Eustachian Tube Dysfunction (ETD): This condition is characterized by the inability of the Eustachian tube to properly regulate air pressure in the middle ear, leading to hearing loss that worsens with air pressure changes, such as during flights. The association with sinusitis, which can cause Eustachian tube obstruction, further supports this diagnosis.

Middle Ear Effusion: This condition, often secondary to sinusitis or upper respiratory infections, can cause bilateral hearing loss due to fluid accumulation in the middle ear. Air pressure changes can exacerbate symptoms.
Otosclerosis: A condition where abnormal bone growth in the middle ear causes hearing loss. While it doesn't directly relate to air pressure changes or sinusitis, it can cause gradual hearing loss and is a common cause of conductive hearing loss.
Patulous Eustachian Tube: A condition where the Eustachian tube remains open, leading to autophony and hearing loss that can be exacerbated by nasal congestion or sinusitis.

Acoustic Neuroma: A rare tumor on the nerve connecting the inner ear to the brain, which can cause gradual hearing loss, often accompanied by tinnitus or balance problems. Although less likely, missing this diagnosis could have significant implications.
Meniere's Disease: An inner ear disorder that involves vertigo, tinnitus, hearing loss, and ear fullness. While the primary symptom is vertigo, the hearing loss can be fluctuating and might seem to worsen with air pressure changes due to the patient's subjective experience of ear fullness.

Osteogenesis Imperfecta: A genetic disorder that can affect the bones of the middle ear, leading to hearing loss. It's a rare condition but could be considered in patients with a relevant family history or other systemic manifestations.
Relapsing Polychondritis: An autoimmune disorder that can affect cartilaginous structures, including those in the ear, potentially leading to hearing loss. It's rare and would typically be associated with other systemic symptoms.