Mastoidectomy

Introduction

The mastoid, along with the tympanic, squamous, and petrous bones, form the temporal bone. A number of critical structures are either located within or traverse through the temporal bone. The temporal bone is located between the occipital bone posteriorly, the parietal bone superiorly, the sphenoid bone anterior medially, and the soft tissues of the neck inferiorly. The mastoid has a cortical osseous covering of varying thickness and is filled with very thin osseous septations, which form an air cell system similar in appearance to the ethmoid paranasal sinus.

A simple mastoidectomy consists of opening the mastoid cortex and identifying the aditus ad antrum.

A complete or canal wall up mastoidectomy necessitates removal of all of the mastoid air cells along the tegmen, sigmoid sinus, presigmoid dural plate, and posterior wall of the external auditory canal. The posterior wall of the external auditory canal is preserved.

A canal wall down mastoidectomy includes a complete mastoidectomy in addition to removal of the posterior and superior osseous external auditory canal. The tympanic membrane is reconstructed to separate the mucosal lined middle ear space from the mastoid cavity and ear canal.

A modified radical mastoidectomy is identical to a canal wall down mastoidectomy except the middle ear space and native tympanic membrane are not manipulated. This procedure is useful when there is no extension of cholesteatoma in the middle ear space or medial to the malleus head or incus body. This procedure is often indicated in patients with a cholesteatoma in their only or better hearing ear.

A radical mastoidectomy is a canal wall down mastoidectomy in which the tympanic membrane and ossicles are not reconstructed, thus exteriorizing the middle ear and the mastoid. The eustachian tube is often obliterated with soft tissue to reduce the risk of a chronic otorrhea. A skin graft can be placed in the middle ear to reduce the risk of mucosalization and otorrhea. ^{[1, 2]}

Key considerations

Successful and safe mastoid surgery requires routine identification of key anatomic structures including but not limited to the tegmen (middle fossa floor), sigmoid sinus, external auditory canal, lateral semicircular canal, and facial nerve.

A high-speed electric or pneumatic drill with various tools and attachments are used in conjunction with copious suction irrigation when performing mastoid surgery. Adequate irrigation serves to wash away bone dust generated by the drill to improve visualization. Irrigation also decreases the risk of injury from overheating of various structures traversing the temporal bone.

The operating microscope with various magnification setting provides the surgeon with improved visualization of anatomic landmarks and critical structures traversing the temporal bone.

Indications

Chronic otitis media (COM), with or without cholesteatoma, is one of the more common indications for performing a mastoidectomy. Patients with chronic otitis media often present with otorrhea and progressive hearing loss. Mastoidectomy permits access to remove cholesteatoma matrix or diseased air cells. In addition, mastoidectomy often provides access to the temporal bone which are more challenging to visualize through the external auditory canal (ie, supratubal recess, epitympanum, facial recess, perilabyrinthine air cells, retrofacial air cells).

Mastoidectomy is one of the key steps in placing a cochlear implant to rehabilitate acquired or congenital sensorineural hearing loss. A mastoidectomy allows the surgeon access to the middle ear through the facial recess. The implant electrode array is placed through the facial recess into a cochleostomy, which is drilled inferior and slightly anterior to the round window.

A mastoidectomy is often an initial step in removal of lateral skull base neoplasms, including vestibular schwannomas, meningiomas, temporal bone paragangliomas (glomus tumors), and epidermoids.

Complications of otitis media, including intratemporal or intracranial suppuration and lateral venous sinus thrombosis, often necessitate a mastoidectomy. ^[3]

Contraindications

Contraindications are as follows:

• Patients with medical conditions precluding general anesthesia.

• Patients with a poorly pneumatized mastoid (sclerotic) may make surgery more complicated, as certain anatomic landmarks may be more challenging to identify (otic capsule, facial nerve).

• Surgeons should proceed with caution in patients with anterior displacement of the sigmoid sinus and a low mastoid or middle ear tegmen (roof). These anatomic variants can be identified preoperatively with a temporal bone CT scan.

Anesthesia

Mastoidectomy procedures are typically performed under general anesthesia. The use of long-acting paralytics is not recommended because this does not allow the surgeon to assess the function of the facial nerve, either through a hand-held stimulator or a nerve integrity monitor.

