Additional value of SPECT/CT in detection of ectopic parathyroid adenoma

Abstract

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Learning Objectives: 1. Clinical cases pictorial review. 2. Obtain knowledge on the additional value of SPECT/CT in detection of ectopic parathyroid adenoma.

Abstract Body: The parathyroid glands are located posterior to the upper and lower poles of the thyroid and are derived from the third and fourth pharyngeal pouches. Usually there are four glands, but 5% of patients have fewer or more glands. Usually there are only two superior glands, whereas only 40% of patients have their inferior glands located near the inferior thyroid poles. Ectopic locations include the carotid sheath, anterior mediastinum, retro-pharynx or intrathyroidal locations. SPECT-CT offers the advantage of combining function and anatomy for exact localization of ectopic parathyroid adenomas. In this pictorial review we present 4 cases of hyperparathyroidism caused by ectopic parathyroid glands and review the literature on the additional value of their localization with SPECT/CT. The first widely accepted technique for radionuclide imaging of the parathyroid glands included 201Tl-thallous chloride-99mTc pertechnetate subtraction imaging. It has several limitations and has generally been replaced by the single isotope double-phase technique using Tc99-sestamibi. Latter method has a reported sensitivity of 88% for solitary and 30% for double adenomas, 45% for multigland hyperplasia, and 33% for parathyroid carcinoma. Combined SPECT/CT scanners permit more reliable localization of ectopic adenomas. The additional information can aid in exact pre-operative localization. In one study of 16 patients, SPECT/CT identified 39% more lesions compared to SPECT imaging alone. In other comparisons of planar, SPECT and SPECT/CT imaging modalities, SPECT/CT permitted the highest reader confidence in localization, especially for mediastinal adenomas.