Mediastinal (Substernal) Parathyroid Adenoma in minimally invasive radioguided parathyroidectomy (MIRP)
This patient presented withhyperparathyroidism. A positive Technetium 99m-Sestamibiscan showed a right inferior parathyroid adenoma in the mediastinum, behind the upper sternum. The Neoprobe was used to confirm the location. In addition, to make the adenoma more visible, an intravenous infusion of methylene blue was administered. This dye stains the parathyroids with a deep blue color. A small 3 cm-incision was made just above the right clavicle. The parathyroid adenoma was very easily identified in the upper mediastinum because its blue color contrasted sharply with the surrounding fat and adjacent thymus.
Two hours after the administration of Tc 99 Sestamibi, the parathyroid scan shows an elongated "hot" density in the upper mediastinum, below the right thyroid lobe, indicating the presence of a parathyroid adenoma.
The parathyroid adenoma was readily visible because of the methylene blue uptake. It was pulled out of the mediastinum and removed from a small cervical skin incision.
This is a close-up of the mediastinal adenoma depicted in the previous picture.
Outpatient Minimally Invasive Endoscopic Video Assisted (MIVAP) or
Parathyroidectomy - Outpatient Procedures
What is a Sestamibi Scan?
Technetium 99m-Sestamibi is a protein that is labeled with radioactive technetium (Tc99). It is injected intravenously for diagnostic use. The precise structure of the technetium complex is Tc99m[MIBI]6+ where MIBI is 2-methoxy isobutyl isonitrile. Tc99m decays by isomeric transition with a half-life of 6.02 hours.
MIBI (2-methoxy isobutyl isonitrile) accumulates in both the thyroid and parathyroid glands. Tc-99m MIBI is sequestered within the mitochondria. The parathyroid glands accumulate the radioactivity and retain it longer than the adjoining thyroid gland. A gamma ray detector similar to a Geiger counter is used to pick up radioactivity at various intervals. Initial images show normal diffuse uptake by the thyroid gland, while delayed images show a persistent activity in the parathyroid glands.
Since normal parathyroid glands are inactive and do not produce parathyroid hormone when there is high calcium in the bloodstream, they do not take up the radioactive particles. The parathyroid adenoma, however, remains active and produces excessive amounts of parathyroid hormone. Because it has large numbers of mitochondria per cell, the adenoma accumulates radioactivity and shows conspicuously on delayed images. The three other parathyroids do not show on the scan or appear very faint, compared to the adenoma. This is why the Sestamibi parathyroid scan will point to the adenoma with 90% accuracy.
Left lower parathyroid adenoma.
What is Radioguided in MIRP? Radioguided parathyroidectomy utilizes the above principles to help the surgeon find the adenoma. An appropriate dose of Tc99m-Sestamibi is injected intravenously, about two hours prior to the operation. By this time, the radioactiviy has already washed out from the thyroid gland and has concentrated in the parathyroid adenoma. A pencil-like gamma ray detector probe is placed on the neck before making the surgical incision. It will show a higher radioactivity over the adenoma, compared to the rest of the neck. This eliminates the guesswork and allows the surgeon to make a much smaller incision, right on top of the parathyroid adenoma.
The same probe is the covered with a sterile sheath and used to point to the adenoma inside the wound. When the adenoma is found and removed, the radioactivity inside the wound drops, while the removed adenoma still registers high radioactive levels.
About 1.5 to 2 inch-incision instead of 3 to 6 inch-incision.
Usually less than one hour in the operating room instead of 1 to 2 hours.
No risk to laryngeal nerves and other structures in the opposite side of the neck.
Less complications than the standard operation.
Much smaller overall operation, therefore, less pain.
Return to normal activities usually by the next day.
Usually performed on an outpatient basis.
Cure rate as high or higher than the standard operation.
Could be performed under local anesthesia instead of general anesthesia.