47 Mastoid Surgery
Mastoid surgery (mastoidectomy) is a procedure performed to remove the mastoid air cells. It is used to treat mastoiditis and chronic suppurative otitis media, both with and without cholesteatoma. It is also used for access when inserting cochlear implants or as part of lateral skull base surgery for vestibular schwannomas and to access temporal bone tumours such as paragangliomas (glomus tumours) and epidermoid cysts.
There are six different types of mastoidectomy:
1. Cortical mastoidectomy also called simple mastoidectomy or Schwartze’s procedure.
2. Radical mastoidectomy—Removal of posterior and superior canal wall, meatoplasty and exteriorisation of the middle ear.
3. Canal wall up mastoidectomy also called closed-cavity mastoidectomy or combined-approach tympanoplasty in which the posterior and superior ear canal walls are kept intact.
4. Canal wall down mastoidectomy or modified radical mastoidectomy in which the ear canal wall is removed and one cavity created and the middle ear repaired with tissue grafts.
5. Canal wall reconstruction mastoidectomy where either a modified radical mastoidectomy is done and the cavity is reduced in size by repairing the ear canal wall as well as the middle ear or the medial portion of the posterior canal wall and superior canal wall are removed by a combined permeatal inside out and cortical mastoidectomy approach. The removed canal wall is then reconstructed with conchal cartilage.
6. Subtotal or total petrosectomy. Every mastoid cell is removed plus or minus the bone down to soft tissue.
There are also the lateral and total temporal bone resections used for cancers.
47.1 Procedure Principles
Mastoidectomy procedures are typically performed under non-paralysing general anaesthesia to allow the use of a nerve integrity monitor. High-speed drills, a microscope, microinstruments and increasingly otoendoscopes are used. The surface landmarks of the bony external ear canal, zygomatic root, spine of Henle and mastoid tip, allow the surgeon to initiate bone removal in the correct location. The first steps are always identifying the tegmen and saucerising the edges of the mastoid cavity using the largest burr possible.
Safe mastoid surgery requires routine identification of key anatomical structures after identifying the tegmen (middle fossa floor), then sigmoid sinus and diagastric ridge, then external auditory canal, lateral semicircular canal, short process of the incus and facial nerve. Microscopic surgery is now being augmented with endoscopes to examine and remove disease from areas challenging to visualise such as sinus tympani, supratubal recess, epitympanum, facial recess, perilabyrinthine air cells and retrofacial air cells.
1. Cortical mastoidectomy—Consists of opening the mastoid cortex and identifying Koerner’s septum and the aditus ad antrum. Removal of mastoid air cells is undertaken without affecting the middle ear. This is typically done for mastoiditis.
2. Radical mastoidectomy—Removal of posterior and superior canal wall, meatoplasty and exteriorisation of the middle ear. A radical mastoidectomy is a canal wall down mastoid-ectomy in which the tympanic membrane and ossicles are not reconstructed, thus exteriorising the disease. The eustachian tube is often obliterated with soft tissue to reduce the risk of a chronic otorrhoea.
3. Canal wall up mastoidectomy—A complete or canal wall up mastoidectomy necessitates removal of all of the mastoid air cells along the tegmen, sigmoid sinus and presigmoid dural plate. The posterior and superior canal walls are kept intact. A posterior tympanotomy via a facial recess approach is usually included.
4. Canal wall down mastoidectomy—It includes a complete mastoidectomy in addition to removal of posterior and superior canal wall and a meatoplasty. The tympanic membrane is left in place or reconstructed. A meatoplasty is always performed to decrease the risk of developing moisture in the cavity and to facilitate future debridement. It entails removal of a varying amount of the conchal cartilage, post-auricular periosteum and cartilaginous ear canal while preserving as much external ear canal skin as possible.
5. Canal wall reconstruction mastoidectomy—The removal of bone is the same as an open-cavity mastoidectomy. The canal wall is reconstructed to avoid a cavity. This is done with some or all of cartilage, soft tissue free grafts, pedicled flaps, bone or occasionally artificial tissue. This is covered with vascularised flaps and leaves a normal-looking ear canal. The middle ear is reconstructed in the same way as a modified radical mastoidectomy. This avoids the long-term drawbacks of canal wall down mastoidectomy while offering surgeons excellent exposure of the middle ear and mastoid. In the world literature, this is the most common type of mastoid surgery and has the highest chance of curing cholesteatoma.
A modification of this is to just remove the medial portion of the posterior canal wall and also the medial superior wall in a combined inside out/cortical mastoidectomy approach to expose the cholesteatoma from both sides of the posterior canal wall but with much wider access than a total canal wall-up technique with posterior tympanotomy.