Congenital Absence of Stapedius Muscle and Tendon: Case Report with Review of Literature

Abstract

Absence of stapedius muscle and its tendon is an extremely rare congenital anomaly, with only nine indexed reports in live patients. It presents with non progressive, occasionally bilateral conductive deafness, although this cannot be confirmed from Pure Tone Audiometry (PTA) and High Resolution Computed Tomography (HRCT). This makes it one of the least probable differential diagnosis of conductive deafness with unremarkable tympanic membrane. The definitive diagnosis is made only at time of surgery. The condition often co-exists with other genetic/acquired disorders of the middle/inner ear (otosclerosis, tympanosclerosis, etc.,). In absence of standardised, evidence based management protocol, diagnosis and appropriate treatment become challenging, and are predominantly situational. Its occurrence follows complex embryologic sequences where the internal portion of the interhyale- the mesenchymal condensation separating the cranial mesenchyme of the second pharyngeal arch (stapedial anlage) from Reichert’s cartilage- remains either absent or undergoes regression. Here, authors presents a case of 19-year-old female with congenital absence of stapedius muscle and tendon. She presented with congenital, bilateral, non progressive, moderate conductive hearing loss, and was diagnosed with this condition at surgery. There was co-existent tympanosclerosis in the middle ear that resulted in ossicular chain fixation and absence of round window reflex. The tympanosclerotic plaques were meticulously removed, ossicular chain mobility was restored, and a type II ossiculoplasty was done, along with reconstruction of the posterosuperior bony canal wall with cartilage perichondrium complex. Apart from the clinical presentation and its management, the present report also emphasises the plausible theories on relevant embryology explaining such an unusual event.