99mTc-MIBI single photon emission computed tomography/computed tomography for the incidental detection of rare parathyroid carcinoma

Abstract

This study aimed to evaluate the characteristics of parathyroid carcinoma and to validate the diagnostic value of Tc-methoxyisobutylisonitrile (MIBI) single photon emission computed tomography/x-ray computed tomography (SPECT/CT) for differentiating between parathyroid carcinoma and hyperparathyroidism. Four consecutive patients with suspected primary hyperparathyroidism were enrolled in this study and underwent Tc-MIBI SPECT/CT, ultrasonography, enhanced CT, and MRI. Serum parathyroid hormone (PTH) and calcium were measured. All primary and recurrent lesions showed high focal uptake on Tc-MIBI image, whereas metastatic lymph nodes gave false negative results. The serum PTH was 165.14 ± 90.26 pmol/L, which declined rapidly after surgery. One patient with a persistently high PTH (147.5 pmol/L) after surgery presented with multiple lymphadenopathy in the neck. Higher expression of chromogranin A (CgA) further confirmed parathyroid carcinoma as a rare endocrine tumor. Parathyroid carcinoma is thus usually diagnosed incidentally based on nonspecific multiorgan symptoms of hypercalcemia and hyperparathyroidism. Tc-MIBI SPECT/CT may help to localize the parathyroid carcinoma, while MRI is valuable for detecting metastasis. Serum PTH and CgA serve as circulating biomarkers in parathyroid carcinoma, and raised levels of PTH and CgA together with locoregional lymphadenopathy may indicate parathyroid carcinoma. Further studies are needed.

Figure 1

A large, hyper-vascular lesion in the left neck detected by multi-modality imaging in parathyroid carcinoma. (A) Early phase and (B) delayed-phase images of ^99mTc-MIBI scintigraphy. (C) Maximum intensity projection fusion image and (D) fusion image. (E) Enhanced CT showing a large hyper-vascular mass with cystic-necrotic degeneration behind the thyroid. (F) A heterogeneous hypoechoic mass with vascular invasion on US. (G, H) Histopathology: hematoxylin-eosin staining (×100). (I) High CgA expression in the tumor (×400). CgA = chromogranin A, MIBI = methoxyisobutylisonitrile, SPECT/CT = hybrid single photon emission computed tomography/x-ray computed tomography, US = ultrasonography.

Figure 2

Dual-phase ^99mTc-MIBI SPECT/CT showed intense uptake in the right inferior parathyroid. (A) Transaxial image, (B) fusion image, (C) coronal CT, (D) coronal image. MIBI = methoxyisobutylisonitrile, SPECT/CT = hybrid single photon emission computed tomography/x-ray computed tomography.

Figure 3

Dual-phase ^99mTc-MIBI SPECT/CT, MRI, and immunochemistry confirmed parathyroid carcinoma (A) Planar image showed no significant radiouptake in the parathyroid before surgery. (B) Focal uptake in the lymph node. (C) CT confirmed lymph node involvement. (D–F) Follow-up MRI (6 months after surgery), fat-suppressed, T2-weighted image showing multiple lymphadenopathy. Histopathological and immunohistochemistry. (G) Proliferation index (Ki-67) was 10% (×100), (H) PTH expression was significantly elevated (×400), and (I) CD56 was positive (×400). MIBI = methoxyisobutylisonitrile, PTH = parathyroid hormone, SPECT/CT = hybrid single photon emission computed tomography/x-ray computed tomography.