Evidence-based MR imaging follow-up strategy for desmoid-type fibromatosis.

OBJECTIVES: To propose a follow-up strategy for desmoid-type fibromatosis (DF) based on tumor growth behavior and the signal on T2-weighted MRI. METHODS: We retrospectively reviewed 296 MRI studies of 34 patients with histologically proven DF. In each study, tumor volume and T2 signal relatively normal striated muscle were assessed. Volume variation and monthly growth rates were analyzed to determine lesion growth behavior (progressing versus stable/regressing lesions). Growth behavior was correlated with T2 signal, tumor location, ß-catenin status, treatment strategy, and follow-up duration. Interobserver variability of volume measurements and interobserver measurement variation ratio were assessed. RESULTS: There were 25 women and 9 men with a mean age of 39.9 ± 19 (4-73) years. Mean follow-up time in the patients included was 55 ± 41 (12-148) months. In progressing lesions, the mean average monthly growth ratio was 10.9 ± 9.2 (1.1-42.5) %. Interobserver variability of volume measurements was excellent (ICC = 0.96). Mean interobserver measurement variation ratio was 20.4 ± 23.6%. The only factor correlated with tumor growth behavior was T2 signal ratio (p < 0.0001). Seventeen out of 34 (50%) patients presented a signal change over the threshold of 1 during follow-up. There were five occurrences of secondary growth after a period of stability with a mean delay until growth of 38.2 ± 44.2 (17-116) months. CONCLUSION: DF growth rate was quantitatively assessed. A threshold for volume variation detection was established. DF growth behavior was significantly related to T2 signal. An evidence-based follow-up strategy is proposed. KEY POINTS: • In progressing desmoid fibromatosis, the mean average monthly growth ratio was 10.9 ± 9.2%. • Lesions with muscle/tumor T2 signal ratios lower than 1 tended to be stable or regress over time. • Given the interobserver measurement variability and MRI in-plane spatial resolution, a variation higher than 42.6% in tumor volume is required to confirm punctual progression.

Subchondral linear hyperintensity of the femoral head: MR imaging findings and associations with femoro-acetabular joint pathology.

PURPOSE: The goal of this study was to evaluate the associations between linear hyperintensity in the subchondral bone of the femoral head on T2-weighted MR imaging and structural bone lesions. MATERIAL AND METHODS: The MR imaging examinations of 63 patients (66 hips) that showed a bone marrow edema pattern (BMEP) of the hip were retrospectively evaluated (study group). The study group comprised 43 men and 20 women, with a mean age of 55.3 years±16.9 (SD) (range: 19-84 years). A control group of 61 patients (77 hips) without BMEP of the hip on MR imaging was created. The control group comprised 30 men and 31 women, with a mean age of 53.1 years±15.6 (SD) (range: 25-83 years). The presence of linear abnormalities of the subchondral bone on T2-weighted fat-saturated sequences (TR/TE=4220-4340/42-45ms) was evaluated and MR imaging findings were correlated with structural femoro-acetabular pathology (advanced chondropathy, osteonecrosis, subchondral insufficiency fractures and macroscopic fractures) and with pain duration. RESULTS: A linear hyperintensity in the subchondral bone on T2-weighted MR imaging was found in 43/66 hips with areas of BMEP (65.1%) and in 3/77 hips without BMEP (3.8%). Subchondral linear hyperintensity was seen in 15/16 (93.7%) hips with a subchondral insufficiency fracture. Among the 16 hips with an ARCO stage III osteonecrosis, 13 (76.9%) presented BMEP associated with a subchondral linear hyperintensity. BMEP was present in 6/8 hips with ARCO stage IV osteonecrosis; however, only two hips (25%) exhibited subchondral linear hyperintensities. Finally, 77.7% of patients with subchondral linear hyperintensities presented with acute or subacute hip pain (P<0.0001). CONCLUSION: Femoral head subchondral linear hyperintensity on T2-weighted MR imaging is common and is associated with acute subchondral bone damage.