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E1296. The Unusual Suspects: Multimodality Scintigraphic Approach to Localizing Intrathoracic Parathyroid Adenomas, with Radiologic Correlation
Authors
  1. Edgar Zamora; Division of Nuclear Medicine - Department of Radiology - Montefiore Medical Center and The Albert Einstein College of Medicine
  2. Kwang Chun; Division of Nuclear Medicine - Department of Radiology - Montefiore Medical Center and The Albert Einstein College of Medicine
  3. Louisiana Rivera Valladares; Division of Nuclear Medicine - Department of Radiology - Montefiore Medical Center and The Albert Einstein College of Medicine
  4. Ana Valdivia; Division of Nuclear Medicine - Department of Radiology - Montefiore Medical Center and The Albert Einstein College of Medicine
  5. Lionel Zuckier; Division of Nuclear Medicine - Department of Radiology - Montefiore Medical Center and The Albert Einstein College of Medicine
Background
Primary hyperparathyroidism is caused by hyperfunctioning parathyroid adenomas often leading to multisystemic complications, including nephrolithiasis, decreased bone mineral density, and neuropsychiatric symptoms. Up to 20% of unexplored parathyroid adenomas are ectopic, most commonly located within the mediastinum. Definitive therapy is surgical excision, indicated in symptomatic patients, and recommended in specific asymptomatic patients (age <50 years, hypercalcemia [>1.0 mg/dL], eGFR <60 mL/min, T-score <-2.5). Imaging is essential for localization prior to surgical exploration. Mainstay modalities, ultrasound and 99mTc-sestamibi (MIBI) scintigraphy, routinely allow accurate identification of non-ectopic adenomas. Localization of ectopic glands is more challenging, while incorrect localization may lead to failed parathyroid explorations. We demonstrate a range of multimodality scintigraphic techniques of localization including dual time-point (early and delayed), dual-radiopharmaceutical (99mTc-Sestamibi and 99mTcO4- scintigraphy), dual technique (planar and tomographic) and dual modality (scintigraphy and CT) imaging for localization of intrathoracic adenomas and presurgical planning. Fusion with prior contrast CT has been frequently helpful in accurate anatomic localization.

Educational Goals / Teaching Points
This image-rich educational exhibit is a compilation of 10 intrathoracic cases, demonstrating use of multimodality scintigraphy for localization and presurgical planning of ectopic glands.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Most ectopic adenomas present within the chest, in variable locations varying according to embryologic origin. Inferior glands locate more anteriorly (e.g. intrathymic, prevascular), while superior glands are typically located more posteriorly (e.g. tracheoesophageal groove, retroesophageal). Our approach for localizing adenomas includes early and delayed planar MIBI, early is SPECT/CT, and subsequent TcO4 planar scintigraphy. Registration and fusion of SPECT to prior contrast CT is useful in localizing intrathoracic adenomas and in some instances has permitted retrospective identification on previously performed CT scans, and/or has directed subsequent guided ultrasound examination. Attenuation of the chest wall has not been an impediment to visualization of adenomas on planar and SPECT scintigraphy while MIBI SPECT/CT has effectively allowed accurate three-dimensional localization for presurgical planning.

Conclusion
Intrathoracic parathyroid adenomas are a potential challenge to parathyroid imaging. Our multimodal approach has allowed accurate localization of ectopic mediastinal glands with early MIBI-SPECT particularly useful in presurgical planning of intrathoracic adenomas located in various mediastinal compartments. Fusion with diagnostic contrast CT is helpful in anatomic localization. TcO4- is less essential for localization of ectopic adenomas but is helpful in excluding orthotopic adenomas within the thyroid gland and neck.