To confirm or refute the notion that only parathyroid adenomas have radioactivity higher than 20% of background.
Retrospective analysis of a prospective patient data set.
Tertiary care referral center.
Forty-six patients (9 men and 37 women; mean ± SD age, 53.7 ± 12.1 years) underwent thyroid and parathyroid surgery between December 2005 and December 2006 to collect data on ex vivo radioactivity percentages on a variety of tissues.
Patients were injected with 296 to 925 MBq of technetium Tc 99m sestamibi 1½ to 3½ hours before surgery. Biopsy specimens were taken of normal parathyroid glands, normal thyroid tissue, and lymph nodes and ex vivo radioactivity was recorded. Hyperplastic parathyroid glands and adenomatous glands were excised. Finally, some enlarged glands were cut into segments, and radioactivity counts were recorded and compared with the weight of the tissue.
Main Outcome Measures
All counts were compared with radioactivity percentages in the surrounding tissues, and results were expressed as a function of these background radioactive counts.
The mean ± SD ex vivo background radioactivity of parathyroid adenomas was 148.5% ± 83.1% of background activity (range, 40.1%-388.9% but never less than 40%). The mean ± SD ex vivo background radioactivity of hyperplastic parathyroid glands was 74.6% ± 18.0% (range, 49.5%-109.1% but never less than 40%). A significant difference was found in ex vivo background radioactivity between pathologic parathyroid tissue and the other tissue specimens studied (normal parathyroid glands [2.4% ± 1.8%], thyroid tissue [4.5% ± 2.8%], lymph nodes [1.6% ± 0.8%], and fat [0.4% ± 0.3%]).
Ex vivo radioactivity percentages can differentiate hyperactive parathyroid tissue from any other tissue, but they cannot differentiate adenoma from hyperplasia and thus are not helpful in ruling out multiglandular disease. Interpretation of ex vivo radioactivity percentages should take into consideration the size of the specimen.