For thousands of years, trepanation--the act of scraping, cutting, or drilling an opening into the cranium--was practiced around the world, primarily to treat head trauma but also for headaches, seizures and mental illnesses. Sometimes it was even done to expel demons.

It sounds garish now, but ancient Peruvians were surprisingly adept at it, so adept that Incan "neurosurgeons" had twice the survival rate for the procedure than better equipped surgeons during the American Civil War centuries later.

Obviously there could be differences in when it was done, so it may be due to confounders that in Incan times the mortality rate was between 17 and 25 percent while during the Civil War it was between 46 and 56 percent. 

A new paper can only speculate on reasons why, but some notions make sense, such as the lack of hygiene during battlefield conditions and during the time of the Civil War. The best surgeons were working in the Civil War and due to harsh conditions surgeons often used unsterilized medical tools and their bare fingers to probe open cranial wounds or break up blood clots. That is why so many soldiers with an injury suffered from infections. 

Credit: University of Miami

In calmer Incan times, they clearly prevented infection, though it is unknown know how the ancient Peruvians did it. Nor is it known what they used as anesthesia, but since there were so many cranial surgeries they likely used something--possibly coca leaves or a fermented beverage. Like most of the America's before the arrival of Europeans, they didn't keep much in the way of written records.

Whatever their methods, ancient Peruvians had plenty of practice. More than 800 prehistoric skulls with evidence of trepanation, sometimes up to seven holes, have been found in the coastal regions and the Andean highlands of Peru, the earliest dating back to about 400 B.C. That's more than the combined total number of prehistoric trepanned skulls found in the rest of the world. Which is why Verano devoted an entire book, Holes in the Head--The Art and Archeology of Trepanation in Ancient Peru, to the 800-plus skulls, most of which were collected from burial caves and archaeological digs in the late 1800s and early 1900s and reside in museums and private collections today.

The researchers gauged survival by classifying the extent of bone remodeling around the trepanned holes, which indicates healing. If there was no evidence of healing the researchers assumed the patient died during or within days of the surgery. If the margins of the trepanation openings showed extensive remodeling, they considered the operation successful and the patient long-lived. Those classifications show how ancient Peruvians significantly refined their trepanation techniques over the centuries. They learned, for example, not to perforate the protective membrane surrounding the brain--a guideline Hippocrates codified in ancient Greece at about the same time, 5th century, B.C., that trepanning is thought to have begun in ancient Peru.

The long-term survival rates from such "shallow surgeries" in Peru during those early years, from about 400 to 200 B.C., proved to be worse than those in the Civil War, when about half the patients died. But, from 1000 to 1400 A.D., survival rates improved dramatically, to as high as 91 percent in some samples, to an average of 75 to 83 percent during the Incan period, the study showed.

By the end of World War I, cranial surgery had evolved into the distinct profession of neurosurgery, which continues to improve our understanding of brain anatomy, physiology and pathology. Now neurosurgeons regularly cut into the brain to remove tumors and blood clots, reduce intracranial pressure from massive strokes and trauma, repair vascular and structural anomalies and treat a myriad of other complex problems--with great success.