By Professor Tony Wright
One common and potentially dangerous condition of the middle ear and mastoid is called cholesteatoma. The name of the condition is not very helpful to understand what is taking place in the ear or what damage can be caused by the failure to diagnose and treat this disease. The suffix – oma as in lipoma, fibroma, and carcinoma comes from the Greek ωμα, meaning a swelling. The prefix defines the type of swelling and in the case of a cholesteatoma means a creamy coloured mass.
The ear canal and eardrum are covered by skin. One of the functions of skin is to protect the body against wear and tear, and to form a waterproof layer called the epidermis [Greek dermis = skin i.e. dermatology]. To achieve this skin grows continually from the depths to the surface and as the dividing cells approach the outside they die and shrink to become a waterproof layer. This surface layer is made waterproof by the presence of a protein called “keratin”. The dead surface layers of skin-cells are shed with wear and tear and on the scalp these scales of discarded skin are commonly known as dandruff. This pattern of growth is found nearly all over the surface of the body, but if this were to happen in the ear canal then it would rapidly become filled with layers and layers of dead keratinised skin-cells. So, to overcome this problem the skin of the eardrum and ear canal has evolved or has been given the special property of migration. In other words, the skin of the eardrum and ear canal grows outwards from the middle of the eardrum, along the ear canal to the external opening of the ear. The outer third of the ear canal has small hairs in it and the oil that is secreted from the little glands in the hair roots, along with modified sweat from the small sweat glands, mixes with the scales of dead skin to form wax. Wax is protective since it kills many common, pathogenic bacteria and fungi, and generally stops insects and other foreign-bodies from inadvertently travelling down the ear canal.
Inadequacy of the Eustachian tube can lead to a failure of aeration of the middle ear and mastoid, and result in the eardrum becoming in-drawn as the middle ear pressure drops. This is made easier if the eardrum has been damaged or scarred by previous infections. The typical site of retraction is the so called “attic” portion of the eardrum which is the small upper part of the eardrum – the Pars Flaccida. If the retraction becomes severe enough, the normal migration of the skin of the surface of the eardrum becomes altered and flakes of dead skin tend to accumulate within the pocket rather than being carried to the outside. This accumulation continues and forces the living skin at the periphery of the retraction pocket to expand into the middle ear and then into the mastoid. This accumulation of dead skin surrounded by a layer of growing skin is called a cholesteatoma. As the cholesteatoma expands, it comes into contact with surrounding bone which it eventually erodes, especially if infection is also present. The structures that can be damaged by a cholesteatoma growing in the middle ear and mastoid are:
1. The ossicles thereby causing a conductive deafness.
2. The inner ear by way of the cochlea in the middle ear or usually by the lateral semi circular canal just above the facial nerve in the upper part of the middle ear, thereby causing a profound sensorineural hearing loss, vertigo and tinnitus.
3. The roof of the middle ear and mastoid – the tegmen – so that a connection develops between the middle ear and the inside of the skull. From this can develop meningitis or brain abscesses.
4. The facial nerve, which runs a tortuous course from the brain, through the middle ear and mastoid on its way to supply the muscles of facial expression. Damage here causes a facial paralysis with an inability to close the eye and a severe, grimacing, lop-sided smile as well as dribbling and difficulties with speaking and eating. The course of the facial nerve through the middle ear is a good example of severely “unintelligent design”.
Once the cholesteatoma becomes infected then a foul smelling discharge occurs. These then are the possible complications of untreated cholesteatomas and in general consistent medical advice is that cholesteatomas should be treated by surgical removal. The images below show the development of an attic cholesteatoma in a right ear.
In the first image the child has a dull bluish tympanic membrane with radial blood vessels clearly visible and changes typical of what is called glue ear. There is also an attic retraction with the Pars flaccida skin being stretched inwards into the attic spaces and on to the heads of the ossicles.
Above: the glue ear element has now resolved and there is an air filled middle ear although the tympanic membrane-the Pars tensa-is slightly retracted onto the long process of the incus. There is also a retraction pocket with the Pars flaccida stuck on the head of the malleus and with some bone erosion but no accumulation of keratin – dead skin
Above: a more extensive retraction with keratin flakes starting to accumulate at the edge of the pocket
Above: The retraction pocket has become filled with keratin which has turned brown. This resembles wax – but is not; hence the old adage “Beware attic wax for beneath is disease”.
Above is a more extensive attic erosion with brown, dried keratin filling the defect and with a white swelling of cholesteatoma dipping down behind the tympanic membrane posterior to the handle of the malleus.
The erosion of bone can lead to reactive polyp formation as the bare bone tries to heal. The polyp is moist and this, in turn, can irritate the deep canal skin with subsequent infection and discharge. The accumulated dead skin in the cholesteatoma can also become infected and generally a foul smelling discharge results. A small polyp is shown in the image below.
Above: an extensive attic cholesteatoma shown by the white, moist mass with more bony erosion and a small smooth red polyp near the top of the picture.
Treatment of cholesteatoma is usually by some form of surgery which is primarily aimed at making the ear safe by removing disease. Modern surgical techniques also aim at making the ear dry and attempt to maintain or even improve the hearing. The risks of surgery are much the same as the risks of untreated disease, but in competent hands the chance of complications occurring from surgery are less.
