25 Many lesions can involve the skull base, with the majority due to extension of adjacent tumors or infection, or metastases. Primary skull base neoplasms are relatively uncommon. The most frequent primary malignancies are chordoma and chondrosarcoma and these lesions are often confused with each other. However, there are imaging features that can aid in their differentiation (Table 25.1).
Skull Base Lesions
| Chordoma | Chondrosarcoma | |
|---|---|---|
| Location | Clivus along sphenooccipital synchondrosis; less commonly petrous apex, sellar region, sphenoid sinusa | Generally off midline in skull base around petrooccipital fissure involving the petrous apex and clivus |
| CT | Expansile hyperattenuating soft tissue mass with lytic bone destruction and irregular calcifications; may have low attenuation areasb | Bone destruction; soft tissue mass with chondroid matrix |
| Enhancement | Moderate to marked; generally heterogeneous; may have “honeycomb” pattern | Heterogeneous; may be mild peripheral and septal (“pepper and salt appearance”) |
| MRI | T1WI: Intermediate to low signalc T2WI: High signal with low signal septad, e | T1WI: Low to intermediatef T2WI: High signal with low signal areasg |
| Vascular Effects | Vascular encasement and displacement are common, narrowing is rare | Vascular encasement and displacement are common, narrowing is rare |
| Calcifications | Irregular, either trapped bone or dystrophic; may have chondroid matrix | Chondroid matrix (linear, globular, arc-like) |
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