What obstetric (OB) emergencies should be considered in a young female presenting with right-sided flank pain?

Obstetric Emergencies in Young Female with Right-Sided Flank Pain

In a young female with right-sided flank pain, the most critical obstetric emergencies to consider are ectopic pregnancy (particularly if ruptured), ovarian torsion, and appendicitis in pregnancy—all of which can cause significant morbidity and mortality if missed.

Immediate Priority: Pregnancy Status

• Obtain a β-hCG test (serum or urine) immediately in any female of reproductive age with abdominal or flank pain, regardless of contraceptive use or reported sexual history 1.
• This single test determines your entire diagnostic pathway and cannot be skipped, as ectopic pregnancy accounts for 1-2% of all pregnancies with a 20% rupture rate 2.

If β-hCG is Positive: Life-Threatening OB Emergencies

Ectopic Pregnancy (Most Critical)

• Right-sided flank/lower quadrant pain with positive β-hCG demands immediate evaluation for ectopic pregnancy, which is the leading cause of first-trimester maternal mortality 1.
• Transvaginal ultrasound is the initial imaging modality of choice 1.
• Key ultrasound findings to assess:
  • Absence of intrauterine pregnancy (IUP) with β-hCG >2,000 mIU/mL suggests ectopic pregnancy (57% likelihood) 1
  • Adnexal mass or free fluid significantly increases ectopic pregnancy risk 1
  • Empty uterus with β-hCG >3,000 mIU/mL has a likelihood ratio of 19 for ectopic pregnancy 1

Critical pitfall: Tachycardia is an unreliable indicator of ruptured ectopic pregnancy—do not wait for hemodynamic instability 3.

Ovarian Torsion

• Ovarian torsion presents with acute-onset unilateral pelvic/flank pain and can occur during pregnancy, particularly in patients undergoing fertility treatment 4, 5.
• Incidence is 2-5% of gynecologic emergencies, with 25% associated with dermoid cysts 2.
• Ultrasound with Doppler is the initial imaging, though normal flow does not exclude torsion 1.
• MRI has 100% sensitivity and 93.6% specificity for ovarian torsion in reproductive-age women 1.
• Requires urgent surgical detorsion to preserve ovarian function 4, 2.

Appendicitis in Pregnancy

• Appendicitis is the most common non-obstetric surgical emergency in pregnancy requiring emergent surgery 1.
• Right-sided pain location may not correlate reliably with appendicitis in pregnant patients due to anatomic displacement 1.
• Ultrasound is the first-line imaging modality 1.
• If ultrasound is indeterminate, MRI without contrast is the next step (sensitivity 96.8%, specificity 99.2%) 1.
• Pregnant women are more likely to present with perforated appendicitis, which carries higher risk of fetal loss 1.

If β-hCG is Negative: Non-Pregnancy OB/GYN Emergencies

Ovarian Torsion (Still Primary Concern)

• Remains a critical diagnosis even without pregnancy 1, 5.
• Transvaginal ultrasound is initial imaging, looking for asymmetrically enlarged ovary with twisted pedicle 1.
• CT findings include twisted vascular pedicle (best seen on multiplanar reformations), abnormal or absent ovarian enhancement, and deviation of uterus to affected side 1.

Tubo-Ovarian Abscess

• Presents with fever, pain, and leukocytosis 1.
• CT shows thick-walled adnexal fluid collection with septations, gas bubbles, and indistinct borders 1.
• Right ovarian vein entering a right pelvic abscess has 100% specificity and 94% sensitivity for tubo-ovarian abscess versus peri-appendiceal abscess 1.

Hemorrhagic Ovarian Cyst Rupture

• Can present with acute flank pain and hemoperitoneum 1, 2.
• Ultrasound typically diagnostic, showing complex cyst with internal echoes and free fluid 1.

Imaging Algorithm

For pregnant patients:

1. Transvaginal ultrasound first 1
2. If indeterminate → MRI without contrast 1
3. Low-dose CT only if MRI unavailable and clinical suspicion high 1

For non-pregnant patients:

• Transvaginal ultrasound for suspected gynecologic pathology 1
• CT abdomen/pelvis with IV contrast if broader differential or ultrasound non-diagnostic 1

Critical Pitfalls to Avoid

• Never assume a young female is not pregnant—always obtain β-hCG 1.
• Do not use standard CT as first-line imaging in pregnant patients when ultrasound and MRI are available 1.
• Normal Doppler flow does not exclude ovarian torsion—clinical suspicion should drive surgical exploration 1.
• Appendicitis pain location is unreliable in pregnancy—maintain high index of suspicion regardless of pain location 1.
• Hemodynamic stability does not exclude ruptured ectopic pregnancy—one-third of patients with large hemoperitoneum have intact fallopian tubes 1.