Revision 18 for 'Chondrosarcoma of the base of skull'

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). 

Pathology

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

Location

• petro-occipital synchondrosis (most common)
• sphenoethmoidal junction
• sella turcica
• other rare sites that have been reported (presumably from metaplasia) include:
  • dura mater
  • arachnoid mater
  • choroid plexus

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. 

Predisposing factors

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

• previous trauma / fractures
• Ollier disease
• Maffucci syndrome

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 : tend to demonstrate high T2 signal, useful in distinguishing from meningiomas (although some meningiomas may have high T2 signal) - axial +/- coronal
• GE (gradient echo) : to demonstrate calcifications, or haemorrhage - axial
• T1 C+ (GAD) with fat saturation : as extension below base of skull is common, fat saturation should be employed to better deliniate inferior component.- axial, coronal +/- sagittal.

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 diagnoses

Considerations include

• chordoma
• meningioma
• metastases
• nasopharyngeal carcinoma (NPC)
• pituitary macroadenoma