Intranodular hyperechogenic figures - Table 2 (large). Comet-tail artifacts or colloid crystals

doi: 10.24390/thyrosite.2018.ihf.02.2

A typical comet-tail artifact consists of a hyperechogenic granule with a dorsal narrowing and a fading tail. The size of the granule is in the range of punctate echogenic foci (microcalcifications), i.e. not greater than 1 mm. The typical presentation of this figure is best seen in cystic part of a mixed nodule; however it might occur within the solid area, as well. In the latter case the narrowing tail is frequently missing.

Benign cystic-colloid goiter (cytological diagnosis) - case 284

The figure marked with white arrowhead is ambiguous because of the lack of dorsal tail. This figure is composed of two granules which might be two punctate echogenic foci. However, there are typical forms of comet-tail artifacts marked with yellow arrows, the presence of which makes it very likely that the equivocal figures are also comet-tail artifacts. Moreover, these are within cystic fluid which theoretically excludes that these might be pathognomonic microcalcifications. In addition t,o it is worth analyzing the dorsal wall of the cyst and the thyroid parenchyma dorsal to the nodule, both have hyperechogenic figures corresponding to a posterior back wall enhancement (blue arrows).
   

Benign follicular proliferation (cytological diagnosis) - case 270
A typical comet-tail artifact is demonstrated.
 

Intact thyroid with cystically dilated macrofolliculi (histological diagnosis) - case 1539

Right lobe: there are typical comet-tail artifacts, two in the left horizontal scan and one in the right longitudinal scan. The latter presents two more cystic lesions (the lower two) in which the hyperechogenic figures have only a vestigial dorsal tail.

 
Left lobe: there are typical comet-tail artifacts in this lobe, too.
 

Benign colloid cyst (cytological diagnosis) - case 402
There are several typical comet-tail artifacts in both lobes.
 

Benign cystic degeneration (cytological diagnosis) - case 624

There are several figures with typical presentation (yellow arrows), while several hyperechogenic granules lack dorsal acoustic shadow (aroowhead) which theoretically might be punctate echogenic foci. On the other hand, in the presence of typical comet-tail artifacts, similarly bright non-typical forms more likely belong to the same category. Moreover, punctate echogenic foci (microcalcifications) cannot be found in cystic fluid.

 

Follicular adenoma (histological diagnosis) - case 443
Before aspiration of 2 mL cystic fluid
Upper and lower transverse section
Longitudinal section

There are numerous hyperechogenic granules in the lower pole of the nodule. These figures might be confused with punctate echogenic foci (microcalcifications), as happened in this case. However, several have dorsal tail and therefore the remaining without a tail likely belong also to the same subgroup.

After aspiration of 2 mL cystic fluid
Upper and lower transverse section
Longitudinal section

After removal of the cystic fluid it became more evident that the figures are comet-tail artifacts.

   

Hashimoto's thyroiditis with several cystic areas but without any nodules (histological diagnosis) - case 1365

In this case we found only hyperechogenic lines. This is an unusual presentation of a comet-tail artifact. The video is clearly superior to a saved image, in the former the hyperechogenic figure appeared in a more typical form.
   

Benign colloid goiter (cytological diagnosis) - case 386

At first sight, this pattern mimics the starry sky phenomenon which would be caused by numerous microcalcifications. However, these granules are found in a cystic fluid, therefore they cannot be punctate echogenic foci (microcalcifications).
   

Benign cystic degeneration (cytological diagnosis) - case 662

It is worth analyzing the hyperechogenic figures marked wih yellow arrows which have a broader than usually fading tail. The figures pointed with blue arrows at the border of the cystic and solid part (right side of the nodule in the right image) are posterior back wall enhancement caused by the microcystic area ventral to them.