In 1865, Ephraim George Squier, an American archaeologist in Cuzco, Peru, found an Inca skull, dated 1400–1530, with signs of trepanation—a surgical intervention in which a hole is drilled or scraped into the skull. This discovery suggested neurosurgery was performed in the early Americas and ignited theories on brain size and intelligence among scientists.1
Squier’s finding sparked conversation with Paul Broca, a French physician, anatomist, and anthropologist best known for his research on Broca’s area (a region of the frontal lobe that is named after him), and other leading researchers who sought to uncover the mystery behind trepanation.
The Peruvian Highlands in the 15th and 16th centuries was an area full of warfare. Weapons used during this period included sling stones and clubs. Bones from Huarochirí, Peru, in the Hrdlicka skeleton collection at the Smithsonian National Museum of Natural History, and archeological crania studies from the south central and Cuzco regions confirm that head trauma was common in the Peruvian Highlands.2 Furthermore, early success from this procedure is evidenced by skulls found with multiple trepanations without fractures. Multiple trepanations may have been intended to treat headaches, convulsions, or other intracranial mass disorders.2
Today, trepanation is known as a craniotomy.3 The Incas performed trepanations using bifacial, obsidian tools to create incisions in patients’ skulls.3,4 In later years, bronze and copper tools were used for these same procedures. The preferred surgical tool was the tumi, a curved metal knife that cut through skin and the pericranium. Natural materials like coca, datura, or yuca often were used as anesthesia in these procedures. Also, large amounts of alcoholic beverages such as chicha, a fermented corn drink, were given to patients to induce drowsiness.4
Although there were different methods of performing trepanation, the Incas most frequently practiced a circular grooving technique, which was the process of scoring an outline on the skull and removing the central plug.3,4 Some skulls were found with gold cranioplasties.4
A 2018 study by Kushner and colleagues analyzed 800 trepanned crania and compared the degree of healing of the Peruvian trepanations with the trepanation practices during “other ancient, medieval, or American Civil War periods.”3 This study concluded that in ancient Peru (400–200 BC), the long-term survival rate was 40% and improved to a high of 91% (1000–1400 AD). The average survival rate was determined to be 75%–83% during the Inca period (1400–1500 AD).3 Kushner compared these findings to the American Civil War, when the average mortality rate was 46%–56% in cranial surgeries. The high survival rates during the Inca Empire may be attributed to procedures being performed in open-air environments, the use of herbal medication, and single-use tools.3
Although trepanation was a worldwide practice, archaeological evidence confirms that Peru has the most trepanned skulls in history.5 Without modern anesthesia and aseptic protocols, it is astonishing that the Incas had such tremendous success with trepanation. All in all, Squier’s skull finding revolutionized the knowledge of ancient surgery and continues to influence medical historians today.
