Role of Elastography in the Evaluation of Parathyroid Disease

Abstract

Primary hyperparathyroidism is a prevalent disease of the parathyroid glands and the third most common endocrinopathy, especially among postmenopausal women. Secondary hyperparathyroidism is a compensatory response to hypocalcemic states due to chronic renal disease, vitamin D deficiency and malabsorption syndromes, and other chronic illnesses. Elastography can be an effective tool in localizing and identifying parathyroid lesions, whether it is a parathyroid adenoma or hyperplastic parathyroid secondary to chronic kidney disease, by differentiating between possible parathyroid lesions and thyroid nodules, cervical lymph nodes, or other anatomical structures. No current guidelines recommendations are available and no established general cutoff values on the elasticity of parathyroid lesions. We have conducted several prospective studies on primary and secondary hyperparathyroidism, using ultrasound imaging and elastography, shear wave, and strain elastography to better identify the parathyroid lesions and improve the preoperative localization and diagnostic. The results were encouraging, allowing us to determine cutoff values that are different for lesions from primary hyperparathyroidism and secondary hyperparathyroidism and comparing them with normal thyroid tissue and surrounding muscle tissue.

1. Introduction

Advancements in the medical field improved diagnostic methods, increasing the incidence of various endocrine diseases [1, 2]. Hyperparathyroidism is a common endocrine disorder, commonly as primary hyperparathyroidism. As incidence it is the third endocrinopathy after type 2 diabetes mellitus and thyroid disease [3].

When discussing primary hyperparathyroidism, parathyroid adenoma being quoted as the most common cause of primary hyperparathyroidism, parathyroid hyperplasia and parathyroid carcinoma follow [4, 5, 6].

Secondary hyperparathyroidism is a prevalent complication of chronic kidney disease, with high prevalence among patients on renal replacement therapy [7, 8].

Nowadays, primary hyperparathyroidism is mostly diagnosed in asymptomatic forms, in premenopausal women mostly, by active screening, with high serum parathormone (PTH) concentrations, and consequently high serum calcium concentrations [1, 4, 5, 6, 9, 10, 11].

Secondary hyperparathyroidism is prevalent among the chronic kidney cohort, determined by the disturbances of the phosphor-calcic metabolism. Prevalence cited in the specialty literature displays high numbers among patients receiving dialysis—of 54% in the United States and Europe—43.8% in France, 46.8% in Russia, and 42.9% in the United Kingdom [7].

The pathophysiological mechanism of primary hyperparathyroidism (PHPT) shows a loss of the homeostatic control of parathormone synthesis and secretion pathway, determining an increased secretion of parathomone and/or marked proliferation of cells with normal levels of PTH. Single adenomas present a monoclonal origin, suggesting that the tumors derive from a single abnormal cell [12], while hyperplastic parathyroid tumor usually presents polyclonal origins from a genetic point of view [1].

On the other hand, secondary hyperparathyroidism (sHPT) has a multifactorial and complex mechanism driven by hypocalcaemia, vitamin D deficiency, hyperphosphatemia, and high levels of fibroblast growth factor. In this case, sHPT could be amended by treating the underlying affection, chronic renal failure, or vitamin D deficiency. However, chronical stimulation of parathyroid glands can become autonomous, resulting in persistent tertiary hyperparathyroidism [4, 13, 14].

Regardless of the etiology of hyperparathyroidism, surgery represents a legitimate, validated, and corrective treatment in both primary and secondary hyperparathyroidism. Minimally invasive parathyroidectomy (MIP) is considered as a preferred approach current recommendation, thus the requirement to correctly identify the number and localization of affected parathyroid glands in preoperative evaluation, ultrasonography being the most cost-efficient method [15, 16, 17, 18, 19].

Given the positive features of ultrasonography, such as the noninvasive character, high resolution in real time, reproducibility, easiness in manipulation, inoffensive to children and pregnant women, and the absence of X-Ray exposure or administration of contrast agents, making it most accessible, reliable, and cost-efficient imaging technique for identifying pathological parathyroid glands [20, 21].

