Perforations of the Tympanic Membrane
In this tutorial you will read about perforations in the eardrum. The word ‘perforation’ simply means ‘a hole’. Perforations are very varied in how they appear and behave. They come in a variety of sizes and can be in any place on the eardrum; they may be inactive and dry or they may be active and wet; they may be associated with hearing loss or normal hearing; they may be caused by trauma or infection.
In the tutorial on anatomical terms you learned how we describe the position of perforations and about the difference between central and marginal perforations. You should re-read that tutorial to refresh your memory. This tutorial will build upon what you already know and will discuss the pathology associated with perforation, the symptoms and signs associated with them and how we treat them. It will also give you some knowledge on how surgeons plan their surgery.
A perforation is a hole in the eardrum. It is usually caused when an infection in the middle ear bursts out through the drum and the drum does not heal afterwards. This is particularly likely if the eardrum is already thin due to the presence of middle ear fluid (e.g. glue ear in children) or if the Eustachian tube doesn’t work well and there is longstanding negative middle ear pressure.
Longstanding middle ear effusion and poor Eustachian tube cause the eardrum to become thinner. This is called drum atrophy. Atrophic drums are weaker. Atrophy may only happen in a small part of the drum or may be present in the entire drum.
The next picture shows atrophy of a small part of the eardrum.
In the postero-inferior segment of the drum there is an atrophic patch that looks darker than the rest of the drum
The middle layer of the drum is missing here and the drum looks thinner. It is sometimes called a ‘dimer’ and can be mistaken for a perforation.
Atrophic sections of the drum may become retracted if negative middle ear pressure continues due to poor Eustachian tube function. A retraction is just a thin piece of drum that has been sucked into the middle ear space.
Atrophic eardrums are thin and weak and they are much more likely to perforate if a middle ear infection occurs. They also lead to retractions and cholesteatoma. These topics will be covered in the next tutorial.
Symptoms of a perforation
Some perforations cause no problems and the patient doesn’t know that they have one. However, other patients suffer with recurring discharge and loss of hearing due to the perforation. Very occasionally a perforation will also lead to cholesteatoma and they can be complicated by meningitis and brain abscess.
The presence of a hole in the eardrum may allow bacteria laden water to get into the middle ear. This will cause an infection, which will produce a discharge that may be yellow, green or blood stained. The discharge is sometimes of a high volume.
Another way in which the ear may become infected is following an upper respiratory infection.
Patients who have a perforation must be instructed to keep their ears dry. This may mean avoiding swimming and taking care during bathing and hair washing.
Patients with a perforation often have hearing loss as well. This is usually a conductive hearing loss and is caused by loss of surface area of the drum. Remember that the size of the drum compared with the oval window is one of the reasons that the ear amplifies sound.
Another reason is that infections that caused the perforation will sometimes damage the ossicles as well. This is particularly a problem for the incus and the incudo-stapedial joint and is more common when the perforation is situated in the posterior half of the drum.
A third reason for deafness is the loss of the ‘baffle effect’ When there is a perforation sound can enter the middle ear directly and make the round window membrane vibrate. This has the effect of cancelling out vibration at the oval window and reducing the sound energy entering the cochlea. There is a section on the Baffle Effect later in the tutorial.
Discomfort, dizziness and tinnitus.
These are all possible in perforations especially when there is an infection present. Pain is not usually severe. Any middle ear infection that is associated with vertigo must be treated very seriously and referred to the hospital without delay. We will learn more about vertigo in future tutorials. Tinnitus is possible in the presence of a perforation whether it is infected or not.
Treatment of perforations
Medical treatment is divided into preventative management and treatment of an acute infection. Surgical treatments are also possible.
The presence of a perforation means that the patient is more likely to get infections in the ear. It is important to tell them that they must keep their ears dry. This is difficult when the patient is a child. Water can get in the ear during swimming, using a shower or while taking a bath. Putting something into the ear during these activities can prevent infection from occurring.
