Study of the Ultrasound Appearance of the Normal Parathyroid Using an Intraoperative Procedure

Normal Parathyroid Glands Are Most Often Seen on Neck Ultrasound

RATIONALE AND OBJECTIVES

The dogma is that normal parathyroid glands (PTGs) are not visible on ultrasound (US). Recently, several studies have shown that PTGs present these US features: ovoid structure, homogeneous and hyperechoic. The primary objective was to assess the detection rate, standard size and locations of normal PTGs in a population of patients consulting for thyroid US exam. The secondary objective was to determine if the presence of a goiter or a thyroiditis could modify the visualization of normal PTGs.

METHOD

Single-center prospective study on 192 patients based on the typical US appearance previously described to identify one or more PTGs.

RESULTS

One or more PTGs were visualized in 75% of patients (144/192). They were visualized preferentially at the lower pole of the thyroid gland and in the infra-thyroid region (66%). The mean (± SD) size of normal PTGs was 5.68 mm (± 1,42 mm)×4.05 mm (± 1,03 mm)×2,68 mm (± 0,61 mm) and mean volume was 33.3 mm3 (± 17.75 mm3). The presence of a goiter made the search for PTGs more difficult whereas the presence of thyroiditis facilitated it.

CONCLUSION

The US detection rate of PTGs is high (75%). The identification of PTGs could be particularly useful in the preoperative assessment before total thyroidectomy or parathyroid surgery. It could reduce the risk of postoperative hypoparathyroidism and improve the accuracy of postoperative US surveillance of thyroid cancer. Better knowledge of the usual anatomical location of normal PTGs could also enable better detection of abnormal glands.

Ultrasonographic features of normal parathyroid glands confirmed during thyroid surgery in adult patients

PURPOSE

This study was performed to examine the ultrasonography (US) features of normal parathyroid glands (PTGs) that were identified on preoperative US and subsequently confirmed during thyroid surgery.

METHODS

This retrospective study included a consecutive sample of 161 patients (mean±standard deviation age, 56±14 years; 128 women) with 294 normal PTGs identified on preoperative US PTG mapping and confirmed during thyroidectomy. A presumed normal PTG on US was defined as a small, round to oval, hyperechoic structure in the central neck. These presumed normal PTGs, as identified on preoperative US, were mapped onto thyroid computed tomography images and diagrams of the thyroid gland and neck. During the preoperative real-time US examinations, the location, size, shape, echogenicity, echotexture, and intraglandular vascular flow of the identified presumed PTGs were assessed. These characteristics were compared between superior and inferior PTGs using the generalized estimating equation method.

RESULTS

The typical US features of homogeneous hyperechogenicity without intraglandular vascular flow were observed in 267 (90.8%) normal PTGs, while atypical features, including isoechogenicity (1.0%), heterogeneous echotexture with focal hypoechogenicity (5.8%), and intraglandular vascular flow (3.7%), were noted in 27 (9.2%). Inferior PTGs were more frequently identified in posterolateral (36.1% vs. 5.3%) and thyroid pole locations (29.9% vs. 5.3%), and less frequently in posteromedial locations (29.2% vs. 88.0%), compared to superior PTGs (P<0.001 for each comparison).

CONCLUSION

Most normal PTGs displayed the typical US features of homogeneous hyperechogenicity without intraglandular vascular flow. However, in rare cases, normal PTGs exhibited atypical features, including isoechogenicity, heterogeneous echotexture with focal hypoechogenicity, and intraglandular vascular flow.

Preoperative ultrasonography parathyroid gland mapping can improve identification of normal parathyroid gland during thyroidectomy: A propensity score-matched case-control study

BACKGROUND

Accurate intraoperative identification of normal parathyroid glands (PTGs) is vital to avoid hypocalcemia post total thyroidectomy. Although ultrasonography (US) has been shown to identify normal PTGs, the significance of preoperative US PTG mapping in this context is not well studied. This study evaluated the impact of preoperative US PTG mapping on intraoperative identification of normal PTGs during total thyroidectomy.

METHODS

The study involved 161 consecutive patients who underwent total thyroidectomy between January 2020 and June 2022. These included patients without preoperative US PTG mapping (group 1, n = 91) and those with the mapping (group 2, n = 70). Propensity score matching yielded 61 matched patients from each group. We developed a preoperative US PTG mapping technique combining US identification of normal PTGs with their localization on thyroid CT images. The intraoperative detectability of normal PTGs during thyroid surgery and detectability of normal PTGs by the preoperative US mapping were assessed by the number of PTGs identified per patient and by location.

