Ultrasound Classification of Benign Thyroid Nodules  (UC-BTN)

Background: Benign thyroid nodules are detected by ultrasound in almost half of the population. However, existing concepts of nodules do not reflect all clinically important signs.Methods: Based on the assessment of 2007 patients during 16 years of ultrasound and clinical practice, a new Ultrasound Classification of Benign Thyroid Nodules (UC-BTN) was proposed in 2013, which was validated and improved in 2025. Results: In addition to the known parameters of the nodular process, the classification for the first time included a description of the stages of nodules, the ratio of nodules to the lobe, segmental organization of the tissue of the nodules, and the intensity and speed of the nodular blood flow. The classification was based on the elements of the pathomorphogenesis of thyroid nodules: the level neurosegmental structure of the tissue and the magnitude of the functional tension. All of them characterize different aspects of one process. UC-BTN 2025 contains nine classes, some of which are subdivided into one or two smaller levels (subclasses and sub-subclasses). Background: From a practical point of view, the advantage of this classification is better continuity between specialists, rationality of the choice of treatment tactics and accuracy of the prognosis.Key words: thyroid ultrasound; thyroid nodules; classification of thyroid nodules; ultrasound classification. IntroductionThyroid nodules are detected in more than half of the population [1]. Of these, benign nodules exceed 95% [2], reaching even 98.9% in recent years [3]. However, the main attention of specialists is focused on differential diagnostics with malignant nodules [1]. It is this aspect of diagnostics that has become the most common in the selection of ultrasound signs of nodules and their classification.Some of these studies are focused primarily on assessing the probability of nodule cancer depending on its size [4-6]. Another part of these publications reports on the "ultrasound classification of thyroid nodules" only in relation to the Thyroid Imaging Reporting And Data System (TI-RADS) [4, 7]. The third part of specialists understands "ultrasound classification of thyroid nodules" as different methods of intelligent computer diagnostics [8-10]. In addition, some authors see the possibility of differential diagnostics of cancer depending on: the location of the nodules in the thyroid [11,12], the number of nodules [13] and fluid in a nodule [14]. Even a comparison of the largest size and volume of nodules has been tested in the differential diagnosis of cancer [15].Specialists also study individual ultrasound features of thyroid nodules to specific diagnostic (fine-needle aspiration) or surgical tactics. These individual features are not combined into full-fledged classifications. For this purpose, attention is paid to the largest size of the nodule (large or small) [16-18], to the change in size after a certain period (19), to calcifications, hypoechogenicity [19], and the presence of cystic cavities in the nodule [14,20]. In other cases, figurative (empirical) designations of some nodule variants are used instead of scientifically substantiated terms indicating pathogenetic principles [21, 22]. As a result, a limited trend has developed in the ultrasound analysis of thyroid nodules. A very significant shift to the area of studying ultrasound features of nodular cancer has removed many other ultrasound landmarks, important for clinical practice, from the attention of doctors. Additionally, there was a substitution of concepts in the form of classification of computer software criteria instead substitute the evaluation and ordering of ultrasound signs visible to the eyes of a sonologist [23, 24].Another unnoticed distortion was the perception of TI-RADS as a classification of nodules (regardless of the authorship of TI-RADS). In reality, TI-RADS only partially contain classification elements; some TI-RADS variants to a greater extent, while others to a lesser extent. For example, TI-RADS version from the American College of Radiology (ACR) contain only groups of ultrasound features, combined according to some of the classification principles [25]. The remaining of the ACR TI-RADS is an algorithm for making a decision on the probability of cancer and indications for a puncture biopsy of the nodule.At the same time, not every list of features and concepts can be