Mastoidectomy 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 c. Labyrinthectomy 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:

Mastoid Ectomy

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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

c. Labyrinthectomy

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

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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.


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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.

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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.


Complications of mastoid surgery:

1. Injury to ossicular chain

2. Injury to facial nerve

3. Injury to dura

4. Injury to lateral semicircular canal

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5. Injury to lateral sinus


COMPLETE MASTOIDECTOMY: an operation to exenterate the air cell system from the mastoid process of the temporal bone for the drainage of the suppuration in acute mastoiditis.

mastoidectomy with exenteration of the air cells and epitympanum but no involvement of the wall of the ear canal. Called also cortical m.

CORTICAL MASTOIDECTOMYCortical mastoidectomy, known as simple or completemastoidectomy or Schwartz operation, is complete exenterationof all accessible mastoid air cells and convertingthem into a single cavity. Posterior meatal wall is leftintact. Middle ear structures are not disturbed.Indications1. Acute coalescent mastoiditis.2. Incompletely resolved acute otitis media with reservoirsign.3. Masked mastoiditis.4. As an initial step to perform:(a) endolymphatic sac surgery(b) decompression of facial nerve(c) translabyrinthine or retro-Iabyrinthine proceduresfor acoustic neuroma.Figure 76.4 shows the various structures and landmarksseen after cortical mastoidectomy.AnaesthesiaGeneral anaesthesia.PositionPatient lies supine with face turned to one side and theear to be operated upper-most.Steps of Operation1. Incision. A curved postaural incision about 1 embehind but parallel to the retroauricular sulcus, startingat the highest attachment of pinna to the mastoid tip(Fig. 76.3B).In infants and children up to 2 years, the incision isshort and more horizontal. This is to avoid cutting facialnerve which is superficial in the lower part of mastoid(Fig. 76.3C).Incision cuts through soft tissues up to the periosteum.Temporalis muscle is not cut in the incision.2. Exposure of lateral surface of mastoid andMacEwen's triangle. Periosteum is incised in the line offirst incision. A horizontal incision may be made alongthe lower border of temporalis muscle for more exposure.Periosteum is scraped from the surface of mastoid andposterosuperior margin of osseous meatus. Tendinousfibres of sternomastoid are sharply cut and scraped down.A self-retaining mastoid retractor is applied.3. Removal. of mastoid cortex and exposure ofantrum. Mastoid cortex is removed with burr, or gougeand hammer. Mastoid antrum is exposed in the area of

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suprameatal triangle (MacEwen's triangle). In an adult,antrum lies 12-15 mm from the surface. Horizontal semicircularcanal is identified.4. Removal of mastoid air cells. All accessible mastoidair cells are removed leaving behind the bony plateof tegmen tympani above, sinus plate behind and posteriormeatal wall in front.5. Removal of mastoid tip and finishing the cavity.Lateral wall of the mastoid tip is removed, exposing musclefibres of posterior belly of digastric. Zygomatic cells situatedin the root of zygoma, retrosinus cells lying betweensinus plate and cortex, behind the sinus, are removed. Afinished cavity should have bevelled edges so that softtissue can easily sit in and obliterate the cavity.6. Closure of wound. MastoiJ cavity is thoroughlyirrigated with saline to remove bone dust, and the woundis closed in two layers. A rubber drain may be left at thelower end of incision for 24-48 hours in case of infectionor excessive bleeding. A meatal pack should be kept toavoid stenosis of ear canal. Mastoid dressing is applied .Post-operative Care1. Antibiotics started pre-operatively are continuedpost-operatively for at least one week. Culture swabtaken from the mastoid, during operation, may dictatea change in the antibiotic.2. Drain, if put, is removed in 24-48 hours and steriledressing done.3. Stitches are removed on the 6th day.Complications1. Injury to facial nerve .2. Dislocation of incus.3. Injury to horizontal semicircular canal. Patient willhave post-operative giddiness and nystagmus.4. Injury to sigmoid sinus with profuse bleeding.5. Injury to dura of middle cranial fossa.6. Post-operative wound infection and woundbreak-down.


