[Multiple myeloma manifesting as a solitary cranial tumor. Case report]

A 76-year-old female struck her head in the parietal region and noticed a soft scalp mass. Approximately 3 months later, the mass was enlarged and she was evaluated at a local hospital. Although the tentative diagnosis was old subcutaneous hematoma, incision of the scalp revealed not hematoma but rather a tissue and bony defect. On admission to the authors' institution, she was found to have a round, smooth, subcutaneous mass in the upper left parietal region. The tumor was about 5 cm in diameter and 4 cm in height, and was soft, nonpainful, and pulsatile. Plain X-rays revealed an osteolytic lesion in the left parietal bone. Computed tomography demonstrated a high-density lesion corresponding to the bony defect, which was homogeneously enhanced by contrast material. Left external carotid angiography showed the mass to be vascular, its main feeder being the middle meningeal artery. It was concluded that the tumor originated from the diploë. The tumor was subtotally removed, and histopathological examination showed it to be a plasmacytoma. Laboratory tests, including protein electrophoresis, disclosed hypergammaglobulinemia with M-spikes. Immunoelectrophoresis demonstrated a serum paraprotein of immunoglobulin G kappa specificity. Multiple myeloma diffusely involving bone is well known, but a soft mass alone with a bony defect in the cranial vault is very rare. The clinical features and treatment of silent, solitary masses associated with multiple myeloma are discussed.