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Pathology of the Ovaries - Ultrasound Review

Anatomy and Normal Appearance

Ovaries are paired, almond-shaped organs located one on each side of the uterus, near the lateral pelvic wall. Their position is variable and influenced by uterine position and ligament attachments. They are ellipsoid with the craniocaudal axis parallel to the internal iliac vessels, which serve as a reference point. Blood is supplied by the ovarian arteries from the abdominal aorta; the right ovarian vein drains into the IVC, while the left drains into the left renal vein. After hysterectomy, ovaries tend to sit more medially and directly superior to the vaginal cuff and may be high in the pelvis or out of the TVS field of view.

Normal Sonographic Appearance

Ovaries typically show homogeneous echotexture. The medulla may be slightly more echogenic than the cortex, and small anechoic or cystic follicles may be seen peripherally in the cortex. Appearance varies with age and menstrual cycle. Follicles are usually few millimeters in size; multiple tiny follicles can be present. On imaging, ovarian volume is calculated as
V = L \times W \times H \times 0.523

Ovarian Function and Phases

In reproductive-age women, the ovary undergoes three ultrasound-detectable phases during each cycle: follicular (proliferative) phase, ovulation, and the luteal phase. These changes reflect rhythmic secretion of FSH and LH from the pituitary. The proliferative phase features growth of follicles up to about 2.0–2.5 cm by ovulation (day ~12–14). Ovulation corresponds to rupture of the dominant follicle and release of the oocyte; the cumulus oophorus may be seen as a cystic mural protrusion in rare cases, indicating maturity. The post-ovulation luteal phase forms the corpus luteum, which forms a visible structure with a thick hyperechoic wall and internal echoes if hemorrhagic, and may appear cystic as the luteal cyst. If pregnancy occurs, the corpus luteum persists until about 10–12 weeks gestation. Endometrial changes progress from proliferative (follicular) to secretory phases in parallel with ovarian activity.

Doppler Evaluation of the Ovary

Ovarian blood flow is assessed with Doppler to help characterize masses. Key indices are:
RI = \frac{PSV - EDV}{PSV}
PI = \frac{PSV - EDV}{V_{mean}}
These indices vary during the cycle and among individuals. Early cycle typically shows higher resistance (higher RI/PI); diastolic flow increases later in the cycle, potentially lowering indices and mimicking benign or malignant processes depending on context. To minimize cycle-related confounding, some experts recommend scanning during the first 10 days of the cycle. Higher diastolic flow suggests neovascularization and may raise concern for malignancy, but RI/PI values are not solely diagnostic. Abnormal waveforms can also be seen with inflammatory masses, active masses, or corpus luteum cysts. A typical, well-circumscribed corpus luteum may show peripheral vascularity and a “ring” of color Doppler, but this is not universal.

Normal and Abnormal Ovarian Size/Volume

Ovarian volume abnormalities are important. In menstrual years, an ovarian volume > 22\,\text{mL} is considered abnormal. A volume larger than twice the opposite ovary is also concerning. Postmenopausal ovaries are difficult to visualize; a volume >8\,\text{mL} is generally considered abnormal in this group. Large or rapidly enlarging ovaries require further workup. Smaller postmenopausal ovaries may appear atrophic with few or no follicles.

Functional Ovarian Cysts

Functional cysts arise from normal ovarian function and are common in young women. They include follicular cysts, corpus luteum cysts, hemorrhagic cysts, and theca-lutein cysts. Most cysts are <5 cm and regress within a single menstrual cycle; follow-up ultrasound in ~6 weeks is typical.

  • Follicular cysts: dominant follicle fails to ovulate; usually unilateral; thin-walled, anechoic to translucent fluid; may reach up to ~20 cm and resolve by resorption or rupture.
  • Corpus luteum cysts: result from failure to regress or from hemorrhage; often <4 cm but may be larger; may accompany irregular menses; may show a cyst with a enhancing or eccentric internal echoes “ring of fire” on color Doppler when hemorrhagic.
  • Hemorrhagic cysts: intracystic hemorrhage; variable internal echoes; may mimic solid masses; typically benign.
  • Theca-lutein cysts: large, bilateral, multiloculated cysts; associated with high hCG (trophoblastic disease), multiple gestations, or fertility treatment.
  • OHSS (Ovarian Hyperstimulation Syndrome): enlarged ovaries, edema, and ascites in iatrogenic contexts; usually resolves in 2–3 weeks with treatment.
  • PCOS: multiple small peripheral cysts (“string of pearls”), bilateral enlargement; endocrine associations and potential endometrial effects.
  • Ovarian remnant syndrome: residual ovarian tissue after oophorectomy.
  • Peritoneal inclusion and paraovarian cysts are non-neoplastic adnexal entities.

