Ovarian Torsion
The most likely diagnosis is ovarian torsion (Option B). This patient presents with the classic triad of sudden-onset severe unilateral pelvic pain, nausea/vomiting, and a palpable adnexal mass confirmed on ultrasound, with a negative pregnancy test effectively excluding ectopic pregnancy 1, 2.
Clinical Reasoning
Why Ovarian Torsion is Most Likely
The 6 cm ovarian mass is the critical risk factor: Ovarian cysts are three times more common in ovarian torsion cohorts than in the general population, and masses of this size significantly increase torsion risk 3.
Sudden-onset severe pain (9/10) with nausea and vomiting is characteristic: Nausea and vomiting occur in 70% of ovarian torsion cases, and acute pelvic pain is the most common presenting symptom 4, 5.
Palpable mass on examination: The presence of both tenderness and a palpable mass on physical examination strongly suggests an adnexal pathology with torsion 2, 4.
Tachycardia (HR 110) without fever: The elevated heart rate likely reflects pain and potential early hemodynamic changes, while the absence of fever argues against infectious etiologies 2.
Why Other Diagnoses are Less Likely
Ectopic pregnancy (Option A) is excluded: The negative urine hCG test essentially rules out both intrauterine and ectopic pregnancy, as serum β-hCG becomes positive approximately 9 days after conception 1. While ectopic pregnancy would present with similar pain and could have an adnexal mass, it requires a positive pregnancy test 1, 6.
Ruptured cyst (Option C) is less likely: While a ruptured hemorrhagic cyst can cause acute pain, it typically presents with more diffuse peritoneal signs and free fluid throughout the pelvis rather than a discrete 6 cm mass 1. The ultrasound confirmed a mass rather than just free fluid, making torsion more probable 2.
Appendicitis (Option D) is unlikely: Appendicitis would not explain the palpable mass on examination 1. While appendicitis can present with right lower quadrant pain and nausea/vomiting, the presence of a confirmed 6 cm ovarian mass on ultrasound points away from this diagnosis 1.
Critical Diagnostic Pitfalls
Normal Doppler flow does NOT exclude ovarian torsion: This is a crucial pitfall—38% to 60% of pregnant patients with confirmed torsion have normal Doppler flow on ultrasound, and the presence of blood flow on Doppler has poor negative predictive value 1, 2. The diagnosis must be made on clinical grounds combined with the presence of an enlarged ovary or mass 2, 5.
Ultrasound findings suggestive of torsion include: An enlarged edematous ovary, presence of an ovarian cyst or mass, and potentially decreased or absent flow on color Doppler—but remember that normal flow does not exclude the diagnosis 2, 4.
Immediate Management
Emergent gynecologic consultation for surgical exploration is required: Once ovarian torsion is suspected based on clinical presentation and imaging, surgery or detorsion is the mainstay of both diagnosis and definitive treatment 4, 5. Delayed diagnosis increases the risk of ovarian necrosis, loss of the ovary, and potential sepsis 2, 5.
Time is ovary: Early laparoscopic management correlates with favorable outcomes and potential ovarian preservation 2. The goal is surgical detorsion before irreversible ischemic damage occurs 4, 5.