Pneumatocele of the Tympanic Membrane

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A pneumatocele refers to a collection of trapped air enveloped by surrounding soft tissue that is usually the result of a traumatic or infectious insult to the tissue. Rarely, pneumatoceles of the mastoid portion of the temporal bone have been described that extend into the external auditory canal (EAC), causing compression or obstruction and thereby leading to hearing loss (1,2). To the best of our knowledge, pneumatoceles originating in the EAC at the level of the tympanic membrane have not been well described in the English language literature and may affect surgical planning (1,2). This case outlines the presentation, development, and surgical considerations of a tympanic membrane pneumatocele in a cochlear implant candidate.
A 69-year-old man presented with right greater than left asymmetric sensorineural hearing loss (SNHL) and a remote history of right chronic otitis media. His clinical history was also significant for intermittent bloody otorrhea from his right ear when using a home continuous positive airway pressure (CPAP) device without otalgia or vertigo. Otoscopic examination of the right ear was notable for a cystic mass filling the mid-portion of the EAC with no associated ulceration. The cystic mass could be laterally displaced by autoinsufflation. Audiometry revealed profound right SNHL with 6% word recognition score and 85 dB pure tone average (PTA), and left moderate SNHL with 68% word recognition score and 72 dB PTA. A magnetic resonance imaging showed no vestibular schwannoma or other retrocochlear lesions. Computed tomography of the temporal bone demonstrated an aerated middle ear, normal ossicles, normal cochlea, and a subtle outline of the cyst wall in the mid-EAC. These series of findings led to the diagnosis of a pneumatocele of the tympanic membrane.
The patient was followed over 1 year and his pneumatocele was intermittently present at office examinations. At some visits, the tympanic membrane appeared normal with no visible defect in the pars flaccida on otomicroscopy. Due to his profound right SNHL and progressive, fluctuating left SNHL, he opted for a staged tympanoplasty with canaloplasty and resection of pneumatocele followed by cochlear implantation. At surgery, the EAC was completely obstructed by the pneumatocele, which extended from a 2 mm hole in the anterior pars flaccida, tunneled under the EAC skin in the posterior/superior quadrant, and extended medial to the superior half of the tympanic membrane (Fig. 1). The ossicular chain and chorda tympani were unaffected. When the EAC skin was removed off the cyst surface, a small vessel was visualized on the mucosalized surface of the air filled cyst, likely the source of intermittent bloody otorrhea experienced by the patient during CPAP use (Fig. 2). Given the anterior marginal location of the perforation in the pars flaccida and extension of the pneumatocele medial to the superior half of the tympanic membrane, a postauricular approach and total drum lateral graft technique was used intraoperatively. Pathology showed columnar epithelium with chronic inflammation.
The origin of the pneumatocele in this case appeared to be the lesion in the pars flaccida. Typically, pneumatoceles are formed due to infectious or traumatic insults to tissue. In traumatic insults, the compressive force of trauma is subsequently followed by rapid decompression, thereby creating a negative pressure that may lead to the formation of an air cavity. Infectious insults cause inflammation and fluid accumulation that can create a potential space between tissues. As fluid is resorbed with resolution of the infectious insult, an air cavity may persist. The tympanic membrane may be subjected to both infectious and traumatic insults, and identifying the causative etiology is difficult (1).

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