Combined approachtympanoplasty

Modified radical mastoidectomy

Cortical mastoidetomy

What are the risks of surgery? As with all surgery, there are some associated risks. The risks are by and large the same as if the disease is left untreated.

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1. The hearing may be worse after the surgery or very rarely it may go altogether. In the two (occasionally more than two) stage (closed cavity) operation, the hearing is usually worse after the first operation and the chain of hearing bones are rebuilt at the second operation if there is no sign of further disease.

2. Tinnitus may occur or become worse after surgery but may improve as time goes on. 3. Taste disturbance: an altered or decreased sense of taste at the front of the tongue on

the operated side can occur because one of the taste nerves runs through the middle ear. This normally becomes less noticeable over the course of a year.

4. Dizziness occasionally occurs in the few days after surgery but rarely lasts more than a week.

5. Tinnitus: If tinnitus is present before the surgery it may improve after but occasionally it becomes worse. Rarely, it occurs for the first time after surgery.

6. Infection. Cholesteatoma is, by its nature, infected. Occasionally, the operation site can be infected post operatively and may increase the time taken for healing.

7. Numbness of the top of the ear. There is often some decreased sensation at the top of the ear which improves over time. This is because the nerve supply to the top of the ear is normally interrupted by the skin incision. Most people do not find this a problem. 8. Facial weakness. The nerve supplying the face muscles runs through the middle ear, normally in a bony channel. If the disease has damaged the bony channel or the nerve runs in an abnormal position or the bony channel has not developed fully then the nerve may be damaged causing a degree of facial weakness. This is very rare and there is less than a 1% chance of damage.

9. Leak of CSF. CSF is the fluid that surrounds the brain. Sometimes the disease erodes the bony partition between the top of the mastoid and the brain. This can leave the thick fibrous lining over the brain (the dura) exposed. Very rarely the dura is damaged while drilling and a leak of the CSF can occur. This would normally be repaired at the time of injury. The chance of a CSF leak is less than 1%. A small number of this 1% of patients who develop a CSF leak could develop meningitis, which would need antibiotic treatment.

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1 Spine of Henle. 2 Cribriform area. 3 Temporal line. 4 Posterosuperior wall of EAC. 5 Area to be drilled. 6 Tympanomeatal flap.7 Head of stapes. 8 Tympanomastoid suture.Cortical MastoidectomyThe aim of this procedure is to remove mastoid air cells and definethe limits of pneumatisation. One of the characteristics of thetemporal bone is its variability and this is especially so withpneumatisation. However, the antrum is always present and at thesame site and so provides a secure landmark no matter how scleroticor pneumatised the bone.

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9 antrum. 10 bone removal to get view of head of malleus. 11 arrowpoints to epitympanum.Begin posterosuperior to the EAC using a 5.5mm bur. Keep the wallof the EAC intact and drill in an anteromedial direction parallel to theEAC. Keep the walls of the cavity sloping so that you can see thepoint of your instrument as you progress medially. Beginners tend todrill down a narrow pit with vertical walls preventing a view of thebusiness end of their instrument. Always be alert for the sigmoidsinus. The antrum is the same distance medially as the TM so keepthe EAC clear of bone dust otherwise you will lose this landmark.Once into the antrum drill anteriorly with 2mm bur to get a view of theepitympanum and head of malleus (incus has previously beenremoved).

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12 Head of malleus. 13 Lateral semicircular canal. 14 Periantralcells. 15 Tegment tympani. 16 Bone to be removed to view sigmoidsinus.Now drill posteriorly to expose the sigmoid sinus.

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17 Sigmoid sinus. 18 Mastoid air cells. 19 Middle fossa plate (dura).20 Arrow points to sinodural angle (Citelli’s angle).Now remove the cells between the middle fossa plate and the sigmoidsinus to identify the sinodural angle.

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19 Middle fossa plate. 21 5mm bur. 22 Sinodural angle. 23 Centralmastoid tractDrill out the cells between the pink of the middle fossa plate a nd theblue of the sigmoid sinus. Do not leave any unopened cells here thatmay in a patient contain cholesteatoma.

