Low-grade myxofibrosarcoma

Case contributed by Dr Cedric Bohyn

Presentation

One month ago, the patient noticed a swelling of the right thigh. No pain nor any other symptoms.

Patient Data

Age: 70 years
Gender: Female
Ultrasound

Well-delineated heterogenic hypoechoic mass (maximum diameter: 5 cm) situated within the vastus medialis muscle belly. No detectable vascularization within the lesion. A small cystic component is present on the lateral side of the lesion. No sonographic evidence of extramuscular extension.

MRI

Circumscribed rounded mass (maximum diameter: 5 cm) situated within the confines of the right vastus medialis muscle belly. The lesion shows homogenous bright T2 signal, homogenous T1 hypointense signal in relation to the surrounding muscle and heterogeneous contrast enhancement.  Significant perilesional soft tissue edema is present,  extending into the adjacent femoral canal where the muscular fascia is less well-defined. No bony abnormalities. The leg musculature, other than the vastus medialis, is normal appearing.

PATHOLOGY REPORT
MACROSCOPIC EXAMINATION:
-166 grams, 92 x 48 x 73 mm (CC x ML x AP) resection piece with a 4.3 x 1.0 cm (CC x ML) skin wedge. 
- Within the muscle, there is a vaguely defined nodule with white-grey glassy myxoid/gelatinous aspect, relatively homogeneous with dimensions 4 x 4.3 x 3.6 cm (CC x AP x ML).
 
MICROSCOPIC EXAMINATION
The nodular mass consists of a cell-poor aqueous myxoid matrix with dispersed spindle-shaped or plump with eosinophilic cytoplasm. Some of the cells have an enlarged hyperchromatic nucleus. There are also cells with eccentrically located basophilic cytoplasm resulting in a plasmacytoid appearance. A minority of cells have cytoplasmic vacuoles. Both obvious mitotic activity and necrosis are not present. The lesions contain elongated thin-walled blood vessels often encompassed by thin collagen fibers. Locally, there is a limited perivascular lymphocytic inflammatory infiltrate. The nodule infiltrates the surrounding skeletal muscle tissue with atrophy of the muscle fibers. The tumor invades the posterior section plan.

CONCLUSION:
Findings are consistent with a low-grade myxofibrosarcoma with a focal invasion of the posterior section plane (consistent with the femoral canal).

Case Discussion

Pathologically proven low-grade myxofibrosarcoma with all the typical features:

  • patient age over 60
  • painless mass
  • located in the lower limb which is the most prevalent area for this lesion
  • high T2 / low T1 signal consistent with myxoid tissue
  • partial enhancement since only the solid (not myxoid) components enhance

The surgical specimen showed invasion into the femoral canal consistent with the MRI findings showing less well-defined fascia and edema focally extending into the femoral canal. This shows the importance of MR-graphic assessment since sonographic evaluation did not allow visualization of the extension into the femoral canal.

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