Disappearing "halo" on thyroid ultrasound
Mass lesion right lobe thyroid.
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Two images, one annotated.
The upper arrow shows the thin lucent halo that differentiates the lesion form the rest of the thyroid parenchyma. The posterior arrow shows the appearance of the halo disappearing.
The halo should be visible in ultrasound imaging in the vast majority of benign thyroid lesions. When it is not visible on imaging, it is a relative indication for FNA. Always best appreciated in real time and not always demonstrated on static images.
This case had three relative indications for FNA:
- coarse calcifications
- loss of the halo posteriorly
- the lesion was almost 2 cm larger than on an ultrasound of 6 months previously
This lesion had benign cytology but the workup and FNA is justified regardless.
The art of thyroid FNA is not exact. Part of the process is aimed at avoiding large numbers of unnecessary procedures that needlessly alarm otherwise healthy people but at the same time intervening where intervention is justified.