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17 Sigmoid sinus inferiorly. 21 5mm bur. 24 Mastoid tip. 25 Openedmastoid air cell. 26 Intact posterior wall of the external auditory canal.27 Arrow points to a yet unopened cell.Remove all the cells from the mastoid tip and the cortical bone of themastoid tip itself. If an extensive cholesteatoma should extend this farinferiorly you need to remove all these cells. Removal of the tip allowssoft tissue to collapse into the tip area, obliterating what wouldotherwise be a sump where wax and keratin could collect.

To convert a cortical mastoidectomy to a modified radical theposterior and superior walls of the EAC have to be removed. Thetympanic membrane, handle of malleus and stapes and tympanumremain.

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Carotid artery

The carotid artery is vital, but not seen often in temporal bone surgery.

Occluding the carotid artery can lead to a stroke, often fatal. There are some situations in which this vessel is intentionally occluded but only after there have been extensive pre-operative investigations to see if this is feasible.

Digastric ridge

Digastric ridge is a ridge of bone, just deep to or medial to the mastoid tip.

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Anterior to that is the tip of the facial nerve.


Dura is the firm fibrous layer, which surrounds the brain, and separates the cerebro-spinal fluid (CSF) from the external environment.

It is above the level of the external ear canal, and is approximately in line with the level of the Zygomatic arch.

The intent of temporal bone surgery in most cases is to leave a very thin layer of bone over the dura.


The eardrum is also called the tympanic membrane.

The membrane separates the middle ear from the external ear.

Facial nerve

The facial nerve is the most vital structure within the temporal bone. It is also called the seventh cranial nerve.

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The facial nerve is either of a pair of nerves that originate in the pons, traverse the facial canal of the temporal bone, and pass through the parotid gland.1 They reach the facial muscles through various branches, control facial muscles, and relay sensation from the taste buds of the front part of the tongue.

1 The facial nerve is responsible for all movements on the same side of the face. It is particularly vulnerable in temporal bone surgery, because it is a structure that doesn’t become apparent until the surgeon is on top of it.

Most of the techniques for a cortical mastoidectomy will rely on the preservation of this nerve. Injury to the facial nerve will cause paralysis of the face.

There are no circumstances where it is preferable or even possible to injure the facial nerve and keep normal facial movement.

Henle spine

Spine of Henle is a surgical landmark, which indicates to the surgeon that they’ve reached the anterior superior canal of the ear canal in an intact canal wall procedure. It is also called the suprameatal spine.

Inner ear

The inner ear is primarily responsible for the senses of hearing and balance.

It contains the fluid-filled labyrinth which converts mechanical energy into neural impulses. The bony labyrinth consists of three main segments: lateral semi-circular canals, vestibule, and the cochlea.

The inner ear must be preserved in surgery.

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Labyrinth is a complex system of interconnecting cavities concerned with hearing and equilibrium.

Damage to the labyrinth will cause loss of hearing, which is permanent sensory neural hearing loss, because the inner ear has been damaged. It may also cause a loss of balance within the same ear.


Lateral semi-circular canal

Lateral semi-circular canal is one of three semicircular (lateral, posterior and superior) canals responsible for maintaining the sense of balance in the body. It is also known as the horizontal canal.

Lateral semi-circular canal is one of the most important landmarks in the temporal bone.

Mastoid tip

Mastoid tip is part of the bone where the sterno-mastoid attaches.

Sterno-mastoid is the major neck muscle that runs from the sternum up to the mastoid tip.

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Ossicles (malleus, incus and stapes) are bones which conduct sound from the tympanic membrane.

The handle and lateral process of the malleus is attached to the tympanic membrane and can be easily seen on the physical exam. The long process of the incus can often be seen through the posterior superior quadrant of the membrane. The stapes is attached to a foot plate which is in direct contact with the fluid of the inner ear.2

Inadvertently touching the ossicles with the drill will cause a large vibration, which will then be transmitted into the inner ear. That is likely to cause a significant permanent hearing loss.

Sigmoid sinus

Sigmoid sinus is an “S” shaped blood vessel on the temporal and occipital bones. It becomes continuous in its inferior limit to the jugular vein, which is the major blood outflow tract of the head into the neck. The sigmoid sinus ends up at the transverse sinus, at the other end of the temporal bone.

