MICRO EAR SURGERY – HOW AND WHY?
Surgery for the human sensory organs like the ear requires precision to achieve desirable results. The unaided eye is not adequate to visualise and work in the narrow confines of the ear where dimensions are measured in millimeters. Holmgren was the first among the many surgeons who pioneered the development of the Microsurgery for the ear. He used magnification spectacle loupes to perform fenestration operations in the 1930’s for the disease of otosclerosis. The American Surgeon Shambaugh in 1940 converted a dissection microscope by adding a light source for illumination thus opening a new vista in reconstructive ear surgery.
Along with the microscopes other developments in medicine and medical technology are contibuted to these developments. Tiny Scissors and forceps, micro electric drills for drilling away bone for exposure and removal of ear disease were developed. Special video Cameras integrated inside operating microscopes help us to teach and develop the micro surgical technique.
A small introduction to the ear is needed before going further. Designed to convey the sense of sound and balance , ear is divided into outer, middle and inner parts. The ear drum and the bone bridge formed by 3 ossicle bones along with other small muscles and bony walls make the middle ear. This space varies in its depth from 2mm to 6mm. The middle ear serves the function of impedence, matching to transfer air borne sound to the inner ear neural elements which are surrounded by fluid. The middle ear is also linked to the nose through the eustation tube which serves to equalise the air pressure in the middle ear to the varying atmospheric pressure. The Inner ear contains neural cochlea for perceiving sound and the labrinthine system for detecting the position of our head in relation to space and for forces of accelaration and deceleration. The nerve for controlling the muscles in our face and part of the taste sensation from the tongue also courses through the middle and inner ears.
Small central perforation
Large central perforation
Status of Operated ear – Hearing levels after operation
Status of Operated ear – Hearing levels after operation
For a successful out come of treatment in this demanding area accurate diagnostic techniques are a must. Audiometry is the time tested tool used to estimate the hearing. Tympanometry gives a clue about what is happening behind a intact ear drum. It is especially useful in children who after getting a head cold suffer from minor degree of hearing loss. This problem encountered in 60-70% of the Paediatric age group at one time or other is caused by accumulation of thick mucus called glue inside the middle ear. Insertion of a small ventilating tube through the drum by microsurgery is currently used when the condition does not resolve with medical treatment. Tympanoscopy using small endoscopes which can look side ways helps us to estimate the damage to the ossicular chain inside a ear drum perforation. Brain stem Evoked Response Audiometry (BERA) provides accurate diagnosis of hearing loss even in new borns.
At the present time these specialised equipement help us to give reliable cures for chronic middle ear infection resulting in deafness and discharge from ears. Otosclerosis, the ENT equivalent of cataract in the eye, produces a gradual worsening of the hearing and can only be relieved by a stapedotomy which involves removal of the third small bone inside the middle ear and replacement with a teflon or platinum prosthesis for conveying sound to the inner ear.
Many consider the problem of ear discharge more a nuisance and social stigmata than a threat. Septic conditions of the middle ear are basically divided into safe and unsafe based on the clinical findings. The safe ear accompanied by discharge, and deafness does not result in life threatening infections for the majority of patients. Left untreated over a long time it can result in permanent nerve deafness when medical help is of no avail. The dangerous type of sepsis arises in the ear due to misplaced skin inside bone, a condition called cholesteatoma. Due to pressure and enzymatic dissolution the surrounding bone of the middle ear is destroyed in a slowly progressive manner and the infection spreads to the brain and other intracranial structures. Prior to the developments mentioned above 50% of the Brain abcess were caused by unsafe ear diseases and many of the victims were permanently disabled and lives were lost. Currently several techniques are available to the ENT specialist to recognise and treat these conditions. Apart from removing the disease, hearing in most cases can be simultaneously restored using patients own or banked ossicle bone, cartilage or ceramic prosthesis. The middle ear is an area in the body where many foreign objects are tolerated without antigenic reaction and rejection and this fact has helped us to use several man made prosthesis. It is note worthy to mention that even patients own tooth have been used after refashioning to aid in sound conduction inside the ear. Sialastic is used to create a new middle ear space in a grossly diseased patient before the sound reconstruction is done at a second operation.
To re-create the torn or missing ear drum a thin membrane called temporalis facia is used. This is the covering of the temporal muscle lying above and in front of the ear. Preserved dura mater (covering of the brain) also is being used for this purpose. For using this tissue it is to be dried which takes some time. To cut short this time some of us use hair driers on this facia. Such adaptation of every day tools in medicine is dictated by the need.
Non cancerous growths occuring in the cerebello pontine angle of the brian, and internal auditory canal is effectively dealt with by a trans otic micro surgical approach. When trouble starts in this area unsteadiness, ringing noices with deafness of one ear are the initial symptoms. Audiometry is a inexpensive non invasive test and is 85% accurate in determining the cause of these symptoms. When a growth is suspected, C.T.Scan or MRI confirms the disease and upto 3cm size growths can thus be effectively dealt with by neuro-otological techniques. Patients who have lost the functioning of the inner ear nerves suffer from sensory hearing loss and the treatment recommended for them is the hearing aid. When a conventional hearing aid is found to be not adequate to perceive sound, an indwelling aid termed cochlear implant can be used.
In India Government owned BEL has been making and supplying these surgical microscopes which has greatly helped the diffusion of this technique throughout the country. Though we cannot boast of the full range, most of the basic equipment for carrying out these surgeries are made here.
Such a precise technique is also not without pitfalls. Even the most skilled surgeons cannot produce a 100% successful result in chronic middle ear sepsis. The factor responsible for this is the Tiny Eustacian tube which makes the ear pop when going up or down a hill. Techniques for assessing and treating the Eustacian tubal problems are still being evolved and looking back at the progress we have made in the past 50 years since the operating microscope was invented the tubal problem will be overcome soon.
Intraoperative facial nerve monitoring-AT MCV :
Intraoperative continuous facial nerve monitoring (IFNM) using an electromyograph (EMG) was first established in neurotologic surgery.This technique monitors muscles innervated by the facial nerve at risk during surgery. Iatrogenic trauma to nerves evokes high-frequency bursts of motor unit potentials called neurotonic discharges that are detected by a monitor.This alerts the surgeon and may help to prevent serious or irreversible injury.
Facial nerve monitoring is very useful especially in revision(secondlook)ear surgeries and parotid surgeries