The planned postauricular incision area is typically infiltrated with lidocaine or Marcaine with diluted epinephrine from the region of the mastoid tip up to the linea temporalis. Infiltration of the ear canal is also necessary in most cases to decrease bleeding. Some surgeons use diluted epinephrine (ie, 1:100,000) without anesthetic because this injected solution sometimes migrates into the middle ear in the vicinity of the facial nerve and may negate the benefits of facial nerve monitoring.

Equipment

An operating microscope with a 200-250 mm objective is used for either the entire procedure or once the superficial drilling has been completed. A number of microscopes are available, which are specifically designed for otologic surgery. These microscopes may have variable or fixed focal lengths and typically have multiple zoom settings. The microscope is typically covered with a sterile drape.

An otologic drill with various tools and attachments, including cutting and diamond burrs, is used for all mastoid surgery. Various manufacturers produce both pneumatic and electric otologic drills. The foot pedal may be controlled by the surgeon or the surgical technician, depending on surgeon preference. Initial bone removal is typically done with a large, round, fluted cutting burr. Burr size is progressively reduced as dissection proceeds medially into the temporal bone. A round diamond burr is typically used adjacent to critical structures to reduce the risk of injury.

Suction irrigators of various sizes allow the surgeon to rinse away bone dust to improve visualization and to reduce the risk of thermal injury from the drill.

Various microinstruments specifically designed for otologic surgery are used to dissect, elevate, remove, or transect structures in the temporal bone.

The facial nerve monitor does not eliminate the risk of a facial nerve injury during mastoid surgery. No substitute exists for thorough anatomic knowledge of the temporal bone in order to avoid complications, especially a facial nerve injury. Facial nerve monitoring can provide the surgeon with mechanical feedback during drilling and microdissection in the vicinity of the facial nerve. This feedback allows the surgeon to modify their technique intraoperatively, potentially avoiding an injury to the facial nerve. Paired electrodes are typically placed in the orbicularis oris and oculi, and a ground electrode is placed in the forehead or upper chest. If the integrity of the facial nerve is a concern, a stimulating probe can be used to confirm anatomic and physiologic integrity of the nerve. ^[4]

Positioning

The patient is almost always placed in the supine position with the head rotated approximately 30-45 º away from the surgeon, depending on the patient's neck range of motion. Careful communication with the anesthesia provider is important because, after induction, the patient is typically rotated 180 º. Positioning the patient's head as close to the edge of the bed adjacent to the surgeon provides a more ideal working distance for the surgeon. The patient's head is typically positioned at the foot of the bed so the surgeon can have their legs under the operating room table while sitting.

The patient's arm is tucked adjacent to their body with adequate padding because arm boards increase the working distance for the surgeon. The patient is secured to the bed with straps at the level of the chest and hips because rotating the operating table is sometimes necessary during certain portions of the procedure.

Complication prevention

A thorough knowledge of temporal bone anatomy and judicious use of landmarks typically allows the surgeon to avoid complications.

Identification of several surface landmarks, including the osseous external auditory canal, zygomatic root, spine of Henle, and mastoid tip, allow the surgeon to initiate bone removal in the correct location. Removal of bone along the lateral aspect of the middle fossa above the linea temporalis allows the surgeon to rapidly identify the dura, which is a critical first step prior to removing mastoid air cells. Saucerizing the edges of the mastoid cavity along the tegmen and sigmoid sinus improves visualization as dissection proceeds more medially into the temporal bone.

Copious suction irrigation removes bone dust, which can reduce visualization of landmarks and critical structures. Irrigation also reduces the risk of thermal injury to critical structures.

Moving the drill parallel to critical structures (as opposed to perpendicular) reduces the risk of complications especially when dissecting the facial nerve.

Hemostasis with bone wax or using a diamond burr prevents blood from obscuring visualization of landmarks and critical structures.

Appropriate drill tool selection, using the largest burr possible when considering the anatomical confines of the mastoid, prevents puncture type injuries into the dura, dural venous sinuses, facial nerve, and otic capsule.

The facial nerve monitor can provide mechanical feedback to the surgeon, which may avoid inadvertent injury to the facial nerve.