RESULTS

In the matched cohort, group 2 demonstrated a higher median number of identified PTGs (3 vs. 2, p = 0.011), a greater proportion of patients with three or more identified PTGs (65.5% vs. 44.3%, p = 0.018), and a higher ratio of identified to expected PTGs (70.5% vs. 60.2%, p = 0.011) than group 1. In group 2, the median number of normal PTGs identified preoperatively was 3, with at least one identified in 95.7% of patients, two or more in 84.3%, three or more in 52.9%, and four or five in 24.3%.

CONCLUSIONS

Preoperative US PTG mapping identified two or more normal PTGs in the majority of adult patients undergoing total thyroidectomy. Those with preoperative mapping showed a higher number of intraoperatively identified normal PTGs, including inferior PTGs, compared to those without. This technique appears to enhance the intraoperative identification of normal PTGs, thereby potentially improving surgical outcomes in total thyroidectomy.

The Parathyroid Gland: An Overall Review of the Hidden Organ for Radiologists

Parathyroid glands are small endocrine glands that regulate calcium metabolism by producing parathyroid hormone (PTH). These are located at the back of the thyroid gland. Typically, four glands comprise the parathyroid glands, although their numbers may vary among individuals. Parathyroid diseases are related to parathyroid gland dysfunction and can be caused by problems with the parathyroid gland itself or abnormal serum calcium levels arising from renal disease. In recent years, as comprehensive health checkups have become more common, abnormal serum calcium levels are often found incidentally in blood tests, after which several additional tests, including a PTH test, ultrasonography (US), technetium-99m sestamibi parathyroid scan, single-photon-emission CT (SPECT)/CT, four-dimensional CT (4D-CT), and PET/CT, are performed for further evaluation. However, the parathyroid gland remains an organ less familiar to radiologists. Therefore, the normal anatomy, pathophysiology, imaging, and clinical findings of the parathyroid gland and its associated diseases are discussed here.

Ultrasound characteristics of normal parathyroid glands and analysis of the factors affecting their display

BACKGROUND

Parathyroid glands are important endocrine glands, and the identification of normal parathyroid glands is crucial for their protection. The aim of this study is to explore the sonographic characteristics of normal parathyroid glands and analyze the factors affecting their display.

METHODS

Seven hundred three subjects who underwent physical examination at our hospital were included. The number, location, size, morphology, echogenicity and blood flow distribution of parathyroid glands were recorded. The ultrasound characteristics and display rate were also summarized. Meanwhile, shear wave elastography was performed in 50 cases to provide the stiffness measurements, and 26 cases received contrast-enhanced ultrasonography for the assessment of microcirculatory perfusion. Furthermore, we analyzed the factors affecting parathyroid display, including basic information of the subjects and ultrasound features of the thyroid.

RESULTS

① A total of 1038 parathyroid glands were detected, among which, 79.29% were hyperechoic, 20.71% were isoechoic, 88.15% were oval-shaped, and 86.71% had blood flow of grade 0-I. ② 81.79% of the subjects had at least one parathyroid gland detected. ③ The Emean, Emax, PI and AUC of the parathyroid glands were significantly lower than those of the adjacent thyroid tissue (P < 0.05). ④ The display of normal parathyroid glands was related to BMI, thyroid echogenicity and thyroid volume of the subjects (P < 0.05).

CONCLUSIONS

Normal parathyroid glands tend to appear as oval-shaped hyperechoic nodules with blood flow of grade 0-I. BMI, thyroid echogenicity and thyroid volume are independent factors affecting the display of parathyroid glands.

US Features of the Parathyroid Glands: An Intraoperative Surgical Specimen Study

Purpose

This study aimed to evaluate the US features of the parathyroid glands (PTGs) using surgical specimens of normal PTGs obtained during thyroid surgery.

Materials and Methods

This study included 34 normal PTGs from 17 consecutive patients who underwent thyroid surgery between December 2020 and March 2021. All normal PTGs were histologically confirmed by intraoperative frozen-section biopsy for autotransplantation. Surgically resected parathyroid specimens were scanned in sterile normal saline using high-resolution US prior to autotransplantation. The US features of echogenicity (hyperechogenicity or hypoechogenicity), echotexture (homogeneous or heterogeneous), size, and shape (ovoid or round) were retrospectively evaluated. The echogenicity of the three PTGs was compared with that of the thyroid parenchyma of the resected thyroid specimens in two patients.

Results

All PTGs showed hyperechogenicity similar to that of gauze soaked in normal saline. Homogeneous hyperechogenicity was observed in 32/34 (94.1%) patients, and the echogenicity of the three PTGs was hyperechoic compared with that of the thyroid parenchyma. The long diameter of the PTGs ranged from 5.1 mm to 9.8 mm (mean, 7.1 mm) and the shape of the PTGs was ovoid in 33/34 (97.1%) patients.