Elastography is a validated, complementary method to ultrasonography, labeled as “palpation imaging,” providing qualitative and quantitative information on the studied tissue such as anatomical architecture and modifications in tissue stiffness [20, 22, 23, 24]. Endorsed as a marker of pathological states in many clinical fields, contributing to the positive identification, differential diagnosis, and ultimately to the therapeutic management, establishing its role in endocrinology for both thyroid and parathyroid evaluation [25, 26], hepato-gastroenterology [20, 27, 28, 29], senology [30, 31], urology [32, 33, 34], and otorhinolaryngology [35].

Two basic principles described for ultrasound elastography: “determination of the strain or deformation of a tissue due to a force (static elastography) and analysis of the propagation speed of a shear wave (shear wave elastography)” [36]. Literature studies have obtained various parameters from these elastography techniques that characterize a modification of a tissue. Three major groups are described using those parameters:

• qualitative criteria obtained from elastograms, which are maps, presented in gray scales or color, depending on the manufacturer, displaying the distribution of elasticities. They are available on most ultrasound machines, regardless of the technique used. A rapport can be determined between the width of tissue on B-mode and elastography.

• semiquantitative criteria are estimation of deformation ratios or elasticity ratios between different regions of interest (ROI).

• quantitative criteria possible by using the shear wave technique, determining the propagation speed of the shear wave. It represents a dynamic evaluation containing multiple subtypes:

1. transient elastography (TE) giving numerical values of the elasticity index, not being able to provide ultrasonographic imagines

2. point shear-wave elastography (pSWE)

3. shear-wave elastography

The last two methods include two-dimensional shear wave elastography and three dimensional shear wave elastography, determining numerical values of the elasticity index and providing color maps [20]. The numerical value data are calculated in Young modulus in m/s or kPa [36].

Strain elastography (SE) is a quasi-static elastographic method first implemented on ultrasound systems. It necessitates an external pressure to induce the deformation of the underlying tissue, or the deformation can be generated by acoustic radiation force impulse (ARFI). The most recent elastographic technologies can use endogenous stress such as muscle contractions or vascularization beam movements [20, 37, 38].

It can determine qualitative evaluation by adding elastograms (color maps) on conventional 2 B mode and, depending on the manufacturer, it can offer real-time elastography, where the refresh rate is equal to that in gray scale or single-image display with the mean relative hardness over a time loop [20].

Shear wave elastography induces shear waves in targeted tissues using acoustic radiation force and ultrasound imaging techniques to track the propagating shear waves. The shear waves induce a perpendicular oscillation to the direction of the wave propagation, expressed by shear modulus G and measured by shear wave speed (cS), which can be then further recorded in m/s or converted by using the Young’s modulus E in kilopascals (kPa). The wave speed is then spatially mapped and directly related to the local stiffness of the evaluated tissue. This manner allows real-time monitoring of shear wave deformation in 2D and measures the shear wave speed or Young’s modulus E and generates quantitative elastograms [2, 22, 39].

Elastography was used in both primary and secondary hyperparathyroidism, with an important clinical impact, proven in our previous studies [11, 25, 40, 41, 42]. Is has been proven to accurately predict the parathyroid tissue when compared with thyroid or muscle tissue.

This chapter aims to identify the characteristics of parathyroid adenomas in primary hyperparathyroidism and the attributes of hyper-plastic parathyroid glands in patients with chronic kidney on renal replacement therapy and to identify if the elastography can add value to the presurgical identification and differential diagnosis.

2. Ultrasound and elastographic evaluation of parathyroid disease

2.1 2B-ultrasonography evaluation

Gray scale ultrasound (US) has become a very accessible imaging technique in the endocrinology field, especially for thyroid and parathyroid evaluation, becoming the gold standard in these domains. The noninvasive character, the low cost, the repeatability, and especially the real-time assessment are some of the many advantages of this imagistic technique [43, 44].

