Clinical
Presentation: Patient is a 51-year-old woman with a known skull base tumor. She has new onset left facial numbness, and left 6th nerve palsy.
Imaging Findings: A large extra-axial mass lesion of 4.7x4.3x3.4 cm is seen in left paracavernous location. Peripheral specks of calcification are seen on non-contrast CT images. The mass shows high T2 signal, with well-defined margin. The left middle cerebral artery is draped over the mass. The mass is seen to extend into left cavernous sinus, with mild encroachment into the left sphenoid sinus and left orbital apex. The mass extends inferiorly into the infratemporal fossa and left retropharyngeal space. There is compression of anteromedial left temporal lobe, but no significant edema.
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Figures 1A-B: Non-contrast CT images show the hypodense lesion in the left paracavernous location. Peripheral specks of calcification are seen.
Figures 2A-B: Scalloping and erosion of the adjacent bones are seen in bone window images.
Figures 3A-B: The lesion has hypointense signal in T1W images. The signal void is due to displaced left ICA.
Figures 4A-B: The lesion shows high T2 signal. The margin is well-defined, and few septations are seen within the lesion. Left MCA is seen draped over the mass in axial section.
Figures 5A-D: Post-contrast images show the strong and heterogeneous enhancement of the lesion. There is extension into the infratemporal fossa and encroachment on the left sphenoid sinus.
Diagnosis: Paracavernous chondrosarcoma
Discussion: Chondrosarcomas are malignant tumors that produce cartilage matrix. The various histological types include conventional intramedullary, clear cell, juxtacortical, myxoid, mesenchymal, extraskeletal, and dedifferentiated. Chondrosarcomas grow with lobular type architecture, and these hyaline cartilage nodules demonstrate high water content and peripheral enchondral ossification [1].
Chondrosarcomas account for 6% of skull base tumors and about 2% of all chondrosarcomas are seen in the craniofacial location, with a predilection for skull base [1]. As the skull base is derived from cartilage, the presence of chondrosarcoma at this site is predictable; in fact, three fourths of all cranial chondrosarcomas are located in the skull base. They can also arise in endochondral bone; or primitive mesenchymal cells in the brain, meninges, membranous bone, or soft tissue. Specific sites of involvement include the parasellar region, cerebellopontine angle, and facial region, especially the sphenoethmoid, maxillary, and posterior nasal-subsphenoid regions. These tumors spread by local invasion. The parasellar and facial lesions can cause extensive destruction of the skull base [2]. Benign chondroid lesions are rare in this location; therefore solitary intramedullary cartilaginous tumors at this site, similar to lesions in the pelvis, ribs, sternum, and spine, should always be regarded as malignant [1].
In a series of 17 cases, the age range of patients with skull base chondrosarcomas was 14–65 years, with a mean age of 36 years. The majority of patients (59%) were between 30 and 44 years of age, and the male-to-female ratio was 2.4:1 [1].
Skull base chondrosarcomas are often very large at presentation, compressing the brain stem and invading adjacent areas such as the cavernous sinus [1]. Presentation depends on location, but typically it is manifested by insidious onset of single or multiple cranial neuropathies [2].
Both CT and MR imaging depict the high water content of these lesions as low attenuation and very high-signal intensity with T2-weighting, respectively [1]. CT is useful in evaluating the calcified matrix so characteristic of this lesion. This is reported to be seen in about 70% of cases. The calcification varies in appearance but can be stippled and amorphous, not unlike the chondroid calcifications seen with extracranial chondrosarcomas. Careful evaluation of the calcifications is necessary to avoid confusion with other lesions such as osteosarcoma, chondroma, osteochondroma, or chordoma. Other CT findings include bone erosion and destruction, an enhancing soft-tissue mass, and a sharp zone of transition to normal tissue. MR imaging is optimal for depicting areas of tumor involvement. The tumor is hypointense relative to brain on T1-weighted images and hyperintense on T2- weighted images. Heterogeneous internal areas of decreased signal represent calcifications [2].
Post-contrast images show mild peripheral and septal enhancement typical of chondroid lesions, which have been described as variegated or having a "pepper-and-salt" appearance. This appearance corresponds to a lack of perfusion at MR angiography, a feature that helps distinguish these lesions from other more vascular skull base tumors, such as metastases and meningiomas. Similarly, skull base chondrosarcomas appear relatively avascular at digital subtraction angiography [1].
Skull base chondrosarcomas may be confused with chordomas. Chordoma is a more common tumor in this location than chondrosarcoma. Differentiation between these two skull base neoplasms is very important because chondrosarcoma has a much better prognosis. The major clinical distinctions between chordomas and chondrosarcomas of the skull base are patient age and rate of growth. Chordomas tend to occur, on average, in patients a decade older than do chondrosarcomas and grow much more rapidly. Unfortunately, these distinctions are not true for mesenchymal chondrosarcomas involving the craniofacial region that also grow rapidly [1].
Treatment of chondrosarcoma involves surgical resection with radiation therapy. Systemic metastases are uncommon, and prognosis is related to histologic grade, site, and extent of involvement. Prognosis also may be affected by the occasional difficulty in distinguishing histologically among chondrosarcoma, benign chondroma, and chondroid chordoma [2].
References:
Murphey MD, Walker EA, Wilson AJ, Kransdorf MJ, Temple HT, Gannon FH. From the archives of the AFIP: imaging of primary chondrosarcoma: radiologic-pathologic correlation. Radiographics. 2003 Sep-Oct;23(5):1245-78. PMID: 12975513 [PubMed]
Ginsberg LE. Neoplastic diseases affecting the central skull base: CT and MR imaging. AJR Am J Roentgenol. 1992 Sep;159(3):581-9. PMID: 1503031 [PubMed]
