Localization: Desmoid fibroma is more frequent in the mandible, long bones, and pelvis. In the long bones, it is more often observed in the meta-diaphysis, but it may be diaphyseal. During adult age, it usually extends to the epiphysis.
Clinical: Symptoms are mild and late (the lesion grows slowly and is not very vascularized) and consist of moderate pain, possible pathologic fractures.
Imaging: The radiographic picture shows a large osteolysis, usually with expansion of the bone. The original cortex may be replaced by a thin shell of newly formed bone. Occasionally and focally, the tumor breaches the cortex with no clear demarcation toward the surrounding tissues. Rather typically, osteolysis has a finely trabeculated, reticulated, or bubbly appearance. Reactive chronic hyperostosis can produce a rind of sclerosis at the edges of the tumor. On angiography and CT, the tumor only moderately takes the contrast, and it appears relatively “cold” on isotope scan. MRI gives a low signal in T1 and T2 suggestive of dense collagenous tissue.
Histopathology: Hypocellular spindle cell tumor associated with large amounts of collagen. Nuclei have a bland appearance with no atypia and few mitotic figures. Areas of relative hypercellularity can be present, but are not common. β-Catenin pathway does not seem to have the same role in the tumorigenesis of desmoid tumor, as it has in the desmoid type-fibromatosis.
Course and Staging: Growth of the tumor is very slow; it may even take several years prior to causing symptoms. The stage is 2 or 3.
Treatment and Prognosis: Although historical data indicated wide en-bloc resection as the treatment of choice, recent experiences show that aggressive curettage is about equally effective providing better functional results. Desmoid fibroma does not metastasize.