Ectopic parathyroid adenoma diagnosed by SPECT-CT imaging using 99mTc-MIBIKing Abdulaziz Specialist Hospital (KAASH), Taif, Saudi Arabia

Primary hyperparathyroidism is a major health problem, causing high parathyroid hormone(PTH), high calcium, and low phosphorus levels in the blood, which can result in a variety of health problems. Surgery is the gold standard treatment of primary hyperparathyroidism, therefore it is of utmost importance to diagnose and localize the hyperfunctioning parathyroid tissue. Technetium parathyroid scintigraphy is the most popular non-invasive diagnostic procedure in patients with primary hyperparathyroidism. However the exact localization of the enlarged hyperfunctioning parathyroid represents a relative limitation to the test, especially in cases of small ectopic adenomas. Hybrid functional-anatomical imaging like SPECT-CT, when added plays an essential role in diagnosing, localizing and describing the size and shape of the adenoma even in small ectopic adenomas like in our case. We report a case of a 68-year-old female presented with signs and symptoms of severe hypercalcemia and osteoporosis. Laboratory investigations were consistent with primary hyperparathyroidism(PHPT). SPECT-CT imaging using 99m Tc-MIBI (methoxyisobutylisonitrile) demonstrated a parathyroid adenoma in the lower neck and showed the anatomical details.

Parathyroid scintigraphy using 99mTc-MIBI, has been proven to be greatly effective for the diagnosis of adenomas, however, despite the relatively high accuracy of planar parathyroid imaging, intrathyroidal adenomas with low 99mTc-MIBI uptake and ectopic adenomas may be overlooked. Another limitation for planar 99mTc-MIBI scintigraphy is a nodular goiter, because thyroid nodules are frequently 99mTc-MIBI avid and can cause false-positive scintigraphic results. More important, depth information and 3-dimensional (3D) location regarding the adenoma are lacking, a crucial factor in planning a limited surgery. Therefore, SPECT/CT fusion imaging has come as a useful tool for localization of parathyroid lesions, particularly parathyroid adenomas.

The hybrid SPECT-CT imaging used in our patient has helped not only in diagnosis with confidence but also provided good information regarding location and anatomical details for surgeon in this re-operative case.

In cases of small, ectopic parathyroid adenomas with history of previous surgery, SPECT-CT imaging can be of great benefit in diagnosis and localization for surgery. Surgical neck exploration for parathyroid lesions without prior scanning, can lead to missing some adenomas even if it's ectopic.