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False-Negative ^99mTc Medi-MIBI Parathyroid Scintigraphies: A Report on the Possible Role of Diagnostic Two-Phase Single-Acquisition CT

Afzelius P, Iyer V, Lelkaitis G and Henriksen SD

Introduction: Dual-phase 99mTc-Medi-MIBI parathyroid scintigraphy is often used for preoperative localization of
primary parathyroid adenomas. The overall accuracy has been reasonably high; however, some false-negative cases
occasionally occur. Two such cases are presented, and the advantages of adding two-phased single-acquisition
diagnostic CT to guide the surgeon are demonstrated.

Case presentations: A 54-year old male was admitted due to persistent elevated parathyroid hormone and
calcium concentrations in the blood despite medical treatment consistent with primary hyperparathyroidism. A dualphase
parathyroid scintigraphy performed 6 months earlier in another hospital was unable to confirm the diagnosis.
There was no change over time in levels of parathyroid hormone and calcium in the blood. In the second case, a 46-
year old woman was examined due to the same symptoms and findings; 18 months earlier she also had no retention
of tracer on late images. In this case, the patient also had had a CT performed, which showed morphological signs
of a parathyroid adenoma. We therefore planned dual-phase parathyroid scintigraphy with single-photon emission
computed tomography/computed tomography (SPECT/CT) in the early phase. The low-dose CT was unable to confirm
the impression of slight amounts of tracer uptake and retention at the lower right thyroid pole in both cases. Diagnostic
in both cases, but still with a low dose, the CT revealed a parathyroid adenoma situated in a common parathyroid
location at the lower pole of the right thyroid lobe, where activity retention was seen in late images. The surgeon was
able to perform minimally invasive neck surgery based on accurate anatomical localization of the adenoma.
Conclusion: This case report highlights the potential of two-phase single-acquisition CT as a useful tool in exact
localization of parathyroid adenoma for guiding the surgeon in minimally invasive surgery.