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Chondrosarcoma of the base of skull

Chondrosarcomas of the base of skull are rare compared with other base of skull tumours, but are an important differential diagnosis as surgical resection and management are affected by the preoperative diagnosis. 

Epidemiology

Chondrosarcomas of the base of skull make up only a small fraction of all chondrosarcomas (head and neck chondrosarcomas in one series making up only 7%). They are an even smaller proportion of intracranial neoplasms (making up only ~ 0.2% of all intracranial neoplasms in one series).  

Predisposing factors

The vast majority of chondrosarcomas of the base of skull are sporadic, however some predisposing conditions are reported, and include:

Clinical presentation

Patients usually present due to mass effect, either on adjacent brain, brainstem, cranial nerves or (if extension inferiorly) structures of the superior neck. 

Pathology

They are thought to arise from embryonal rest cells (remember that the base of skull forms via enchondral ossification).

Location

The majority of chondrosarcomas of the base of skull are located off the midline (82% in one series) a helpful sign compared to chordomas which are usually midline. 

Local extension is common, extending intracranially, into the cavernous sinuses, paranasal sinuses and soft tissues beneath the base of skull. 

Radiographic features

Chondrosarcomas of the base of skull follow the same general imaging characteristics of chondrosarcomas elsewhere. (see generic chondrosarcoma article)

As a historical note, skull x-rays were important in the diagnosis of these lesions, and demonstrated lytic lesions in 50% and calcifications in approximately 60%. The differentiation of chondrosarcomas from other skull base tumours was very difficult prior to cross-sectional imaging.

MRI protocol

Useful sequences include :

  • T2 - high signal
  • GE - calcifications typically in rings and arcs
  • T1 C+ 
    • usually heterogeneous enhancement
    • fat saturation should be employed to better delineate inferior component

Treatment and prognosis

They are relatively slow growing but locally aggressive. Metastatic disease is uncommon. Local resection is often the treatment of choice. Radiotherapy may sometimes be employed although sensitivity is thought to be minimal. 

Differential diagnosis

Imaging differential considerations include :

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