Elderly female present with pain and swelling in the thigh. Xray shows multiple lytic lesions in distal femur with no periosteal reaction. Aspirate from the swelling shows homogenous serosanguinous fluid with RBCs. Which investigation can confirm the diagnosis?

History is suggestive of blood filled bone tumor seen in Hyperparathyroidism. HYPERPARATHYROIDISM May be primary (due to adenoma or hyperplasia), secondary (due to persistent hypocalcemia) or tertiary (when secondary hyperplasia leads to autonomous overactivity). Fig. X-ray hand--hyperparathyroidism Fig. Brown tumor Figs. A and B: (A) Lamina dura and (B) Resorption of lamina dura Salt pepper skull Parathyroid adenoma Most common cause of primary hyperparathyroidism. Presents with subperiosteal resorption, and replacement of endosteal cavitation marrow by vascular granulation and fibrous tissue (osteitis fibrosa cystica). Classical and pathognomic feature of hyperparathyroidism is subperiosteal coical resorption of middle phalanges on radial aspect Clinical features- Abdominal groans (dyspepsia), psychic moans, renal stones and weak bones (Groans, moans, stones and Bones). Ix- Parathyroid hormone and S. alkaline phosphate are raised. Calcium is high, serum phosphate is low.