Chordoma
Findings:
Multiple MR images demonstrate a heterogeneous exophytic lesion extending from the dorsal margin of the clivus, associated with mixed signal and mass effect on the ventral pons. The lesion demonstrates diffusion restriction, some degree of hemorrhagic change, and a component of T1 precontrast hyperintensity.
Differential diagnosis:
Chordoma, chondrosarcoma, metastasis, Ecchordosis Physaliphora
Discussion:
More discussion of chordomas can be found here and
here.
Ecchordosis Physaliphora (EP), which is an uncommon benign prepontine notochordal remnant that histologically resembles chordoma, and is typically small and nearly follows CSF signal, but may have a stalk to the clivus and could cause focal mass effect on the pons. EP may also be large and have more heterogeneous signal, in which case absent enhancement is helpful to distinguish from chordoma. More information regarding EP may be found