MSFinals-1696

MSFinals-1696

A 35-year-old woman presents with increasing abdominal distension and feeling bloated, which has been getting worse over the last six months. She has no other medical history of note. She has regular periods with a 30-day cycle without heavy or intermenstrual bleeding.
On examination, there is an abdominal mass in the region of the left iliac fossa which is tender to palpation. The doctor orders blood tests and arranges an urgent ultrasound scan of the abdomen to assess the mass further.
Which of the following is the most likely diagnosis in this patient?