Background: Establishing thyroid size as large, normal or small in newborn infants with TSH elevation and in situ thyroid is important for diagnosis and informing molecular genetic studies.
Objective and hypotheses: To compare intra-observer variation in the objective (Ox) measurement of thyroid volume (vol) by ultrasound (US); and the correlation between subjective (Sx) and Ox assessment.
Method: Joint blinded retrospective review of static images by two observers on two separate occasions in infants referred 20072013 with TSH elevation and eutopic thyroid. Combined vol was derived from the sum of each lobe using the formula length×depth×breadth×π/6. Images were then blindly reviewed subjectively as five categories: small, small-normal, normal, large-normal and large. Equivalent Ox size was determined using population-specific mean±S.D. of 2.4±0.4 ml to give corresponding vols <0.7, 0.7<0.9, 0.9<2.1, 2.12.3 and >2.3 ml. Correlation between Ox and Sx was defined as concordant, partial or discordant if categories were equivalent, 1 apart or 2 apart.
Results: Of 48 infants images were available in 42 (25 males: 17 females) comprising 17 with definite congenital hypothyroidism (CH), 18 status uncertain and seven transient TSH elevation. Causes of definite CH were dyshormonogenesis (DHG) in 13 defined by proven mutation±thyroglobulin elevation±increased uptake on radioisotope scan; and thyroid hypoplasia in four (all with proven mutations). Length could not be measured in the images of five patients while assessment was not possible in a patient with allo-immune thyroiditis due to surrounding oedema. Mean±S.D. intraobserver difference in vol was 0.1248±0.23 ml, reducing to 0.06±0.05 ml after excluding three infants in whom extrapolation was needed because of enlarged glands. Ox vs Sx was concordant in 15 and partial in nine but discordant in 11 including two infants with bulky glands on Sx but vol 0.70.9 ml on Ox (PAX8 mutation in one, suspected NKX.2 disorder in the other) and in five DHG infants with enlargement on Sx but normal size on Ox.
Conclusion: Intra-observer error for newborn thyroid US volume assessment is small. Sx assessment may be markedly misleading. However, our method of Ox measurement ignores the isthmus, which may be enlarged in DHG. This may explain the discordance in some of infants with DHG and underlines the place of both objective and subjective thyroid US assessment in newborn infants.
01 Oct 2015 - 03 Oct 2015