Ectopic Parathyroid Adenoma Mimicking as a Neuroendocrine Tumor on Ga68- DOTANOC Positron Emission Tomography/Computed Tomography Imaging.

Parathyroid adenoma sometimes present in ectopic location and may pose a difficulty in both diagnosis and localization. We report a case of a young lady suspected to have neuroendocrine tumor of the mediastinum demonstrating synaptophysin positivity on an initial core needle biopsy. Ga-68 DOTANOC positron emission tomography-computed tomography revealed a somatostatin receptor-expressing lesion in the anterior mediastinum with tracer avid multiple lytic bone lesions. On further biochemical and imaging workup with Tc-99 m SESTAMIBI, a diagnosis of ectopic parathyroid adenoma was made which was further confirmed with surgical excision. Copyright:

A 43-year-old hypertensive woman presented with history of breathlessness. Initial chest X-ray examination showed mediastinal widening. Noncontrast computed tomography (CT) of the chest showed an anterior mediastinal lesion with extension to the hilar region of the right lung. A core needle biopsy was obtained, and immunohistochemistry (IHC) showed synaptophysin positivity, suggesting a grade I neuroendocrine tumor. Subsequently, a Ga-68 DOTANOC positron emission tomography/CT (PET/CT) was performed for staging the disease, which showed increased tracer uptake in the mediastinal region (Maximum Intensity Projection (MIP) image; [Figure 1a] Trans-axial contrast-enhanced CT [Figure 1b] and fused PET/CT [Figure 1c] images showed a heterogeneously enhancing mass (~5.8 cmx 5.6 cm, with few areas of necrosis) in the anterior mediastinum and extending to the right parahilar region with a SUVmax 9.6. A few tracer avid lytic lesions were also noted in the bilateral iliac bones [Figure 1d and e, SUVmax 6.2] and scapula (SUVmax 4.6).

Figure 1

Maximum intensity projection image (a) of Ga-68 DOTANOC PET/CT demonstrate tracer uptake in the mediastinal region which on transaxial contrast enhanced CT (b) and fused PET/CT (c) images localised to anterior mediastinal mass. Axial CT (d) and fused PET (e) demonstrated tracer avid lytic lesion in the iliac bone.

The patient was planned for surgical excision of the mass lesion and on preoperative workup, her biochemical investigations demonstrated hypercalcemia (Serum calcium 17.6 mg/dl). Further biochemical evaluation revealed elevated serum parathormone levels (PTH – 1295 pg/ml). A Tc-99 m SESTAMIBI scan was planned to detect the presence of any parathyroid adenoma. Dual time point Tc-99 m SESTAMIBI scan ([Figure 2a]-early image at 10 min postinjection [p. i.] and [Figure 2b] – delayed image 2 h p. i.) revealed the presence of a tracer avid mass lesion (white arrow) in the mediastinum, corresponding to the site of the lesion visualized on Ga-68 DOTANOC PET/CT. She underwent surgical excision of the anterior mediastinal mass. Postoperative histopathology findings confirmed a diagnosis of an ectopic parathyroid adenoma. Her serum PTH levels 1 week after surgery significantly reduced to 82 pg/ml. Ectopic parathyroid adenomas account for about 4%–10% of the pathology in patients with hyperparathyroidism.[1] They can be present anywhere from the base of the tongue to the mediastinum.[2] USG, 4D CT, and Tc-99 m Sestamibi scan are the first line investigations used to evaluate parathyroid adenomas.[3] Tc-99 m SESTAMIBI localizes to parathyroid adenomas because of the presence of high mitochondrial content in oxyphil cells.[4] The parathyroid adenomas are known to express Somatostatin Receptors (SSTRs)[5] and may also show positivity with synaptophysin on IHC, leading to a misinterpretation as a tumor of neuroendocrine origin.[6] Ga68-DOTANOC PET/CT has previously demonstrated detection of parathyroid adenomas at their native location due to the expression of SSTRs.[7] The present case highlights that parathyroid adenomas at the ectopic location may pose a diagnostic challenge because of the resemblance with neuroendocrine tumors with such SSTR targeted imaging agents.

Figure 2

Tc-99m SESTAMIBI scan early image at 10 minutes (a) and delayed image at 2 hrs (b) revealed tracer avidity in the mediastinal mass lesion (white arrow).

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