Tympanic Membrane Retraction Pocket

Retraction pocket (Latin sinus retractionis) is a pathological condition characterized by localized retraction (invagination) of a portion of the tympanic membrane into the tympanic cavity. It is not an anatomical structure but an acquired pathology resulting directly from chronic negative pressure in the middle ear.

The presence of a retraction pocket indicates prolonged dysfunction of the auditory tube. This condition is a significant clinical problem, as it serves as a precursor to serious diseases such as adhesive otitis media and, most importantly, cholesteatoma.

Aetiology and pathophysiology

The primary and only cause of retraction pocket formation is chronic dysfunction of the auditory (Eustachian) tube. Normally, the auditory tube opens periodically, equalizing pressure within the tympanic cavity with that of the atmosphere.

This mechanism may become impaired due to adenoid hypertrophy, chronic rhinosinusitis, or allergic reactions. As a result, the gas in the closed tympanic cavity is gradually absorbed by the mucosal lining, leading to the development of persistent negative pressure (vacuum). Under the influence of external atmospheric pressure, the most pliable portion of the tympanic membrane is drawn inward. Most often, the pocket forms in the flaccid part (pars flaccida), as this area lacks a rigid fibrous layer.

Over time, the base of the pocket may become adherent to structures of the middle ear, such as the ossicles or the cavity walls. The normal process of epidermal migration is disrupted within the pocket, resulting in the accumulation of desquamated keratin. This accumulation serves as a substrate for the development of cholesteatoma—an aggressive lesion capable of causing bone destruction.

Clinical Significance

In its early stages, a retraction pocket may be asymptomatic. As the pocket deepens and complications arise, various clinical symptoms may develop.

Symptoms and clinical manifestations include:

• Hearing loss: Conductive hearing loss due to impaired mobility of the tympanic membrane and ossicular chain.
• A sensation of fullness or pressure in the affected ear.
• Recurrent otitis: Infections of the pocket contents.
• Otorrhea: Foul-smelling purulent discharge, often associated with cholesteatoma formation.

Diagnosis is primarily based on otoscopic findings and can be further detailed through otomicroscopy or endoscopic examination of the ear. Depending on the depth and fixation of the pocket, several stages can be identified (e.g., according to the Tos classification), which guide treatment strategy.

Treatment depends on the stage and behavior of the pocket. Shallow, ventilated pockets may be monitored while addressing the underlying cause of auditory tube dysfunction. Deeper or fixed pockets may require insertion of a ventilation tube to equalize middle ear pressure. Deep, not self-cleaning pockets, particularly when cholesteatoma is suspected, are indications for surgical intervention — typically tympanoplasty with excision of the pocket and reinforcement of the tympanic membrane, often using cartilage grafts.

Differential Diagnosis

The main diagnostic task is to differentiate a simple, stable retraction pocket from an early-stage cholesteatoma. The key determinant is the pocket’s ability to self-cleanse of keratinous debris. If keratin accumulates at the base of the pocket, the risk of cholesteatoma formation is extremely high. The pocket should also be distinguished from a dry perforation of the tympanic membrane. Otomicroscopy with gentle instrumental palpation of the pocket walls, along with high-resolution computed tomography of the temporal bones (if bone erosion is suspected), play a decisive role in accurate diagnosis and treatment planning.