Preoperative imaging

A preoperative temporal bone CT scan provides useful information with respect to the location of the tegmen, sigmoid, sinus, facial nerve, and inner ear. CT scans are particularly useful if the normal anatomy of the temporal bone has been significantly distorted by disease or previous surgery. Identification of dehiscences in the tegmen or the sigmoid sinus may reduce the risk of a cerebrospinal fluid leak, encephalocele, copious bleeding, a rarely an air embolus. Fistulas into the otic capsule are readily visible on CT scans, which may alter the surgical planning and allow for improved preoperative counseling. ^[5]

A curvilinear postauricular incision from the mastoid tip to the linea temporalis is made 5-10 mm posterior to the postauricular sulcus. The skin and subcutaneous tissue is elevated off the mastoid periosteum and temporalis fascia with either sharp dissection with a scalpel or with monopolar cautery. The skin subcutaneous flap is elevated until the osseous external auditory meatus can be palpated through the periosteum. Some surgeons advocate minimal elevation of the skin and subcutaneous tissue off the periosteum to prevent postsurgical postauricular proptosis and malposition.

Once the periosteum is exposed, an incision is made along the linea temporalis from the zygomatic root to the occipital mastoid suture. Bleeding that is commonly encountered when making the anterior limb of this incision can be minimized by making the incision with a monopolar cautery. A perpendicular periosteal incision is then made from the linea temporalis to the mastoid tip. The periosteum is then elevated off the mastoid cortex up to the osseous external auditory canal. A retractor is then placed to hold the auricle forward.

An operating microscope with a 200-250 mm focal length lens is typically used once the bone work has started. Some surgeons advocate cortical mastoidectomy without the microscope and then use the microscope once the antrum has been opened. The microscope provides improved visualization with magnification at the expense of a narrower field of view.

Drilling commences at the level of and parallel to the linea temporalis. Copious suction irrigation is used to remove bone dust and to prevent thermal injury to the bone and underlying structures. Identification of the temporal lobe dura (tegmen), leaving a thin osseous covering, is an initial step of mastoidectomy.

Once the dura has been identified, the sigmoid sinus is indentified by drilling from the mastoid tip area to the posterior superior aspect of the tegmen. The sigmoid sinus has a blue tinge that is easily identified once enough air cells and cortical bone have been removed. Air cells along the posterior aspect of the external auditory canal are removed until cortical bone is identified. Koerner's septum, a thin plate of bone which is the lateral wall of the aditus ad antrum, is removed. The aditus ad antrum is typically centered over the cribriform area of the mastoid cortex, which is located just posterior and superior to the osseous external meatus.

Once Koerner's septum has been opened, the lateral semicircular canal is identified along the medial surface of the aditus ad antrum. The otic capsule bone covering the lumen of the semicircular canals is yellow and is almost always a different color than the adjacent bone. The lateral semicircular canal is a critical landmark in mastoid surgery, as the second genu of the facial nerve is almost always inferior to the mid point of the canal. The mastoid facial nerve can then be skeletonized once the lateral semicircular canal has been identified. The facial nerve typically courses in a more lateral and anterior position in its course from the second genu to the stylomastoid foramen. The zygomatic root cells superior to the osseous external auditory canal and adjacent to the glenoid fossa are often opened in patients with extensive cholesteatoma in the epitympanum and/or supratubal recess.

The middle ear can be visualized through the mastoid by opening the facial recess. The facial recess is defined by the mastoid facial nerve, chorda tympani nerve, and the incus buttress. The incus buttress is a bridge of bone that connects the lateral semicircular canal to the medial aspect of the osseous posterior superior external auditory canal. The short process is attached to the incus buttress with a small ligament. Opening the facial recess provides excellent visualization of the oval and round window, the anterior aspect of the sinus tympani, hypotympanum, and the protympanum. The facial recess is typically opened in cochlear implant surgery in order to drill a cochleostomy for insertion of the electrode array. Opening the facial recess in the setting of cholesteatoma is frequently beneficial, allowing the surgeon to remove disease from the region with direct visualization.

A canal wall down procedure entails removal of the superior and posterior osseous external auditory canal. The superior osseous ear canal is removed up to the root of the zygoma, and the posterior aspect of the anterior osseous ear canal is thinned out. The posterior osseous ear canal is removed down to the level to the mastoid facial nerve. The transition between the inferior osseous ear canal and the mastoid tip is smoothed out with a diamond burr. All air cells in the mastoid are removed to reduce the risk of postoperative cavity infections. A well-pneumatized temporal bone may necessitate removal of the mastoid tip and generous saucerization to decrease the eventual size of the cavity. The malleus and incus are typically removed if the ossicles are not in continuity or they are encased in cholesteatoma.

