What are the differential diagnoses for a patient presenting with right lower quadrant abdominal pain and an ultrasound showing a lesion adjacent to the right ovary with peripheral flow?

Differential Diagnoses for Right Lower Quadrant Pain with Adnexal Lesion and Peripheral Flow

The primary differential diagnosis for a lesion adjacent to the right ovary with peripheral flow on ultrasound is ovarian torsion, followed by tubo-ovarian abscess, ruptured hemorrhagic cyst, and ectopic pregnancy (if pregnancy test positive). 1, 2

Critical First Step: Pregnancy Test

• Obtain β-hCG immediately to exclude ectopic pregnancy, as this is a life-threatening diagnosis that can present with similar imaging findings of an adnexal mass with peripheral vascularity 2, 3
• A negative pregnancy test effectively excludes ectopic pregnancy and narrows the differential significantly 2

Primary Gynecologic Differentials

Ovarian Torsion (Most Time-Sensitive)

• Peripheral flow pattern ("rim sign") is highly suggestive of ovarian torsion, representing preserved peripheral ovarian blood supply while central flow is compromised 1
• An enlarged edematous ovary with an associated cyst or mass is characteristic 2
• Critical pitfall: Normal Doppler flow does NOT exclude torsion—38% to 60% of confirmed torsion cases show normal flow on ultrasound 2, 4
• The twisted vascular pedicle may be visible on multiplanar imaging 1
• Requires emergent gynecologic consultation for surgical exploration, as early laparoscopic management correlates with ovarian preservation 2

Tubo-Ovarian Abscess (TOA)

• Presents as a thick-walled adnexal mass with peripheral enhancement and possible internal septations 1
• Associated findings include indistinct borders between uterus and adjacent structures, possible gas bubbles within the mass, and thickening of the round ligament 1
• The presence of a right ovarian vein entering a right pelvic abscess has 100% specificity and 94% sensitivity for TOA versus peri-appendiceal abscess 1
• Typically accompanied by fever and elevated inflammatory markers, though absence of fever does not exclude infection 2

Ruptured Hemorrhagic Cyst

• Presents with an irregular peripherally enhancing adnexal cyst, usually accompanied by hemorrhagic pelvic free fluid 1
• Typically causes more diffuse peritoneal signs and free fluid throughout the pelvis rather than a discrete mass 2
• Pain onset may be more acute and associated with activity or intercourse

Ectopic Pregnancy (If β-hCG Positive)

• Can present with an adnexal mass showing peripheral vascularity ("ring of fire" on Doppler) 3
• Must be considered even in patients with prior hysterectomy if ovaries remain in situ 3
• Associated with free fluid (hemoperitoneum if ruptured) 3

Secondary Differentials to Consider

Endometrioma

• Architectural distortion with possible thickening of bowel serosa may be present 1
• Typically presents as a homogeneous "ground glass" appearance on ultrasound, though this varies
• Usually associated with chronic rather than acute pain

Ovarian Neoplasm

• Borderline or malignant ovarian tumors can present with complex adnexal masses 5
• Peripheral flow may represent tumor vascularity
• Consider if mass has solid components, papillary projections, or septations 5

Appendicitis with Adjacent Ovarian Involvement

• Would not explain a palpable ovarian mass on examination 2
• CT findings would show appendiceal wall thickening >6 mm, periappendiceal fat stranding, and possible appendicolith 1
• The confirmed ovarian mass on ultrasound points away from this diagnosis 2

Recommended Diagnostic Algorithm

1. Obtain β-hCG stat (serum preferred over urine for quantification) 2, 3

2. If ultrasound findings are equivocal or torsion cannot be excluded clinically:

   • Proceed to CT abdomen/pelvis with IV contrast for definitive diagnosis 1, 6
   • CT has 74-95% sensitivity and 80-90% specificity for adnexal torsion 1
   • CT can identify twisted pedicle, abnormal ovarian enhancement, and alternative diagnoses 1

3. Assess for clinical signs of torsion:

   • Palpable adnexal mass on examination 2
   • Acute onset severe pain (often intermittent if intermittent torsion)
   • Elevated heart rate reflecting pain and potential hemodynamic changes 2
   • Nausea/vomiting common

4. If high suspicion for torsion based on imaging and clinical presentation:

   • Obtain emergent gynecologic consultation immediately—do not delay for additional imaging 2
   • Time to surgery directly impacts ovarian salvage rates 2

Critical Pitfalls to Avoid

• Do not rely on presence or absence of Doppler flow alone—torsion can have normal, decreased, or absent flow 2, 4
• Do not assume normal inflammatory markers exclude TOA—elderly or immunocompromised patients may have blunted responses 6
• Do not discharge without definitive diagnosis if torsion cannot be excluded—ovarian viability decreases rapidly with time 2, 7
• Do not forget to check pregnancy test even in patients with "reliable" contraception or atypical presentations 2, 3