A 16-year-old girl comes to the emergency department due to left lower quadrant abdominal pain that suddenly started overnight. The pain does not radiate and is 5/10 in severity. The patient does not report fever, vomiting, dysuria, diarrhea, or vaginal bleeding. She is sexually active with her boyfriend and is using condoms with spermicide for contraception. Her last menstrual period was 2 weeks ago. Menses occurs every 28 days with 5 days of moderate bleeding and some associated cramping on the first 2 days. Temperature is 37.2 C (99 F), blood pressure is 110/66 mm Hg, and pulse is 80/min. BMI is 22 kg/m2. Abdominal examination shows mild left lower quadrant tenderness with no rebound. Pelvic examination shows a small, anteverted uterus with tenderness over a slightly enlarged left adnexa; the right adnexa is normal. Urine pregnancy test is negative. Pelvic ultrasound shows the left ovary with a 3-cm cyst with several subcentimeter cysts in the periphery. There is normal Doppler blood flow with a small amount of free fluid in the posterior cul-de-sac. Which of the following is the most likely diagnosis for this patient?
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This patient has sudden left lower quadrant pain and an enlarged left adnexa; in reproductive-aged women with these findings, initial evaluation includes a pregnancy test and transvaginal ultrasound to rule out gynecologic emergencies (eg, ectopic pregnancy, ovarian torsion).
This patient's negative pregnancy test and an ultrasound that shows a simple ovarian cyst with a small amount of free fluid in the pelvis suggest a benign etiology. With the timing of the patient's last menstrual period 2 weeks ago (eg, late follicular phase of menses), the most likely cause of her symptoms is ovulation (ie, Mittelschmerz). In women with ovulatory menstrual cycles, a dominant follicle (ie, a large cyst with multiple smaller cysts) is formed during the follicular phase (resulting in an enlarged adnexa); when the oocyte is released during ovulation, pain can develop due to rupture of the follicle and subsequent release of a small amount of blood and fluid that irritates the peritoneum. Most patients can be managed with reassurance and pain management (eg, nonsteroidal anti-inflammatory medications).
(Choice A) An ectopic pregnancy can present with abdominal pain and a large adnexa; however, patients typically have a complex adnexal mass and a positive pregnancy test, making this diagnosis unlikely.
(Choice B) An endometrioma arises from ectopic endometrium within the ovary that bleeds and forms a hematoma, which appears on ultrasound as a homogenous ovarian cyst with a ground-glass appearance.
(Choice D) Ovarian torsion results from a large ovarian mass twisting around the infundibulopelvic ligament causing occlusion of the ovarian vessels, resulting in ovarian ischemia. It often presents with severe unilateral pain with associated nausea and vomiting; however, ultrasound typically shows absent blood flow to the adnexa, making this diagnosis less likely.
(Choice E) Polycystic ovary syndrome is characterized by menstrual irregularities, hyperandrogenism, and polycystic ovaries on ultrasound. This patient has normal menstrual cycles; in addition, the large follicle with multiple subcentimeter follicles on ultrasound is consistent with normal postovulatory ovarian changes.
(Choice F) A tuboovarian abscess presents with fever, diffuse lower abdominal pain, and a complex, multicystic adnexal mass with thickened walls on ultrasound. This is an unlikely diagnosis in this patient without fever and with imaging that shows a simple ovarian cyst.
Educational objective:
Mittelschmerz is a physiologic cause of unilateral abdominal pain in young women. The pain occurs in the middle of the menstrual cycle (ie, follicular phase), corresponding with ovulation.