Infantile digital fibromatosis: a study of the development and regression of cytoplasmic inclusion bodies.

: An 8-yr-old Japanese boy developed infantile digital fibromatosis in the right ring finger with recurrence and another lesion in the right middle finger. Histologic investigation of the tumor disclosed that the size and frequency of inclusion bodies were inversely proportional to the degree of fibrosis. Electron microscopic study revealed a variety of stages in the development of inclusion bodies, ranging from small, dense aggregates of filaments into bundles with dense bodies traversing the cytoplasm to typical inclusion bodies that also contained cytoplasmic organelles. In areas of dense fibrosis, the cytoplasm of the tumor cells showed areas of constriction and compression by adjacent bundles of collagen. The tendency for a decrease in the number of inclusion bodies in these areas necessitated a differential diagnosis from other fibrous or fibro-histiocytic lesions. Our findings suggest that the tumor may undergo a decrease in the numbers of inclusion bodies and spontaneously may become fibrotic with time. Thus, even as a form of fibromatosis featuring both recurrence and multiple lesions, it may not have a consistently aggressive nature. These findings support the concept that infantile digital fibromatosis should be managed by limited excision rather than by immediate aggressive surgical treatment.