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Parathyroid Adenoma

Ariane Staub Neish, MD
J Stevan Nagel, MD
B Leonard Holman, MD

October 28, 1994

Presentation

A 42-year-old woman presented with hypercalcemia and elevated parathyroid hormone.

Imaging Technique

Parathyroid Scintigraphy: The patient was injected with 18 mCi of Tc-99m Sestamibi. Fifteen minutes later, an anterior cervicothoracic view was obtained using a low energy, high resolution, parallel hole ollimator.

Repeat images were obtained at 3 hours post injection. Both initial and delayed views were acquired for ten minutes.

Imaging Findings

Initial scans
Delayed scan

Initial images show normal diffuse uptake by the thyroid gland. A focal area of increased tracer uptake is present in the medial aspect of the upper pole of the left thyroid lobe (arrows).

Delayed images reveal washout of activity from the thyroid gland and persistent activity in the medial aspect of the upper pole of the left lobe (arrow).

Diagnosis

Parathyroid adenoma

Discussion

Ninety percent of cases of hyperparathyroidism are caused by a single benign adenoma. Five percent are caused by secondary hyperplasia (resulting from renal failure or malabsorption), 4% by primary hyperplasia, and 1% by parathyroid carcinoma. Dual isotope parathyroid scintigraphy using Tl-201/Tc-99m pertechnetate has been suggested to evaluate hyperparathyroid disease, although disadvantages are unfavorable Tl-201 dosimetry, the low photon energies of thallium-201, prolonged patient immobilization, and poor thyroid uptake of Tc-99m due to interfering medication or recent iodinated ontrast media.

MIBI (2-methoxy isobutyl isonitrile) accumulates in both the thyroid and parathyroid glands with a peak activity at 4-6 minutes. Tc-99m MIBI is sequestered within the mitochondria. Parathyroid adenomas have large numbers of mitochondria per cell. The washout rate of activity from the thyroid gland exceeds the washout rate from parathyroid adenomas. Hence parathyroid adenomas are particularly onspicuous on delayed images.

References

1. Oates E. Improved parathyroid scintigraphy with Tc-99m MIBI a superior radiotracer. App Rad 1994:37-40.

2. Chiu ML, Kronauge JF, Piwnica-Worms D. Effect of mitochondrial and plasma membrane potentials on accumulation of Hexakis (2-methoxyisobutylisonitrile) technetium in cultured mouse fibroblasts. J Nucl Med 1990: 31:1646-1653.

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