The frontal sinus opens in front of the frontal crypt in the middle nasal tract, and is one of the four pairs of sinuses that open in the middle nasal tract. The posterior group of septal sinuses opens in the upper nasal tract, and the pterygoid sinuses open in the pterygoid sieve fossa of the upper nasal tract. The sinuses that open in the middle nasal tract are called the anterior group of sinuses, depending on the opening of each sinus. The sinuses that open in the upper nasal tract are called the posterior sinuses. Clinically, if a purulent discharge is found in the middle nasal tract during anterior rhinoscopy, the mucous membrane of the anterior sinuses is considered to have purulent inflammation. If a purulent discharge is found at the olfactory fissure, it is considered to be caused by posterior sinusitis. If a clear diagnosis of which sinus inflammation is needed, a sinus CT examination is required at the Department of Otolaryngology. In primary care hospitals that are not equipped to do sinus CT, a low head position test can be performed to determine the presence of sinusitis based on the drainage characteristics of the sinus opening location.