A meatoplasty is always performed in the setting of a canal wall down procedure to decrease the risk of developing moisture in the cavity and to facilitate future debridements. A meatoplasty entails removal of a varying amount of the conchal cartilage, postauricular periosteum, and adjacent skin of the membranous ear canal. Packing the meatoplasty with sponge dressing or strip gauze impregnated with antibiotic ointment facilitates favorable healing.

The tympanic membrane is typically reconstructed in most patients undergoing mastoidectomy for chronic otitis media with or without cholesteatoma. Temporalis fascia harvested through the postauricular incision early in the procedure is thinned out and dried prior to placement. The graft is trimmed depending in the size of the tympanic membrane perforation. A cartilage graft harvested from the tragus or concha is used in patients with eustachian tube dysfunction who are more prone to develop recurrent retraction. Cartilage is especially important in patients with a history of attic retraction cholesteatoma, as this disease commonly recurs if the lateral wall of the epitympanum is not reconstructed. Cartilage is also used to cover prosthetic ossicles to prevent extrusion through the tympanic membrane.

The postauricular incision is then closed in layers using resorbable sutures to close the periosteum and subcutaneous tissues. The skin can be closed with resorbable or nonresorbable sutures, skin glue, or Steri-Strips. A mastoid dressing is typically placed after completion of the procedure.

The videos below, shown in two parts, depict a complete mastoidectomy in a well-aerated and pneumatized temporal bone.

Postoperative care

A mastoid dressing consisting of gauze wrapped around the head or a neoprene flexible dressing is placed over the operative site to collect drainage from the ear and to decrease the risk of a wound hematoma. These dressing are typically removed 24 hours after surgery. Patients are typically instructed to keep the operative ear dry by covering it with a cup or placing a petroleum jelly covered cotton ball over the external ear canal while bathing.

Postoperative care typically entails a visit to remove packing in the ear canal 1-2 weeks after surgery. Patients can start topical antibiotic drops the following day after surgery or several days before the initial postoperative visit. The topical antibiotic drops serve a dual purpose of decreasing the risk of a postsurgical infection and to keep the packing moist to ease removal at their initial postoperative visit.

Patients undergoing a canal wall down procedure may have sponge packs, strip gauze, or resorbable packing in the mastoid cavity and/or meatus. This packing is often removed in the first 2 weeks after surgery. Canal wall down cavities can take weeks to months to completely heal. Intermittent debridements of the canal wall down cavity is required periodically (3-12 months), even after the cavity has completely healed.

Complications

Facial nerve injury

Facial nerve paralysis is the most dreaded complication of mastoidectomy. The incidence of this complication is fortunately exceeding low (~0.1%). Revision surgery, operator experience, extensive disease, osseous dehiscence of the nerve all increase the risk of an iatrogenic facial nerve injury. A transient facial weakness can be seen in the immediate postoperative period from local anesthetic, which enters the middle ear space adjacent to the facial nerve. This typically resolves within a period of 2-4 hours. Postoperative facial nerve paralysis that does not resolve after a few hours should be taken back to the operating room for exploration. A partial-thickness injury can be decompressed or observed, while a full-thickness injury should be repaired with a primary anastomosis or interposition graft. Drilling in the direction of the nerve with a diamond burr using copious irrigation significantly reduces the risk of a facial nerve injury. ^{[6, 7]}

Hearing loss

A temporary conductive hearing loss is very common after mastoidectomy, as blood, serous fluid, and packing frequently fill the middle ear space. In the setting of chronic otitis media with cholesteatoma, the ossicles are frequently eroded or absent, which results in a preoperative significant conductive hearing loss. Depending on the extent of the cholesteatoma and surgeon preference, an ossicular chain reconstruction with autologous materials or implants can allow for improvement in conductive hearing loss. A significant sensorineural hearing loss is rarely encountered in patients undergoing surgical intervention for chronic otitis media. Sensorineural hearing loss may arise from the high-speed drill contacting an intact ossicular chain, labyrinthine fistula, or noise exposure from the drill. ^{[8, 9]}

Vertigo

Vertigo and/or dizziness is frequently seen in patients undergoing otologic surgery. A number of factors contribute to these symptoms including the type and duration of anesthesia, cool irrigation adjacent to the labyrinth, and possible manipulation of the ossicles. Permanent vestibular symptoms are quite rare after mastoidectomy. An iatrogenic injury to the labyrinth is fortunately quite rare (0.1%). A labyrinthine fistula, especially involving the lateral semicircular canal, typically results in severe room-spinning vertigo that typically lasts up to 72 hours.