The ultrasound evaluation of both thyroid and parathyroid glands involves a large ultrasound framework. Anatomical structures must be well observed and identified both in longitudinal and transverse modes [23, 45, 46]. Additional auxiliary techniques, including the rotation of the head to improve the ultrasound framework on the neck structures or swallowing, could improve the correct identification of anatomical structures and of ectopic parathyroid glands [45].

The sensitivity of ultrasound identification of parathyroid tumors varies from 70 to 80% [47] with higher positive identification for parathyroid hyperplasia 30–90% [48], but precision is dependent on the location and size of the tumor [16], by body habitus and gland morphology, and by the experience of the evaluator [46]. Increased false-positive ultrasound results are caused by structures mimicking parathyroid adenomas such as thyroid nodules, lymph nodes, muscles, vessels, and esophagus [16].

2.1.1 Adding color Doppler mode

Parathyroid adenomas typically present a peripheral vascular rim and an abnormally increased blood flow than the thyroid gland [49]. Therefore, by adding color Doppler mode in the ultrasound evaluation can increase the accuracy and sensitivity of ultrasound by 54% [50].

2.2 Ultrasound elastography: description and method

Elastography can be a helpful complementary imaging technique in the evaluation of parathyroid disease, adding additional information on tissue stiffness.

Neoplastic, fibrous, or atherosclerotic transformation in tissues is translated by tissue stiffness in elastographic evaluation [38]. The development of neoplastic tissue can be identified even in early stages, as from the physiopathological point of view, we can have an increased production of connective tissue, changes in cell density, and increased blood flow, all these changes determining a change in the tissue matrix, thus a change in the elasticity of the tissue [2]. Elastography can identify the differences between benign and malignant tissues from the early development of the disease, offering high sensitivity and resolution for deep-situated structures [51].

Elastography evaluates tissue stiffness by applying an external stress and calculating the distortion degree. The distortion in elastography is obtained by applying external pressure, manually or via ultrasound transducer. In acoustic radiation force impulse (ARFI), the distortion is induced by using crossing deformation, with converged ultrasound beams or by emitting of short duration focused acoustic beam that will generate shear waves that diffuse transversally through the tissue [52]. It thus determines qualitative information about tissue stiffness through color maps and color codes and quantitative information through numerical values [38].

An elastographic evaluation follows a 2B-mode ultrasound evaluation of the parathyroid glands. It can be performed in all patients; it is cost-efficient and adds valuable information. The elastography module is available on multiple ultrasound machines such as Aixplorer Mach 30 machine (SuperSonic Imagine, France), Philips, Fujifilm, Hitachi Preirus (Hitachi Medical Corporation, Tokyo, Japan) machine.

Elastography on the parathyroid is performed using a linear, high-resolution transducer of 15–4, respectively, 18–5 MHz chosen depending on the clarity of the image, profound parathyroid glands being evaluated with 15–4 probe, obtaining better images. The patient was examined in a supine position with neck hyperextension, maintaining regular superficial breathing. The following parathyroid parameters are to be evaluated—localization, form, parathyroid dimensions, and total volume of the gland.

Two elastographic procedures will be discussed in the chapter—2D shear wave elastography and real-time elastography.

The procedure depends on the type of elastography performed, for example, for shear wave elastography, the examiner must maintain a precise adherence for minimal 6 seconds to the probe on the examined area, with careful attention not to apply any manual compression, permitting the transducer to induce the acoustic vibrations in the parathyroid tissue. After image stabilization, a real-time elastogram will overlap on the B-mode image, obtaining an elastogram or color map (Figure 1). Afterimage stabilization, quantitative measurements can be performed on a frozen image.

Figure 1.

(a) 2B-mode ultrasound evaluation of parathyroid adenoma, with complementary color Doppler mode; (b) Elastogram of parathyroid adenoma overlying B mode image and color map of tissue elasticity, with Q-box on the region of interest and quantitative evaluation [53] .

Quantitative information, described as the elasticity index (EI) obtained on the frozen elastogram image, using a quantification box (Q-box), placed in the regions of interest (ROI). After software computing evaluates the mean SWE, minimum SWE, maximum SWE, and standard deviation, the elasticity parameters are displayed. All measurements are numerically expressed in kilopascals (kPa). As there is no scale setting recommended for the parathyroid examination, we recommend using a thyroid scale (0–100 kPa).

