MON-774 Primary hyperparathyroidism Presenting with Osteitis Fibrosa Cystica of the Mandible in a Young Pregnant Female

Abstract Disclosure: T. Rave: None. A.E. De Rosairo: None. D.H. Sacoto: None. D. Patel: None. S. Tariq: None. R. Belokovskaya: None. A.A. Franco Akel: None. Osteitis fibrosa cystica, or Brown Tumor, is a rare complication of both primary and secondary hyperparathyroidism (HPT), with a reported incidence of 2-3% and 1.5-1.7%, respectively. These tumors typically arise in the clavicle, mandible, maxilla, ribs, or pelvic bones. We present a case of primary HPT manifested as a mandibular brown tumor in a young pregnant female. A 24-year-old G2P1 female at 30 weeks gestation with a past medical history of nephrolithiasis, hyperemesis gravidarum, and gallstone pancreatitis status post laparoscopic cholecystectomy presented with a tender right-sided mandibular mass. She denied any fever, nausea, vomiting, difficulty breathing, dysphagia, odynophagia, or voice changes. A pedunculated gingival mass between teeth #31 and #32 and extending to the lingual side of the mandible was visible. No purulence or fluctuance noted. A biopsy showed an unencapsulated spindle cell lesion with clusters of osteoclast type giant cells in a hemorrhagic background along with bland fibroblasts and peripheral woven bone formation, consistent with central giant cell granuloma. Initial labs showed calcium 10.5 mg/dL [8.6 - 10.0 mg/dL] and iPTH 859 pg/mL [15 - 65 pg/mL]. Patient subsequently had a spontaneous uncomplicated delivery. Repeated labs post-delivery revealed Calcium 10.5 mg/dL, albumin 3.8 mg/dL [3.5 - 5.2 mg/dL], Magnesium 2.3 mg/dL [1.4 - 2.6 mg/dL], Phosphorous 2.1 mg/dL [2.5 - 4.5 mg/dL], iPTH 1320 pg/mL, vitamin D 25 hydroxy 13.3 ng/mL [30.0 - 80.0 ng/mL] and vitamin D 1, 25 dihydroxy >600 [19.9 - 79.3 pg/mL]. A Maxillofacial CT scan with IV contrast showed a 3.3 x 1.7 x 2.6 cm lingular portion and a 3.2 x 2.2 x 3.2 cm buccal portion mass with an 11 mm and a 9 mm inferior mandibular lymph node. A Parathyroid CT scan with and without contrast showed a 1.5 cm lesion in the left tracheoesophageal groove inferior to the left lower thyroid lobe, suspected to be a parathyroid adenoma. She underwent left superior parathyroidectomy and right mandible tumor resection and reconstruction. The pathology report of the right mandibular tumor and left superior parathyroid gland showed a giant cell-rich tumor consistent with Brown Tumor of HPT. Brown Tumor is rare, especially with earlier diagnoses of HPT. However, it is important to note that Primary HPT symptoms during pregnancy can be overseen as part of the normal maternal physiology, leading to misdiagnosis. Fetal complications can arise in cases of hypercalcemia, including intrauterine fetal loss. Considering our patients near normal calcium levels at presentation, manifestations of PHPT in pregnancy other than severe hypercalcemia, including Brown Tumor, should be considered in order to monitor and avoid HPT and pregnancy complications. Presentation: Monday, July 14, 2025