Labyrinthine injury carries an additional risk of sensorineural hearing loss. If a fistula is identified, intraoperatively suctioning over the area should be avoided and the opening should be covered with fascia immediately. Packing the fistula with bone wax or other materials may increase the risk of hearing loss or vertigo, especially in the setting of inflammation or infection. ^{[10, 11]}

Change in taste

The chorda tympani nerve travels through the middle ear space from its origin along the mastoid portion of the facial nerve. This nerve may need to be sacrificed if it is encased in cholesteatoma or inflammatory tissue. This nerve is typically removed in patients undergoing revision surgery or a canal wall down procedure. Patients typically notice an altered sensation of taste, typically described as a metallic or sour taste on the affected side. This sensation may be persistent but often resolves over a period of months.

Mastoid cutaneous fistula

Mastoid cutaneous fistulas are rarely encountered after mastoidectomy. This may be seen in patients who have undergone multiple postauricular incisions or have poor wound healing. This defect can be closed with local advancement or rotational flaps. ^[12]

Dural injury

Dural exposure without injury can be observed without repair. A suspected dural injury from drilling or a microinstrument should be carefully inspected even if a cerebrospinal fluid leak is not identified. A partial or nearly full-thickness dural injury should be repaired with either fascia, cartilage, autologous bone, or bone cement depending on the extent and size of the injury. If bone cement is used, it should be covered with fascia after it has dried. Failure to repair this may result in an encephalocele. A cerebrospinal fluid leak involving the middle fossa plate typically abates if the dura is closed primarily or is covered with a graft. Posterior fossa dural plate injuries can be more challenging to close and may require mastoid obliteration with fat or bone cement. Caution is advised using nonautologous materials in an infected field. A cerebrospinal fluid leak often necessitates admission, elevation of the head of the bed, and, in refractory cases, placement of a lumbar drain. ^{[13, 14]}

Vascular injury

The sigmoid sinus is one of the initial landmarks used to mastoid surgery. This large vessel can be injured with a drill or microinstruments. Injury typically results in copious venous bleeding. Since the sigmoid sinus is a low-flow system, gentle pressure with a moist cottonoid with Gelfoam or Surgicel over the injured area frequently results in the cessation of bleeding. Care must be taken not to displace packing into the sinus lumen with resultant embolization. ^[15] An arterial injury to the petrous carotid artery should be taken to interventional neuroradiology immediately. Gentle continuous pressure is required over the vessel until the bleeding is controlled. Temporary or permanent occlusion may be necessary if the vessel injury cannot be repaired primarily. ^[16]

Long-term monitoring

Patients with cholesteatoma need to be followed long term, as recurrence can occur in up to 50% of patients in whom the canal wall was preserved and up to 10% of patients in whom a canal wall down procedure was performed. Recurrent tympanic membrane retraction can usually be identified with otomicroscopy in clinic. Residual disease in the middle ear can sometimes be visualized in cases in which the tympanic membrane is translucent. Residual disease in the mastoid, epitympanum, hypotympanum, sinus tympani, facial recess, and protympanum are not typically visible on clinical examination.

Non-ECHO planar diffusion weighted magnetic resonance imaging (MRI) may in some cases detect pearl-like recurrences down to 2 mm in size. Sheetlike cholesteatoma recurrences are very difficult to detect with CT scanning or MRI until significant debris is present. ^[17] In patients undergoing canal wall up procedures, a second-look procedure 6-12 months after the initial surgery allows for assessment and removal of residual disease, and, in some cases, staged ossicular chain reconstruction if this was not undertaken at the initial procedure.

Patients with poor eustachian tube function or obstruction of the aditus ad antrum often develop a depression in the postauricular area. This depression has no significant long-term implications. Some surgeons advocate obliterating the mastoid with soft tissue flaps, bone dust, or covering the defect with titanium mesh to prevent skin depression into the mastoid. ^[18]