The Simple Mastoidectomy

The Cortical Mastoidectomy

The cortical mastoidectomy is also known as the simple mastoidectomy or complete mastoidectomy.
The purpose of the mastoidectomy is to remove nearly all the air cells in the petromastoid bone. It is the most basic operation of the ear and when done correctly provides access to all the vital structures of the ear.

Indications for cortical mastoidectomy

Removal of infected air cells as seen in coalescent mastoiditis.
It provides an approach to structures like the endolymphatic sac, facial nerve, the labyrinth, the posterior fossa and its contents, the jugular bulb.

Type of Incision

The authors prefer the postaural incision. However some surgeons prefer to use the endaural incision.

Anesthesia

The surgery can be performed under general or local aesthesia with sedation. General anesthesia offers the surgeon more control over the patient and the operative site. A struggling patient under local anesthesia can frustrate even the most experienced surgeon.

Are CT scans necessary before performing a cortical mastoidectomy?

A CT scan is necessary because:-

It alerts the surgeon in advance as to the kind of anatomy that will be encountered. Distortions and anomalies in anatomy will be clearly seen.
The extent of disease will be clearly delineated.
A comparison with the contralateral ear is possible.
Clinical symptoms and signs can be correlated with CT scan findings.
It can help determine if the disease has extended beyond the confines of the temporal bone.
It is necessary for documentation of disease prior to surgery.
It serves as a medicolegal document in the event of litigation.

Boundaries of the cortical mastoidectomy

Superior:- The tegmen of the middle fossa.
Posterior:- The sigmoid sinus
Inferior:- The digastric ridge
Anterior:- The posterior canal wall.
Medial: The bony labyrinth
It should be understood by the surgeon that these boundaries will vary according to the pneumatization of the temporal bone. In a large well pneumatized mastoid air cells may extend well beyond these structures. Structures like the dura, sigmoid sinus and semicircular canals serve to alert the surgeon to identify these structures around which drilling may proceed.

Surgical Technique

After prepping and draping the patient in the standard way using aseptic precautions under general anesthesia a postaural incision is taken.
A graft if needed is taken from the collagen fascia just lateral to the temporalis fascia. If that is not available then an adequate graft is taken from the temporalis fascia.
A mastoid retractor is placed to keep the incision open to provide adequate exposure of the mastoid.
The temporal line and the spine of Henle is identified and drilling is commenced. These are important landmarks to approaching the mastoid antrum.
Some surgeons preserve the bone dust that has accumulated as bone pate for future usage.

Tips

Start with the biggest size burr
Don’t drill the bone with the burr pressed in one direction. The burr can drill into the bone and pass into a vital structure.
Use stroking movements pressing the burr firmly against the bone.
Create a large opening so that it allows better visualization of structures beneath.
Pour water continuously while drilling. This helps cool the heat generated by the burr and prevents the blades of the burr from getting clogged with bone dust.
Use the microscope all the time. Excellent visualization is mandatory for ear surgery. Keep shifting magnification to identify various structures as they are exposed.

Purpose of the first stage of surgery

The purpose of the first stage of surgery is to correctly identify the mastoid antrum, enter it, widen exposure to it and then widen the mastoidectomy. The key to a successful mastoidectomy is correct identification of the mastoid antrum.

Tips

The mastoid antrum is the single largest air cell in the temporal bone.
The bulge of the lateral semicircular canal is seen in the floor of he antrum. The color of the lateral semicircular canal is ivory and the bone appears to be more compact.
When exposed further anterior the incus can be visualized.

Purpose of the second stage of surgery

The purpose of the second stage of surgery is to delineate the boundaries of the cortical mastoidectomy.

Tips

Do not drill over the bony labyrinth.
Do not allow the rotating burr to touch the incus. Vibrations transmitted to the ossicles can cause permanent sensorineural hearing loss.
Thin the posterior canal wall but do not fracture it or perforate it.
Open up the aditus so that the body of the incus as well as the head of the malleus can be visualized.
Skeletonize the tegmen. The dura can be seen as a pinkish glow through the bone
The sigmoid sinus can be seen as a bluish glow through the bone.
Identify correctly the digastric ridge.

What are the likely problems that can be encountered during the cortical mastoidectomy?

Bleeding can be encountered. This can be controlled by drilling over the blood vessel with a polishing burr. On some occasions bone wax may be needed. Rarely electrocoagulation may be needed. This should always be done using a bipolar cautery machine. If an ooze is present then this can be stopped by using gel foam pledglets soaked in adrenaline.
On occasion the surgeon can inadvertently expose dura during cortical mastoidectomy. The surgeon must recognize that the structure he has exposed is the dura. If observed carefully it can be seen to be pulsatile and of a different consistency from that of the surrounding tissue and will be crisscrossed by numerous blood vessels. If the dura is exposed and a cortical mastoidectomy is performed it can be left alone provided the dura has not been traumatized. If it is traumatized then this could result in a CSF leak. If a CSF leak is created it must be identified immediately. The dural exposure can be closed using cartilage to seal off the dura from the environment. Antibiotics are given and a lumbar drain inserted for a few days until the surgeon is confident that the leak has sealed.

Trauma to the Sigmoid Sinus

Trauma to the sigmoid sinus can result in torrential bleeding. The surgeon should not put gel foam into the lumen of the sigmoid sinus as this could get dislodged and get embolized. If the tear is small then bipolar coagulation can on occasion halt the bleed. Bone wax can be effectively used to stop the bleeding.
If the bleeding is significant and is not controlled with the first 2 methods then the surgeon may need to pack the sigmoid sinus extraluminally with surgical proximal and distal to the tear.
Once the superior, posterior, anterior and inferior limits of the cortical mastoidectomy have been correctly identified the surgeon may then consider the cortical mastoidectomy complete.
The key to correct cortical mastoidectomy lies in creating adequate exposure. The surgeon should first start by using the largest size in cutting burrs. Always create a large exposure before drilling further so that the surgeon can avoid inadvertent damage to structures beneath. Always achieve hemostasis before drilling further. When the mastoidectomy is complete the surgeon should wash out all the bone dust that has collected in the mastoid cavity. Bone dust can clog the aditus and interfere with patency of the aditus ad antrum.
Before ending the surgery the surgeon should ensure complete hemostasis.

Closing up after Mastoidectomy

Careful reposition of the vascular strip if it has been taken is vital. If it is repositioned carelessly and is inadvertently placed in the mastoid cavity it can result in cholesteatoma. If not repositioned properly it can delay healing with granuloma formation.
Once hemostasis has been achieved the incision is sutured in layers. A mastoid bandage is placed and this bandage is usually removed after 7 days. The patient returns for removal of sutures. Ear drops are given which should be placed into the external canal. This helps to removed gelfoam which has been placed there. The senior author prefers to place an antibiotic ointment into the canal. These are usually aqueous based ointments and liquefy at room temperature. The ointment liquefies and thus gets evacuated after a week and prevent bacterial colonization of the canal.
Patients can wash their hair safely following suture removal with instructions that they should not allow water to enter their external canals. Results of surgery can only be determined a month to a month and a half following surgery.

References

Glasscock Me, Shambaugh GE (2003): Surgery of the ear. (Eds) Glasscock ME and Gulya AJ. Publishers BC Decker, Ontario.
Brackmann DE, Shelton C, Arriaga MA (!994): Otologic surgery. WB SaundersCompany Ltd.