The Caritas Medical Centre said a doctor removed a female patient's fallopian tube when it was her appendix that was supposed to be taken out.

In announcing the incident on Friday, the hospital promised to investigate the case and apologised to the patient and her family.

The patient, 48, was admitted for abdominal pain on June 17. A CT scan suggested she had early appendicitis, mild colitis and a small paratubal cyst near one of her fallopian tubes.

"The patient was arranged for an emergent minimally invasive laparoscopic appendectomy operated by a higher surgical trainee," a statement said.

A laparoscopic appendectomy is a surgical procedure to remove the appendix through small incisions in the abdomen.

The hospital noted the cyst was torn during the procedure but the bleeding later stopped, adding the patient remained in stable condition afterwards.

But the woman developed a fever and reported more abdominal pain on Monday, and had another scan.

"The report revealed the appendix remained intact and the pathology report... showed that the excised tissue was a fallopian tube instead of the appendix," the hospital said.

The woman then underwent an operation to have the inflamed appendix removed.

A preliminary investigation suggested the doctor mistook the fallopian tube for the appendix "due to tissue adhesion near the surgical site", the hospital added.

The hospital has told its surgery unit to review procedures involving a minimally invasive surgical technique.

A root cause analysis panel comprising five members will investigate the incident and submit a report on the findings within eight weeks.