Treating the infection when it is present is something with which you are very familiar. You use careful and thorough aural toilet (using cotton wool or suction under the microscope) and topical antibiotics such as ciproxin drops. You should refer to the CSOM guidance sheets for more details on this.
In the last section of this tutorial, I want to discuss what surgery can be done for perforations.
Myringoplasty is an operation to repair the eardrum. It is the easiest type of a wider range of operations known as tympanoplasty. Tympanoplasty comes in a number of different types that involve repair of perforations and rebuilding a route for sound to enter the inner ear. This section gives an overview of these operations together with some ideas as to how surgeons decide which cases to operate on and when to do the operation.
Types of operation.
In the text above I said that myringoplasty is a simple type of tympanoplasty. The table below lists the types of tympanoplasty and describes what the operations do.
There is another middle ear operation that repairs the ossicles and this is called ossiculoplasty. It can be done by itself when the eardrum is healthy or may be added to a bigger ear operation.
How do surgeons decide when to operate?
In deciding whether to operate on a patient the surgeon must take into account a wide range of issues. These include the following:
1. Is the ear dry?
An operation on a wet or infected ear is not as successful as one on a dry clean ear. Surgeons will not usually want to operate on an infected ear so it is important that the ear is treated properly before the surgery.
Some ears get infected very often and it can be difficult to get the operation done because of this.
2. Have the causes of infection been removed?
If the patient has sinus or nasal disease that make infection in the ear more common the surgeon will want to treat these first. This may make the chance of success for the tympanoplasty higher.
If the patient has symptoms of chronic rhinosinusitis remember to treat this as well as the ear infections.
3. How good is the patient’s other ear?
Surgery has risks. One risk is that the patient may be made deaf by the operation. If the patient’s other ear is already deaf then it would be unwise to operate on the perforated ear because that may become deaf too.
Before referring for an operation on the perforated ear be sure to do a hearing test to find out if it has better hearing than the other ear. If it does, the surgeon is unlikely to want to operate.
4. Size and site of the perforation.
Perforations in the anterior half of the eardrum do not repair as easily as those in the posterior half. It is also widely believed that large perforations are harder to treat than smaller ones.
5. Age of the patient.
Many surgeons avoid operating on very young children. This is because their immune systems are not fully developed and they are prone to infections in the nose and sinus. They believe that when the child is older the success rate of surgery is higher.
Poor health, cholesteatoma, and the presence of complications of middle ear disease such as meningitis or brain abscess are all reasons not to operate.
Not all surgeons are able to perform middle ear surgery or they may be working in a hospital that does not have the equipment needed to perform the operation. Some surgeons doubt their skill or have an illness that prevents them performing middle ear surgery. Any of these reasons may stop the surgeon from offering surgery.
It is important to know who the good ear surgeons are and to refer patients to them in preference.
How is the operation done?
There are a number of different ways that a myringoplasty (Type 1 tympanoplasty) can be done. The way chosen will depend upon the surgeon’s skill, the size of the perforation, the health of the ossicles and the size of the patient’s outer ear canal.
There are many videos of myringoplasty on Youtube. This one shows the basic steps well:
The surgeon has made an incision behind the pinna and pulled the ear forwards. He then opens the skin of the ear canal from behind to show the eardrum and perforation. The video calls this a posterior meatotomy.
The edges of the perforation must be freshened. This means that the edges are removed so that they bleed a little. The surgeon uses a combination of different instruments including a needle and sickle knife and some forceps.
Once he is happy with this he raises a flap of skin up so that he can get into the middle ear behind it. He then pushes the skin flap out of his way and takes his graft that has been specially dried so that it is stiff, and pushes it into the middle ear. (A graft is a piece of tissue that is taken from one place and moved to another place or person).
He them puts the ear canal skin flap back into its original position. The final result can be seen at 7min 30 seconds into the video.
