A 7-year-old boy presents with bilateral progressive sensorineural hearing loss detected on routine school screening. His parents report a sudden worsening of hearing 2 weeks after a minor head injury during play. On examination, he has a firm, non-tender thyroid mass. Audiometry shows bilateral high-frequency predominant SNHL with an air-bone gap at low frequencies. High-resolution CT temporal bone reveals a cystic apex with only 1.5 cochlear turns, dilated vestibule, and enlarged vestibular aqueduct (midpoint width 2.2 mm). The audiogram pattern marked **A** in the diagram is consistent with which of the following diagnoses?

Explanation

## Why Mondini inner ear malformation (Incomplete Partition Type II), likely associated with Pendred syndrome is right The clinical presentation and imaging findings are pathognomonic for Mondini malformation (Incomplete Partition Type II per Sennaroglu classification). The key diagnostic triad is present: (1) only 1.5 cochlear turns with cystic apex (normal = 2.5 turns), (2) dilated vestibule, and (3) enlarged vestibular aqueduct (EVA; midpoint >1.5 mm, opercular >2 mm). The audiogram pattern marked **A** — bilateral high-frequency progressive SNHL with sudden drops after minor head trauma — is the classic presentation. The sudden hearing loss after head injury occurs because the enlarged vestibular aqueduct transmits intracranial pressure changes to the inner ear, causing endolymphatic ruptures and acute hair-cell loss. The presence of a thyroid mass in a euthyroid child suggests Pendred syndrome (SLC26A4 mutation), which is strongly associated with Mondini malformation. The small air-bone gap at low frequencies reflects the third-window effect from the enlarged vestibular aqueduct. Per Dhingra and Cummings, this constellation is diagnostic of Mondini with Pendred phenotype. ## Why each distractor is wrong - **Otosclerosis with secondary endolymphatic hydrops**: Otosclerosis presents with conductive or mixed hearing loss (stapes fixation), not bilateral sensorineural loss. The imaging findings (cystic apex, dilated vestibule, EVA) are not features of otosclerosis. Otosclerosis does not cause sudden hearing loss after minor head trauma. - **Noise-induced hearing loss with congenital stapes fixation**: Noise-induced loss requires significant acoustic exposure history, which is absent in a 7-year-old. The characteristic "4 kHz notch" is not described. The imaging findings (cystic apex, EVA) are incompatible with noise-induced loss. Congenital stapes fixation would not explain the bilateral progressive SNHL pattern or the thyroid mass. - **Presbycusis with concurrent autoimmune inner ear disease**: Presbycusis is age-related and does not occur in children. The sudden drop after head trauma and the imaging findings (Mondini triad) are not consistent with presbycusis or autoimmune inner ear disease. The thyroid mass and euthyroid status point to Pendred, not autoimmunity. **High-Yield:** Mondini malformation = 1.5 cochlear turns + dilated vestibule + enlarged vestibular aqueduct (EVA) → bilateral progressive SNHL with sudden drops after head trauma; if euthyroid goiter present → Pendred syndrome (SLC26A4 mutation); counsel strict avoidance of contact sports and head trauma. [cite: Dhingra Diseases of Ear Nose & Throat 7e Ch 17; Cummings Otolaryngology 7e Ch 195]