Influence of Multigland Parathyroid Disease on 99mTc-Sestamibi SPECT/CT.

PURPOSE: 99mcTc-sestamibi (MIBI) imaging is performed for preoperative parathyroid lesion localization in patients with primary hyperparathyroidism. Decreased sensitivity in multigland disease (MGD) compared with single-gland disease (SGD) is well recognized for planar and SPECT imaging, but few data are available on MIBI SPECT/CT in MGD. METHODS: We retrospectively analyzed 246 patients with primary hyperparathyroidism who underwent preoperative MIBI SPECT/CT. Surgical and pathology reports were used to confirm numbers, weights, and locations of excised glands. Two experienced physicians independently read MIBI SPECT/CTs, grading lesion certainty on a 5-point scale ("definitely normal" to "definitely abnormal"). RESULTS: Three hundred one parathyroid lesions were excised at surgery. Thirty-nine patients (16%) had MGD, and 207 patients (84%) had SGD; 26 patients had 2 lesions, 10 had 3 lesions, and 3 had 4 lesions. Lesion weights were significantly lower in MGD than in SGD (390 ± 604 vs 866 ± 933 mg, P < 0.0001) and decreased with increasing numbers of lesions (P < 0.0001). MIBI SPECT/CT was less sensitive for MGD than SGD (66% vs 98%, P < 0.0001). Sensitivity was lower for 66 MGD lesions matched to 66 SGD lesions (64% vs 98%, P < 0.0001) and decreased with increasing lesion numbers (ρ = -0.45, P < 0.0001), despite similar weights (526 ± 678 vs 525 ± 686 mg, P = 0.99) and similar locations (P = 0.47). Specificity was similar for MGD (95%) and SGD (90%). CONCLUSIONS: 99mcTc-MIBI SPECT/CT sensitivity is significantly lower in MGD than in SGD. This does not appear to be related to lesion weight or location.