What are the differential diagnoses for a female patient of reproductive age presenting with an ovarian cyst?

Differential Diagnosis for Ovarian Cyst in Reproductive Age Women

The three most important differential diagnoses for an ovarian cyst in a reproductive-age woman are: (1) functional/physiologic cysts (follicular or corpus luteum), (2) hemorrhagic cyst, and (3) ovarian torsion—with the critical imperative being immediate exclusion of torsion to preserve fertility. 1, 2

Primary Differential Diagnoses

1. Functional Cysts (Follicular/Corpus Luteum)

• Most common etiology in reproductive-age women, with simple cysts being benign in 98.7% of cases 1, 3
• Follicular cysts are physiologic when <3 cm and typically resolve spontaneously without intervention 4, 5
• Corpus luteum cysts develop after ovulation and may cause pain due to capsular stretching 3
• Ultrasound characteristics: Simple, unilocular appearance with smooth walls, classified as O-RADS 2 (almost certainly benign with <1% malignancy risk) 4
• Management: No follow-up needed for cysts ≤3 cm; cysts >5 cm but <10 cm require ultrasound follow-up in 8-12 weeks 4

2. Hemorrhagic Cyst

• Most common cause of pelvic pain in reproductive-age women with ovarian cysts on ultrasound 3
• Results from spontaneous bleeding into a functional cyst (follicular or corpus luteum) 6, 7
• Ultrasound findings: Spiderweb-appearing or retracting clot with peripheral vascularity; low-level internal echoes 1, 3
• Clinical presentation includes acute pelvic pain, often unilateral, with peritoneal irritation if rupture occurs 7
• Management: Hemorrhage is often self-limiting; conservative "wait-and-see" approach with supportive therapy (analgesics, fluid resuscitation) avoids unnecessary surgery 7

3. Ovarian Torsion

• Life-threatening emergency requiring immediate diagnosis to prevent adnexal necrosis and infertility 2
• Most common in presence of an ovarian cyst, particularly dermoid cysts 5, 8
• Clinical presentation: Severe, constant unilateral pain radiating from groin to loin with nausea/vomiting; pain may fluctuate but rarely resolves without intervention 2, 5
• Ultrasound findings (first-line imaging): 1, 2
  • Unilaterally enlarged ovary (>4 cm or volume >20 cm³)
  • Peripheral follicles (present in 74% of cases)
  • Abnormal/absent venous flow (100% sensitivity, 97% specificity)
  • Whirlpool sign (90% sensitivity when present)
  • Absent arterial flow (76% sensitivity, 99% specificity)
• Critical pitfall: Normal arterial flow does NOT rule out torsion—venous flow abnormalities are more sensitive 2, 3
• If ultrasound inconclusive: Proceed to MRI (80-85% sensitivity) showing enlarged ovary with stromal edema and absent/diminished enhancement 2

Additional Important Differentials

4. Endometrioma

• Common in reproductive-age women with deep dyspareunia 3
• Ultrasound characteristics: Low-level internal echoes with "ground-glass" appearance, mural echogenic foci, nonvascular solid components 1, 3
• Transvaginal ultrasound has 98% sensitivity and 100% specificity for rectosigmoid/retrocervical endometriosis 3

5. Dermoid Cyst (Mature Cystic Teratoma)

• Most common ovarian neoplasm in reproductive-age women 1
• Ultrasound findings: Echogenic attenuating component or small horizontal interfaces 1
• Highest risk for torsion among benign cysts 5

6. Tubo-Ovarian Abscess (TOA)

• Accounts for 20% of acute pelvic pain cases in reproductive-age women with gynecologic etiology 1
• CT findings: Thick-walled adnexal fluid collection with septations, indistinct borders, gas bubbles within mass 1
• Right ovarian vein entering right pelvic abscess has 100% specificity and 94% sensitivity for TOA versus peri-appendiceal abscess 1

Diagnostic Algorithm

Step 1: Obtain β-hCG to exclude pregnancy-related causes (ectopic pregnancy) before imaging 1

Step 2: Transvaginal ultrasound with Doppler is the initial imaging modality of choice 1, 4

• Combined transabdominal and transvaginal approach provides most comprehensive assessment 2, 3
• Color/power Doppler is mandatory to assess vascular flow patterns and differentiate solid components from debris 3

Step 3: Risk stratification based on ultrasound findings 1, 4

• Simple cyst ≤3 cm: No follow-up needed
• Simple cyst >3-5 cm: No additional management typically required
• Cyst >5 cm: Follow-up ultrasound in 8-12 weeks
• Complex features or concerning Doppler findings: Consider MRI or gynecology referral

Step 4: If torsion suspected despite normal ultrasound, proceed immediately to MRI or surgical exploration 2, 3

Critical Pitfalls to Avoid

• Failing to perform Doppler evaluation when assessing ovarian cysts—essential for detecting torsion and distinguishing hemorrhagic cysts from solid masses 3
• Assuming normal arterial flow excludes torsion—venous flow abnormalities are more sensitive and specific 2, 3
• Not recognizing signs of torsion requiring urgent surgical intervention—delay leads to ovarian necrosis and infertility 2
• Inadequate follow-up for cysts >5 cm, which may harbor malignancy or complications 4
• Confusing torsion with other conditions (appendicitis, ureteric colic, UTI) due to overlapping symptoms—maintain high index of suspicion 2, 5