Utility of MIBI SPECT-CT and contrast-enhanced CT in primary hyperparathyroidism

Objectives The utility of morphologic and functional imaging in initial identification of parathyroid glands causing hyperparathyroidism (HPT) is unclear. We undertook this study to determine the relative utility of 99m-technetium MethoxyIsoButylIsonitrile (MIBI) SPECT-CT and contrast enhanced CT (CECT) in the identification of parathyroid lesions causing primary HPT.

Methods Patients (n=61, median age 62, F:M 2.8:1) with primary HPT underwent MIBI SPECT and CECT obtained from the angle of the mandible to 3 cm below the tracheal bifurcation. All imaging was performed as standard of care. Parathyroidectomy was performed in 34 patients. Based on clinical symptoms, biochemical profiles, and imaging findings, 27 patients did not undergo surgery. Surgical success was defined as >50% drop of intravenous parathyroid hormone (PTH) level 10 minutes after resection. Positive SPECT-CT was defined as persistent increase in MIBI accumulation in a parathyroid gland on delayed images. Positive CT was defined as enlargement of a gland >50 mg.

Results Of the 40 resected parathyroid glands in the 34 patients, 21 were positive on both MIBI and CT for an adenoma, and 13 were positive on CT and negative on MIBI. Resection of 3 enlarged glands, including 1 MIBI-avid gland, did not result in expected PTH decrease after resection. Overall, MIBI SPECT-CT correctly localized 21 lesions and 97 normal glands (sens. 54%, spec. 99%, PPV 95%, NPV 84%). CT correctly localized 34 lesions and 97 normal glands (sens. 92%, spec. 97%, PPV 92%, NPV 97%).

Conclusions The sensitivity of CECT is greater than that of MIBI SPECT-CT in preoperative localization of parathyroid adenomas, in our study of 61 patients with primary HPT being considered for curative surgery. MIBI SPECT-CT had higher specificity and a higher PPV than CT. This is in contrast to the published literature concerning the utility of MIBI SPECT-CT in recurrent HPT. These novel observations are currently being refined and developed in a larger, prospective study.