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Tc-99m MIBI scans of neck and thoracic region obtained at 5, 10, 60 and 120 min showing a solitary focus of increased MIBI uptake (arrow) in the ectopic parathyroid located in the anterior mediastinum
Source publication
In this report, we describe a rare case of brown tumor and mediastinal parathyroid adenoma. This report emphasizes the value of radionuclide scintigraphy in the setting of persistent disease following parathyroid surgery.
Citations
... Typical locations include the pelvis, ribs, clavicles, and extremities (5). There are several case reports of brown tumors mimicking cancer metastatic to bone (6-10), but only a few reported cases of brown tumors associated with ectopic parathyroid adenomas (11,12). ...
Objective: Mediastinal parathyroid adenomas are rare in clinical practice. We report a case that mimicked cancer metastatic to bone on initial workup to increase awareness of this differential diagnosis in the evaluation of patients presenting with multiple foci of uptake on technetium bone scanning without an established primary neoplasm. We also outline other diagnostic pitfalls that may be encountered in the workup and management of this uncommon condition.
Results: A 26 year-old man presented with a several month history of back and pelvic pain. Initial plain radiography showed multiple lytic lesions in the pelvis. Technetium bone scanning revealed multiple foci of increased uptake in the thoracic vertebrae, ribs, clavicles, pelvis and extremities. A CT scan demonstrated a mediastinal mass and an initial diagnosis of metastatic disease from a mediastinal primary malignancy was entertained. Further workup revealed a markedly elevated serum ionized calcium of 1.97 mmol/L (N 1.19–1.31) and parathyroid hormone (PTH) of 154.8 pmol/L (N 2.0–9.4). Parathyroid scintigraphy showed intense tracer accumulation in the anterior mediastinal mass. A median sternotomy was performed and histopathology was consistent with a parathyroid adenoma. Post-operatively the patient's ionized calcium and PTH levels normalized and pain resolved.
Conclusion: This case illustrates two clinical pearls: 1) brown tumor secondary to hyperparathyroidism is an important differential in the evaluation of patients presenting with widespread lytic bone lesions on CT or multiple foci of uptake on bone scan; and 2) the mediastinum is a rare location but should be considered in the workup of primary hyperparathyroidism.
Brown tumors (BT) are abnormal bone-repair processes and a consequence of hyperparathyroidism. The diagnosis of these lytic lesions in nuclear medicine, while a challenge, is not so rare, because functional imaging is used both in the management of cancer and hyperparathyroidism. The main objective of this review is to summarize the knowledge and the evidence concerning BT and the different imaging modalities in nuclear medicine. A systematic review was performed in Embase, PubMed and Google Scholar from 2005 to 2022. We included articles describing BT in the following imaging modalities: [18F]-fluorodeoxyglucose PET/CT, [18F]-fluorocholine or [11C]-fluorocholine PET/CT, [99mTc]-Sestamibi scintigraphy, bone scan, [18F]-sodium fluoride PET/CT, [68Ga]-FAPI PET/CT; [68Ga]-DOTATATE PET/CT; [11C]-methionine PET/CT. For each modality, appearance, avidity for radiotracer, available quantitative parameters and imaging evolution after parathyroidectomy were collected and analyzed. Fifty-two articles were included for a total of 392 BT lesions. If the diagnosis of BT is evoked on a known lesion, performing a [18F]-fluorocholine PET/CT imaging seems the most appropriate. In [18F]-fluorodeoxyglucose, [18F]-fluorocholine, [18F]-sodium fluoride PET/CT and bone scan, BT can mimic metastatic disease. BT uptakes appear reversible after parathyroidectomy, with a more or less rapid decrease depending on the imaging modality used.
MIBI scintigraphy is the most widely used modality to identify parathyroid adenomas preoperatively. However, MIBI is also known to accumulate in multiple benign and malignant lesions. In renal cell carcinoma, 30% of the patients present with distant metastasis, commonly lungs and bone; however, jaw bone metastases are extremely rare (<1% of oral malignancies). Here we present a rare case of MIBI-avid mandibular metastasis in bilateral renal cell carcinoma on 99mTc-MIBI scintigraphy. Thus, we emphasize on careful interpretation of 99mTc-MIBI scans, which in addition to parathyroid adenomas can incidentally detect concurrent malignant lesions.
