Tympanomastoidectomy and Ossicular Chain Reconstruction

1

What is a mastoidectomy? What is a tympanomastoidectomy?

The mastoid is a portion of the temporal bone that houses air cells connected to the middle ear space. A mastoidectomy is a surgical procedure in which mastoid bone and air cells are removed. A tympanomastoidectomy is a tympanoplasty plus mastoidectomy. This procedure is commonly used to address chronic ear disease in the mastoid bone as well as a tympanic membrane that is perforated, severely retracted, or involved with cholesteatoma.

2

What are the main types of mastoidectomy?

There are a number of different types of mastoidectomy surgery, broadly grouped into canal wall up (CWU) and canal wall down (CWD) procedures.

In a CWU mastoidectomy, the mastoid air cells are removed, leaving the posterior external auditory canal wall intact. The borders of a complete mastoidectomy are the tegmen superiorly, the sigmoid sinus posteriorly, and the posterior canal wall anteriorly.

A CWD mastoidectomy is one in which the mastoid air cells are removed along with the posterior wall of the external auditory canal. This creates a mastoid cavity or “bowl.” With this procedure, a meatoplasty is also usually performed, which widens the opening of the outer ear canal in order to improve visualization and access to the mastoid bowl. A canal wall down mastoidectomy effectively “exteriorizes” the mastoid.

In a modified radical mastoidectomy the canal wall is taken down and the epitympanum, mastoid antrum, and external auditory canal are converted into a common cavity. The middle ear space, tympanic membrane, and ossicles are preserved. This procedure is sometimes called the Bondy modified radical mastoidectomy.

In a radical mastoidectomy, a CWD mastoidectomy is performed and the tympanic membrane and ossicles, except for the stapes, are also permanently removed. These structures are not reconstructed.

3

What are the indications for a mastoidectomy?

The most common indication for a mastoidectomy is chronic disease such as cholesteatoma or mastoiditis. A mastoidectomy is also indicated for some complications of acute otitis media, such as acute mastoiditis or a subperiosteal abscess.

A mastoidectomy is a key portion of the approach for cochlear implantation or facial nerve decompression. A mastoidectomy may be performed as part of a transmastoid approach for excision of temporal bone tumors, such as vestibular schwannoma, glomus tumor, or meningioma. In unusual cases, a mastoidectomy may be required for repair of a cerebrospinal fluid leak.

4

What are the important landmarks in mastoidectomy surgery? ( Fig. 41.1 )

The superior border of a mastoidectomy is the tegmen, which is the thin bone layer separating the middle cranial fossa from the ear. The posterior border is the sigmoid sinus. The anterior border is the posterior wall of the external auditory canal. The deep (medial) border is the lateral semicircular canal and incus, which are found in the aditus ad antrum, the connection between the mastoid cavity and the middle ear space. Another key landmark is the facial nerve.

5

When is a canal wall down procedure indicated?

A canal wall down procedure is indicated in the following situations:

• Cholesteatoma involving the sinus tympani area, not accessible transcanally or through the facial recess

• Semicircular canal fistula with adherent cholesteatoma matrix

• The posterior canal wall is extensively damaged by disease

• The mastoid is contracted and sclerotic, preventing adequate visualization and access via a CWU approach

• Unresectable cholesteatoma matrix on the dura or posterior cranial fossa

• Attic or mastoid cholesteatoma in a patient unable to maintain follow-up or unable to safely tolerate further surgery

6

What are the disadvantages of a CWD mastoidectomy?

The mastoid bowl often fills with cerumen and requires periodic debridement to prevent infection. Although not necessarily unsightly, the meatoplasty is often visible. Hearing outcomes may be slightly diminished due to the change in the acoustic properties of the ear canal. Water restrictions are recommended due to risk of mastoid bowl infection.