The sigmoid sinus should not be injured under normal circumstances. If it is inadvertently injured, there are well established techniques for dealing with the bleeding and the outcome for the patient is usually very good.

The sigmoid sinus can however be occluded if necessary.

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It is sometimes intentionally: (1)  divided, particularly when a glomus tumour is invading into the vessel.

2. compressed to gain access to the internal auditory meatus.

3. entered when there is a lateral sinus thrombosis. This vessel is involved in an inflammatory and infectious situation where the blood within it is clotted up, leading to a condition known as benign intracranial hypertension. It is sometimes the intent to open up and evacuate that clot.

Temporal bone

Temporal bone is an area which includes the ear canal and extends to the mastoid tip, and the air filled space known as the mastoid, which is encompassed within that bone.

Zygomatic arch

Zygomatic arch is a piece of bone that is lateral to the eye and the masseter bone, and defines the profile of the lateral part of the face.

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Cutting burr

The cutting burr is designed to remove large amounts of bone rapidly. It has flutes orientated like the lines of longitude on the globe. This means that the maximum speed or excursion of those cutting edges will be at the equator of the drill.

Always use the equator, or as close to the equator as possible. To drill end on with the burr will be a very counter productive exercise.

Cutting burrs with very few flutes (6 or so) are too aggressive for use in the mastoid region.

 Polishing burr

The polishing burr is generally covered with diamond paste or is a cutting burr with very fine flutes. The polishing action will be most effective around the waist of the drill.

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If the end of the burr is engaged with the specimen, there will be virtually no effect at the tip of the burr.

Drill selection

Choose a size that will be relatively large compared to the structure that you are trying to preserve.

To find a large structure, such as the sigmoid sinus, choose the largest burr you can. Even if a structure is small, it is important to choose the largest burr.

The most important structure in the temporal bone is the facial nerve and the burr needs to fit in with the constraints of the area which is being drilled. However if using a large drill, one that is even larger than the structure you are trying to find, you will usually find that the tubular structure will be found along a broad plane. If using a small burr there is a chance of drilling right through that structure without even identifying that you have found it.


Engaging the burr

The drill is running in a clockwise direction.

It is best if you not only have the freedom to use the equatorial side of the burr but also a view of this surface acting on the bone.

When finding a tubular structure start by removing bone that could jerk the burr down into the structure being sought. Then drill along the plane you have created parallel to the structure - not across it. The reason is that if the drill were to become in any way uncontrolled when drilling across the structure there is a chance of the drill damaging that structure.

Drilling along the structure identifies irregularities or deviations from a straight line. This provides a better guide to the depth of the target.


The sucker/irrigator is used to unclog and cool the burr. It is particularly important when using the diamond burr, which may create a lot of heat.

To keep a polishing burr free of bone dust requires that the burr is working in a puddle constantly.

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Facial nerve monitor 

This is a device that passes current through tissue to a return electrode, usually located somewhere else on the head and neck.

If there is neural tissue present then because neural tissue is a pathway of less resistance for electricity this will activate the nerve and the face will move.

The movements in the face are detected by electrodes, placed on the face usually around the mouth and lateral to the eye.


Uncover the antrum

Choose an appropriately sized burr.

Thin down the external ear canal. A thin external ear canal is preferable over a particularly thick one. The reason is this gives you best line of sight to visualise important structures within, such as the incus and gives you the proper orientation to the facial nerve.

Identify the dura of mastoid region

The dura of the tegmen tympani is not smooth. It has irregularities corresponding to the gyri on the surface of the brain and it is curved. The most inferior part of the tegmen dura is at the most lateral part of the region. It curves down at the lateral extremity of the middle cranial fossa. As you extend drilling into the mastoid cavity you will notice the dura actually curves upwards and requires reorientation of the head if the equator of the burr is to be kept visible. Note that if you don’t remove that bone over the dura deep in the cavity, you will have a more limited access to structures like the incus. The space for the drill will be somewhat restrained.

