PAPILLON COURSE on THYROID ULTRASOUND
Section 1 Introductory courses
Nomenclature of individual ultrasound characteristics
Composition
This feature relies on the presence of cystic areas and on the ratio of cystic and solid parts of the nodule. The term 'mixed' can be used if the nodule has both cystic and solid areas and the ratio of these components exceeds 5% measured in surface.
| Figure 1 Types of nodules according to their composition. |
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Considerations
Cystic area
This term is not used in the literature. I suggest using cystic area for normally occurring dilated macrofolicles which are normal finding in the thyroid. These structures can reach even 1 cm in diameter and has no solid area. The use of 'nodule' for such normally occurring lesions would be inappropriate and could cause unnecessary anxiety to the patient.
Spongiform area and spongiform nodule
We speak of spongiform area if this is composed of tiny cystic areas divided by fibrous tissue and lacking solid parts. According to the suggestion of the European Thyroid Association, a spongiform nodule must be composed entirely of spongiform areas.
Pure cyst
To use this term according to the ETA, the nodule can have neither any solid area nor any wall thickening. Other societies are satisfied with less than 5% solid areas.
Central-type (concentric) vs. peripheral-type (eccentric) cystic nodule
In the former, solid part runs all along the inner wall of the cyst in a concentric position along the cyst wall. In the event of peripheral-type cysts, the solid part is in contact with the cyst wall only at one part of the lesion the position of the solid part is eccentric.
Echogenicity
This feature relies on the grey scale level of the solid part of the nodule. Traditionally we compare this to two reference tissues, to the strap muscle running ventral to the thyroid and to the non-nodular part of the lobe.
| Table 1 Classification of nodules according to their echogenicity. | ||||
Types |
Reference tissue |
Handling in the protocols |
Grouping in TIRADS 1 |
Grouping in TIRADS 2 |
Hyperechoic |
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Iso/hyperechoic |
Iso/hyperechoic |
Iso/hyperechoic |
Isoechoic |
Normal thyroid |
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Minimally hypoechoic |
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Minimally/moderately hypoechoic |
Minimally/moderately hypoechoic |
Hypoechoic |
Moderately hypoechoic |
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Strap muscle |
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Deeply or very hypoechoic |
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Deeply hypoechoic |
Deeply hypoechoic |
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Considerations
Heterogeneous nodule
Can be used only for those nodules which have both hypoechoic and iso/hyperechoic parts. A nodule can be a dominantly hypoechoic (with an iso/hyperechoic minority part) or dominantly iso/hyperechoic one (with a hypoechoic minority part).
It is not defined what proportion the part in the minority must reach to be called heterogeneous.
I suggest using a 10 mm (regarding the largest diameter) or 10% contiguous area in surface for cut-off level.
The strap muscle as reference tissue
It is not defined in the literature which part of the muscle tissue should be considered. I suggest for reference tissue those part of the muscle fiber which low adipose tissue content.
How to define the normal thyroid as reference tissue in hypoechoic thyroids?
There is no clear resolution for this situation in the literature. If we consider the hypoechoic (diseased) non-nodular part as reference for normal thyroid, we should describe this in our report. E.g., compared to the moderately hypoechoic thyroid the nodule is... The other, more consistent approach if we compare the nodule' echogenicity to an imagined healthy thyroid, like how we otherwise establish that the non-nodular part is hypoechoic.
Intranodular echogenic figures
| Table 2 Intranodular echogenic figures | |||
Type |
Origin |
Presentation |
Size |
Normal connective tissue |
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Normal architecture of the thyroid |
Synchronous presence of hyperechogenic lines and granules |
Granule around 1 mm, line 3-30 mm |
Proliferation of connective tissue |
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Proliferation of connective tissue |
Synchronous presence of hyperechogenic lines and granules |
Granule around 1 mm, line 3-30 mm |
Comet-tail artifact |
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Colloid crystal |
A hyperechogenic granule with a dorsal fading and narrowing tail |
Granule 0.5-1.5 mm, tail 0-4 mm |
Back wall figures |
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Optical artifact caused by posterior back wall enhancement |
Hyperechogenic granule and line in the dorsal wall of a cystic area |
1-30 mm
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Microcalcification |
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Microcalcification and probably hyperplastic papillary structures |
Bright hyperechogenic granule |
Max. 1 mm |
Macrocalcification |
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Coarse calcification |
Irregular, thick bright line (not always found) |
2 mm-several cm |
Considerations
Microcalcification
This is an exclusion diagnosis. Those echogenic spots belong to this group which are (1) less than 1 mm in diameter and correspond (2) neither to comet-tail artifacts (3) nor to back wall figures (4) nor to connective tissue.
If we have any doubt whether a hyperechoic spot is not a microcalcification, then our doubt must be described in the medical report.Punctate echogenic figures
This term was introduced by the ACR TIRADS and include microcalcification and short comet-tail artifact. The cause for this new term was that the microcalcification is indeed a misnomer in thyroid ultrasound. Microcalcification is a pathological finding and is found almost exclusively in papillary cancer and many other echogenic spots have a similar appearance in ultrasound. To avoid the very often unfounded use of microcalcification, the ACR suggested the use of this term.
Comet-tail artifact
The typical form is found in the cystic portion of a mixed or cystic lesion and has a typical narrowing tail. The finding of even a single typical comet-tail artifact makes very unlikely that the lesion is malignant.
Nodule' borders
The irregular borders together with the irregular shape and ultrasound signs of extrathyroidal extension rely on the invasive nature of papillary thyroid cancer.
| Figure 2 Classification of nodules according to their border. |
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Considerations
Irregular border
This includes only lobulated and spiculated margins.
