Mesenchymal chondrosarcoma of the orbit: imaging features of CT and MRI.

Objective:: Mesenchymal chondrosarcoma (MCS) of the orbit is a rare and aggressive form of chondrosarcoma. The purpose of this study was to retrospectively identify the imaging features of mesenchymal chondrosarcoma of the orbit.

Methods:: This study included five patients with histologically confirmed MCS of the orbit who had undergone either CT, MRI, or both. Images were evaluated for the following: location, size, margin, CT density and presence or absence of calcification and/or ossification, MRI findings including dynamic contrast-enhancement and time-intensity curves.

Results:: CT was performed in four of the five patients, and all four (100%) demonstrated calcification and ossification of the mass. MRI was performed in all five patients. In two patients (40%), the mass demonstrated areas of hyperintensity on T weighted images.

Conclusion:: The presence of a well-defined, orbital mass with calcification and ossification on CT and, marked heterogenous enhancement and a rapid-washout pattern on dynamic MRI indicate a high probability of MCS of the orbit. In addition, MCS of the orbit can demonstrate areas of hyperintensity on T weighted images, representing bone marrow fat tissue of ossification.

Advances In Knowledge:: MCS of the orbit is a highly malignant tumor, and early diagnosis by imaging is important. Radiologists should be aware of the imaging features of MCS of the orbit.