considered a classification. After all, classification is a scientific methodological direction, and not the arbitrary unification of something. There are mandatory rules (principles) that must always be taken into account when classifying [26]. A review of the available literature on the topic of "ultrasound classifications of benign thyroid nodules" has not revealed any comprehensive, ordered lists that cover the maximum possible number of ultrasound features of benign nodules based on pathogenesis. Consequently, specialists lack a convenient intellectual tool that demonstrates all the variants and features of benign thyroid nodules, allowing them to be correctly seen, understood, terminologically described, predicted, and the best tactics to chose.The purpose of this publication was to present and describe the advantages for the practical use of the "Ultrasound Classification of Benign Thyroid Nodules" (UC-BTN).Elements of the research methodology and creation of UC-BTNIn the analysis and evaluation of ultrasound manifestations of the nodular process in the thyroid gland, mainly data from practice and principles of (human) logic were mainly used. All cases of benign nodules over the past 16 years in a specialized thyroid clinic were included (2007 patients out of 3112). The first version of UC-BTN was created in 2010 and published in 2013 [27]. The UC-BTN was tested, improved and supplemented in the clinic over the following years. As patients came to the clinic, each case with a benign nodule(s) was assessed according to UC-BTN. As additional information and a better understanding of the nodular process appeared, UC-BTN was adjusted.The study of the condition and changes in the nodules was mainly carried out using ultrasound, but in some cases it was performed cytologically and scintigraphically. Ultrasound examination (in gray scale and Doppler mode) of these cases was performed by one specialist (the author). Particular attention was paid to comparing control ultrasound data (after 1-3 years or more). For each case, the medical history and blood test results were also analyzed.The following basic methodological principles were used to classify and create UC-BTN [26]:1) The division into classes should be carried out on a single basis (order);2) The division should always be proportionate;3) The members of the division of one series should exclude each other;4) The principle of ordering the members of the series can only be such a feature of objects (concepts) that can be extended to the entire classification;5) The members of the division in relation to the concept being divided should be the closest types, i.e. immediately lower concepts, and in relation to each other – subordinate concepts;6) The basis of the division should be a feature indicating a significant difference between the members of the division.The literature search was conducted in the PubMed system. At the same time, manuals, monographs and dissertations from library collections were used. The main objectives of the study were to understand the pathogenesis of thyroid nodules, their morphological features (cytological and histological), and all ultrasound characteristics of the nodules. The ultrasound machine used was Logiq P9 GE Healthcare. In grayscale mode, the overall gain was set to 60+/-2 dB (automatic correction was used to improve contrast). The depth gain was selected in the mid-range with a slightly gradual increase in depth. The blood flow intensity was determined in power Doppler mode at a pulse repetition frequency (PRF) of 8.1 kHz with a Gain of 22.5 dB. A longitudinal projection of each thyroid lobe at the maximum of the pulse wave was used. The projection with the largest number of nodule vessels was selected. Peak systolic velocity (PSV) was determined in the main vessels approaching the nodule or in the larger vessels of the nodule. The highest value was selected.The procedures followed in this study were in accordance with the requirements of the World Medical Association Declaration of Helsinki, revised in 2013. The Ethics Committee of Ushakov Thyroid Clinic approved the study.Ultrasound Classification of Benign Thyroid Nodules (UC-BTN)1. By location in the gland.1.1. Unilateral (left or right).1.2. Bilateral (including predominant on the left or right).1.3. In the isthmus.1.4. Totally nodular.2. By number of nodules.2.1. Single nodule.2.2. Multinodular.3. By size.3.1. Smallest.3.2. Small.3.3. Medium.3.4. Large.4. By