Definition: Mastoidectomy is defined as a surgical procedure which opens up the mastoid cavity, cleans up the infected air cells, improves middle ear ventilation by widening of the aditus.
Indications of mastoidectomy:
1. Chronic mastoiditis not responding to conventional medical treatment
2. Chronic suppurative otitis media with cholesteatoma
3. Chronic suppurative otitis media not responding to medical management
4. As a preliminary step to other surgical procedures like:
a. Cochlear implants
b. Facial nerve decompression
d. Endolymphatic sac decompression
5. Subperiosteal abscess
6. Malignant lesions of middle ear
7. Benign tumors of middl ear i.e. Glomus jugulare
Types of mastoid surgeries:
1. Cortical mastoidectomy
2. Modified radical mastoidectomy
3. Radical mastoidectomy
Cortical mastoidectomy: Also known as simple mastoidectomy, Schwartz surgery, or complete mastoidectomy.
1. Chronic suppurative otitis media not responding to medical management
2. As a preliminary step to other surgical procedures i.e. facial nerve decompression, cochlear implant etc
Commonly cortical mastoidectomy is preformed for chronic suppurative otitis media which are resistant to medical managment.
The aims of cortical mastoidectomy when performed for infective conditions are:
1. To exenterate the infected mastoid air cells
2. To widen the aditus to facilitate better ventilation
3. To clear the middle ear of infections and hypertrophied mucosa
It is performed either under local anesthesia or general anesthesia. It is better to perform this surgery under general anesthesia in anxious patients. Whatever may be the choice of anesthesia, the following steps are more or less the same.
Infiltration: The post auricular area is infiltrated using 2% xylocaine with 1 in 80,000 units adrenaline. The whole of the post auricular sulcus is infiltrated. About 2 - 3ml of xylocaine can be used for this purpose. The infiltration serves two purposes:
1. It reduces bleeding due to local vasoconstriction
2. It elevates the periosteum from the mastoid cortex making it stripping easier.
Incision: Commonest incision used is William Wild's post auricular incision. It is a curviliner incision hugging the post auricular sulcus begining from the root of helix superiorly, extending up to the mastoid tip.
Figure showing the post aural incision being made
Gradual deepening of the skin incision exposes the periosteum. This is stripped away from the mastoid cortex using a sharp periosteal elevator. A post auricular skin flap is raised, and is pushed anteriorly to be held in place by a roller gauze tied through it. Now the external auditory canal, ear drum and the mastoid cortex becomes visible in the same view.
Cutting burrs are used to drill out the cortical bone from the mastoid cortex. Two incisions are made. One horizontal and one vertical. The horizontal cut is made just below the supra mastoid crest. This starts from the anterior portion of the Maceven's triangle extending posteriorly up to the sino dural angle. This line approximately indicates the level of dura and hence dissection should not go above this line. The second vertical cut is made along the external auditory canal starting from the Maceven's triangle up to the mastoid tip.
MacEven's triangle: is the surface marking for mastoid antrum in adults. The antrum lie about 1.5 cm below this triangle.
It is bounded above by the supra mastoid crest, antero inferiorly by posterior superior margin of external auditory canal and posteriorly by a tangential line drawn from the zygomatic arch. The spine of Henle lies within this triangle.
Figure showing the Maceven's triangle and Henle's spine
Antrum is entered by drilling the mastoid cortex. The antral and periantral air cells are exentrated. The aditus is identified. It is widened in the anterosuperior direction. It should not be widened in an inferior direction because the incus could become dislodged. After the aditus is widened, the posterior meatal wall is thinned out.
The middle ear is cleared off the infective material and oedematous mucosa after elevation of tympanomeatal flap. Ossicular chain is checked for functional continuity. If the incus is necrosed, ossicular prosthesis is introduced.
Wound is closed in layers.
Modified radical mastoidectomy: The initial steps are the same as for cortical mastoidectomy. After the aditus is widened, and posterior canal wall is thinned out, the Posterior canal wall is removed (removal of bridge). The facial ridge is lowered till the level of lateral semicircular canal. After the surgery is completed, a meatoplasty is performed making the external canal, middle ear cavity and mastoid cavity into one continuous self cleaning cavity lined by skin.