Mastoidectomy

Anatomy and Physiology

Knowledge of the anatomy of the temporal bone is a critical and necessary qualification for performing mastoid surgery safely. The temporal bone connects to the parietal, occipital, zygomatic, and sphenoid bones. It can be described as a pyramidal bone with the apex pointing in the anteromedial direction.

There are three main subdivisions of the temporal bone: petrous, squamous, and mastoid. Intuitively, mastoidectomy involves creating an open cavity within the mastoid portion of the temporal bone. The anterior border of the mastoid cavity is demarked by the posterior bony ear canal. The spine of Henle is an important landmark found at the posterior superior lateral edge of the ear canal, which marks the level of the antrum of the mastoid. The superior border of the mastoid cavity is marked by the temporal line. The temporal line is found at the inferior limit of the temporalis muscle, and it approximates the level of the middle fossa floor. The posterior border of the mastoid cavity is limited by the sigmoid sinus. Medially, the Koerner septum is a flat shelf of bone, deep to the superficial mastoid cells, which marks the boundary between the petrous and squamous parts of the temporal bone. Further medially, the lateral semicircular canal, as well as the mastoid antrum, are reliable landmarks that can help surgeons assess the depth of dissection relative to the middle ear space.

Indications

There are multiple indications for mastoidectomy. The common philosophy in mastoid surgery is to create a safe and dry ear. The main indications for performing a mastoidectomy include acute mastoiditis, chronic mastoiditis with its sequelae, and cholesteatoma.[1] Mastoidectomy can be performed in coordination with tympanostomy tube placement in patients with complications of chronic otitis media or acute otitis media. Mastoidectomy also serves as a key surgical approach for many otological procedures, including labyrinthectomy, endolymphatic sac surgery, facial nerve surgery, cochlear implantation, petrous apex lesions, and lateral skull base tumors.

Broadly, there are two major types of mastoidectomy: canal wall up and canal wall down.[1] Canal wall up mastoidectomy preserves the posterior bony external auditory canal, which separates the ear canal from the mastoid cavity. Typically, patients will undergo a canal wall up mastoidectomy for their initial episode of acute mastoiditis. Canal wall down mastoidectomies are usually reserved for patients who have had persistent chronic otitis media or recurrent cholesteatoma. The final decision regarding which type of procedure to perform depends on many factors, including the inherent anatomy, the overall extent of disease, management of risk to hearing and/or balance function, and the patient’s likelihood to follow up consistently.[2] A canal wall down the mastoid cavity requires patient cooperation with reliable follow-up for mastoid cleaning visits.

Contraindications

Patients who are medically unfit for elective surgery should not undergo mastoidectomy.

Equipment

Mastoidectomy is typically performed under general anesthesia in an operating room. Surgeons will need an operating microscope, a high-speed drill with appropriately-sized cutting and diamond-type burrs, otologic instruments, and other minor surgical instruments. Although facial nerve monitoring is not required, it is an often-used tool to improve the safety and speed of surgeons performing mastoidectomy.[3]

Personnel

Each operation requires a team approach for optimal outcomes. Aside from the surgeon, the team includes an anesthesiologist or CRNA, circulating surgical nurse, surgical technician, and sometimes a video technician. The surgical time-out ensures that all personnel in the room confirm the correct patient and plan for the day.

Preparation

Although a computed tomography (CT) temporal bone is not required prior to a mastoidectomy, some surgeons find that a review of the CT can be helpful when planning the surgery, particularly revision surgery.[4] If a CT temporal bone is available, it can be reviewed for any aberrant anatomy or congenital malformations. Any dehiscences of the facial nerve canal should be noted.

Prior to the induction of anesthesia, the need for facial nerve monitoring is discussed with the anesthesia team to make sure no long-acting paralytic is used.[1] After general anesthesia has been induced and the patient has been intubated, the bed is typically turned 180 degrees. Postauricular hair is shaved to allow a sterile field that is free of hair. Some surgeons will separate the hirsute areas out of the sterile field with adhesive drapes. Facial nerve monitoring is set up. Unless contraindicated, most surgeons will inject local anesthesia to reduce pain and promote vasoconstriction.

Technique or Treatment

The procedure begins by making an incision in the postauricular sulcus; an incision made popular by Sir William Wilde.[5] A longer postauricular incision can be used in revision cases to facilitate wider exposure.[6] Monopolar cautery is continued down to the level of the temporoparietal fascia. Then anterior and posterior flaps are elevated to allow a fascial graft if needed. A T or 7-shaped incision is then made through the periosteum with the top of the T at the linear temporalis. The periosteum is elevated to expose the spine of Henle and the ear canal.[7] A Wietlander can be used to retract the soft tissue away from the area of dissection.

