Skills Laboratory: How to perform a myringotomy
Careful preparation and technique are essential when performing this procedure.
Step 1 >
If you suspect otitis media in a patient, a myringotomy-an incision into the tympanic membrane-may be a useful diagnostic test to help you confirm the presence of fluid or masses in the middle ear and collect a sample for bacterial culture. But myringotomies can also be therapeutic, relieving the pressure in the middle ear and permitting flushing of any exudate or debris.
While advanced imaging such as computed tomography or magnetic resonance imaging is best to definitively diagnose fluid or masses in the middle ear, it is not 100% accurate, and many owners cannot afford these tests. Radiographic examination of the bullae can give useful information, but it can be difficult to position patients and interpret the findings. A myringotomy can often be done at a reasonable price, and the usual procedure time is 30 to 60 minutes. Thus, in many cases, a myringotomy is often a useful and appropriate procedure.
A myringotomy can be performed in both large and small dogs, as well as in cats. The technique is slightly more difficult in cats and small dogs because of the more narrow diameter of the external canal, but the technique is the same.
Is it otitis media?
Middle ear infections are not uncommon in small-animal veterinary patients. Predisposing factors in dogs include otitis externa, masses, and allergies. Predisposing factors in cats include masses and chronic upper respiratory disease. Computed tomographic scans in cats have shown that many patients with sinonasal disease had concurrent middle ear disease. These cats did not show any of the previously listed clinical signs of otitis media. Further studies are needed, but middle ear disease seems to play an important role in feline sinonasal disease.
Patients with otitis media often exhibit typical signs of concurrent otitis externa (shaking head, pawing at ear); many times these are the only signs seen. Less commonly, patients may exhibit pain on palpation of the ear canal and opening of the mouth, facial nerve paralysis, and Horner syndrome. Concurrent otitis interna with ataxia, nystagmus, and head tilt is not common but can occur. Any patient with chronic, intractable otitis externa, should be suspected of also having otitis media.
Step 1
Administer general anesthesia. Endotracheal intubation is necessary to prevent fluid aspiration from auditory (eustachian) tube drainage. Place the patient in lateral recumbency with the affected ear up. Use towels to cover the patient's face (the saline solution will flow out of the canal and over its face during the procedure).
Step 2
Use the video otoscope to visualize the external ear canal and tympanic membrane. It is usually necessary to pull the pinna up toward you to straighten out the external canal and see the tympanic membrane (see photo above).
If the tympanic membrane is ruptured or missing, proceed with flushing the canal. But if the canal is too swollen to access with the otoscope, treat the patient with prednisone (0.5 to 1 mg/kg/day) for two weeks to open the canal before attempting a myringotomy.
Pour warm sterile saline solution in a sterile bowl, and fill the 6-ml syringes. Cut one to four inches off the tip of a red rubber catheter at a slanted angle with sterile scissors, leaving it 12- to 15-in long with a pointed tip (see photo below).
Step 3
Since there is almost always some debris to remove, flush the external canal by using the 6-ml syringes filled with the warm sterile saline solution and the red rubber catheter through the video otoscope port. This part of the procedure works best if one person holds the pinna and directs the otoscope (drives), a second person holds the catheter and flushes the saline solution (see photo above), and a third person monitors anesthesia and refills the syringes with saline solution, if possible.
If wax plugs or hair is obstructing visualization, carefully remove it with biopsy forceps or hemostats. Sometimes the video otoscope obstructs the outflow of large pieces of debris, so you may need to remove the otoscope and gently flush with the catheter blindly until large pieces come out.
Once the external canal is clean and the tympanic membrane is visible, take a photo (see photo below; an example of a clean canal and bulging tympanic membrane). After cleaning, you can flush the external canal with 0.1% chlorhexidine or dilute iodine solution and then rinse with sterile saline solution and remove the fluid. This can help prevent spread of infection into the middle ear and prevent contamination of middle ear samples, but it is not advised if the tympanic membrane is not obviously intact since both of these substances can be ototoxic.
Step 4
The myringotomy incision should be made in the caudoventral quadrant of the pars tensa (see photo above). If the manubrium (one of the ossicles in the middle ear) can be seen, actively avoid touching it with the catheter. If it cannot be seen (because of fluid or masses in the middle ear or thickening of the tympanic membrane) then do your best to avoid the dorsal rostral area of the tympanic membrane to minimize damage to the ossicles.
Sometimes the tympanic membrane is already torn, or it is completely gone and you can see directly into the bulla. If it is already torn in the correct area for myringotomy, you can obtain samples and flush through the existing tear. If the tear is not in the correct area, we recommend proceeding with your own myringotomy in the correct area.
With sterile scissors, cut 7 to 10 in off the tip of the rigid sterile catheter at a 60-degree angle, leaving 12 to 15 in of catheter with a sharp point (see photo below). Feed this catheter through the otoscope port until it is just in front of the tympanic membrane. With one firm motion, poke the catheter through the tympanic membrane. Sometimes fluid or debris will leak out of the bulla through the myringotomy site. If so, note the appearance of any fluid or debris and take a photo.