The dura over the sigmoid sinus balloons out smoothly and if the equator of the burr is to be kept visible the head should be rotated towards the surgeon.

The intent of temporal bone surgery in most cases is to leave a very thin layer of cortical bone over the dura.

Identify the lateral semi-circular canal

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Several drilling techniques are required to clear pneumatised bone from the sinodural angle, over the antrum, and into the epitympanum and its lateral extension. As you drill anteriorly towards the epitympanum and find that the drill is too large for the task, change to a burr that will fit easily into this space.

In the superior part of the region you can use a large sized burr because you are not likely to damage the vital structures particularly in the air filled space. The orientation of the drilling should be changed in the sino-dural angle. It has no vital structures.

In the region between the tegmen and the external ear canal use a burr that is large enough to occupy the space between them. Apply the drill first at the level of the antrum and use its shoulder to remove the bone with an outward sweeping action.

Identify the incus

Re-orientate to the surgical position. Anterior to the lateral semi-circular canal is the short process of the incus. Always use a diamond burr in the vicinity of the structure and you could use a slightly smaller burr so that you can see around it.

Be aware that the incus can be immediately underneath this area, so run parallel to the external ear canal and just keep taking the very leading edge of bone away. In this situation the disadvantage of using a large burr is that you might not be able to see around it. You should see the incus. Remove the bone nearby in a very controlled manner, by using a slightly smaller burr and drilling along the edge of the bone. You could use a little more magnification at this stage before the dissection proceeds any further. You can also rotate the patient away. In doing so it becomes very clear that the incus is close by.

Identify the facial nerve

The facial nerve is inferior to the lateral semi-circular canal, as it passes from its vertical segment through to its horizontal segment. We know that the facial nerve is never lateral to the lateral semi-circular canal. It is always medial. And that is best seen by rotating the temporal bone.

The line of the short process of the incus is virtually that of the facial nerve at its knee point or genu. The first genu is seen at the anterior end of the first dissection, and here the nerve passes very sharply before it enters the internal auditory meatus. The second genu passes from the horizontal tympanic segment to the vertical segment or mastoid segment.

So the nerve will be inferior to the lateral canal, it’s roughly along the line of sight of the incus, and is anterior and deep to the sigmoid sinus. If you orientate the bone back into the surgical position, and safely drill along the anticipated line of the mastoid or vertical segment of the facial nerve, you can expect to see it within the bone, before the drill engages it. So make sure that the dissection is carried well into the mastoid and inferiorly to the surface of the digastric ridge.

Keep a thin layer of bone over the external ear canal so that if possible both the line of sight down the external ear canal and the posterior portion of the dissection and the anterior rim of the dissection, ie the posterior part of the external ear canal are both visible. This is the best orientation.

You have now set up an orientation where drilling along this line of sight will take you directly to the facial nerve. The facial nerve is most safely found in its vertical or mastoid segment, not at the genu.

Since the anterior wall of the external ear canal is relatively thin, drill along the anticipated line of sight of the nerve, using long brushstrokes keeping away from the genu. Try to find the nerve in its vertical segment prior to finding it at its genu. Once you have a much clearer impression of a redder change of colour, there is much better evidence that you are approaching the facial nerve.

Use the facial nerve monitor probe again and you should hear the facial movements and also see them marked on the screen. If you move away from the nerve to another piece of bone, you won’t have the same effect. Change to a slightly smaller burr, so it will fit in the region.

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Key points

When drilling behind the semicircular canal, it is important to use long brush strokes and to keep an even depth. This keeps a widely open valley. Run around the edges of this valley, deepening slightly and taking away the outer layer of the cortical bone.

Do not allow the dissection to become too deep in one particular place.

Drill along the dura, using long strokes running from anterior to posterior, or the reverse, depending on the handedness of the surgeon. Appropriate techniques include using often shorter and sharper brush strokes to define the plane of interest.

Leave a very thin layer of bone over the dura and the sigmoid sinus. If you inadvertently uncover the dura, this is not usually a big problem provided the area that is left uncovered is relatively small. The same can be said for the sigmoid but the risks are of causing a bleed if you enter the sigmoid.

