(A) Planar images 20 minutes and 3 hours after Tc99m MIBI injection (parathyroid scan) demonstrate persistent, focally increased activity in the expected locations of the four parathyroid glands as well as a fifth focus inferior to the thyroid on the right (arrow). (B) Early and delayed SPECT images confirm the planar findings (circle).

Differential Diagnosis

•  Parathyroid hyperplasia with a supernumerary gland: The multiple foci in typical locations together with the history make parathyroid hyperplasia the most likely etiology in this patient with five parathyroid glands.

•  Multiple parathyroid adenomas: These will also appear as persistent increased foci and can be multiple but would be extremely unlikely to present as five adenomas.

•  Multiple thyroid adenomas: