Next Step: Pelvic Ultrasound with Doppler
The next step is transvaginal and transabdominal pelvic ultrasound with Doppler, which is the first-line imaging modality for evaluating reproductive-age women with lower abdominal pain of suspected gynecologic origin. 1, 2
Rationale for Pelvic Ultrasound First
Pregnancy must be ruled out first with a urine or serum β-hCG test, even though the patient reports no chance of pregnancy, as this is mandatory in all reproductive-aged women with pelvic pain and will guide all subsequent management decisions 1, 2
Pelvic ultrasound is the appropriate initial imaging because the clinical presentation (31-year-old female, lower abdominal pain, nausea, mid-cycle timing 2 weeks post-menses, negative UA, normal vitals) points toward gynecologic pathology as the most likely etiology 1, 2
The timing is critical: pain occurring 2 weeks after last menstrual period corresponds to mid-cycle, raising suspicion for ovulation-related pathology (hemorrhagic corpus luteum cyst, ovarian cyst rupture) or early ovarian torsion 1, 3
What the Ultrasound Should Assess
The ultrasound evaluation should specifically examine:
Ovaries for cysts, masses, or torsion, with Doppler assessment of ovarian blood flow (sensitivity 86-100% for torsion when arterial flow is absent) 2, 4
Uterus and adnexa for masses, free fluid, or signs of pelvic inflammatory disease (thick tubal wall has 100% sensitivity, "cogwheel" sign has 86% sensitivity for PID) 2
Presence of free fluid in the pelvis, which may indicate cyst rupture, hemorrhage, or other acute pathology 1
Why NOT CT First
Starting with CT instead of ultrasound in reproductive-aged women exposes patients to unnecessary radiation when gynecologic causes are most likely, and ultrasound provides superior characterization of ovarian and uterine pathology 2
CT is reserved for when ultrasound is nondiagnostic or when non-gynecologic pathology (appendicitis, diverticulitis) becomes more likely based on clinical findings 1
If Ultrasound is Equivocal or Negative
MRI pelvis without and with IV contrast is the next appropriate step if ultrasound findings are equivocal or require further characterization, as it is superior for detecting endometriosis and characterizing complex adnexal masses 2, 4
Consider non-gynecologic causes including appendicitis (though typically presents with right lower quadrant pain and fever), urologic pathology, or gastrointestinal causes if pelvic ultrasound is entirely normal 1, 3
Common Pitfalls to Avoid
Do not skip the pregnancy test even with patient denial of pregnancy risk—ectopic pregnancy can present with similar symptoms and has serious morbidity/mortality implications 1, 2
Do not order plain radiographs, as they have very limited utility in evaluating pelvic pain and should not be used 2
Do not assume benign pathology based on normal vitals alone—ovarian torsion can present with normal vital signs early in its course, and delayed diagnosis leads to ovarian loss 5
A complete pelvic examination is always indicated in cases of lower abdominal pain to identify the source, which may be pelvic inflammatory disease, ovarian mass or torsion, or ectopic pregnancy 1