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Gynaecologic Imaging
Demonstration data

Ovarian Volume (Ellipsoid)

Calculates ovarian volume from three ultrasound diameters using the prolate-ellipsoid formula to distinguish a normal ovary from an enlarged or postmenopausal ovary.

The ovary approximates a prolate ellipsoid, so its volume is the product of the three orthogonal diameters and 0.523 (≈ π/6). Ovarian volume normally declines after the menopause; a value above the age-appropriate threshold, or marked asymmetry between the two ovaries, raises concern for a mass or functional process.

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📐 Formula

Volume (cm³) = 0.523 × length × width × height

When to Use

  • Characterising a suspected ovarian enlargement or mass.
  • Assessing a postmenopausal ovary, where any measurable volume increase is more concerning.
  • Follow-up of functional cysts and baseline for polycystic ovary assessment.

How It Works

  • Measure the ovary in three orthogonal planes (length, width, anteroposterior height) in cm.
  • Compute volume = 0.523 × length × width × height.
  • Compare against the menopausal-status threshold and against the contralateral ovary.

Interpreting the Result

  • Premenopausal upper limit of normal ≈ 10 cm³ (mean ~5–6 cm³).
  • Postmenopausal upper limit ≈ 8 cm³; some references use ≤6 cm³, with a >2× volume difference between ovaries considered abnormal.
  • A polycystic-appearing ovary is typically ≥10 cm³ with ≥20 antral follicles (2017 international PCOS criteria).

Limitations & Pitfalls

  • The ellipsoid model underestimates volume for irregular or multiloculated masses; measure the mass separately.
  • Follicular and functional changes cause physiological volume variation across the menstrual cycle.
  • Transabdominal measurement is less accurate than transvaginal, especially in obese patients.

References

  • Cohen HL, Tice HM, Mandel FS. Ovarian volumes measured by US: bigger than we think. Radiology. 1990;177(1):189-192.
  • Pavlik EJ, DePriest PD, Gallion HH, et al. Ovarian volume related to age. Gynecol Oncol. 2000;77(3):410-412.

⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.