Morgagni hernia (MH) is a form of congenital diaphragmatic hernia (CDH) characterized by an incomplete formation of diaphragm, resulting in the protrusion of abdominal organs into the thoracic cavity. The estimated incidence of CDH is between 1 in 2000 and 1 in 5000 live births, although the true incidence is unknown. MH typically presents in childhood and can be diagnosed either prenatally or postnatally. However, it can also be asymptomatic and carry the risk of developing into a life-threatening condition in adulthood.

A 76-year-old female with no history of prior abdominal surgeries presented for an elective colonoscopy for polyp surveillance. During the procedure, when approaching the hepatic flexure, the scope could not be advanced further despite multiple attempts. The patient experienced mild abdominal discomfort, leading to the abortion of the procedure. While in the recovery area, she developed increasing abdominal pains and hypotension. Urgent abdominal imaging revealed herniation of the proximal transverse colon through a MH into the chest with evidence of perforation. The patient underwent laparoscopic urgent colonic resection and primary hernia repair and was discharged uneventfully 2 d later.

A MH is a rare condition in adults that can present as a life-threatening complication of colonoscopy, even in patients with a history of uneventful colonoscopies. This case highlights the importance of considering congenital and internal hernias when faced with sudden and unexplained difficulties during colonoscopy. If there is a suspicion of MH, the endoscopist should halt the procedure and immediately obtain abdominal imaging to confirm the diagnosis.