The Los Angeles County Medical Examiner reported that the obstruction was caused by adhesions that developed after the surgery, which is a known long-term complication.
Presley had a history of overmedicating, often forgetting that she had already taken her prescription medication and repeating her doses.
The toxicology report revealed therapeutic levels of oxycodone and other medication in her blood, but they were not considered contributing factors to her death.
Lisa Marie Presley passed away on January 12, six months prior to the medical examiner's report.
She was survived by her daughters, actress Riley Keough, and 14-year-old twins Finley and Harper Lockwood.
Lisa Marie Presley had a successful music career with two albums, "To Whom It May Concern" and "Now What," both of which reached the top 10 of the Billboard 200 album chart.