NEW CONCEPTS IN UNDERSTANDING EVOLUTION OF DESMOID TUMORS - MR-IMAGING OF 30 LESIONS

The objective of this study was to evaluate the appearance and the nat ural evolution of desmoid tumors on MR imaging, given histologic corre lation. The MR images of 30 desmoids (20 primary and 10 recurrent) in 26 patients were scored for a multiplicity of morphological parameters , signal intensity (SI) on different pulse sequences, and behavior aft er contrast administration. Natural evolution was evaluated in 2 prima ry and 3 recurrent lesions, and correlated with evolution on histologi c specimens. Desmoid tumors are mostly found in muscles of shoulder an d hip girdle and are often fusiform with partially ill-defined margins . Rare subcutaneous desmoids have a more stellar morphology. Variable amounts of low-SI areas are present on all sequences. On T1-weighted i mages (T1-WI), most lesions are near homogeneous and isointense to mus cle, whereas on T2-WI they are more heterogeneous with an overall SI e qual to or slightly lower than fat. Histologic correlation reveals tha t SI on T2-WI cannot be explained solely by cellularity. After initial growth, spontaneous evolution of desmoids is characterized by shrinki ng and an increase in low-SI areas on T2-WI. While distal lesions shri nk, the more recent lesions in asynchronous multicentric desmoids have a tendency to develop proximally in the same limb, and should not be confused with recurrences. Fast growth, extracompartmental spread, and bone involvement are often seen in recurrences. Follow-up MR imaging of desmoids indicated natural regression of desmoids and more aggressi ve behavior of recurrences, which may justify a more conservative ther apeutic approach.