Conclusion

The echogenicity of normal PTG specimens was consistently hyperechoic, and the small ovoid homogeneously hyperechoic structure was a characteristic US feature of the PTGs.

Preoperative ultrasound identification and localization of the inferior parathyroid glands in thyroid surgery

INTRODUCTION

The parathyroid glands are important endocrine glands for maintaining calcium and phosphorus metabolism, and they are vulnerable to accidental injuries during thyroid cancer surgery. The aim of this retrospective study was to investigate the application of high-frequency ultrasound imaging for preoperative anatomical localization of the parathyroid glands in patients with thyroid cancer and to analyze the protective effect of this technique on the parathyroid glands and its effect on reducing postoperative complications.

MATERIALS AND METHODS

A total of 165 patients who were operated for thyroid cancer in our hospital were included. The patients were assigned into two groups according to the time period of surgery: Control group, May 2018 to February 2021 (before the application of ultrasound localization of parathyroid in our hospital); PUS group, March 2021 to May 2022. In PUS group, preoperative ultrasound was used to determine the size and location of bilateral inferior parathyroid glands to help surgeons identify and protect the parathyroid glands during operation. We compared the preoperative ultrasound results with the intraoperative observations. Preoperative and first day postoperative serum calcium and PTH were measured in both groups.

RESULTS

Our preoperative parathyroid ultrasound identification technique has more than 90% accuracy (true positive rate) to confirm the location of parathyroid gland compared to intraoperative observations. Postoperative biochemical results showed a better Ca²⁺ [2.12(0.17) vs. 2.05(0.31), P=0.03] and PTH [27.48(14.88) vs. 23.27(16.58), P=0.005] levels at first day post-operation in PUS group compared to control group. We also found a reduced risk of at least one type of hypoparathyroidism after surgery in control group:26 cases (31.0%) vs. 41 cases (50.6%), p=0.016.

CONCLUSION

Ultrasound localization of the parathyroid glands can help in the localization, identification and in situ preservation of the parathyroid glands during thyroidectomy. It can effectively reduce the risk of hypoparathyroidism after thyroid surgery.

Ultrasound Identification of Normal Parathyroid Glands

Ultrasound has become indispensable for identification of thyroid and parathyroid pathology, but normal parathyroid glands have historically been considered too subtle to accurately detect. Inability to identify and protect parathyroid glands can result in hypoparathyroidism and hypocalcemia during thyroidectomy surgery as well as misinterpretation of central neck structures in the postoperative neck. Advances in ultrasound resolution have opened the door to novel applications for this technology. In this study, we report the first surgeon-performed ultrasound identification of normal parathyroid glands in a series of 6 patients, confirmed by parathyroid tissue aspirate or parathyroid autofluorescence. Recognition of normal parathyroid glands using ultrasound can be valuable for preventing postoperative hypoparathyroidism and in increasing the accuracy of postsurgical ultrasound surveillance.

The Value of Preoperative and Intraoperative Ultrasound in the Localization of Intrathyroidal Parathyroid Adenomas

AIM

Intrathyroidal parathyroid adenoma (IPA) is rare and may easily be mistaken for thyroid nodule in ultrasonography. The aim of this study was to investigate the characteristic features of IPA and explore the value of preoperative and intraoperative ultrasound in the diagnosis and localization of IPA.

METHODS

13 of 216 patients who were found to have intrathyroidal parathyroid lesions underwent parathyroidectomy in our hospital because of PHPT. According to the relationship between parathyroid adenoma and thyroid gland, parathyroid adenoma was divided into extra-thyroid type or intra-thyroid type (partial or complete) and the results were compared with surgical and histopathological reports as gold standard. The sonographic features of intrathyroidal parathyroid lesions were analyzed retrospectively.

RESULTS

A total of 12 intrathyroidal lesions showed profoundly hypoechoic solid nodules with well-defined border, abundant blood flow and polar feeding vessels originating from the superior or inferior thyroid artery (92.3%, 12/13). These nodules were finally confirmed as IPA (or IPAC) after surgery. Polar feeding vessel was not detected in one case of parathyroid hyperplasia confirmed by pathology (7.7%, 1/13). 12 cases were diagnosed and localized on ultrasonography before operation and 10 cases were localized on Tc-99m MIBI SPECT/CT.

CONCLUSIONS

The color Doppler ultrasound findings of IPA were confirmed as profoundly hypoechoic nodules with clear boundary and abundant internal blood flow. The presence of polar feeding vessels which originate from thyroid artery were identified as characteristic features of US for IPA. Preoperative and intraoperative ultrasound could be helpful in the localization and treatment of intrathyroidal parathyroid diseases.

