Aggressive fibromatosis: MRI features with pathologic correlation.

OBJECTIVE: We present the MRI features with pathologic correlation of aggressive fibromatosis, incorporating 203 cases over a 5-year period from the Royal Marsden Hospital Sarcoma Unit database.

MATERIALS AND METHODS: Sixty patients had imaging available for retrospective review of which 29 had preoperative MRI and final histopathologic diagnosis of aggressive fibromatosis.

RESULTS: The average age at diagnosis was 41.3 years with a female-to-male sex ratio of 1.2:1. Twenty lesions were extraabdominal; six, intraabdominal; and three, in the abdominal wall (classic desmoid). The average tumor size was 6.4 cm (range, 2.2-13.7 cm). Intraabdominal aggressive fibromatosis produced the largest tumors, averaging 9.5 cm. Most lesions were ovoid (52%) or infiltrative (34.5%) in outline with an irregular or lobulated contour (76%). The lesions crossed major fascial boundaries in 31% of cases overall and in 66% of patients referred for recurrent disease. On MRI, homogeneous isointensity or mild hyperintensity on T1-weighted images and heterogenous high signal on T2-weighted or STIR images were seen. All lesions enhanced after IV gadolinium, usually avidly. In contrast to previous reports, 38% of cases failed to show low signal on all pulse sequences and no abnormalities were seen in local bone structures. Histology showed sheets of bland spindle cells in dense collagen and did not vary with the MRI signal characteristics of the lesion. Patients referred for recurrent disease were most likely to have a recurrence after surgery. MRI and pathology findings did not predict recurrence.

CONCLUSION: Accurate diagnosis and staging of aggressive fibromatosis by MRI have important treatment and prognostic implications.