Rm e tumores mixóides

Does MRI allow differentiation between myxoid liposarcoma and intramuscular myxoma?

Purposes

To study MRI semiotics of myxoid liposarcoma (MLS) and intramuscular myxomas (IMM) of the extremities. To highlight any criteria which would allow radiologic distinction between the conditions.

Materials and methods
A retrospective MRI evaluation of 40 patients with 42 histologically proven myxoid tumors, composed of 20 MLS and 22 IMM of the extremities was performed. One case was a Mazabraud Syndrome with three lesions and the remaining cases had one lesion per patient. These patients were identified using the pathology department database of the Cochin Hospital and all had an initial MRI study. Thirty-six of these studies also included acquisitions after contrast dye administration (gadolinium).
The semiotic analysis included topography, size, limits, signal, contrast after intravenous contrast dye injection (homogeneous, heterogeneous), pseudo-capsule, partitions, intra-tumoral fat and surrounding edema.
Statistical analysis was performed using the Fisher’s exact test and the Pearson chi-square.

Results

The statistically significant criteria to differentiate between a myxoid liposarcoma and an intramuscular myxoma in MRI are: heterogeneous signal in T2 (85% of MLS, __% of IMM, p<0,0001), hyposignal in T1, the presence of partitions (100% of LPS), the pseudo-capsule (90% of LPS)and the quota fat (0% of myxomas).

Conclusion

The myxoma and myxoid liposarcoma both have an overall high signal on T2, characteristic of a myxoid component. The myxoid liposarcoma must be considered in the presence of a heterogeneous signal, partition, a pseudo-capsule, and a fat quota.

MRI characteristic | MLS | IMM | p | Heterogenous signal | 90% (36/40) | 10% (4/40) | .05 (chi square) | Partition | 10% (5/50) | 90%(etc..) | .001 (t-test) | Pseudo-capsule | 1% | 99% | .01 | Fat quota | 99% | 1% | .003