KEY FACTS
Imaging
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Round or oval, well-circumscribed, solid mass
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Typically 1-3 cm in size
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Most are hypoechoic to thyroid and homogeneous
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Some show cystic degeneration
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Calcification is rare; more common in carcinoma or hyperplasia due to hyperparathyroidism
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Location
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Upper glands: Posterior to upper or mid pole of thyroid
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Lower glands: 65% inferior, lateral to lower pole of thyroid
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≤ 20% in ectopic location: Tracheoesophageal groove, thymus, carotid sheath, superior mediastinum, intrathyroid (~ 6%)
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Color Doppler: Adenomas are hypervascular; vessels enter at poles, unlike lymph nodes
Top Differential Diagnoses
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Exophytic thyroid nodule
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Paratracheal lymph node
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Parathyroid carcinoma
Clinical Issues
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Asymptomatic hypercalcemia, kidney stones, low bone density
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Single adenoma responsible for 75-85% of primary hyperparathyroidism: ↑ serum calcium and PTH
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Secondary hyperparathyroidism in chronic kidney disease: Usually 4 enlarged parathyroid glands
Scanning Tips
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Scan with patient supine and neck hyperextended, ask patient to turn neck or swallow if adenoma is not found
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Look deep to thyroid (and in mediastinum with lower frequency transducer)
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Use color Doppler to find vascular supply from inferior thyroid artery
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US may be limited in obese patients with short necks, postoperative necks, or ectopic parathyroid adenomas
and their relationship to the thyroid gland. Ultrasound is sensitive for the detection of adenomas in these locations.
. The adenoma is lobulated and homogeneously hypoechoic. It is separate from the thyroid 
and lies anterior to the esophagus 
.
, hypoechoic to thyroid. Incidental colloid cysts 
are noted in the thyroid. Note the common carotid artery 
.
