The overall prevalence of acute, transient thyroid swelling was previously reported to be 0.46% [9], 0.15% [10], 0.13% [11], and 0.10% [6]. In past reports, this swelling subsided within 1–20 h, and none of the patients developed airway obstruction. This is the first report in the English literature to describe a patient who required tracheal intubation for airway obstruction after acute thyroid swelling following FNA. A fatal case of cervical hemorrhage was reported in a forensic journal, indicating the need to be aware of potentially fatal airway obstruction following FNA of the thyroid gland [12].
Acute, transient thyroid swelling exhibits several specific US findings. In the present case, characteristic hypoechoic “cracks” (i.e., a crack-like pattern) [13] were observed, along with swelling, in both lobes of the thyroid gland, despite the fact that only one lobe was punctured. These hypoechoic cracks reflect fluid accumulation in the loose interstitial space of the thyroid parenchyma. The acute nature of the swelling in this case and its spontaneous and relatively rapid resolution suggested diffuse capillary leakage caused by puncture of the thyroid parenchyma. In our case, relatively minimal hemorrhage may have coexisted with non-hemorrhagic swelling of the thyroid gland and surrounding tissues. The hypervascular nodule and elevated central venous pressure were risk factors for hemorrhage, but most of the swelling was probably non-hemorrhagic in nature because it resolved within 24–48 h after FNA.
The mechanism of acute, transient thyroid swelling remains unclear. Its acute onset and short recovery time suggest that intrathyroidal hemorrhage is an unlikely etiology. Other possible explanations include intrathyroidal edema induced by endogenous substances [14], or allergic reaction to metal needles, disinfectants, or ultrasound gel [15]. Acute transient thyroid swelling after catheterization of subclavian vein was reported in an apparently normal thyroid gland [16]. Fifteen minutes after multiple unsuccessful attempts to insert a central venous catheter in the neck, the authors noted progressive diffuse swelling of the neck. US findings revealed a diffusely swollen thyroid gland without evidence of bleeding. The swelling resolved spontaneously within 4 h, and the authors concluded that the normal thyroid gland was inadvertently punctured during the attempted catheterization. Thus, thyroid nodules themselves might not be inherently associated with a risk of acute, transient thyroid swelling.
Although it is rare, FNA can lead to acute, transient thyroid swelling. When neck swelling is noticed after FNA, US findings are especially important to assess potential causes. If airway obstruction is suspected, CT findings and fiberscope observation of the pharynx provide particularly useful information.