Trephine

A trephine (also sometimes spelled trepan) is a surgical instrument used to remove a circular section of tissue. It functions similarly to a drill or hole saw.

The term "trephine" can refer both to the instrument itself and the surgical procedure that uses it, called trephination or trepanning. The procedure dates back to prehistoric times, with evidence of trephination found in archaeological sites around the world.

Traditionally, trephines were used to remove a circular piece of skull bone, often to relieve pressure from swelling or bleeding under the skull (subdural hematoma or epidural hematoma), or to treat skull fractures. This allows the brain to expand and reduces intracranial pressure.

Modern trephines are often powered and come in various sizes. They are still used in neurosurgery, though less frequently due to the availability of other techniques. They are also used in other surgical fields, such as ophthalmology, to remove a circular section of the cornea for corneal transplantation. Biopsies of various tissues can also be obtained using a trephine.

The historical use of trephination is often attributed to primitive attempts at healing, addressing headaches, seizures, or mental disorders. Some believe it was used to release "evil spirits." While these interpretations are common, the exact reasons for ancient trephination remain a subject of ongoing research and debate.