Another elastographic technique that requires external pressure in order to induce a deformation of the examined tissue that is further quantified by the machine software. This method is called real-time elastography (RTE) or strain elastography (SE). The examiner must apply controlled external pressure, usually manually pressure, which determines a mechanical deformation. An elastographic map is overlayed on the 2B greyscale that is displayed as a color map (red for liquid, green for soft tissue, blue for hard tissue), permitting the examined to obtain qualitative information about tissue stiffness for the examined area (Figure 2) [38].

Figure 2.

Ultrasound evaluation and strain elastography of parathyroid adenoma [54].

Semiquantitative values can be obtained using strain elastography by comparing tissue strain in the region of interest (ROI) of the targeted tissue with another adjacent tissue, calculating a strain ratio (SR) ratio.

2.3 Strain elastography

The experience with strain elastography on parathyroid disease is primarily focused on parathyroid adenomas as parathyroid hyperplasia is more difficult to evaluate with this form of elastography [54]. The evaluation scale used to evaluate parathyroid lesions is the Rago criteria, frequently used for thyroid pathology. Rago criteria [38, 55], described for thyroid pathology, especially nodular goiter, was used to assess the qualitative strain elastography evaluation, as it follows: a score 1 means that the elasticity in the whole lesion is soft tissue, a score 2 means that the tissue is mostly soft, a score 3 is defined by soft tissue in the peripheral part of lesion, a score 4 implies that the examined lesion is entirely stiff, and a score 5 involves stiffness that exceeds beyond the examined lesion’s margins, infiltrating in the enclosing tissues.

The leading disadvantage of this qualitative technique is the depth of the evaluated tissue or lesion, determining an incomplete, unusable, and uninterpretable color map for higher depths. Most of the parathyroid adenomas evaluated in the paper previously published were of score 1 according to the Rago criteria (Figure 3) [25].

Figure 3.

Color map with strain elastography with Hitachi machine showing a score 1 on Rago criteria [54].

The first study conducted evaluated strain elastography on primary hyperparathyroidism on 20 consecutives patients evaluating qualitative and semiquantitative values. Out of the total 20 cases, two parathyroid adenomas could not be evaluated and for the rest a score 1 according to the Rago criteria was found [25].

The size and localization of the parathyroid adenoma were also quantified, so on ultrasound evaluation, the mean parathyroid adenoma dimensions were 0.776 ± 0.50 cm, the maximum size found was 2.46 cm, and the minimum was 0.34 mm. Most of the parathyroid adenomas were found near the right superior thyroid lobe (nine adenomas), three were located near the right inferior thyroid lobe, three were located near the left superior lobe, and five near the left inferior lobe. As for ultrasound appearance 13 parathyroid adenomas had cystic appearance (65%), 5 parathyroid adenomas homogeneously solid and hypoechoic appearance (25%), and 2 adenomas had a mixed appearance (10%)—mostly cystic and one with an elongated shape.

Semiquantitative information was also achieved using strain elastography, by comparing tissue strain the parathyroid adenoma parenchyma and thyroid or muscle tissue. No significant differences were found between the strain ratio determined using SE for the parathyroid adenoma and the thyroid tissue (nine out of twenty cases) with a mean SR of 1.465 ± 1.458, respectively, strain ratio of the parathyroid adenoma compared with the strain ratio of the thyroid tissue with autoimmune disease (11 out of 20 cases) with a mean SR = 1.656 ± 1.746, p = 0.481 [25].

Other literature studies have compared the elasticity of parathyroid pathology using strain elastography, identifying that parathyroid adenomas appear as stiff lesions (median SR = 3.56) and parathyroid hyperplasia has a lower stiffness and a higher elasticity score (median SR = 1.49) [56].