Blurred or ill-defined borders
Although this is not included among irregular borders and therefore, this feature is not considered as suspicious finding in any TIRADS system, ill-defined borders should not be neglected because this significantly increases the likelihood of malignancy.
Nodule' shape
| Table 3 Classification of nodules according to their shape. | ||
Type |
Feature |
In which plane is it measured? |
Regular |
Width > Depth |
Transverse |
Round |
Width = Depth |
Transverse |
Taller-than-wide |
Width < Depth |
Transverse |
Taller-than-long |
Length < Depth |
Longitudinal |
Considerations
How to judge the nodule shape?
We do not need to measure but only visually judge and compare the largest diameters of a nodule. We should compare not a diameter in a single section but the largest diameters.
How to handle taller-than-long shape?
Although not all TIRADS include this kind on nonparallel orientation among suspicious findings, there is minimal if any uncertainty about the fact that taller-than-long shape is equally important to taller-than-wide shape.
Ultrasound signs of extrathyroidal spread
These signs rely on the integrity of the pseudocapsule of the thyroid and the contours of the nodule.
Kinds of thyroid' pseudocapsule
Continuous
Not visible
Discontinuous
Kinds of nodule' contours
Normal contour means that the nodule is all along covered by thyroid tissue.
Abutting contour means that the nodule in close contact with the outer surface of the thyroid.
Bulging contour means that the nodule protrudes into anatomical structures outside the thyroid.
Table 4 Risk of extrathyroidal extension in relation to nodule' contour and thyroid' pseudocapsule. Capsule Continuous Discontinuous Considerations
Ultrasound has a quite good diagnostic performance regarding the minimal degree of extrathyroidal spread, however, the positive predictive value of US (PPV) is only around 50% regarding the gross extrathyroidal extension.
According to the newest, 8th TNM classification minimal ETE has no role in the staging while gross ETE deeply influences the further management of patients.
The newest TNM classification states that gross extrathyroidal extension can be based either on preoperative ultrasound, intraoperative surgical or postoperative macroscopic pathological finding, so microscopic evaluation has no role in the judgement. This places a huge and considering the 50% PPV, a clearly unfounded responsibility on the ultrasonographer. Only in completely clear (and extremely rare in everyday practice) cases can it be described on the ultrasound that a macroscopic ETE is present, because a mistake can affect the patient's further treatment and prognosis assessment.Ultrasound signs of ETE are used in two different meanings. First, for prediction of ETE. Second, as a suspicious finding irrespectively of ETE. The latter is backed by the observation that significantly more thyroid cancers present abutting contours compared with benign lesions.
Halo sign
Halo is a sonolucent rim around a discrete thyroid lesion, best maintained for complete rim. This can correspond to fibrous capsule or to compressed thyroid tissue or to compressed vessels.
Controversial importance
While halo is the sign with a huge negative predictive value for papillary and medullary cancer, this is the most frequently occurring feature of follicular cancers; in the latter halo corresponds to the capsule of the follicular tumor.
Nodule' vascularity
Vascular patterns
Perinodular
Vascularity is observed at least 25% on the circumference of the nodule.
Intranodular
Vascular spots within the nodules
Classification according to the ETA guideline
Type 1 Neither perinodular nor intranodular flow can be detected
Type 2 Perinodular vascularity is present while intranodular is absent or only slight.
Type 3 Intranodular vascularity is marked while perinodular is only slight.
Comment
It is worth describing nodule' vascularity according to its appearance since colleagues are not necessarily aware of the classification. Moreover, guidelines use different classifications.
Considerations
According to the general opinion, examining the circulation of the nodule adds very little to the diagnosis.
Despite the limited role in tumor diagnosis, vascularity remained essential part of thyroid ultrasound. There are many special fields where vascularity has important auxiliary role, e.g., differentiation of deeply hypoechoic structures, differential diagnostics of neck lymph nodes.
There is a special pattern, the lack of halo and perinodular vascularity, which makes follicular tumor unlikely even if the cytology is FLUS or suspicious of follicular tumor (Bethesda 3 or 4 subgroup).
The European TIRADS (see Figure 3)
| Figure 3 The European TIRASDS |
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Comment
Although extrathyroidal spread and the presence of suspicious lymph nodes are not included in the TIRADS score, if they are present, FNA is mandatory.
Final considerations
Suspicious for thyroid cancer? NOT. Suspicious only for papillary cancer!
Regarding all suspicious characteristics and halo sign, papillary thyroid cancer (PTC) behaves just the opposite as the second most common thyroid cancer, the follicular thyroid cancer (FTC). This difference is not only of statistical but of practical relevance. Taking into account the fact that PTC is 10-15 times more common than FTC, therefore the characteristics of the former dominate our impression of thyroid cancers in a statistical sense. At the same time, it is extremely misleading that the reports forget to mention this circumstance and, in fact, mistakenly extend the characteristics of PTC cancer to all thyroid cancers.
Relying on suspicious characteristics (of PTC) in our judgement on cytology, can lead to overlooking FTCs. This risk is much higher in Europe compared with North America, Australia, or Southeast Asia because of the higher prevalence of FTC in Europe.Describe the reality!
Despite the surprisingly low, occasionally only by chance interobserver agreement even among experts regarding all suspicious thyroid ultrasound characteristics, the wording of most guidelines is deceptive; they behave as if the judgement on ultrasound features would not share a significant degree of uncertainty.
Don't let yourself be fooled and don't fool others either! If you are uncertain about the assessment of something, write it down on the report.
