Multi-modality parathyroid imaging: A shifting paradigm

Abstract

The goal of parathyroid imaging in hyperparathyroidism is not diagnosis, rather it is the localization of the cause of hyperparathyroidism for planning the best therapeutic approach. Hence, the role of imaging to accurately and precisely localize the abnormal parathyroid tissue is more important than ever to facilitate minimally invasive parathyroidectomy over bilateral neck exploration. The common causes include solitary parathyroid adenoma, multiple parathyroid adenomas, parathyroid hyperplasia and parathyroid carcinoma. It is highly imperative for the radiologist to be cautious of the mimics of parathyroid lesions like thyroid nodules and lymph nodes and be able to differentiate them on imaging. The various imaging modalities available include high resolution ultrasound of the neck, nuclear imaging studies, four-dimensional computed tomography (4D CT) and magnetic resonance imaging. Contrast enhanced ultrasound is a novel technique which has been recently added to the armamentarium to differentiate between parathyroid adenomas and its mimics. Through this review article we wish to review the imaging features of parathyroid lesions on various imaging modalities and present an algorithm to guide their radiological differentiation from mimics.

Keywords: Contrast enhanced ultrasound; Four-dimensional computed tomography; Magnetic resonance imaging; Nuclear Imaging; Parathyroid adenoma; Ultrasound.

Figure 1

Diagrammatic representation of location of eutopic (yellow) and ectopic (red) parathyroid glands.

Figure 2

Left inferior parathyroid adenoma. A: High resolution ultrasound image of the neck in the transverse plane demonstrates a well-circumscribed homogenously hypoechoic ovoid lesion located at the lower pole of the left lobe of thyroid gland; B: Colour Doppler shows a big feeding vessel, likely from the inferior thyroid artery (arrow) supplying the lesion.

Figure 3

In a patient with MEN-1 syndrome. A-F: Ultrasound neck images show multiple (3) parathyroid adenoma in the right superior and left superior and inferior parathyroid glands respectively.

Figure 4

Contrast-enhanced ultrasound in parathyroid adenoma. A-C: A 33-year-old female with raised parathormone levels (87 IU) was assessed using contrast enhanced ultrasound. A circumscribed lesion at the lower pole of the left lobe of thyroid gland was found consistent with parathyroid adenoma, demonstrating early peripheral enhancement with central washout.

Figure 5

Imaging features of parathyroid adenomas on four-dimensional computed tomography. CT: Computed tomography.

Figure 6

Right superior adenoma: Four-dimensional computed tomography. A: Non-contrast computed tomography shows a small oval hypodense lesion which shows B: Intense enhancement on the arterial phase; C: Washout on the venous phase consistent with right superior parathyroid adenoma; D: Coronal image and E: Coronal maximum intensity projection image in the arterial phase better demonstrate the lesion with the feeding vessel (black arrow).

Figure 7

Left inferior parathyroid adenoma. In a patient with raised parathormone levels (290 IU), grey scale ultrasound A: and colour doppler flow imaging; B and C: Showed a hypoechoic lesion with vascularity just below the left lobe of the; D: 4-dimensional computed tomography showed the lesion to be hypodense on noncontrast computer tomography; E: Hyperenhancing with central necrosis on arterial phase; F: Washout on the venous phase; G: Coronal image better demonstrates the lesion.

Figure 8

Ectopic parathyroid adenoma in the anterior mediastinum. A: 4-dimensional computed tomography done in the 12-year-old female with hyperparathyroidism showed a well-defined lesion in the anterior mediastinum just behind the sternum which was hypodense on non-contrast computed tomography; B: intense arterial enhancement; C: washout on the venous phase; D: Multiplanar reformatted coronal; E: sagittal images in the arterial phase show the lesion better; F: Oblique sagittal maximum intensity projection image shows the feeding vessel (black arrow); G: Sternotomy followed by thymectomy was done and the thymus opened - the adenoma can be seen within the thymic parenchyma as pointed by the forceps.

Figure 9

Ectopic parathyroid adenoma in the anterior mediastinum. A: Computed tomography in a 45-year-old male patient showed a well-defined ovoid lesion in the prevascular space just posterior to the sternal notch and anterior to the inferior thyroid vessels appearing hypodense on the non-contrast phase; B: Showing intense enhancement on the arterial phase; C: washout in the venous phase; D: Coronal maximum intensity projection image demonstrates the inferior thyroid artery supplying the lesion (feeding vessel - black arrows); E: Fluoro-choline positron emission tomography shows a small tracer avid lesion in ectopic location which correlates with the computed tomography images.

Figure 10

Ectopic Parathyroid Adenoma in the Supraclavicular fossa. A: Grey scale ultrasound of the neck on a 49-year-old male patient, with history of bilateral renal stones and elevated parathormone reveals a hypoechoic lesion in the right supraclavicular location; B: On color doppler, internal vascularity was detected; C: 4-dimensional computed tomography showed a lesion with arterial enhancement; D: Washout seen on the venous phase; E: Coronal reformatted image better depicts the ectopic parathyroid adenoma in the right supraclavicular fossa.

Figure 11

Intrathyroidal parathyroid adenoma. In a patient with raised parathormone (208 IU), A: Color doppler ultrasound of the neck showed a circumscribed solid hypoechoic lesion within the left lobe of thyroid gland; B: 4-dimensional computed tomography revealed the lesion to be hypodense as compared to thyroid tissue on non-contrast; C: showed intense arterial hyperenhancement; D: Washout on the venous phase, consistent with the diagnosis of intra-thyroid parathyroid adenoma; E and F: Coronal (E) and Sagittal maximum intensity projection images better depict the lesions with vascular pedicle (black arrow) seen supplying the lesion (F); G: Single photon emission computed tomography image showing a thyroid nodule which is mildly tracer avid; H: Left hemithyroidectomy was done and the cut open section confirmed the presence of the tumor.

Figure 12

Right superior parathyroid adenoma. A 50-year-old female with raised parathormone levels (96 IU) was examined using duplex ultrasound for parathyroid glands. A: Grey scale sonography in the transverse and longitudinal plane showed a well circumscribed lesion posterior to the right lobe of thyroid gland and separated from it by a clear fat plane; B: Colour doppler image shows a feeding vessel. Corroborative magnetic resonance imaging axial images show a subcentimetric lesion (arrows) posterior to the middle third of the right lobe of thyroid gland which is C: T1 hypointense; D: T2 hyperintense; E: Coronal T2w image better demonstrates the lesion; F: Correlative single photon emission computed tomography component of MIBI scan showing tracer avid lesion at the superior pole of the right lobe of thyroid; G: Image of the resected adenoma weighing 1.05 g.

Figure 13

Parathyroid carcinoma. A 62-year-old male patient with recurrent hyperparathyroidism (previously operated parathyroid carcinoma), 4-dimensional computed tomography done showed few hypodense lesions with ill-defined margins near the lower pole of the left lobe of thyroid gland which showed, A: arterial enhancement however; B: No washout on the venous phase - atypical contrast kinetics for parathyroid adenoma; C: Coronal image better demonstrates the lesion. Surgical exploration and histopathological examination revealed parathyroid carcinoma recurrence.