Endometriosis presenting with recurrent massive hemorrhagic ascites and diagnosed by core needle biopsy: A case report

RATIONALE: Recurrent massive hemorrhagic ascites secondary to endometriosis is extremely rare in the medical literature. PATIENT CONCERNS: We report the case of a 24-year-old nulliparous woman presenting with severe abdominal distention, massive ascites, moderate anemia, menstrual pain, and an elevated CA-125 level. DIAGNOSIS: We found a thickened peritoneum in the left lower abdomen by ultrasound during the follow-up period, and endometriosis was subsequently diagnosed by performing core needle biopsy (CNB). INTERVENTIONS AND OUTCOMES: The patient received medical treatment for endometriosis and had a good response to the treatment. LESSONS: This is the first case in which endometriosis ectopic to peritoneum was diagnosed by CNB. Endometriosis should be considered a differential diagnosis when recurrent massive hemorrhagic ascites occur. CNB should be valued as a method for diagnosing endometriosis.