Eustachian Tube Dysfunction: This condition is characterized by the inability of the Eustachian tube to properly regulate air pressure in the ear, leading to a sensation of fullness or fluid in the ear, which might be perceived as "running" of the ears. It's a common issue and can be caused by various factors such as allergies, colds, or sinus infections.

Middle Ear Effusion: Fluid accumulation in the middle ear can cause a sensation of fullness or running in the ears. This condition often follows an upper respiratory infection and can be associated with hearing loss.
Allergic Rhinitis: Allergies can lead to nasal congestion and Eustachian tube dysfunction, resulting in ear fullness or a sensation of fluid running in the ears.
Sinusitis: Inflammation of the sinuses can lead to Eustachian tube dysfunction and cause similar symptoms.

Acoustic Neuroma: A rare tumor on the nerve connecting the inner ear to the brain, which can cause hearing loss, balance problems, and less commonly, a sensation of fullness in the ear. Although unlikely, missing this diagnosis could have significant consequences.
Temporal Bone Fracture: Trauma to the temporal bone can cause leakage of cerebrospinal fluid (CSF) into the ear, leading to a sensation of fluid running. This is a medical emergency.
Meningitis: Infection of the protective membranes covering the brain and spinal cord can cause CSF leakage into the ears, among other severe symptoms.

Patulous Eustachian Tube: A rare condition where the Eustachian tube remains open, causing an abnormal patency and leading to autophony (hearing one's own breathing sounds) and a sensation of ear fullness.
Cholesteatoma: A type of skin cyst located in the middle ear that can cause destruction of the surrounding bone and tissue, leading to various symptoms including hearing loss and ear fullness.