Step 5
With an empty, sterile syringe and a new, sterile red rubber catheter, aspirate fluid from middle ear, and retain it for cytologic examination and culture. Store the fluid in the syringe for now. Later it can be dripped onto a culture swab for bacterial culture. If there is no fluid or debris, infuse 0.5 to 1 ml of sterile saline solution into the middle ear and aspirate to collect a culture sample.
An alternate method involves setting the video otoscope aside and temporarily using a hand-held otoscope with a sterilized otic cone. You can feed a small-tipped culturette through the sterile cone, down the straightened external canal without touching the sides, through the tympanic membrane, and into the bulla to collect a culture sample. You won't be able to visualize well around the culturette, so this will be done more by feel. Pull the canal very straight toward you, aim straight toward the tympanic membrane, and feel for the gritty bone that indicates you are in the bulla. This technique requires a lot of practice, and there is a chance of contamination from accidentally touching the external canal walls, so the initially mentioned catheter and saline method is preferable for beginners.
If a mass is present in the bulla, collect one to three small pieces with flexible biopsy forceps (see photo above) through the existing myringotomy site. The flexible biopsy forceps have such a small head that it's usually only possible to get a few small pieces for histopathologic examination, rather than an excisional biopsy. We have experienced more post-procedure vestibular complications when trying to pull out a mass whole, so we don't recommend it. Patients with large masses in the middle ear will likely need to be referred to a surgeon for further removal (bulla osteotomy). The mass shown in the photo below is protruding from the bulla out into the external canal.
Step 6
Using the new red rubber catheter and syringes filled with warm sterile saline solution, gently flush the bulla 10 to 20 times (about 60 to 120 ml saline solution total) until no more debris or opaque fluid comes out of the bulla and you can feel the bone of the bulla with the catheter (the catheter scrapes against something hard and gritty). You should not aspirate during this part of the procedure, as the goal is to flush the bulla with large amounts of saline solution to remove as much bacteria and debris as possible. Be careful not to flush with too much pressure since there is a chance of tearing the tympanic membrane further. However, if the tympanic membrane is accidentally further torn, it should grow back within 21 to 28 days.
Examine the patient's nose and inside its mouth for fluid coming from auditory tube-it is a good sign if the fluid drains because it means the auditory tube is open. Sometimes the external canal will become swollen or bleed from irritation from the video otoscope (see photo above). If this becomes severe, discontinue flushing, but it is best to remove all debris from bulla and external canal if possible.
Step 7
Aspirate fluid from the bulla and external canal with syringes, and take a photo of the clean ear canal. A mixture of aqueous injectable antibiotics and corticosteroids, as appropriate, can be instilled through red rubber catheter into the bulla (see the package insert and current research for ototoxicity studies before administering each drug).
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Step 8
If the patient has bilateral ear disease, turn it over and repeat the procedure on the other ear with new supplies. Allow the patient to recover from anesthesia normally.
After the procedure
Rarely, patients will develop vestibular signs after the procedure (cats more often than dogs). It is usually temporary and can be treated as needed, usually with systemic antibiotics based on culture results, systemic glucocorticoids, and antiemetics based on severity. In our experience, decreased hearing or deafness can rarely occur after the procedure, but this is usually temporary.
Submit cytologic and bacterial culture samples and any masses removed or biopsy samples obtained for histopathologic examination. Give a copy of the photos taken during the procedure to the owner, and keep the originals in the medical record.
We usually send patients home later that same day. Do not use any oil-based ear medications with a ruptured tympanic membrane. You can make a mixture of aqueous ear flush with added antibiotics, antifungals, and corticosteroids, as appropriate. Consult package inserts and drug formularies for information about safety of specific drugs in the middle ear. If vestibular signs are present along with otitis media, they are likely related to bacterial otitis interna extending from the middle ear, so oral antibiotics can be added to improve response. Although oral antibiotics do not usually get good penetration into the external ear canal, they do penetrate into the middle and inner ear. Change antibiotics based on the culture results, if appropriate. As most of these patients are already receiving corticosteroids for their otitis, medication for pain is only rarely needed. In those cases, we prescribe tramadol.
Follow-up
Always recheck the patient two weeks later to make sure the ear canal is still open, the tympanic membrane is starting to heal, the patient is comfortable, and the owners are giving medications correctly (we make this a free-of-charge quick appointment to ensure owners come back). The tympanic membrane usually has not completely healed at this recheck appointment, so if we cannot visualize it while the patient is awake, we usually do not sedate the patient. However, at a four-week recheck appointment, the tympanic membrane should be healed; thus, a difficult patient can be sedated so that a complete otoscopic examination may be performed. Patients often need topical and possibly also systemic antibiotic treatment for six to eight weeks after the myringotomy to completely clear the infection. Make sure to address any underlying causes (e.g. food allergy, environmental allergy, tumors) so the infection does not recur.
SUGGESTED READING
1. Harvey RG, Harari J, Delauche AJ. Ear diseases of the dog and cat. Ames: Iowa State University Press, 2001;43-79,147-155.
2. Cole LK. Anatomy and physiology of the canine ear. Vet Dermatol 2009;20(5-6):412-421.
3. Detweiler DA, Johnson LR, Kass PH, et al. Computed tomographic evidence of bulla effusion in cats with sinonasal disease: 2001-2004. J Vet Intern Med 2006;20(5):1080-1084.
