Pathophysiology
Clinical meaning
Acute otitis media (AOM) is an infection of the middle ear space most commonly precipitated by viral upper respiratory infection that causes inflammation and edema of the eustachian tube (ET) mucosa. The eustachian tube normally serves three critical functions: ventilation (equalizing middle ear pressure with atmospheric pressure), drainage (mucociliary clearance of secretions from the middle ear to the nasopharynx), and protection (preventing nasopharyngeal pathogens from refluxing into the middle ear). In children aged 6-24 months, the ET is anatomically shorter (~18 mm vs 36 mm in adults), more horizontal (10 degrees vs 45 degrees from horizontal), and more compliant (cartilaginous support is immature), making it inefficient at all three functions and explaining the peak incidence of AOM in this age group. When a viral URI causes ET mucosal edema, the tube becomes functionally obstructed. Negative pressure develops in the middle ear, drawing nasopharyngeal secretions and bacteria retrograde through the ET into the sterile middle ear space. The three most common bacterial pathogens colonizing the nasopharynx are Streptococcus pneumoniae (most virulent, highest complication rate including mastoiditis and meningitis), non-typeable Haemophilus influenzae...