Phosphaturic mesenchymal tumor (mixed connective tissue variant): a case report with spectral analysis

We present a further case of a rare mesenchymal neoplasm termed phosphaturic mesenchymal tumor (mixed connective tissue variant). The patient was a 42-year-old man with a long history of osteomalacia of unknown etiology with pathological bone fracture, abnormality of parathyroid glands, kyphosis, scoliosis, and spondylosis. Laboratory investigation disclosed hypophosphatemia, elevated serum alkaline phosphatase activity, and normal serum calcium level. The patient had a soft tissue mass in the right inguinal area, measuring 11 x 6 x 5 cm, which was previously interpreted as a calcified hematoma on sonography. The tumor was surgically removed. Grossly, the tumor was well circumscribed, unencapsulated, and had soft to dense consistency. The cut surface had a variegated appearance due to the presence of large hemorrhagic areas admixed with foci of grey-yellow tissue. Histologically, the tumor was composed of primitive mesenchymal cells, osteoclast-like cells, and cells showing myofibroblastic features without cytologic atypia. There were a well developed vascular network, microcystic areas, and poorly formed cartilaginous foci. Unusual and hitherto unpublished prominent features were flower-like, slate-gray crystals, widespread hemosiderin deposits and large areas of hemorrhages, with the latter comprising approximately 60% of the tumor. A spectral analysis indicated that chemically, the crystals mainly consisted of calcium phosphate and sodium nitrate.