An unusual pelvic mass.

Background: The differential diagnosis for a solid pelvic mass is broad and includes non-gynecologic masses such as retroperitoneal schwannoma. Theses benign nerve-sheath tumors can be mistaken for adnexal masses or cause non-specific bulk symptoms, which may lead patients to present to their Ob/Gyn or ultimately be referred to gynecologic oncologists for evaluation and possible resection. Cases: We discuss two cases of pelvic schwannoma: a 79-year-old woman who initially presented with a two-year history of left lower extremity cramping, paresthesia, and back pain, and a 40-year-old woman with right-sided flank pain and worsening dysmenorrhea, who presented with initial concern for adnexal mass. Conclusion: The differential diagnosis for a smooth, fixed, pre-sacral or sidewall mass on pelvic exam includes pelvic schwannoma. These nerve sheath tumors are typically benign; however, can cause a variety of symptoms due to regional mass effect and may significantly impact quality of life. Associated symptoms, if present, may be non-specific or difficult to localize (i.e. pelvic pain/fullness, urinary symptoms, constipation, and radiculopathy), which can lead to a delay in diagnosis if a comprehensive pelvic exam is not performed or if suspicion for an etiology of non-gynecologic origin is not considered. Recommended workup includes pelvic MRI followed by CT-guided biopsy. Management is guided by the patient's symptoms; if surgery is warranted, a minimally invasive, interdisciplinary approach is strongly preferred.