A study based on another type of elastographic evaluation–Elastoscan Core Index (ECI) evaluating parathyroid adenomas and lymph nodes found that the ECI index was significantly higher in malignant lesions than in benign lesions. They concluded that combining ECI index with conventional US, particularly with shape and vascularization, can improve the differentiation of parathyroid lesions from lymph nodes and thyroid nodules [57].

2.4 Shear-wave elastography

We conducted several studies on primary and secondary hyperparathyroidism, comparing the results to evaluate the differences between the two clinical entities, as the pathophysiological mechanism is quite different.

Our first study [25] (previously published) evaluated the values of shear wave elastography on primary hyperparathyroidism. Twenty consecutive patients with primary hyperparathyroidism presenting a solitary adenoma were included. The parathyroid tissue was compared with thyroid and muscle tissue, as normal parathyroid adenomas cannot be evaluated using ultrasonography. The best parameter identified for evaluating parathyroid adenomas was mean SWE, with the highest specificity, sensitivity, and accuracy. The results are displayed in Table 1 [25].

	SWE-min PTX/T	SWE-mean PTX/T	SWE-max PTX/T	SWE-min PTX/M	SWE-mean PTX/M	SWE-max PTX/M
Area under curve (AUC) value	0.957	0.950	0.765	0.998	0.997	0.955
Specificity	85%	90.0%	70.0%	95.0%	95.0%	80.0%
Sensitivity	95%	95.0%	80.0%	100%	100%	100%
PPV	86.4%	90.5%	72.7%	95.2%	95.2%	83.3%
NPV	94.4%	94.7%	77.8%	100%	100%	100%
Accuracy	90.0%	92.5%	75.0%	97.5%	97.5%	90.0%
p value	<.0.001	<0.001	<0.001	<0.001	<0.001	<0.001
Cut-off value	<3.14 kPa	<7.28 kPa	<9.14 kPa	<5.32 kPa	<10.47 kPa	<15.16 kPa

Table 1.

Sensitivity, specificity, ROC curve for measured elastographic index SWE-min, SWE-max, and SWE-mean for primary hyperparathyroidism.

Statistical analysis has found significant difference between parathyroid elasticity (kPa) compared with thyroid and muscle elasticity (p < 0.001).

A second study [40] (previously published) was conducted on patients on renal replacement therapy with consequential secondary hyperparathyroidism. A cohort of 120 patients was evaluated, founding 59 with secondary parathyroid hyperplasia. A total of 97 hyperplastic parathyroid glands were evaluated, comparing normal thyroid and muscle tissue with hyperplastic parathyroid tissue. Statistical differences were found in this cohort and identified the best parameter to evaluate the elasticity of parathyroid tissue and the cut-off values (Table 2) [40].

	SWE min PTX/T	SWE mean PTX/T	SWE max PTX/T	SWE min PTX/M	SWE mean PTX/M	SWE max PTX/M
AUC value	0.943	0.940	0.858	0.957	0.949	0.882
Specificity	86.6%	90.7%	75.3%	95.9%	90.7%	84.5%
Sensitivity	94.8%	94.8%	83.5%	86.6%	93.8%	78.4%
PPV	87.6%	91.1%	77.1%	95.9%	91%	83.5%
NPV	94.4%	94.6%	82.0%	87.7%	93.6%	79.6%
Accuracy	90.7%	92.26%	79.4%	91.2%	91.75%	81.45%
Cutoff value	< 6.02 kPa	< 9.74 kPa	< 15.3 kPa	< 7.94 kPa	< 9.98 kPa	< 17.3 kPa

Table 2.

Sensitivity, specificity, AUROC for measured SWE min, SWE max, and SWE mean for secondary hyperparathyroidism [40].

After analyzing the two cohorts, a natural question has appeared—are there any differences between primary and secondary hyperparathyroidism on elastographic evaluation?

The third study answered this question—evaluating a total of 68 patients divided into two groups of 27 patients diagnosed with primary and 41 patients diagnosed with secondary hyperparathyroidism (Figures 4 and 5).

Figure 4.

