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Endocrine Imaging
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Thyroid Volume (Ellipsoid)

Estimates single-lobe and total thyroid volume from ultrasound lobe dimensions using the ellipsoid formula, to grade goitre and guide radioiodine or surgical planning.

The thyroid lobe approximates a prolate ellipsoid, so its volume is the product of the three orthogonal diameters and a correction factor of 0.529 (ฯ€/6 โ‰ˆ 0.524 in idealised form; 0.529 is the empirically validated coefficient). The isthmus is conventionally excluded. Total gland volume is the sum of both lobes; when only one lobe is measured, a symmetric gland can be approximated by doubling.

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๐Ÿ“ Formula

Lobe volume (mL) = length ร— width ร— depth ร— 0.529; total โ‰ˆ right lobe + left lobe

When to Use

  • Grading diffuse goitre and monitoring change over time.
  • Dosimetry planning before radioiodine therapy for hyperthyroidism or non-toxic goitre.
  • Pre-operative sizing and assessment of retrosternal extension risk.

How It Works

  • Measure each lobe in three planes: craniocaudal length, transverse width and anteroposterior depth (cm).
  • Compute lobe volume = length ร— width ร— depth ร— 0.529.
  • Sum the right and left lobe volumes (excluding the isthmus) for total gland volume.
  • If only one lobe is measured, doubling gives an estimate for a grossly symmetric gland.

Interpreting the Result

  • Normal adult total volume is roughly 7โ€“10 mL in women and 8โ€“11 mL in men (upper reference limit commonly cited near 18 mL for women and 25 mL for men).
  • Total volume >18 mL (women) / >25 mL (men) indicates goitre.
  • Serial change of a discrete nodule or the whole gland is more informative than a single reading.

Limitations & Pitfalls

  • The 0.529 coefficient is a population approximation; irregular or multinodular glands deviate from the ellipsoid model.
  • Retrosternal or very large glands may extend beyond the sonographic field, causing underestimation.
  • Operator-dependent caliper placement introduces measurement variability of up to 10โ€“15%.

References

  • Brunn J, Block U, Ruf G, et al. Volumetric analysis of thyroid lobes by real-time ultrasound. Dtsch Med Wochenschr. 1981;106(41):1338-1340.
  • Ozgen A, Erol C, Kaya A, et al. Interobserver and intraobserver variations in sonographic measurement of thyroid volume. Eur J Endocrinol. 1999;140(6):505-509.

โš•๏ธ For clinical decision support only. Always verify calculations and apply clinical judgment.