The drill is brought into the field, and a cutting burr is used to mark the boundaries of the mastoidectomy. The boundaries include the tegmen superiorly, the sigmoid sinus posteriorly, the posterior bony external ear canal anteriorly, and the digastric ridge inferiorly. Bone is removed evenly from superficial to deep with the deepest portion of the dissection, both superior and anterior. Saucerization is encouraged to improve visualization and avoid working behind bony ledges. The identification of the lateral semicircular canal provides a landmark to notify the surgeon that the dissection has reached the depth of the facial nerve. The antrum is often identified at the deepest and most anterior part of the dissection. The tegmen can be followed anteriorly to assist with the identification of the antrum. Opening the antrum provides a ventilation pathway between the mastoid and the middle ear.

Cholesteatoma can extend from the middle ear to the mastoid through this area as well. A facial recess may or may not need to be created. The facial recess offers a second ventilation pathway between the mastoid and the middle ear. It also provides access for any middle ear work that needs to be done, such as cholesteatoma dissection, ossicular chain reconstruction, or cochlear implant insertion. The facial recess is a triangular-shaped opening into the middle ear delineated by the facial nerve posteriorly, the chorda tympani anteriorly, and the incus buttress superiorly. There are variations and modifications of the mastoidectomy, but once the lateral mastoid cells have been removed and the proper landmarks have been identified, the drilling can be concluded for a canal-wall-up mastoidectomy. A canal-wall-down procedure removes the posterior bony external auditory canal to create a large common cavity that is accessible in a non-surgical setting.[8] 

The wound is typically then closed with absorbable deep sutures to bring the periosteum back together. An additional layer of buried interrupted sutures is placed in the deep dermal layer. Finally, the epidermis can be approximated either by a superficial running layer or by a tissue adhesive. A Glasscock dressing can then be placed over the ear for one to two days.

Complications

Complications of mastoidectomy include facial nerve injury, hearing loss, vertigo, taste disturbance, cerebrospinal fluid leak, need for revision surgery, postoperative infection, and bleeding. Facial nerve injury is a rare but devastating complication with lifelong consequences to the patient.[9] Unfortunately, acute mastoiditis or chronic mastoiditis that is not treated appropriately can also progress and cause similar complications. Knowledge of anatomy and surgical practice is mastered to ensure facial nerve risk is decreased as much as possible.[10]

Clinical Significance

Patients who undergo mastoidectomy for acute mastoiditis may avoid complications of mastoiditis and will benefit from a faster clearance of the infection compared to antibiotics alone. Patients who undergo mastoidectomy for chronic diseases, such as infection or cholesteatoma, experience relief from chronic ear drainage and irritation. They, more often than not, will experience some improvement in hearing. They also avoid complications of chronic disease such as extemporal spread, especially toward the brain.

Enhancing Healthcare Team Outcomes

Patients that undergo mastoidectomy require an interprofessional team approach for optimal outcomes. Aside from the surgeon, the team includes an anesthesiologist or certified registered nurse anesthetist (CRNA), circulating surgical nurse, surgical technician, and sometimes a video technician. Good communication among all of the team members during the procedure will help to improve outcomes and minimize complications. Post-anesthesia care unit nurses monitor the patient closely after the procedure and good communication with the surgeon is vital should any postoperative complications arise. Postoperative ototopicals are often utilized. Sometimes enteral antibiotics are also prescribed. Pharmacy staff can enhance postoperative care by answering the patient’s questions regarding the medication. There are various randomized controlled trials regarding different techniques, training exercises, and postoperative care. Future high-quality studies will likely address indications for mastoidectomy.

Nursing, Allied Health, and Interprofessional Team Interventions

Skilled nursing is invaluable in the immediate postoperative period as the patient can sometimes experience pain, vertigo with nausea and vomiting, facial nerve weakness. Experienced nurses can notify the surgeon quickly of any facial nerve weakness. Additionally, American sign language interpreters can be utilized for patients with severe sensorineural hearing loss that may be undergoing this procedure.

Nursing, Allied Health, and Interprofessional Team Monitoring

An audiologist can aid with the monitoring of facial nerve function during the surgery. Active monitoring can alert the surgeon of his or her proximity to the facial nerve.