The usefulness of neck pinhole SPECT as a complementary tool to planar scintigraphy in primary and secondary hyperparathyroidism

Pinhole SPECT (P-SPECT) has proven to be a high-resolution and sensitive method in both experimental and clinical studies. In this study, we investigated whether P-SPECT combined with conventional planar scintigraphy can give additional information in hyperfunctioning parathyroid gland detection in both primary hyperparathyroidism (pHPT) and secondary hyperparathyroidism (sHPT) since planar imaging has proved partially limited, especially in sHPT.

METHODS: We studied 110 consecutive patients with HPT, selecting 67 patients who underwent neck surgery and had definitive histology: 48 with pHPT and 19 with sHPT. All patients underwent planar scintigraphy, (99m)Tc-methoxyisobutylisonitrile ((99m)Tc-MIBI) double-phase scintigraphy (n = 22) or (99m)Tc-tetrofosmin subtraction scintigraphy (n = 45), using a gamma-camera with a parallel-hole collimator. P-SPECT was then performed (180 degrees; matrix size, 128 x 128; zoom factor, 2; time per frame, 40 s) using a tilted detector equipped with a pinhole collimator (insert, 4.45 mm).

RESULTS: In the 48 pHPT patients, 49 lesions (43 adenomas, 1 carcinoma, and 5 hyperplastic glands, including 1 intrathyroidal) were found at surgery; in the 19 sHPT patients, 51 lesions (49 hyperplastic glands, including 1 in persistens thymus, and 2 adenomas) were found. P-SPECT proved to be a highly sensitive method, identifying more lesions than planar imaging in both pHPT (97.9% vs. 87.7%) and sHPT (92.1% vs. 78.4%), significantly (P < 0.05) in the latter. P-SPECT, positive in all adenomas, increased planar sensitivity especially in small and light-weight ones, 30.8% of which missed on planar imaging, and also identified a significantly higher number of hyperplastic glands, irrespective of their size. P-SPECT improved image quality and resolution, offering a more correct lesion localization in eutopic and ectopic sites. Neither P-SPECT nor planar imaging had false-positive findings. Moreover, P-SPECT correctly predicted the status found at surgery in 97.9% of pHPT patients and in 82.3% of sHPT patients with multigland disease, whereas planar imaging correctly predicted the status in 89.6% and 58.8%, respectively. P-SPECT was the only positive procedure in 8.9% of all patients, also revealing more lesions in 6% of sHPT patients when both methods were positive.

CONCLUSION: P-SPECT appears a highly sensitive, high-resolution method. We suggest its use as a preoperative complementary tool to neck planar scintigraphy, selectively in pHPT patients but extensively in sHPT patients.