Ectopic Atypical Parathyroid Adenoma Presenting With Pancreatitis

Background: Atypical Parathyroid Adenoma (APA) and parathyroid carcinomas (PC) are rare parathyroid tumors (<1%) causing primary hyperparathyroidism. We present a case of ectopic APA in the left anterior mediastinum. Case: A 38 year old male with hyperlipidemia admitted for acute pancreatitis noted to have calcium level of 13.4 mg/dl (8.6–10.3mg/dl) in the absence of family history of hypercalcemia or kidney stones. He was treated with zoledronic acid, intravenous fluids and calcitonin for hypercalcemia. Pancreatitis resolved with fluid management. Calcium on discharge was 9.9 mg/dl. 8 week follow-up labs showed PTH of 420 pg/ml (14–64 pg/ml), calcium 10.2 mg/dl, phosphorus 1.9 mg/dl (2.5–4.5 mg/dl), vitamin D 19 ng/ml (30–100 ng/ml), 24-hour urinary calcium 115 mg/24 hour (55–300 mg/24 hour) and calcium to creatinine ratio 0.41. Hence diagnosis of primary hyperparathyroidism was made but given the degree of calcium and PTH elevation there was a concern for PC. Ultrasound of the neck demonstrated no abnormality. Sestamibi scan showed irregular focal accumulation of radiotracer in the left upper mediastinum suggestive of mediastinal ectopic parathyroid adenoma (EPA). CT chest with contrast showed a 3.9 x 2.2 x 3.4cm lobulated, heterogenous, hypodense, minimally enhancing mass in the left anterior prevascular space. Diagnosis of EPA was made and he underwent left video assisted thoracic surgery. Operative findings showed a multilobular mass at the level of the aortic arch between vagus and phrenic nerves. Intraoperative PTH went from 1124 pg/ml pre-incision to 160 at 15-minute post-excision. Postoperative calcium was 9.6 mg/dl and PTH 51 pg/ml. Final pathology showed 3.7 x 2.5 x 2cm, hypercellular parathyroid with prominent fibrous band and parafibromin retention compatible with APA. Discussion: APA is an intermediate form of parathyroid neoplasm with uncertain malignant potential, showing atypical histological features without evidence of invasive growth. This poses a diagnostic challenge of PC as the histopathological features overlap and requires an expert pathologist to make the diagnosis. Inactivating CDC73 mutations, encoding parafibromin, is the most common genetic abnormality. Loss of parafibromin has been seen in 100% cases of PC and predicts poor prognosis. Due to rarity of the disease there are no clear guidelines on follow up. Based on literature, annual follow up is suggested with biochemical testing and imaging for the first 5 years after surgery and every 2–3 years thereafter due to 3% recurrence rate and potential progression to PC. Cetani et al in 2019 reported 672 cases of APA, only 3 were ectopic in the mediastinum thus making our case rare. APA is a rare entity as biochemical profile and histopathological features overlap with PC and can be misdiagnosed. Greater awareness of APA may improve capture of cases, allowing the development of guidelines to recognize and treat it.