Incidental Tc-99m MIBI Lung Uptake in Parathyroid Scintigraphy

A 70-year-old woman underwent Tc-99m MIBI parathyroid scintigraphy because of primary hyperparathyroidism. In addition to, an intense 99mTc-sestamibi avid focus noted at the region of the left lower pole of the thyroid seen both on the early and the delayed images suggesting a parathyroid adenoma, we observed incidentally, diffusely increased ^99mTc-sestamibi uptake was noted in bilateral lung fields on both early and delayed images. This unusual aspect has been linked to the heart failure for which the patient is being followed [Figure 1].

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Figure 1 Early (a) and delayed (b) static images of ^99mTc-sestamibi parathyroid scan showed a focal persistent increased activity in the inferior pole of the left lobe of the thyroid gland suggestive of parathyroid adenoma and an incidental diffuse increased uptake in the lungs, especially in early image

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The mechanism of Tc-99m MIBI lung uptake in parathyroid scintigraphy has not been clearly established. . 99mTc-sestamibi is a lipophilic cationic complex that has specific affinity for negative potential of the cytoplasmic membrane which allows to its to undergo passive diffusion into the mitochondria, it has a predilection for tissues that demonstrate both high mitochondrial content and negative plasma membrane potentials.[1] The pulmonary uptake of this radiopharmaceutical is unusual. Hassan et al. were one of the first who reported increased uptake of Tc-99m MIBI in lung cancer.[2] Choy and Leslie concluded that lung uptake of Tc-99m MIBI may occur in patients with chronic heart failure because of left ventricular failure, which causes the persistence of the radiotracer in the lung arterioles rather than reaching the systemic circulation.[3] Giubbini et al. demonstrated that pulmonary uptake of 99mTc-sestamibi is higher in patients with cardiac dysfunction, especially left ventricular failure, in particular when the ejection fraction is lower than 40%.[4] Our patient was followed up for left cardiac dysfunction with an ejection fraction estimated at 42%; therefore, her cardiac pathology was retained as the cause of this uncommon pulmonary uptake of Tc-99m MIBI. The differential diagnosis includes much other serious pathology, such as systemic lupus erythematosus, pulmonary embolism, amyloidosis, sarcoidosis, and lung cancer.[5] This aspect of diffuse and bilateral pulmonary uptake of Tc-99m MIBI is to be recognized, and it is most often linked to an underlying pulmonary or cardiac pathology.