99mTc-methoxyisobutylisonitrile single-photon emission computed tomography/computed tomography parathyroid imaging in the diagnosis of functional parathyroid cysts: an initial experience.

Background: Functional parathyroid cysts (FPCs) are rare and difficult to diagnose with noninvasive methods. The aim of this study was to evaluate the diagnostic value of 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) single-photon emission computed tomography/computerized tomography (SPECT/CT) parathyroid imaging in the diagnosis of FPCs and to account for its performance. Methods: The data from 10 patients with suspected parathyroid cysts (PCs) who underwent 99mTc-MIBI SPECT/CT parathyroid imaging between 2012 and 2022 were retrospectively evaluated. The diagnostic value of 99mTc-MIBI SPECT/CT parathyroid imaging for FPCs was analyzed. Results: Surgical resection was performed in six cases and parathyroid puncture was performed in four cases. The sensitivity of 99mTc-MIBI SPECT/CT for FPCs was 100.0% (3/3), with a specificity of 100.0% (7/7) and an accuracy of 100.0% (10/10). The postoperative pathological findings in three cases of FPCs were parathyroid adenoma, parathyroid adenoma with hemorrhage, and parathyroid adenoma with cystic degeneration, respectively. The diagnostic accuracy of ultrasound and CT for PCs was only 22.22% (2/9) and 25.0% (1/4), respectively, and neither modality could indicate whether the cysts were functional or not. Conclusions: 99mTc-MIBI parathyroid SPECT/CT imaging has a high value in the diagnosis of FPCs in patients with suspected PCs, and an intense ring-shaped accumulation of radioactivity in the cyst wall on 99mTc-MIBI imaging suggests that the patient may have FPCs.

Multiple Endocrine Neoplasia Type 1 with Functional Parathyroid Cysts.

A 51-year-old woman was admitted because of hypercalcemia. Neck ultrasonography and computed tomography revealed the presence of parathyroid cysts on both sides. After primary hyperparathyroidism was diagnosed by technetium-99m-methoxyisobutylisonitrile scintigraphy, the patient was successfully treated with total parathyroidectomy and autotransplantation. She also had a non-functioning pancreatic neuroendocrine tumor, prolactinoma, and adrenal tumors with subclinical Cushing's syndrome. Given these clinical features and her family history, multiple endocrine neoplasia type 1 (MEN1) was suspected, and germline DNA sequencing revealed a missense mutation (c.1013T>C, [corrected] p.Leu338Pro) in exon 7 of MEN1. This case demonstrates the phenotypic and genetic diversity of MEN1.