Adjust the degree of water escaping from the sucker/irrigator so that the operative field is moist at all times.

Rapid vs Gentle bone removal

The mastoid bone is surrounded by structures that must be left intact but there is scope in a dissection for both rapid bone removal and gentle polishing action. The cortical bone of the surface of the mastoid bone may be removed aggressively when the dissection is well forwards of the sigmoid sinus. Parts of the cellular pneumatised bone may be removed aggressively when the cortical bone has been removed enough to

establish the area of the pneumatised bone. 

Use burr equator

Cutting burrs are most effective if the equator is used. Adjust the handpiece so the equator of the burr is always visible against the bone. In this way the burr cuts most effectively and safely, with the least pressure. Avoid using the pole of the burr. Select a burr with sharp flutes and keep them clean through constant irrigation. Note that the direction of the sweep is different when bone is removed quickly from each of the walls of a deep slot.

Use largest burr

Select the largest burr that will fit into the site easily. Use a sweeping action that is as long as possible. When completing landmarks see that it will be possible to execute a sweeping action along the length of the next structure to be identified. In this way you will detect any irregularities and its curvilinear nature.

Small areas of the dura may be exposed by this technique but the drill will not penetrate it. Gain the confidence that with this technique the position and depth of most the next structure will be apparent well before the structure itself is visible. In practice the dura is often exposed deliberately to determine the thickness of the cortical bone in the region. It is not acceptable to expose the skin of the bony ear canal, or the lateral semicircular canal.

The facial nerve should only be exposed when the dissection is prepared for this step.


Step 1. Prepare the surgical site

Shave the region of the incision. Palpate and mark the position of the temporal line and incision. Apply antiseptic to the region of the ear.

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Apply the facial monitor electrodes: red electrode lateral to the lips and blue electrode lateral to the eye. Tap the patient’s face to check that the facial monitor is working well.

Apply and secure absorbent woven drapes and an adhesive transparent drape with water trap. Secure the following: suction for the wound and trap, monopolar diathermy, and bipolar diathermy.

Check and drape the microscope.

Step 2. Expose temporal bone

Confirm the site of the mastoid process.

With a scalpel, incise the skin layer and dissect skin free of the deep fascia.

Expose the root of the zygoma and display the spine of Henle, while working to secure haemostasis.

Incise the deep fascia based on the flap required and elevate it based on the ear canal.

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Step 3. Identify the sigmoid sinus

3.1 With a cutting burr inscribe three lines in the mastoid region that demonstrate the likely position of the sigmoid sinus, floor of middle fossa and facial nerve. The first is the temporal line. The second is a tangent to the external ear canal from the mastoid tip to the first line. The third is parallel to where one expects to find the sigmoid sinus.

Step 4. Identify the antrum

4.1 Continue removing cells evenly in this area up to the limits defined by the facial nerve and middle fossa inscriptions. Concentrate on defining the cortical bone over the sigmoid sinus with sweeps that pass from the middle fossa to the tip of the mastoid process.

4.2 Continue in this way into the depth of bone while defining the feature of sinodural angle. If there is a Korner septum the lateral surface of the lateral sinus will appear to form a barrier nearly as far as the ear canal. Remove cells over this plane till a gap is found near the ear canal or floor of the middle fossa. Remove the septum when the areas of cortical bone over the middle fossa and lining the mastoid process have been defined.

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Step 4. Identify the antrum

4.1 Continue removing cells evenly in this area up to the limits defined by the facial nerve and middle fossa inscriptions. Concentrate on defining the cortical bone over the sigmoid sinus with sweeps that pass from the middle fossa to the tip of the mastoid process.

4.2 Continue in this way into the depth of bone while defining the feature of sinodural angle. If there is a Korner septum the lateral surface of the lateral sinus will appear to form a barrier nearly as far as the ear canal. Remove cells over this plane till a gap is found near the ear canal or floor of the middle fossa. Remove the septum when the areas of cortical bone over the middle fossa and lining the mastoid process have been defined.

Step 6. Identify the facial nerve

6.1 Identify the bone over the lateral semicircular canal.

6.2 Remove cellular bone from the deep aspect of the ear canal and the gutter between the sigmoid sinus and facial nerve.

