Antrum

AntrumThe anatomical expression antrum describes the widening of cavities in various organs or bones:

pyloric antrum: the oral initial portion of the stomach

antrum cardiacum: the ampulla shaped dilated part of the esophagus in the region between diaphragm and cardia

antrum mastoideum: the largest pneumatised cavity in the mastoid process of the os temporale

Source: Atlas of Endoscopy