Background: 99mTc-sestamibi parathyroid SPECT scintigraphy is a useful tool in the pre-operative study of hyperparathyroidism. False negatives (FN) have been reported in 5.7-14% of the examinations.
Aim: To characterize 99mTc-sestamibi FN in cases referred for primary hyperparathyroidism (PHP) to a university hospital.
Material and methods: Descriptive retrospective analysis. We included patients with PHP, studied with SPECT scintigraphy, operated at our center between 2008 and 2015. Clinical and surgical data were recorded; biopsies of the FN were blindly reviewed by one pathologist.
Results: One hundred twenty one scintigraphies fulfilled the inclusion criteria. Seven (5.8%) were negative and 114 positive. There was no difference in age, sex and PTH levels between FN and true positive scintigraphies. At surgery, one FN case had two hyperplasic glands and two cases had ectopic glands. Pathology reported adenoma in three cases, hyperplasia in three and carcinoma in one. The largest diameter of the lesion was lower in FN (1.3 and 2.1 cm respectively, p = 0.02) and the proportion of adenomas was higher in true positive cases (29% and 75% respectively; p < 0.01). The interval between scintigraphy and parathyroidectomy was greater in FN with a median of 92 days (range 20 days-3.2 years, p < 0.01). The percentage of oxyphilic cells observed was similar in both groups.
Conclusions: FN parathyroid SPECT scintigraphies in PHP are uncommon. They corresponded to lesions under the equipment's resolution limit and resulted in longer time lags between scintigraphy and surgery.