Which altitude-related condition occurs both on ascent and descent?

Barosinusitis is the correct answer because it refers specifically to the pressure-related discomfort and inflammation experienced in the sinus cavities that can occur during both ascent and descent. As air pressure changes when ascending or descending in altitude, it can impact the sinuses, leading to pain, discomfort, and in some cases, infection if the pressure differences can't be equalized effectively.

In contrast, while variations of barometric pressure can affect air-filled spaces in the body, not all conditions manifest during both ascent and descent. For instance, barotitis mainly arises during descent as the pressure from the water or altitude can affect the ear's ability to equalize pressure. Barondontalgia relates specifically to dental pain experienced during changes in altitude and is also more prevalent during descent. Hypoxia, while a critical condition associated with altitude, is primarily related to reduced oxygen availability at high altitudes rather than the pressure changes experienced during ascent or descent. Therefore, the defining characteristic of barosinusitis is its occurrence related to pressure variations during both phases of altitude change.