Oncogenic osteomalacia associated with a meningeal phosphaturic mesenchymal tumor. Case report.

A 60-year-old woman suffered from hypophosphatemic osteomalacia secondary to a frontal intracranial tumor. Oral administration of phosphate and 1-alpha-hydroxyvitamin D3 provided only temporary symptomatic relief. A computerized tomography (CT) scan of the patient's head revealed a large subfrontal tumor attached to the dura. Following removal of the tumor, the patient's hypophosphatemia subsided; her level of 1,25-dihydroxyvitamin D3, which was undetectable preoperatively, returned to normal, and she had symptomatic improvement. Three years later, decreasing levels of phosphate and 1,25-dihydroxyvitamin D3 indicated tumor recurrence, before it was detected by CT scan. Histological examination of the tumor provided the diagnosis of "mixed connective tissue variant of phosphaturic mesenchymal tumor." The characteristic histological features of this relatively rare entity are discussed. This is the first report of a surgically treated intracranial phosphaturic mesenchymal tumor that caused oncogenic osteomalacia.