Antrum

In biology, antrum is a general term for a cavity or chamber, which may have specific meaning in reference to certain organs or sites in the body.

In vertebrates, it may refer specifically to:

• Antrum cardiacum, a dilation that occurs in the esophagus near the stomach (forestomach)
• Antrum follicularum, the cavity in the epithelium that envelops the oocyte
• Mastoid antrum, a cavity between the middle ear and temporal bone in the skull
• Pyloric antrum, the initial portion of the pyloric part of the stomach. This is what is usually referred to as "antrum" in stomach-related topics.
• Maxillary antrum or antrum of Highmore, the maxillary sinus, a cavity in the maxilla and the largest of the paranasal sinuses

In invertebrates, it may refer specifically to:

• Antrum of female lepidoptera genitalia