We will be exploring Round Window Shielding Effect of CSOM. Let’s take a deeper look into its first type, i.e, Tubotympanic CSOM, also called safe CSOM or benign CSOM. Click to jump to Atticoantral CSOM. We discussed about CSOM or Chronic Suppurative Otitis Media in general in our previous section.
The Etiology of Tubotympanic CSOM is as follows:
- Sequela of Acute Otits Media following exanthematous (eruptive) fever and leaving behind a large central perforation which becomes permanent and permits repeated infections from external ear.
- Ascending infections via Eustachian tube like from tonsils, adenoids and infected sinuses.
- Persistent mucoid otorrhoea is sometimes result of allergy to ingestants such as milk, eggs,fish etc.
It remains localized to mucosa and mostly to anteroinferior part of middle ear. Pathological changes seen in Tubotympanic CSOM is as follows:are:
- Perforation of pars tensa- Central perforation
- Middle ear mucosa- Normal when disease is inactive but oedematous and velvety when active
- Polyp- Pale
- Ossicular chain- usually intact and mobile but may show some degree of necrosis, especially of long process of incus.
- Tympanosclerosis- It is hyalinisation and subsequent calcification of subepithelial connective tissue. It is seen as white chalky deposits on promontory, ossicles, joints, tendons, oval and round windows. It interferes with mobility of these structures, hence, causing conductive deafness.
- Fibrosis and adhesion- They are result of healing process and may further impair mobility of ossicular chain or block eustachian tube.
The bacteriology of Tubotympanic CSOM is as follows:
- Pseudomonas aeruginosa, proteus, E.coli, Staph aureus
- Bacteriodes fragilis and anaerobic streptococci
The Clinical Features of Tubotympanic CSOM are as follows:
Non-offensive, mucoid or mucopurulent, constant or intermittent. Discharge appears mostly at time of upper respiratory tract infection or accidental entry of water into ear.
Round Window Shielding Effect- Hearing loss
Conductive type and rarely exceeds 50dB. Sometimes, patient reports of paradoxical effect, i.e, hears better in presence of discharge than when ear is dry. This is due to ‘Round Window Shielding Effect‘ produced by discharge which helps to maintain phase differential. In dry ear with perforation, sound waves strike both oval and round windows simultaneously, thus, cancelling each others effect.
Always central which is anterior,posterior or inferior to handle of malleus or subtotal/extending upto annulus.
Middle Ear Mucosa
Pale pink and moist on normal but when inflamed, it looks red, oedematous and swollen and occasionally with polyps.
Investigations done in Tubotympanic CSOM are as follows:
- Examination under microscope- can reveal granulation, ingrowth of squamous epithelium, status of ossicular chain, tympanosclerosis and adhesion.
- Audiogram- Conductive deafness but sensorineural deafness element may be present.
- Culture and sensitivity of ear discharges- may help to select proper antibiotic ear drugs.
- Mastoid Xrays/CT scan temporal bone- Mastoid is usually sclerotic but may be pneumatized with clouding of air cells. There’s no evidence of bone destruction (which is a feature of atticoantral csom)
The aim of treatment is to control the infection and eliminate ear discharge and at a later stage, surgery may be done to assist hearing loss. Following are treatment regimes for Tubotympanic CSOM:
- Aural toilet- All discharge and debris from is ear is removed to enhance effect of topical antibiotics.
- Ear drops- Neomycin, Polymysin and gentamycin are used.
- Systemic antibiotics- Only in acute cases.
- Precautions- Avoiding hair washing, water in ears or blowing nose hard can be helpful.
- Surgical treatment- Polyps in ear or granulation is removed to facilitate ear toilet though avulsion is strictly avoided.
- Treatment of contributory causes- Corrects of infection of adenoids, maxillary antra and nasal allergy.
- Reconstructive surgery- Once ear is dry, myringoplasty with/without ossicular reconstruction and closure of perforation can stop recurrent infections.