Parathyroid MIBI Scan

Authors: Dr Dee Nandurkar*
                            Dr Peter Francis *

What is a parathyroid MIBI scan?

A parathyroid MIBI scan is used in nuclear medicine to look at possible problems involving the parathyroid gland(s).

The parathyroid scan uses the radioisotope, technetium-99m sestamibi (or MIBI), which is injected into the body and absorbed by the overactive parathyroid mitochondria. A hyperactive gland is picked up by the scan on the images taken by a gamma camera.

In some cases, another radioactive material (sodium pertechnetate) is given before the MIBI, so that the thyroid gland alone can be identified. This allows the position of the parathyroids to be assessed in relation to the thyroid gland.

What are the generally accepted indications for a parathyroid MIBI scan?

1. Localisation of parathyroid adenomas.This is a preoperative assessment to confirm or exclude a parathyroid adenoma in patients with hypercalcaemia and inappropriately elevated parathyroid hormone level.
2. Localisation of persisting parathyroid tissue in patients with persistent or recurrent disease.Many of these patients will already have had one or more surgical procedures, making re-exploration more technically difficult. Preoperative localisation of active parathyroid tissue will likely increase surgical success, by helping to direct the surgical approach to active areas.

What are the prerequisites for having a parathyroid MIBI scan?

• Documentation of elevated serum calcium and parathyroid hormone.
• Documented increased urinary excretion of calcium is also advised when other laboratory abnormalities are mild.
• History of prior thyroid or parathyroid surgery should be provided.
• Results of computed tomography (CT), magnetic resonance imaging (MRI) or ultrasound scans when imaging shows pathology possibly representing abnormal parathyroid tissue.

What are the absolute contraindications for a parathyroid MIBI scan?

Due to the radioactivity of the MIBI scan, the study may not be suitable for pregnant women. The benefit versus risk should be discussed with the nuclear medicine specialist.

If the patient is unable or not willing to remain still for a prolonged period of time or is claustrophobic, you may need to consider another procedure, such as an ultrasound looking for enlarged gland/s in the neck or a four-dimensional computed tomography.

What are the relative contraindications for a parathyroid MIBI scan?

• Iodine-containing preparations, such as CT contrast, in the past 8 weeks, as this might prevent the thyroid from taking up the tracer. Knowing the position of the thyroid can be very beneficial in identifying the position of the parathyroid glands.
• Thyroid disease and thyroid hormones, such as thyroxine.

Both the relative contraindications above will interfere with thyroid gland uptake, making it difficult to obtain a technetium subtraction image, where the abnormal parathyroid gland(s) can be separated from the thyroid gland.

What are the adverse effects of a parathyroid MIBI scan?

Generally, there are no adverse reactions. However, on rare occasion the patient may experience a metallic taste that lasts a few moments.

Very rarely a patient could experience:

• tingling;
• flushing;
• nausea;
• erythema;
• diffuse rash;
• headache.

Is there any specific post procedural care required following a parathyroid MIBI scan?

Women who are breast-feeding and people who are the primary or sole carer for small children may need to make special preparations after the test to stop breast-feeding for 4 hours,¹ and to avoid close contact with young children due to the small amount of radioactivity released for 4 hours¹ after the test. See InsideRadiology: Nuclear Medicine for further information about the precautions to take with nuclear medicine studies for breast-feeding patients and those in close contact with children.

Are there alternative imaging tests, interventional or surgical procedures to a parathyroid MIBI scan?

• Ultrasound is a useful screening test for parathyroid adenomas; however, it lacks specificity.
• Computed tomography and/or magnetic resonance imaging may prove complimentary.
• A sestamibi scan preceded by a technetium scan is useful to subtract the thyroid gland, which would therefore make the detection of small parathyroid gland(s) easier to locate. SPECT-CT scans can further enhance the sensitivity and specificity for detection of parathyroid adenomas using sestamibi.

Reference

1. ARPANSA – Radiation Protection Series No 14.2. Date of publication: 8 August 2008 pages 31-32.

*The author has no conflict of interest with this topic.

Page last modified on 18/5/2018.