Congenital hypothyroidism: analysis of discordant US and scintigraphic findings.

PURPOSE

To retrospectively review discordant cases of congenital hypothyroidism according to a comparison of findings of ultrasonography (US) and scintigraphy.

MATERIALS AND METHODS

Institutional review board approval was obtained for this retrospective study with a waiver of informed consent. Data of 300 pediatric patients (mean age, 4.7 weeks; range, 1-48 weeks; male-to-female ratio, 169:131) with congenital hypothyroidism who underwent technetium 99m radioisotope scintigraphy and US were reviewed. Scintigraphic scans were analyzed for location and range of the radioisotope uptake. US images were analyzed for location and thyroid volume. If a normal thyroid was not detected, ectopic thyroid was evaluated. Detection of focal thyroid abnormalities was recorded. Correlation between radioisotope uptake at scintigraphy and volume of normally located glands measured at US was analyzed by using the Pearson correlation test. Differences between results of thyroid function testing and radiologic data among subtypes of congenital hypothyroidism were analyzed with analysis of variance and Scheffe multiple comparison test.

RESULTS

Among 55 patients with no radioisotope uptake, the appearance of the thyroid gland on US scans was normal in 42 patients (76%). This finding was attributed to hypopituitarism (n = 3), maternal antibody-induced hypothyroidism (n = 4), transient elevated thyrotropin (n = 5), and unknown causes (n = 30). Ectopic tissue was not detected at US (sensitivity, 78%; specificity, 100%) in six patients with a diagnosis of ectopy based on scintigraphic findings. Correlation between radioisotope uptake and US thyroid volume was statistically significant (P < .001). Correlation of results from thyroid function testing (thyrotropin, thyroxine, thyroglobulin) and radiologic data (radioisotope uptake, US measurement of volume) with subtypes of congenital hypothyroidism was significant (P < .001). Solid thyroid nodules were present in the thyroid gland in 0.7% (two of 300) of cases.

CONCLUSION

Use of both scintigraphy and US results in a more complete depiction of neonatal congenital hypothyroidism than either test alone.