Origin

Chondroma and chondrosarcoma arise from the dura and/or the adjacent bony skull.

Macroscopic appearance and general characteristics

Chondrosarcomas are slow-growing locally invasive tumors, arising from the skull base. Most lesions originate in the vicinity of the petrooccipital synchondrosis and therefore, unlike chordomas, are off midline. Midline lesions originate from the sphenoethmoidal junction, sella turcica or the clivus.

Extension into adjacent structures is extensive and involves the cavernous sinus, sella turcica, orbit, parapharyngeal space and jugular foramen. Posterior extension to the middle cranial fossa or posterior fossa is common. Tumor encasement of arteries is common.

Besides a slow-growing subtype, more aggressive forms exist.

Microscopic appearance (image 2)

The most typical and most common subtype contains many round or oval cartilaginous cells with single or multiple large nuclei. In anaplastic tumors dedifferentiated foci can be found.

Imaging features (see case reports)

- On CT, chondrosarcomas appear as off-midline soft tissue masses, eroding and invading the skull base. Diffuse irregular hyperdensity of the tumor is due to chondroid mineralization.

- On T1 weighted MRI, signal intensity is low to intermediate.

On T2 weighted MR images, the signal is generally very high but heterogeneous. Hypointense areas are felt to be caused by matrix mineralization, fibrocartilaginous elements or both.

After Gd-administration enhancement is marked and mostly inhomogeneous (image 3). MRI accurately demonstrates the extension of the tumor in the skull base, the cranial compartment and the soft tissues. Vascular invasion is well seen.

Case report

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Chondroma

The ESNR CD-Rom Series

Chondrosarcoma, skull base