[A case of malignant lymphoma of the cranial vault]

We report a rare case of malignant lymphopma of the cranial vault. A 71-year-old woman developed an asymptomatic subcutaneous mass on the scalp. The skin over the lesion was normal and the mass was firm and attached to the skull. Neurological examination revealed no abnormalities. Plain CT scans showed a high-density lesion that was widely attached to the skull and the surface of the skull was slightly irregular. About 25 days later, enhanced CT showed that the mass was well enhanced and extended into the cranium, and decalcification of the skull adjacent to the lesion had progressed. MRI showed long T1 and T2 values of the mass and the adjacent bone marrow. Bone scintigraphy and gallium scintigraphy showed prominent accumulation of radioisotopes in the scalp lesion. The mass, dura, and infiltrated bone were resected, and the surface of the brain was found to be intact. Histological examination revealed that the tumor was non-Hodgkin's lymphoma (diffuse, medium-sized, B cell lymphoma). The fact that the tumor first developed extracranially and then extended into the cranium without severe bone destruction and the fact that the dura completely protected the brain surface may indicate that the malignant lymphoma originated from the skull and showed infiltrative growth, while the dura provided a strong barrier to its intracranial extension. Thus, malignant lymphoma originating from the skull may tend to extend outside the cranium first and within the cranium subsequently, as in our case, and this may be the reason why the complaint at presentation of more than half of the reported patients is a scalp mass rather than any neurological sign.