Palestro Christopher J, Tomas Maria B, Tronco Gene G
Department of Nuclear Medicine and Radiology, Albert Einstein College of Medicine, Bronx, NY, USA.
Semin Nucl Med. 2005 Oct;35(4):266-76. doi: 10.1053/j.semnuclmed.2005.06.001.
The parathyroid glands, which usually are situated behind the thyroid gland, secrete parathyroid hormone, or PTH, which helps maintain calcium homeostasis. Primary hyperparathyroidism results from excess parathyroid hormone secretion. In secondary hyperparathyroidism, the normal PTH effect on bone calcium release is lost. Serum PTH rises, causing generalized hyperplasia. In tertiary hyperparathyroidism, a complication of secondary hyperparathyroidism, normal feedback mechanisms governing PTH secretion are lost, parathyroid gland sensitivity to PTH decreases, and the threshold for inhibiting PTH secretion increases. 99mTc sestamibi, or MIBI, the current radionuclide study of choice for preoperative parathyroid localization, can be performed in various ways. The "single-isotope, double-phase technique" is based on the fact that MIBI washes out more rapidly from the thyroid than from abnormal parathyroid tissue. However, not all parathyroid lesions retain MIBI and not all thyroid tissue washes out quickly, and subtraction imaging is helpful. Many MIBI avid thyroid lesions also accumulate pertechnetate and iodine, and subtraction reduces false positives. Single-photon emission computed tomography provides information for localizing parathyroid lesions, differentiating thyroid from parathyroid lesions, and detecting and localizing ectopic parathyroid lesions. The most frequent cause of false-positive MIBI results is the solid thyroid nodule. Other causes include thyroid carcinoma, lymphoma, and lymphadenopathy. False-negative results occur because of several factors. Lesion size is important. Cellular function also may be important. Parathyroid tissue that expresses P-glycoprotein does not accumulate MIBI. Parathyroid adenomas that express either P-glycoprotein or the multidrug resistance related protein MRP are less likely to accumulate MIBI. MIBI scintigraphy is less sensitive for detecting hyperplastic parathyroid glands. In secondary hyperparathyroidism, MIBI uptake is more closely related to cell cycle than to gland size. Mitochondria-rich oxyphil cells presumably account for MIBI uptake in parathyroid lesions. Fewer oxyphil cells, and hence fewer mitochondria, may explain both lower uptake and rapid washout of MIBI from some lesions. MIBI is also less sensitive for detecting multigland disease than solitary gland disease.
甲状旁腺通常位于甲状腺后方，分泌甲状旁腺激素（PTH），该激素有助于维持钙稳态。原发性甲状旁腺功能亢进是由甲状旁腺激素分泌过多所致。在继发性甲状旁腺功能亢进中，PTH对骨钙释放的正常作用丧失。血清PTH升高，导致全身增生。在三发性甲状旁腺功能亢进（继发性甲状旁腺功能亢进的一种并发症）中，控制PTH分泌的正常反馈机制丧失，甲状旁腺对PTH的敏感性降低，抑制PTH分泌的阈值升高。99mTc 甲氧基异丁基异腈（MIBI）是目前术前甲状旁腺定位的首选放射性核素检查，可通过多种方式进行。“单同位素双相技术”基于这样一个事实，即MIBI从甲状腺中洗脱的速度比从异常甲状旁腺组织中更快。然而，并非所有甲状旁腺病变都能保留MIBI，也并非所有甲状腺组织都能快速洗脱，减法成像很有帮助。许多摄取MIBI的甲状腺病变也会摄取高锝酸盐和碘，减法可减少假阳性。单光子发射计算机断层扫描可为甲状旁腺病变定位、区分甲状腺病变与甲状旁腺病变以及检测和定位异位甲状旁腺病变提供信息。MIBI结果假阳性最常见的原因是实性甲状腺结节。其他原因包括甲状腺癌、淋巴瘤和淋巴结病。假阴性结果的出现有多种因素。病变大小很重要。细胞功能可能也很重要。表达P-糖蛋白的甲状旁腺组织不会摄取MIBI。表达P-糖蛋白或多药耐药相关蛋白MRP的甲状旁腺腺瘤摄取MIBI可能性较小。MIBI闪烁扫描对检测增生性甲状旁腺的敏感性较低。在继发性甲状旁腺功能亢进中，MIBI摄取与细胞周期的关系比与腺体大小的关系更密切。富含线粒体的嗜酸性细胞可能是甲状旁腺病变摄取MIBI的原因。嗜酸性细胞较少，因此线粒体较少，可能解释了一些病变中MIBI摄取较低和洗脱较快的原因。MIBI对检测多腺体疾病的敏感性也低于单腺体疾病。
