Parathyroid scintigraphy is a nuclear medicine diagnostic procedure for imaging the parathyroid glandulae (parathyroid glands). The parathyroid glands are also known as epithelial bodies and, as hormonal glands, secrete vital hormones that are essential for bone metabolism or calcium balance. Scintigraphy is an imaging procedure in the course of which a radionuclide (radioactive substance, so-called tracer) is applied to the patient. In the so-called scintigram, the radiation that has previously accumulated in the organ to be examined can then be visualized with a special camera (gamma camera). The resulting images can be used for diagnostic purposes.
Indications (areas of application)
- Preoperative imaging of adenomas and hyperplasias of the parathyroid gland in primary hyperparathyroidism (HPT): imaging of the parathyroid gland is performed primarily for localization of adenomas or hyperplasias of the parathyroid glands when this is insufficiently possible with other imaging techniques. Prior to surgical intervention, this serves for more precise planning and optimization of the removal of adenomas or hyperplasias. An adenoma is a primarily benign neoplasm of glandular tissue that can degenerate malignantly. A hyperplasia is a proliferation of a tissue by increasing the number of cells, but not the size of the cells. The medical problem of an increase in glandular tissue is the associated increased secretion of thyroid hormones, which can lead to hyperparathyroidism, for example. In this disease, the hormone parathormone is secreted in increased amounts, which leads to a disturbance of the calcium balance. Consequences of these disorders are osteoporosis (bone loss) due to increased calcium release from the bone, nephrolithiasis (kidney stones) due to increased calcium excretion (excretion) in the urine, atherosclerosis (arteriosclerosis, arteriosclerosis) due to deposition of calcium and phosphate in the vessels, as well as other, partly unspecific symptoms.
Contraindications
Relative contraindications
- Lactation phase (breastfeeding phase) – breastfeeding must be interrupted for 48 hours to prevent risk to the child.
- Repeat examination – no repeat scintigraphy should be performed within three months due to radiation exposure.
Absolute contraindications
- Gravidity (pregnancy)
Before the examination
- The patient should be informed of the risks and benefits of the procedure.
- Pregnancy should be excluded anamnestically.
- There is no need for special patient preparation.
The procedure
- The radionuclide used is usually 99mTc-MIBI (99mTechnetium-methoxyisobutyl-isonitrile). The substance MIBI (methoxyisobutyl-isonitrile) accumulates particularly well in mitochondria. These small cell organelles are also known as the power plants of the cells and provide large amounts of energy for cell metabolism. In the parathyroid glands, there is a type of cell that is histologically characterized by its high proportion of mitochondria (so-called oxyphilic cells). For this reason, 99mTc-MIBI accumulates in the parathyroid glands.
- The procedure of parathyroid scintigraphy is as follows: The patient is in the supine position and is injected with 600-800 MBq (unit for radioactivity) of 99mTc-MIBI. Several images are then taken, first after 10-15 minutes, then after about 2 hours. In addition, another early image may be taken to document the dynamics of 99mTc-MIBI accumulation.
- Supplementary SPECT (single photon emission computed tomography) images are often obtained to provide a better spatial representation of the findings. Starting at the base of the skull, the images include the entire neck, as well as the thorax up to the diaphragm (diaphragm).
- To clearly differentiate the parathyroid glands from the thyroid gland, subtraction scintigraphy is performed. Because 99mTc-MIBI also accumulates in the thyroid gland, a kind of background noise is generated, so that the epithelial bodies can be poorly delineated. In subtraction scintigraphy, for example, only 99mTc is initially injected and a scintigraphy of the thyroid is obtained.This image corresponds to the background noise of the actual parathyroid scintigraphy. Now this image can be “subtracted” from the image with 99mTc-MIBI, so that the parathyroid glands can be delineated.
Possible complications
- Intravenous application of radiopharmaceutical may result in local vascular and nerve lesions (injuries).
- Radiation exposure from the radionuclide used is rather low. Nevertheless, the theoretical risk of radiation-induced late malignancy (leukemia or carcinoma) is increased, so that a risk-benefit assessment should be performed.