Benign Adnexal Cysts and Related Syndromes

Benign adnexal cysts include follicular, corpus luteum, hemorrhagic, and theca-lutein cysts, along with functional cysts related to OHSS and PCOS. Peritoneal inclusion cysts form from adhesions trapping peritoneal fluid around ovaries. Paraovarian cysts originate from Wolffian duct remnants and usually lie adjacent to the broad ligament, often simple and asymptomatic.

Complex and Solid Ovarian Masses

Most simple cysts are benign; a complex mass or solid component raises suspicion for neoplasia. Common complex masses include cystadenoma, dermoid (mature cystic teratoma), tubo-ovarian abscess, granulosa cell tumor, endometrioma, and ectopic pregnancy. Solid tumors (e.g., serous or mucinous cystadenocarcinoma, fibroma, dysgerminoma) may be malignant, especially when accompanied by solid components, thick irregular septations, mural nodules, or ascites. Dermoids often show heterogeneous echotexture with fat-fluid levels or Rokitansky protuberances.

Endometriosis and Endometrioma

Endometriosis is ectopic functioning endometrial tissue outside the uterus; it can involve the ovary (endometrioma), fallopian tubes, broad ligament, cul-de-sac, or peritoneum. Endometriomas (chocolate cysts) appear as bilateral or unilateral ovarian cysts with variable internal echoes depending on blood content; they are often well-defined, unilocular or multilocular, and predominantly cystic with internal low-level echoes.

Endometriosis vs Adenomyosis

Endometriosis refers to endometrial tissue outside the uterus. Adenomyosis refers to endometrial tissue within the myometrium. Endometriosis can form ovarian cysts (endometriomas); adenomyosis typically affects the uterine wall and is distinct from ovarian involvement.

Ovarian Torsion

Ovarian torsion results from rotation of the ovarian pedicle, compromising lymphatic and venous drainage first, leading to edema and eventually impaired arterial perfusion with infarction risk. It often involves the ovary and the fallopian tube. It is a surgical emergency. Clinically, presents with acute severe unilateral pain; Doppler may show absent or reduced flow and free fluid in the pelvis. The classic “whirlpool” sign (twisted pedicle) is highly specific but not highly sensitive. Follicular edema (follicle ring sign) and unilateral enlargement support torsion diagnosis; contralateral torsion risk exists (~10%).

Case Examples and Imaging Considerations

  • Doppler is one piece of the puzzle; robust diagnosis relies on gray-scale morphology, size, walls, septations, mural nodules, and clinical context.
  • A-well-defined, thin-walled, anechoic unilocular cysts are more likely benign; thick irregular walls, multiple septations, mural nodules raise concern for malignancy.
  • Postmenopausal ovaries that are enlarged with abnormal echogenicity or solid components are more concerning for malignant processes.

Quick Reference Points

  • Formula for ovarian volume: V = L \times W \times H \times 0.523; abnormal reproductive-age volume > 22\,\text{mL}; postmenopausal abnormal > 8\,\text{mL}; volume asymmetry (>2x opposite side) is suspicious.

  • Doppler indices: RI = \frac{PSV - EDV}{PSV}, \quad PI = \frac{PSV - EDV}{V_{mean}}; cycle timing affects values; higher diastolic flow may mimic malignancy; use in conjunction with morphology.

  • Endometriosis and endometrioma can mimic other adnexal masses; look for bilaterality, internal echoes, and characteristic patterns.

  • Suspect torsion with acute pain and absent Doppler flow; whirlpool sign is highly specific.

  • Always correlate sonographic findings with clinical history, cycle phase, and laboratory data when available.