The graft is usually taken from fascia on the surface of the temporalis muscle. Fascia is a type of tissue that is made mostly of collagen. It is thin and strong and is perfect for repairing holes in an eardrum. We can also use pieces of vein, periosteum and perichondrium. All these tissues make good grafts.
The next few pages show some of the steps in diagrammatic form.
Remember that the eardrum has three layers: an outer epithelium, a middle fibrous layer, and an inner mucosal layer.
When a perforation appears the middle fibrous layer disappears and the outer and inner layers join one another.
The surgeon must ‘freshen’ the edges of the perforation. This is usually done with a needle as shown.
By doing this the surgeon makes the perforation larger but it is a very important step and without it the operation will fail.
Once the edges are freshened the skin of the ear canal is cut. This will allow the surgeon to get under the skin and lift it up.
In this picture, the skin is being lifted. The surgeon will lift the skin as far as the eardrum.
Once the eardrum has been reached the surgeon will lift the annulus of the drum out of its groove and enter the middle ear.
This will create a way into the middle ear for the graft to be inserted through.
A graft is then placed under the perforation. It is on the medial side of the eardrum and is shown as a brown line here.
As a final step the surgeon places a dissolvable sponge into the middle ear. This pushes the graft against the medial side of the perforation and helps the graft to stick in place.
The sponge will disappear in a few weeks and by that time the drum will have healed.
The Baffle Effect
Below is a diagram with three panels.
Panel A is the normal situation
Panel B is an ear with a perforation but with intact ossicles
Panel C shows an ear with a perforation and diseased ossicles
To understand the Baffle effect you must remember a few simple rules.
The inner ear is filled with fluid (perilymph and endolymph)
Fluid is incompressible – that is it is not possible to squeeze fluid and make its volume smaller. To understand this better try this experiment.
Take two syringes
Fill one with water and the other with air
Put your finger over the nozzle and push the plunger
The plunger of the air filled syringe will move because the air is compressible
The plunger of the water filled syringe will not move because water is incompressible
Vibration enters the scala vestibuli of the cochlea via the stapes in the oval window. When the stapes moves into the inner ear the round window membrane bulges outwards (because fluid is incompressible). This is shown in the next diagram.
So lets look at the diagram above. In normal ears (A) sound vibrates the eardrum and this vibration passes along the ossicular chain to the oval window. The sound is amplified during this. A small amount of sound passes directly into the air of the middle ear and this causes a small amount of vibration in the round window. However, the effect of this is very small compared with the amplification caused by the ossicles and drum.
If there is a perforation (B) things are slightly different. The drum collects the sound and passes it down through the ossicles and amplification happens but this time sound falls directly on the round window as well. This sound has more energy than it did when the eardrum was intact and it acts against the vibrations going through the oval window. The patient experiences this as slight deafness. It is slight because the middle ear amplifier is still mostly working.
In the last panel there is both a perforation and ossicular disease (C). This means that the middle ear amplifier is not working well and the patient only hears because the sound is travelling through the perforation and vibrating the footplate of the stapes directly. However, there is sound falling onto the round window as well. This means that less sound energy will get through the oval window to the cochlea and the patient will feel deafer.
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This diagram shows the effect close up. In panel A the drum is intact and sound is amplified by the ossicles and drum and passes into the stapes. The stapes pushes into the inner ear perilymph and this pressure is later transmitted to the endolymph. The pressure wave caused by the stapes moving is transmitted along the length scala vestibuli of the cochlea, through the helicotrema (H) and around into the scale tympani. The pressure pushes the round window membrane outwards towards the middle ear.
In panel B there is a perforation present. It allows some sound to fall onto the round window. In this situation the fluids of the cochlea are being pushed from both ends: a big push through the oval window into the scala vestibuli and a small push in the opposite direction via the round window membrane. This means that less energy passes into the cochlea and sounds seem quieter.