BTA ultrasound "U" classification of thyroid nodules

Last revised by David Luong on 27 Jun 2021

The ultrasound "U" classification of thyroid nodules has been developed by the British Thyroid Association (BTA) as part of their 2014 guidelines on the management of thyroid cancer 1.

It allows for the stratification of thyroid nodules as benign, suspicious or malignant based on ultrasound appearances termed U1-U5. This is used to streamline further investigation and management.


U1 (normal)
  • no nodules
U2 (benign)
  • hyperechoic or isoechoic with a halo
  • cystic change with ring-down artifact (colloid)
  • microcystic or spongiform appearance
  • peripheral egg-shell calcification
  • peripheral vascularity
U3 (indeterminate)
  • solid homogenous markedly hyperechoic nodule with halo (follicular lesions)
  • hypoechoic with equivocal echogenic foci or cystic change
  • mixed or central vascularity
U4 (suspicious)
  • solid hypoechoic (compared with thyroid)
  • solid very hypoechoic (compared with strap muscles)
  • hypoechoic with disrupted peripheral calcification
  • lobulated outline
U5 (malignant)
  • solid hypoechoic with a lobulated or irregular outline and microcalcification
  • solid hypoechoic with a lobulated or irregular outline and globular calcification
  • intranodular vascularity
  • taller than wide axially (AP>ML)
  • characteristic associated lymphadenopathy

Size does not have a role in this grading system.

Treatment and prognosis

U2 nodules do not require fine needle aspiration (FNA) or follow-up imaging in the absence of concerning clinical features.

U3 - U5 nodules require FNA with further management based on resultant cytology, radiology and clinical findings. Many units have a low threshold for performing diagnostic hemithyroidectomies for nodules that are both radiologically- and cytologically-suspicious.

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