6.3 Safe dissection of the facial nerve uses the incus and lateral semicircular canal landmarks above and the digastric ridge below. These in turn require that the position of the middle fossa, sigmoid sinus and outer ear canal are demonstrated.  Make a point of carefully removing the cells against the canal wall that form a slope from the digastric ridge to the incus.

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6.4 In a well pneumatised temporal bone there are two more features that indicate the position of the facial nerve. The sentinel cell marks the start of the posterior tympanotomy through which fluid may be aspirated from the middle ear.

6.5 A series of cells pass medial to the facial nerve toward the jugular bulb.


Step 7. Extension to posterior tympanotomy

7.1 The dissection for the posterior tympanotomy should start by displaying the origin of the chorda tympani and the position of the facial nerve.


Using the cutting burr

Using the cutting burr end on will generate a lot of heat. It is slow and inefficient. The heat will damage surrounding structures including:

the bone itself and its viability, and the facial nerve. Many facial nerves have ultimately been injured and facial movement lost because of heat


Entering the antrum

The size of the burr required for this task depends on the space between the external ear canal and the dura. Use a burr that is sufficiently small to fit within this space. Not to do so will likely damage the external ear canal.

Also it is important to have the external ear canal sitting in an orientation where you can see the posterior aspect of the canal wall. If you are looking straight down the external ear canal, you need to be aware that there is a posterior bowing of this canal, which means that there is still a chance that the drill could go through the mastoid and completely drill away a portion of the canal and damage this structure.

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Thinning the external ear canal

If you drill through the bone of the external ear canal, you will find yourself of course, in the ear canal. The problem with that is, it is likely that skin will fall then into the mastoid air system, and that you can create a cholesteatoma. Also there is a risk of skin becoming completely buried in the mastoid and not then visible from observation.

If you leave a great deal of bone along the posterior aspect of the external ear canal you can be fooled into thinking that the facial nerve is in a different location to what it really is. If you inadvertently made a dissection too deep on the posterior areas near the mastoid tip you could arrive at the facial nerve before you had found two other landmarks (lateral semicircular canal and incus) that are known to be critical in terms of a safe location of this structure.

Identifying the dura

In cortical mastoidectomy, you will be thinning the bone over the dura and it’s quite possible that some dissections will expose the dura. This is usually not a problem. It’s not easy to go through the dura with a drill. You have to have the drill engaged on the dura for more than an instant in this circumstance for that to happen. You shouldn’t be overly worried when you are drilling near the dura that you will inadvertently go straight through it. This is actually very difficult to do, though worth mentioning that under some situations, the bone overlying the dura will be missing. In fact the dura may be hanging down into the mastoid cavity. Always be aware of that possibility and if there has been previous infection or inflammation in the mastoid, and previous surgery, there can be scarring between the dura and there can be fibrous tissue surrounding the dura that can present much more of a risk to the naïve surgeon who can be drilling along not recognising this.

Not being aware that there is some bone missing, and not realising the fact that the dura is immediately behind the scar tissue, the surgeon may cause a breach in the dura and therefore a CSF leak. Part of the training for the cortical mastoidectomy is to be able to identify the general direction and orientation of the dura, so that the position of this particular structure can be predicted by the surgeon and that their drilling technique will be in an orientation that will take them parallel to the structure and therefore they will be highly unlikely, even in cases of unusual pathology to inadvertently damage or cause a tear within the dura.

Repair the dura or exposure of the ear canal with a fibrous sheet of temporalis fascia supported by bone paté.

Identifying the incus

Inadvertently touching the short process of the incus is likely to cause a sudden and possible permanent sensory hearing loss.

Inadvertent drilling in this area (superiorly the dura and inferiorly the incus) when on the dura might mean making contact with the incus and in doing so it is quite possible that there might be an injury to this structure.

Prevention of Infection

 EA2. Antibiotic and iodine sensitivity

 EA3. Bleeding

 EA4. Cerebrospinal fluid leak

 EA5. Post operative facial weakness

 EA6. Cut facial nerve