A special form of hyperostosis frontalis interna.

The article describes a very severe case of hyperostosis of the frontal bone and discusses its possible differential diagnosis. What makes this case special is the fact that the osseous changes include all 3 layers of the bone. Macroscopically the lesion resembles an osteoma as described by Burkhardt (1970) and v. Eiselsberg (1906). The histological examination lead to the final diagnosis of hyperostosis frontalis interna. One must note that there were certain effects caused by a metastasis of a lobular carcinoma of the breast which influenced the osseous changes from the outer surface. The rough, spicula-like structure in the centre of the frontal squama should be put down to tumour erosion. The peripheral areas of the hyperostosis, however, still exhibit the original smoother texture of the disease. The final diagnosis in this unusual and possibly unique case was an intense hyperostosis frontalis interna with secondary changes due to the metastases of a lobular carcinoma of the breast.