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Thyroid ultrasound ‘not highly accurate’ for malignancy in children

Ultrasound has only limited value for diagnosing thyroid cancer in children, say the authors of a meta-analysis.

“Ideally, a diagnostic test will accurately predict the presence or absence of a disease”, say Alaa Al Nofal (Mayo Clinic, Rochester, Minnesota, USA) and co-authors.

But their systematic review and meta-analysis showed that, although certain ultrasound features are more likely to be found in either malignant or benign nodules, no feature provided an accurate means of distinguishing between the two.

Ten of the included studies assessed a total of 581 thyroid nodules in children without a stated history of radiation exposure; they had a histologically confirmed cancer rate of 23.2%. In these studies, five features were significantly associated with an increased likelihood of malignancy, with internal calcifications and enlarged lymph nodes having the highest positive likelihood ratios, at 4.46 and 4.96, respectively. The presence of a cystic nodule suggested benign disease, but the association was not strong.

Two studies included only children with significant radiation exposure, in whom the rate of histologically confirmed thyroid cancer was 40.8%. In these children, irregular margins were the strongest predictor of malignant disease, with a positive likelihood ratio of 3.33.

However, none of these predictors had a strong diagnostic effect; for example, for a pre-test probability of cancer of 23.2%, the presence of a cystic nodule reduced the post-test probability only to 17.2% and the presence of internal calcifications increased it only to 57.4%.

“Based on these findings, we suggest that practitioners should have a lower threshold to perform fine needle aspiration in children presenting with thyroid nodules compared to adults (where the accuracy of certain features can rule out malignancy)”, the researchers write in Clinical Endocrinology.

They also caution that the presence of a cystic nodule does not completely rule out thyroid cancer, so children with this feature should be closely monitored.

The team adds that their findings also imply that “children with a history of significant radiation exposure, as in cases of neck irradiation for nonthyroid malignancies, require special attention, closer monitoring and an even lower threshold for fine needle aspiration compared to patients with no history of radiation exposure, because of the significantly higher risk of malignancy in patients with a history of radiation exposure.”