Why can the inflammatory process spread from the nasopharynx to the middle ear?

There is a small tube between the nasal cavity (nasopharynx) and the ear. It connects the middle ear, where there is an air cavity and the pharynx. This tube is necessary to balance the pressure in the tympanic cavity and relieve us of the feeling of congestion that occurs when atmospheric pressure changes, for example, when flying on an airplane, when sneezing. But the tube also has negative sides: along it, the infection spreads very quickly from the nose to the middle ear. Therefore, a runny nose is often accompanied by otitis media (ear inflammation).