Superior surface: Tegmen tympani.
• Inferior surface: Superior cortex of the EAC.
• Anterior face: Bone removal to expose the incus and its articulation with the malleus head.

Monitor all bony surfaces in contact with the burr to prevent damage to critical structures (5).

Attico-Antrotomy Technique

1. Exposure of the Middle Fossa Dural Plate: Drill parallel to the dural plate, moving anteriorly to posteriorly. Thinning the superior canal wall and drilling toward the zygomatic root widens access to the attic and antrum.
2. Guiding Dissection in Anatomical Variations: Curved posterior bony canal walls necessitate careful dissection, aided by detaching meatal skin in live surgery or cadaver specimens. This approach helps preserve the posterior canal wall and expose the incus.

The epitympanum is anatomically defined by:

• Superiorly: Middle fossa dural plate.
• Medially: Tegmen tympani.
• Laterally: External ear canal.
• Anteriorly: Cog.
• Posteriorly: Antrum.
• Inferiorly: Tensor tympani muscle and facial nerve.

Given the proximity of the ossicular chain at the short process of the incus (approximately 0.2 mm), medial-to-lateral drilling minimizes the risk of damaging the ossicles and inner ear. Initial visualization of the incus may be achieved through irrigation in the posterior epitympanum. Complete exposure requires removing the root of the zygoma and skeletonizing the posterior and superior bony canal walls to access the ossicular chain (11).

Completion of Attico-Antrotomy

The final steps involve exposing the body of the incus, head of the malleus, and their associated ligaments. These maneuvers complete the attico-antrotomy, ensuring a comprehensive view of the attic while preserving critical anatomical structures (11).

Unroofing the Epitympanum in Chronic Otitis Media

In cases of chronic otitis media, the epitympanum often harbors cholesteatoma, with common involvement of the ossicles, particularly the body of the incus and the head of the malleus. Despite this, complete exposure of the epitympanum can be achieved without destroying the scutum. This involves removing additional air cells at the root of the zygoma. Landmarks such as the middle fossa dura, the thinned posterior canal wall, and the tegmen tympani guide the procedure.

For low-lying middle fossa dura, small diamond burrs are preferred to avoid fracturing the thin tegmen tympani. Dissection may extend anteriorly through the zygomatic root to the glenoid fossa. The dissection’s floor is delineated by the horizontal semicircular canal, the superior semicircular canal, and the facial nerve. Important anatomical landmarks include the incus, malleus, tegmen tympani, horizontal canal, and facial nerve (1).