MON-771 Scanning the Unscannable: Navigating CT Imaging for Parathyroid Localization in Pregnancy

Abstract Disclosure: P. Pile: None. M. Khalifa: None. I. Alpertunga: None. Introduction: Primary hyperparathyroidism (PHPT) during pregnancy is a rare but clinically significant condition due to its potential to cause severe maternal, fetal, and neonatal complications. Hence, early diagnosis and management are critical in fetal development. The physiological changes in calcium metabolism during pregnancy can mask or exacerbate symptoms, complicating diagnosis and management. Untreated PHPT poses risks such as hypercalcemic crisis, pre-eclampsia, and fetal complications, including intrauterine growth restriction (IUGR) and preterm delivery. Case Presentation: A 33-year-old woman with history of pituitary adenoma presented at 26 weeks of gestation with hypercalcemia. Initial laboratory findings showed corrected total calcium of 14.2 mg/dL (8.6-10.2 mg/dL), phosphorus 1.9 mg/dL (2.5-4.5 mg/dL), parathyroid hormone (PTH) 131 pg/mL (16-77 pg/mL) and 25-hydroxy vitamin D 19 ng/mL (30-100 ng/mL). She denied any personal or family history of hypercalcemia or kidney stones. Initial management included aggressive intravenous isotonic fluids with minimal improvement in calcium levels. Neck ultrasound (US) did not reveal any evidence of parathyroid adenoma. After discussion with radiology about the safe diagnostic options during pregnancy, a 4D computed tomography (CT) parathyroid protocol scan was done and it showed 1.1 cm × 0.7 cm × 1.6 cm nodule posterior to the lower pole of the right thyroid gland, consistent with a parathyroid adenoma. Given the severity of hypercalcemia and the patient’s gestational age, she underwent parathyroidectomy during the third trimester with pathology confirming a parathyroid adenoma. Postoperatively, calcium levels normalized, and PTH levels decreased to 3 pg/mL. She was eventually referred to genetic testing for MEN which came back negative. Discussion/Conclusion: The diagnosis of PHPT during pregnancy can be very challenging, PTH levels may decline due to the physiological rise in PTH-related protein (PTHrP) which must be taken into consideration when making the diagnosis of PHPT. Imaging should only be considered if the patient is referred for surgery which during pregnancy is best limited to neck US which has a sensitivity up to 87% in identifying abnormal parathyroid tissue and a specificity up to 96%. One should keep in mind that the sensitivity of US is lower in multiglandular disease and may be only 15–35%. Magnetic resonance imaging (MRI) has lower sensitivity of 82%. The use of CT in pregnancy is generally considered safe when medically necessary, though it requires careful consideration of the risks and benefits. Presentation: Monday, July 14, 2025