Round Window Shielding Effect in Tubotympanic CSOM

Tubotympanic CSOM, often referred to as the “safe” or benign form of chronic suppurative otitis media, is known for its limited middle ear involvement and lower risk of complications.

One of its key features is the round window shielding effect, which helps protect the inner ear from infection-related damage.

In this section, we’ll take a closer look at how this protective mechanism works in tubotympanic CSOM.

Etiology

Tubotympanic CSOM usually develops due to:

• After-effects of Acute Otitis Media: It often follows an episode of acute otitis media, especially after exanthematous (eruptive) fevers, which can leave a large central tympanic membrane perforation. This permanent opening allows repeated infections from the external ear.
• Ascending Infections through the Eustachian Tube: Infections from nearby structures such as the tonsils, adenoids, or sinuses can spread upward to the middle ear, contributing to chronic infection.
• Allergic Reactions: In some cases, persistent mucoid ear discharge (otorrhoea) may be linked to allergies to certain foods like milk, eggs, or fish.

Pathological Changes in Tubotympanic CSOM

Tubotympanic CSOM remains localized to the mucosa, mostly affecting the anteroinferior part of the middle ear. The key pathological changes seen include:

1. Central Perforation of Pars Tensa: A persistent perforation in the central part of the tympanic membrane.
2. Middle Ear Mucosa: Appears normal when the disease is inactive; becomes oedematous and velvety when active.
3. Pale Polyp Formation: Non-granulation type, pale in appearance.
4. Ossicular Chain: Usually intact and mobile, but there may be some necrosis, especially affecting the long process of the incus.
5. Tympanosclerosis: Hyalinisation and calcification of the subepithelial connective tissue. It appears as white, chalky deposits on the promontory, ossicles, joints, tendons, and around the oval and round windows. This can reduce the mobility of these structures, leading to conductive hearing loss.
6. Fibrosis and Adhesions: These result from the healing process and may further restrict ossicular chain movement or block the Eustachian tube.

Bacteriology of Tubotympanic CSOM

The bacteria commonly involved in tubotympanic CSOM include both aerobic and anaerobic organisms:

• Aerobic Bacteria:
  • Pseudomonas aeruginosa
  • Proteus species
  • Escherichia coli (E. coli)
  • Staphylococcus aureus
• Anaerobic Bacteria:
  • Bacteroides fragilis
  • Anaerobic streptococci

Clinical Features of Tubotympanic CSOM

The main clinical features of Tubotympanic Chronic Suppurative Otitis Media (CSOM) include:

Ear Discharge

Typically non-offensive, mucoid or mucopurulent in nature. The discharge may be constant or intermittent, often appearing during upper respiratory tract infections or when water accidentally enters the ear.

Hearing Loss – Round Window Shielding Effect in Tubotympanic CSOM

Hearing loss is usually conductive and rarely exceeds 50 dB. Some patients report a paradoxical experience—hearing feels better when there is discharge than when the ear is dry.

This is explained by the round window shielding effect: in a dry ear with perforation, sound waves hit both the oval and round windows simultaneously, cancelling each other’s effects. The presence of discharge helps maintain a phase differential, improving sound transmission.

Perforation

Always central in location. It can be anterior, posterior, inferior to the handle of malleus, or subtotal, extending up to the annulus.

Middle Ear Mucosa

Normally pale pink and moist. When inflamed, it appears red, oedematous, swollen, and may show occasional polyp formation.

Investigations in Tubotympanic CSOM

The following investigations help assess tubotympanic CSOM:

• Microscopic Ear Examination:
  Reveals granulation tissue, squamous epithelium ingrowth, the condition of the ossicular chain, tympanosclerosis, and adhesions.
• Audiogram:
  Typically shows conductive hearing loss. A sensorineural component may also be present in some cases.
• Culture and Sensitivity Testing:
  Identifying the bacteria from ear discharge helps in selecting effective antibiotic ear drops.
• Mastoid X-rays or CT Scan (Temporal Bone):
  The mastoid may appear sclerotic or pneumatized with clouding of air cells. Importantly, there’s no bone destruction—unlike in atticoantral CSOM.

Treatment of Tubotympanic CSOM

Advise: Seek NHS guide to ear infections, including chronic cases or your GP if you have concerns.

The main goals are to control infection, stop ear discharge, and later, improve hearing. Management includes:

• Aural Toilet:
  Careful cleaning to remove discharge and debris, enhancing the effect of topical antibiotics.
• Ear Drops:
  Antibiotic drops such as neomycin, polymyxin, or gentamicin are commonly used.
• Systemic Antibiotics:
  Reserved for acute exacerbations or when there is systemic infection.
• Precautions:
  Patients should avoid getting water into the ears (e.g., during hair washing) and avoid forceful nose blowing.
• Surgical Treatment:
  Removal of polyps or granulation tissue as part of ear cleaning (aural toilet). Avulsion techniques are avoided.
• Addressing Contributory Causes:
  Treatment of related conditions like adenoidal infection, maxillary sinusitis, or nasal allergies.
• Reconstructive Surgery:
  Once the ear is dry, procedures like myringoplasty, with or without ossicular chain reconstruction, can help close the perforation and prevent recurrence.