Ultrasound is a first-line, non-invasive imaging tool for evaluating parathyroid glands. Its ability to provide real-time, high-resolution images makes it essential in the assessment of patients with suspected primary hyperparathyroidism.
While the normal parathyroid glands are often not visualised, ultrasound plays a pivotal role in identifying enlarged glands, guiding further investigations, and assisting in preoperative localisation.
A thorough understanding of parathyroid anatomy, pathology, and ultrasound techniques is crucial for accurate diagnosis.
Six key points:
- Clinical presentation and prevalence
Primary hyperparathyroidism, the most common indication for parathyroid ultrasound, is diagnosed via blood tests showing raised serum calcium and parathyroid hormone (PTH) levels. A 24-hour urine test may also show elevated urinary calcium.
Secondary hyperparathyroidism (low calcium, high PTH) is associated with renal disease and does not typically require ultrasound. Primary hyperparathyroidism affects ~3:1000 of the general population and is more common in postmenopausal women (21:1000).
- Anatomy
There are typically four parathyroid glands located posterior to the thyroid, though variations exist (e.g., 3 or 5 glands). Glands originate from the 3rd and 4th pharyngeal pouches and are often within 1 cm of the thyroid’s lower pole but may be ectopically positioned as low as the mediastinum. Normal glands measure ~3–4mm and are usually not visible on ultrasound.
- Ultrasound technique
Use a high-frequency linear probe and adjust depth/focus to visualise posterior to the thyroid. Enlarged parathyroid glands appear hypoechoic, solid, and ovoid, occasionally with cystic changes or calcification. Colour Doppler can help identify "polar vascularity" (vessels entering at one gland pole), distinguishing adenomas from lymph nodes (vessels enter at the hilum).
- Pathology
Parathyroid adenoma: The most common pathology (~80%), typically solitary, causing enlargement of the parathyroid. Multiple adenomas are less common (~10%
Hyperplasia: ~10% of cases, often involving all glands
Carcinoma: Rare (<1%)
- Ectopic and equivocal findings
Adenomas may be ectopically located, sometimes embedded within the thyroid, leading to diagnostic challenges. Sestamibi scans may assist but can also show uptake in thyroid nodules. Lymph nodes in the tracheal groove or adjacent neck vessels can mimic parathyroid pathology
- Other imaging modalities
Diagnosis often combines ultrasound with Sestamibi scanning (SPECT-CT or NM). 4D-CT may be used for unclear cases, with MRI rarely employed. Post-diagnosis imaging often includes renal ultrasound (to check for nephrolithiasis) and DEXA bone scans (to assess for osteopenia/osteoporosis caused by calcium imbalance).
Reflection prompts
Are you familiar with blood test findings for primary hyperparathyroidism? Can you differentiate between primary and secondary causes?
Do you consider anatomical variants of parathyroid gland locations during scanning?
Have you reviewed other imaging (e.g., Sestamibi scans) to confirm ectopic findings or provide additional diagnostic confidence?
Can you identify ultrasound features of a parathyroid adenoma and differentiate it from lymph nodes?
Are you aware of supplementary imaging and its role in patient management?
Further reading:
Gokozan HN, Scognamiglio T. Advances and Updates in Parathyroid Pathology. Adv Anat Pathol. 2023 Jan 1;30(1):24-33. https://doi.org/10.1097/pap.0000000000000379
Mete O, Erickson LA, Juhlin CC, de Krijger RR, Sasano H, Volante M, Papotti MG. Overview of the 2022 WHO Classification of Adrenal Cortical Tumors. Endocr Pathol. 2022 Mar;33(1):155-196. https://doi.org/10.1007/s12022-022-09710-8
National Institute for Health and Care Excellence. Hyperparathyroidism (primary): diagnosis, assessment and initial management, 2019 [NG132]. https://www.nice.org.uk/guidance/ng132
(Image credit: Fotostorm via Getty Images)