Pediatric hyperparathyroidism: review and imaging update

Hyperparathyroidism, due to increased secretion of parathyroid hormones, may be primary, secondary or tertiary. Most pediatric patients with sporadic primary hyperparathyroidism will be symptomatic, presenting with either end-organ damage or nonspecific symptoms. In younger patients with primary hyperparathyroidism, there is a higher prevalence of familial hyperparathyroidism including germline inactivating mutations of the calcium-sensing receptor genes that result in either neonatal severe hyperparathyroidism or familial hypocalciuric hypercalcemia. Parathyroid scintigraphy and ultrasound are complementary, first-line imaging modalities for localizing hyperfunctioning parathyroid glands. Second-line imaging modalities are multiphase computed tomography (CT) and magnetic resonance imaging. In pediatrics, multiphase CT protocols should be adjusted to optimize radiation dose. Although, the role of these imaging modalities is better established in preoperative localization of hyperfunctioning parathyroid glands in primary hyperparathyroidism, the same principles apply in secondary and tertiary hyperparathyroidism. In this manuscript, we will review the embryology, anatomy, pathophysiology and preoperative localization of parathyroid glands as well as several subtypes of primary familial hyperparathyroidism. While most of the recent imaging literature centers on adults, we will focus on the issues that are pertinent and applicable to pediatrics.

Efficacy of ultrasonography and Tc-99m MIBI SPECT/CT in preoperative localization of parathyroid adenomas causing primary hyperthyroidism

Background

Primary hyperparathyroidism (PHPT) results from an excess of parathyroid hormone (PTH) produced from an overactive parathyroid gland. The study aimed to explore the sonographic features of parathyroid adenomas and assess the diagnostic performance of ultrasonography (US) and Tc-99m MIBI SPECT/CT for preoperative localization of parathyroid adenomas.

Methods

A total of 107 patients were enrolled in this retrospective study who had PHPT and underwent parathyroidectomy. Of the 107 patients, 97 performed US and Tc-99m MIBI SPECT/CT examinations for preoperative localization of parathyroid nodules. The sensitivity and accuracy of each modality were calculated.

Results

In this study, residual parathyroid sign and polar vascular sign were identified as characteristic US features of parathyroid adenomas. These manifestations were closely related to the size of the abnormal parathyroid lesions. Among the 108 parathyroid nodules from 97 patients with PHPT, the sensitivity and accuracy of US for locating the parathyroid nodules were significantly higher than those of Tc-99m MIBI SPECT/CT (93.0% vs. 63.0% and 88.0% vs. 63.0% respectively; ²=26.224, 18.227 respectively, P<0.001). The differences between US+Tc-99m MIBI SPECT/CT and Tc-99m MIBI SPECT/CT-alone were statistically significant (²=33.410, 21.587 respectively, P<0.001), yet there were no significant differences in the sensitivity or accuracy between US+Tc-99m MIBI SPECT/CT and US-alone (²=0.866, 0.187 respectively, P=0.352 and 0.665).

Conclusions

US shows significantly better sensitivity and accuracy for localization of parathyroid adenomas than Tc-99m MIBI SPECT/CT. However, US combined with Tc-99m MIBI SPECT/CT is of great clinical value in the preoperative localization of parathyroid nodules in patients with PHPT.

Novel techniques for intraoperative parathyroid gland identification: a comprehensive review

INTRODUCTION

The parathyroid glands (PGs) are critical for calcium regulation and homeostasis. The preservation of PGs during neck surgery is crucial to avoid postoperative hypoparathyroidism. There are no existing guidelines for intraoperative PG identification, and the current approach relies heavily on the experience of the operating surgeon. A technique that accurately and rapidly identifies PGs would represent a useful intraoperative adjunct.

AREAS COVERED

This review aims to assess common dye and fluorescence-based PG imaging techniques and examine their utility for intraoperative PG identification. A literature search of published data on methylene blue (MB), indocyanine green (ICG) angiography, near-infrared autofluorescence (NIRAF), and the PGs between 1971 and 2020 was conducted on PubMed.

EXPERT OPINION

NIRAF and near-infrared (NIR) parathyroid angiography have emerged as promising and reliable techniques for intraoperative PG identification. NIRAF may aid with real-time identification of both normal and diseased PGs and reduce the risk of postoperative complications such as hypocalcemia. Further large prospective multicenter studies should be conducted in thyroid and parathyroid surgical patient populations to confirm the clinical efficacy of these intraoperative NIR-based PG detection techniques.