What is the most likely diagnosis for a patient with acute right lower abdominal pain, nausea, rebound tenderness, and recent menstrual period?

Ovarian Torsion

The most likely diagnosis is ovarian torsion (Option B), given the acute onset of right lower abdominal pain with rebound tenderness in a reproductive-age woman with normal vital signs except tachycardia and normal laboratory values. 1

Clinical Reasoning

Why Ovarian Torsion is Most Likely

• The absence of fever argues strongly against infectious etiologies like pelvic inflammatory disease, which typically presents with fever, elevated white blood cell count, and bilateral pain 1
• The elevated heart rate (100/min) likely reflects pain and potential early hemodynamic changes characteristic of ovarian torsion, rather than systemic infection 1
• Normal white blood cell count (9.8 x 10^9/L) makes appendicitis and pelvic inflammatory disease less likely, though it does not exclude them entirely 2
• The presence of rebound tenderness indicates peritoneal irritation from an acute adnexal process, most consistent with ovarian torsion 1

Critical Diagnostic Pitfall to Avoid

Do not rely on the absence of a palpable mass or normal Doppler flow to exclude ovarian torsion—38% to 60% of patients with surgically confirmed torsion have normal Doppler flow on ultrasound. 1 The diagnosis is clinical and requires urgent imaging confirmation.

Immediate Diagnostic Workup

First-Line Testing

• Obtain serum β-hCG immediately before any imaging to exclude ectopic pregnancy, which can present identically but requires positive pregnancy test 2, 1
• Transvaginal ultrasound with Doppler is the initial imaging study of choice for suspected gynecologic pathology in reproductive-age women with negative β-hCG 3, 2

Ultrasound Findings Suggestive of Torsion

• Enlarged edematous ovary 1
• Presence of an ovarian cyst or mass 1
• Potentially decreased or absent flow on color Doppler (though normal flow does NOT exclude torsion) 1

Why Other Diagnoses Are Less Likely

Pelvic Inflammatory Disease (Option D)

• Requires fever and elevated WBC, both absent in this patient 1
• Typically presents with bilateral lower abdominal pain, cervical motion tenderness, and purulent cervical discharge 2

Ureterocele (Option A)

• Would not explain rebound tenderness or acute onset pain 3
• Typically presents with urinary symptoms and flank pain, not isolated right lower quadrant pain 2

"Honeymoon Cysts" (Functional Ovarian Cysts) (Option C)

• A ruptured hemorrhagic cyst can cause acute pain, but typically presents with more diffuse peritoneal signs and free fluid throughout the pelvis rather than localized rebound tenderness 1
• Most functional cysts are asymptomatic or cause mild discomfort, not acute surgical abdomen 4

Management

Emergent gynecologic consultation for surgical exploration is required once ovarian torsion is suspected based on clinical presentation and imaging. 1 Early laparoscopic management correlates with favorable outcomes and potential ovarian preservation, with shorter hospital stay and fewer postoperative complications compared to laparotomy 5, 4

The diagnosis of ovarian torsion is missed in approximately 50% of patients initially because clinical features are nonspecific, emphasizing the need for high clinical suspicion in reproductive-age women with acute lower abdominal pain 5, 4