A female patient with a history of a 3-cm right ovarian cyst, chlamydial cervicitis, and dysmenorrhea, presents with sudden onset severe right lower quadrant pain, nausea, vomiting, and a negative urine pregnancy test, what is the most likely diagnosis?

Ovarian Torsion

The most likely diagnosis is ovarian torsion (Option D), given the sudden onset of severe, constant right lower quadrant pain, nausea, vomiting, known 3-cm ovarian cyst, and negative pregnancy test in this reproductive-age woman. 1

Clinical Reasoning

Why Ovarian Torsion is Most Likely

The clinical presentation is classic for ovarian torsion:

• Sudden onset of severe, constant pain is the hallmark presentation, with pain that may fluctuate in intensity but rarely completely resolves without intervention 1
• Pre-existing ovarian cyst is the most common risk factor for torsion, occurring in 2-15% of patients with adnexal masses who undergo surgical treatment 2
• Nausea and vomiting occur in approximately 90% of ovarian torsion cases 3
• Right-sided predominance is common, with 60% of cases presenting with right lower quadrant pain 3
• The 6-hour duration fits the typical presentation, as 78.9% of patients present within 24 hours of symptom onset 3

Why Other Diagnoses are Less Likely

Acute appendicitis (Option A) is less likely because:

• While appendicitis can present similarly, the presence of a known ovarian cyst makes torsion more probable 1
• The sudden onset of severe pain is more characteristic of torsion than the typical periumbilical pain migrating to the RLQ seen in appendicitis 4

Ectopic pregnancy (Option B) is excluded:

• The negative urine pregnancy test essentially rules out intrauterine or ectopic pregnancy 4
• Serum β-hCG becomes positive approximately 9 days after conception, making a negative test highly reliable 4

Endometriosis (Option C) is unlikely because:

• Endometriosis typically causes chronic cyclic pain and dysmenorrhea, not sudden-onset acute pain 5
• The acute presentation over 6 hours does not fit the chronic pain pattern of endometriosis 5

Tuboovarian abscess (Option E) is less likely because:

• While the history of chlamydial cervicitis is a risk factor for pelvic inflammatory disease, tuboovarian abscess typically presents with fever, which is not mentioned in this case 4
• The sudden onset is more consistent with torsion than the subacute presentation of abscess 6

Critical Diagnostic Considerations

Immediate Next Steps

Ultrasound is the essential first-line imaging modality and should be performed urgently:

• Transvaginal ultrasound combined with transabdominal views provides the most comprehensive assessment 1
• Key findings include unilaterally enlarged ovary (>4 cm), peripheral follicles, abnormal or absent venous flow (100% sensitivity, 97% specificity), and whirlpool sign (90% sensitivity) 1
• Doppler evaluation is mandatory, as color/power Doppler has 80% sensitivity and 88% specificity for torsion 1

Critical Pitfall to Avoid

Normal arterial blood flow does NOT rule out ovarian torsion 1, 7:

• Torsion can be intermittent or partial 1
• Venous flow abnormalities are more sensitive than arterial flow changes 1
• The presence of blood flow on Doppler has poor negative predictive value 7

Urgency of Management

This is a gynecological emergency requiring immediate surgical consultation 1, 8:

• Early detection is essential to prevent adnexal necrosis and preserve fertility 1
• Laparoscopic detorsion with ovarian preservation is the standard of care, even when the ovary appears necrotic 1
• Only 18-20% of ovaries that appear necrotic intraoperatively are actually necrotic on pathological examination 1
• Most patients (94.7%) have viable ovaries if surgery is performed promptly 3