Parathyroid adenoma

Parathyroid adenomas are benign tumours of the parathyroid glands, and are the most common cause of primary hyperparathyroidism.

Patients present with primary hyperparathyroidism: elevated serum calcium levels and elevated serum parathyroid hormone levels. This results in multisystem effects including osteoporosis, renal calculi, constipation, peptic ulcers, mental changes, fatigue, and depression.

They are usually oval or bean-shaped, but larger adenomas can be multilobulated. The vast majority (up to 87% 2) of adenomas occur as solitary lesions.

The majority of parathyroid adenomas are juxtathyroid and located immediately posterior or inferior to the thyroid gland. Superior gland parathyroid adenoma may fall posteriorly in the tracheo-oesophageal groove or para-oesophageal location or even fall inferior as far as the mediastinum 12.

Up to 5% of parathyroid adenomas can occur in ectopic locations. Common ectopic locations include 1,12:

  • mediastinum
  • retropharygneal
  • carotid sheath
  • intrathyroidal

Parathyroid hormone levels are usually elevated (usual normal reference range 1.6-6.9 pmol/L or 10 to 55 pg/mL).

Ultrasound is one of most commonly used initial imaging modalities.

  • most nodules need to be >1cm to be confidently seen on ultrasound
  • parathyroid adenomas tend to be homogeneously hypoechoic to the overlying thyroid gland
  • an echogenic thyroid capsule separating the thyroid from the parathyroid may be seen

Can commonly show a characteristic extrathyroidal feeding vessel (typically a branch off the inferior thyroidal artery 1,6), which enters the parathyroid gland at one of the poles. Internal vascularity is also commonly seen in a peripheral distribution. This feeding artery tends to branch around the periphery of the gland before penetration. This feature can give a characteristic arc or rim of vascularity. The overlying thyroid gland may also show an area of asymmetric hypervascularity that may help to locate an underlying adenoma.

Can be very useful for localising the lesion when the site is not known. Shows increased uptake with agents such as technetium (Tc) 99m Sestamibi (MIBI) (commonly used agent) and Tc-99m tetrofosmin. The nuclear medicine scan can be fused with the CT scan as a SPECT scan to increase diagnostic accuracy and aid in anatomical localisation. 18F-fluorocholine PET/CT may also have a role 18.

In the past, CT was more commonly used in the setting of a failed parathyroidectomy for the detection of suspected ectopic glands (often mediastinal) 6.  However, in recent years, 4D-CT has emerged as valuable modality especially in the era of minimally invasive parathyroidectomy. This type of surgery requires precise localization with anatomical detail and a confident diagnosis of parathyroid adenoma. 4DCT has been shown to be more sensitive than sonography and scintigraphy for preoperative localisation of parathyroid adenomas 13,15.

On 4D-CT parathyroid adenomas typically demonstrate intense enhancement on arterial phase, washout of contrast on delayed phase and low attenuation on non-contrast imaging 12.

Secondary signs include 14:

  • the polar vessel which represents an enlarged feeding artery or draining vein to the hypervascular parathyroid adenoma
  • a larger lesion size increases the confidence of diagnosis
  • parathyroid adenomas can also have cystic change

MRI is infrequently utilized in initial work up because of lower spatial resolution and artifacts. Adenomas can show variable signal intensity on MRI. Reported signal characteristics include:

  • T1
    • typically intermediate to low signal
    • subacute haemorrhage can cause high signal intensity 6
    • fibrosis or old haemorrhage can cause low signal intensity 6
  • T2
    • typically hyperintense
    • subacute haemorrhage can cause high signal intensity 6
    • fibrosis or old haemorrhage can cause low signal intensity 6

Since most lesions demonstrate high T2 signal intensity, the addition of contrast for MR scanning does not significantly increase detection.

Surgery is successful in treating primary hyperparathyroidism caused by parathyroid adenomas in 95-98% of cases 17.

For a non-ectopic adenoma on ultrasound, consider:

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Article information

rID: 23949
System: Head & Neck
Section: Pathology
Synonyms or Alternate Spellings:
  • Parathyroid adenomas
  • Parathyroid adenomata
  • Adenoma of parathyroid gland
  • Adenomas of parathyroid gland
  • Adenoma of parathyroid glands

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Cases and figures

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    Case 1: on ultrasound
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    Case 2: scintigraphy - ectopic adenoma
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    Case 3
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