Elastograms using 2D SWE. In image A – Elastogram overlaying gray scale ultrasound of a right inferior parathyroid adenoma; In image B – Elastogram overlaying gray scale image of a right inferior parathyroid hyperplasia in secondary hyperparathyroidism [41].

Figure 5.

Elasticity index evaluation for parathyroid and thyroid tissue. In image A – Elastographic evaluation of a right inferior parathyroid adenoma from primary hyperparathyroidism; In image B – Elastograohic evaluation of a left inferior parathyroid hyperplasia from secondary hyperparathyroidism [41].

The baseline characteristics of the primary and secondary hyperparathyroidism study are presented in Table 3 [41].

Characteristics	Primary hyperparathyroidism	Secondary hyperparathyroidism	p-value
Male-to-female ratio	2/25	22/19	<0.001
Age (years)	61 [48.67]	58 [50–65.5]	0.763
Parathormone (PTH) (pg/ml)	160.6 [115.0–206.3]	1117 [785.95–1407]	<0.001
Serum phosphorus (mg/dl)	2.60 [2.30–3.12]	6.00 [5.15–7.77]	<0.001
Total serum calcium (mg/dl)	10.50 [10.10–11.40]	9.00 [8.35–9.35]	<0.001
Serum vitamin D (ng/ml)	21.33 [15.55–25.52]	35.80 [24.20–44.70]	<0.001
Parathyroid volume (ml)	0.120 [0.068–0.240]	0.251 [0.109–0.332]	0.107
Maximum diameter (mm)	8.30 [6.20–12.00]	9.50 [7.25–11.75]	0.543
Dialysis years	—	5.10 [4.00–8.10]	NA
Kt/v	—	1.350 [1.30–1.46]	NA

Table 3.

Baseline characteristics of patients evaluated with primary and secondary hyperparathyroidism.

When comparing the results of the two studied lots, we found statistically significant differences in sex distribution between the two lots (p < 0.001, Fischer-exact Test).

Keeping the different pathophysiology pathways for primary and secondary hyperparathyroidism in mind, we conducted diagnostic tests to evaluate the elastographic differences between the two types of hyperparathyroidism [41].

A statistically significant difference (p < 0.001) was found when comparing the results of SWE-mean parathyroid tissue between primary and secondary hyperparathyroidism, with higher values for the secondary hyperparathyroidism group (Figure 6).

Figure 6.

Shear wave differences between mean value SWE for primary hyperparathyroidism and secondary hyperparathyroidism. [41].

There are multiple research studies on the elastographic evaluation of primary hyperparathyroidism, but this method is less approached for secondary hyperparathyroidism.

Different threshold values for parathyroid adenomas have been established by various authors in the field of primary hyperparathyroidism, depending on the elastography techniques used. By using shear wave virtual touch imaging quantification, higher values have been found for parathyroid adenomas (2.16 ± 0.33 m/s) compared with parathyroid hyperplasia (1.75 ± 0.28 m/s), identifying a cutoff value superior to 1.92 m/s for parathyroid adenomas [44]. Another study presented their results between the elastographic differences between thyroid and parathyroid tissue, using the same elastograohic method as the previous. Their conclusion was that the elastographic index of parathyroid adenomas is lower than of the thyroid tissue, presenting a shear wave velocity of 2.01 m/s, respectively 2.77 m/s [58].

Another representative study performed an analysis using the ARFI imaging 2D SWE, comparing parathyroid adenomas with malignant and benign thyroid pathology. They have identified that parathyroid adenomas present a higher elasticity index than benign thyroid pathology (3.09 ± 0.75 m/s versus SWV of 2.20 ± 0.39 m/s) and an even higher elasticity than malignant thyroid lesions with a mean SWV of 3.59 ± 0.43 m/s [59].

In the 2D SWE elastography field, a study conducted on parathyroid adenomas and benign thyroid nodules has identified that parathyroid adenomas present a significantly lower elasticity index than benign thyroid nodules (mean SWE 5.2 ± 7.2 kPa, respectively mean SWE of 24.3 ± 33.8 kPa) [60]. The results are similar with our conclusion using the same elastographic method.

