Mixed Bag for Wednesday, June 3rd, 2026

Contributed by Children's National Hospital
Anh Le, BS, and Hassan Ahmed Aboughalia, MD.

History

An 18-year-old female with hypercalcemia and lab findings consistent with primary hyperparathyroidism.

Images (Click any image to enlarge)

Planar images acquired immediately and 2 hours following injection of Tc99m Sestamibi show bilateral symmetric supraclavicular and cervical radiotracer uptake.

Question

What is the most reasonable diagnosis?

Your answer

Please log in to see your results.

Correct answer

Brown fat activation

Discussion

On Sestamibi parathyroid imaging, brown fat activation appears as bilateral symmetric uptake in the neck, supraclavicular regions, and sometimes the mediastinum or paravertebral areas. This uptake pattern is seen in approximately 6-33% of patients undergoing parathyroid imaging. The uptake persists in both early and delayed images because Tc-99 m Sestamibi accumulates in metabolically active mitochondria.

Brown fat activation is more common in younger patients, females, and those exposed to cold temperatures. The SPECT/CT component of the scan is essential for distinguishing brown fat from parathyroid adenomas or other pathology. On SPECT/CT, brown fat localizes to low-attenuation fatty areas, whereas parathyroid adenomas appear as soft tissue nodules.

Brown fat activation is a recognized limitation of Sestamibi scintigraphy because it can obscure small parathyroid lesions in the same anatomic regions. Brown fat activation itself is a normal  physiologic finding and does not indicate disease. When brown fat uptake is present, the sensitivity of sestamibi SPECT/CT for detecting parathyroid adenomas may be reduced from its pooled sensitivity of 86%. Recent studies have also begun exploring the necessity of sestamibi scans in cases of primary hyperparathyroidism (PHPT). Neck ultrasound was shown achieving 100% sensitivity for localization and adding Tc-99m sestamibi scintigraphy did not improve sensitivity in PHPT. In adults, it was found that if a stepwise approach were followed, sestamibi would not have changed the operative plan in 95.9% of patients with a positive ultrasound.

References

  • Goetze S, Lavely WC, Ziessman HA, Wahl RL. Visualization of brown adipose tissue with 99mTc-methoxyisobutylisonitrile on SPECT/CT. J Nucl Med. 2008;49(5):752-756. doi:10.2967/jnumed.107.048074
  • Wong KK, Brown RK, Avram AM. Potential false positive Tc-99m sestamibi parathyroid study due to uptake in brown adipose tissue. Clin Nucl Med. 2008;33(5):346-348. doi:10.1097/RLU.0b013e31816a795a
  • He Y, Luo Y, Jin S, et al. Can we skip technetium-99 m sestamibi scintigraphy in pediatric primary hyperparathyroidism patients with positive neck ultrasound results?. Pediatr Radiol. 2023;53(11):2253-2259. doi:10.1007/s00247-023-05702-w
  • Expert Panel on Neurological Imaging, Zander D, Bunch PM, et al. ACR Appropriateness Criteria® Parathyroid Adenoma. J Am Coll Radiol. 2021;18(11S):S406-S422. doi:10.1016/j.jacr.2021.08.013
  • Yeh R, Tay YD, Tabacco G, et al. Diagnostic Performance of 4D CT and Sestamibi SPECT/CT in Localizing Parathyroid Adenomas in Primary Hyperparathyroidism. Radiology. 2019;291(2):469-476. doi:10.1148/radiol.2019182122
  • Yalon T, Neymark M, Rottenberg A, et al. The Added Value of Technetium-99 m Sestamibi Scan in Patients with Primary Hyperparathyroidism and Positive Ultrasound. World J Surg. 2021;45(7):2148-2154. doi:10.1007/s00268-021-06066-8