Chondrosarcoma

Juan E Small, MD - Case Coordinator
Victoria A Clague, MD - Radiology Discussion
Jian Shen, MD, PhD - Pathology Discussion
Russell Alan Blinder, MD - Attending Radiologist
Piran Aliabadi, MD - Attending Radiologist
Steven E Seltzer, MD - Attending Radiologist
Pablo R Ros, MD, MPH - Attending Radiologist

October 27, 2003

Presentation

Imaging Findings

A single T1-weighted, post-contrast MR image shows an extra-axial lesion arising from the middle cranial fossa. The lesion enhances heterogeneously. Low-signal areas may be flow voids or calcifications. A T1-weighted, pre-contrast image confirms flow voids. A coronal T1-weighted image shows the lesion's involvement with the skull base. Mass effect on the left temporal lobe is apparent.

Differential Diagnosis

CT would have been very helpful in this case, as it would have allowed an evaluation of the matrix of the bone.

Diagnosis

Discussion

No gross images were presented for this particular case; the samples received were in the form of fragmented tissue. The typical gross appearance of a chondrosarcoma is white and homogeneous. Areas of necrosis and hemorrhage may also be present.

A case-specific, low-power microscopic image shows chondrocyte proliferation. At higher power, the chondrocytes are seen to be crowded together. Some areas show highly atypical morphology.

Radiology Discussion:

Chondrosarcomas usually arise from a pre-existing cartilaginous lesion, such as an osteochondroma or enchondroma. In the skull base, they typically originate from synchondroses or cartilage endplates (e.g., petro-occipital suture). These lesions represent only 8% of malignant bone tumors, but they are the third most common bone tumors after multiple myeloma and osteosarcoma. Most arise in long bones, pelvis, sternum, or ribs. The most common sites in the head and neck include the paranasal sinuses, skull base, and parasellar region. Most craniofacial chondrosarcomas are low grade. In general, this tumor responds well to treatment. The median age for diagnosis is 45 years.

The typical imaging appearance of chondrosarcoma of the petrous apex is not pathognomonic; there are a number of diagnoses that should be considered for a lytic lesion in this region. On CT, chondrosarcoma is an irregular, destructive mass centered off midline at the petro-occipital suture. Characteristic "rings and arcs" or snowflake/punctate calcifications are seen in 70% of cases. It is often associated with a large soft tissue mass and endosteal cortical thickening. On MR, these lesions demonstrate homogeneously low T1 signal and high T2 signal; they also enhance with contrast. The margins are scalloped and well circumscribed. The differential diagnosis includes chondrosarcoma, plasmacytoma, metastases, extension of nasaopharyngeal malignancies, epidermoid, glomus jugulare tumor, cholesterol granuloma, and chordoma (midline). The table below presents a comparison of MR features of particular lesions.

Lesion	MR/T1	MR/T2	Enhancement
Chondrosarcoma	Dark	Bright	Avid
Chordoma	Dark	Bright	Minimal
Cholesterol Granuloma	Bright	Bright	None
Epidermoid	Dark	Bright	None

Two lesions from the list above are quite similar on MR imaging. Chondrosarcoma and chordoma are both dark on T1, bright on T2, and show some level of contrast enhancement (though chondrosarcoma is typically more avid). Therefore, it is important to consider other features to distinguish one from the other. Chordoma is the more likely diagnosis if the lesion shows a significant intraosseous component, marked bone destruction, and relatively little internal mineralization; these generally occur in midline locations (usually centered in the clivus). Chondrosarcoma is more likely if there is a significant soft-tissue component, little bone destruction, and visible arcs and nodules of calcification; these most often occur in eccentric locations (usually centered in the foramen lacerum).

References

Dahnert, WF. Radiology Review Manual, 4th Ed. Lippincott Williams & Wilkins.

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