Some elastographic studies on parathyroid hyperplasia have been published, but they not focused on patients with chronic kidney disease on hemodialysis. There are currently no other threshold values for secondary hyperparathyroidism, apart those presented [40, 41].

2.5 Strain versus shear-wave elastography

Strain elastography is a very useful elastographic technique that requires external pressure in order to produce deformation of subjacent tissue that has been validated in the field of thyroid and breast evaluation.

Even if strain elastography can be without any doubt a very useful qualitative tool by using the color mapping, 2D-SWE elastography can offer a better identification of parathyroid tissue.

There are certain limitations of the elastography in the evaluation of parathyroid glands, the most important is the difficulty in evaluating ectopic and supranumerary parathyroid glands, especially when located in the thymus or posterior mediastinum. When using elastography, a low value, near to zero could indicate the presence of a liquid lesion or a depth lesion, inaccessible to the linear probe. It is very important to verify the signal intensity, to distinguish between liquid lesions and depth lesion, and to opt for a linear probe with lower frequencies is available. Another limitation to consider is that the trachea or the carotid movement could generate artifacts, in this case, elastographic noise can be decreased by increasing the gain. One of the most important aspects in the elastographic evaluation is the external pressure applied to the probe that can produce false-positive values. This is a limitation because it is operator-dependent, less present in shear-wave elastography than in strain elastography. Another aspect to be considered is the choice of the elastography scale, as there is no recommendation for parathyroid evaluation, we have used in our studies a scale between 0 and 100 kPa.

3. Conclusions

The clinical implications of elastography in the evaluation of primary or secondary hyperparathyroidism are undeniable. As a complementary method to conventional ultrasonography, elastography is a simple, noninvasive, repeatable, and reproducible method that can improve diagnosis and preoperative evaluation of the patient with either primary or secondary hyperparathyroidism.

Even if there are certain limitations to the technique, such as operator experience and some techniques are more operator-dependent that others, we have to take in mind that it is a complementary technique and that is noninvasive, highly reproducible, easy to manipulate, presents a high resolution in real time, it is harmless to children and pregnant women with absence of X-ray exposure or need of contrast agents, making it a very accessible and cost-efficient imaging technique for complementary evaluation of parathyroid disease.

We have found significant differences between primary and secondary hyperparathyroidism, identifying a cutoff elastographic value for parathyroid adenomas below 5.96 kPa [41].

One of the essential questions of the studies has been answered, the following question was to determine a general cutoff value for parathyroid tissue. Thus, we have considered into analysis both parathyroid adenomas and parathyroid hyperplasia values, permitting us to establish a mean SWE cutoff value for parathyroid tissue below 9.58 kPa [41].

Further studies could help establish the elastographic differences between pathological parathyroid tissue and thyroid nodules. Current literature studies had determined that there is a major difference between malignant and benign thyroid nodules, the first being stiffer than the ladder. Furthermore, benign thyroid nodules present a higher elasticity index than normal thyroid tissue. We can imagine that if parathyroid tissue should be compared with benign or malignant thyroid tissue, a significant elasticity difference should be found.

Elastography is a proven and validated method in many clinical areas and recognized by the current guideline, including thyroid disease [61, 62]. It most certainly presents a major role in the localization of the parathyroid disease as useful tool for both qualitative, but mainly quantitative evaluation of parathyroid tissue. Significant elastographic differences between parathyroid adenoma and parathyroid hyperplasia have been identified, but in both cases, the parathyroid tissue is significantly lower than the healthy thyroid tissue and the surrounding muscle tissue.

Acknowledgments

We would like to thank all our contributors—Prof Dr. Ioan Sporea, Prof Dr. Adalbert Schiller, and Dr. Oana Schiller for the guidance and for allowing us to conduct our studies in their services.

Conflict of interest

The authors declare no conflict of interest.

Notes

The current chapter represents a summary of our experience with the elastography techniques applied in the field of parathyroid disease. Six papers were published on this subject. Images and statistical values were previously published in our studies.