relation to the lobe.4.1. Intralobar.4.1.1. Minor lobar.4.1.2. Semilobar.4.1.3. Subtotal lobar.4.1.4. Total lobar.4.1.5. Total thyroid.4.2. Extralobar.4.2.1. Slightly protruding.4.2.2. Moderately protruding.4.2.3. Significantly protruding.4.2.4. Absolutely protruding.5. By stage.5.1. Development.5.2. Wasting.5.2.1. Initial.5.2.2. Moderate.5.2.3. Significant.5.3. Scarring.6. By structural organization.6.1. Small-segmented.6.2. Large-segmented.7. By condition.7.1. Tissue.7.2. Small-cystic.7.3. Large-cystic.7.3.1. Mild.7.3.2. Moderate.7.3.3. Total-cystic (or Cystyc).8. By course.8.1. Progressive.8.1.1. Slow.8.1.2. Moderate.8.1.3. Significant.8.1.4. Very significant.8.2. Stable (or Persistent).8.2.1. Short.8.2.2. Moderate.8.2.3. Long-term.8.3. Regressing.8.3.1. Slow.8.3.2. Moderate.8.3.3. Quick.9. By blood flow Manifestation.9.1. By blood flow intensity.9.1.1. Unmanifested.9.1.2. Minor.9.1.3. Moderate.9.1.4. Significant.9.2. By peak systolic velocity.9.2.1. Decreased.9.2.2. Normal.9.2.3. Slightly increased.9.2.4. Moderately increased.9.2.5. Significantly increased.Class by the location of a nodule(s) in the thyroid The location of a nodule(s) in the thyroid gland serves as a simple and important reference point. Location of the nodule(s) in only one lobe or simultaneously in the lobe and the isthmus corresponds to the concept of Unilateral. However, a specific designation should be used in the diagnosis (Left-sided or Right-sided).The presence of nodules in two lobes is designated by the term Bilateral (nodular process). If nodules are predominate in one of these lobes, it is appropriate to use the additional term "predominant". For example: Bilateral nodular process, predominant on the right.A nodule in the isthmus is designated according to its location. In this case, it is necessary to indicate the part of the isthmus (right, left, central). For example: nodule of the left part of the isthmus.The location of nodules in all parts of the thyroid gland corresponds to the subclass “Totally nodular”. In this case, the nodules are determined in two lobes and the isthmus. The concept “Totally nodular” does not depend on the number of nodules. The presence of even one nodule in each part of the gland will correspond to this subclass.Class by the number of nodules in the thyroid The thyroid gland may have a different number of nodules. A common variant is one nodule in any part of the thyroid gland. This is the subclass Single nodule. Any other number of nodules represents the subclass Multinodular (process).In some cases, it may be clinically important to indicate the number of nodules in the ultrasound protocol or diagnosis, if the several exist. The classification, however does not contain the following sublevel in the Multinodular subclass (Binodular, Threenodular, etc.) due to such an elementary systematization.Class by the size of a thyroid nodule(s)The traditional criterion for distinguishing elements of this class is the largest size of a nodule. Up to 5 mm – Smallest nodule, from above 5 mm and up to 10 mm – Small nodule, from above 10 mm and up to 30 mm – Medium nodule, more than 30 mm – Large nodule.Class by the ratio of a nodule(s) to the thyroid lobeThis class consists of two subclasses. The ratio of a nodule(s) to the rest of the gland (lobe or isthmus) corresponds to the Intralobar subclass, consisting of four levels of a smaller order depending on the percentage ratio between the volumes of nodular and extranodular tissue (Figure 1). Up to 35% of the nodular tissue in the lobe represents the Minor lobar variant of the nodular process. 35-70% – Semilobar nodular process. 70-90% – Subtotal lobar nodular process. A nodule or nodules occupying the entire lobe (or almost the entire lobe) correspond to a Total lobar nodular process. Nodules in the entire gland (in two lobes and the isthmus) represent a Total-thyroid process (Figure 2). The Extralobar subclass includes variants of the location of either a portion or the entire nodule outside the proportional border of the gland lobe (Figure 3). Protrusion of the nodule beyond the conventional limits of the gland up to 20% corresponds to a Minor protrusion. Protrusion of the nodule from the lobe or isthmus by 21-50% is designated as a Moderate protrusion. Protrusion of the nodule beyond the border of the gland by more than 50% is a Significant protrusion. Protrusion of the nodule from the gland by 100% is rationally called an Absolute protrusion.