34-year-old female showed a palpable hard mass in the abdominal wall. The surgical resection specimen of the rectus abdominis muscle is shown.
- Several tissue fragments containing proliferations of plump, uniform fibroblasts, some of which are arranged in bundles within a collagen containing matrix.
- The fibroblasts display regular nuclei. Mitoses are rare and giant cells are not observed.
- The tumor grows in an infiltrative fashion into the adjacent skeletal muscle.
A superficial and deep form of fibromatoses is distinguished. Deep fibromatoses affect the abdomen, the muscles of the trunk and the extremities. Deep fibromatoses grow locally in an aggressive manner and have a tendency to recur. Total excision is hard to achieve due to the infiltrative growth pattern and the resulting difficulty in delineating the borders of the tumor. However, in contrast to fibrosarcoma, fibromatoses do not metastasize. Deep fibromatoses are considered semi-malignant tumors.