Posterior fossa ependymomas: new radiological classification with surgical correlation

Childs Nerv Syst (2010) 26:1765–1772. DOI 10.1007/s00381-010-1251-6

The key determinant of long-term outcome in infratentorial ependymomas remains the extent of surgical resection. We describe a new radiological classification system which is validated against surgical findings and correlated with risk of post-operative residual tumour.

Methods Twenty-five consecutive patients (12 females, mean age 4.9 years, range 0.5–17 years) with infratentorial ependymomas were studied. Lesions were classified on preoperative MRI according to the pattern of extension, brainstem displacement and involvement of the obex, as lateral-type or midfloor-type tumours. Twenty-one operative records were reviewed with respect to the microanatomical tumour origin by a paediatric neurosurgeon, blinded to MRI findings. Follow-up imaging studies were evaluated for residual tumour.

Results There were 15 cases of midfloor-type tumour (anterior displacement of brainstem, infiltration of obex) and 10 cases of lateral-type tumour (lateral displacement of brainstem, obex free of tumour). Extension into prepontine or cerebellopontine cisterns was more common in lateraltype tumours. Agreement between the radiological classification and tumour origin, as defined by operative records, was seen in 18 out of 20 cases. Risk of residual tumour in lateral-type tumours was more than twice that of midfloortype tumours (80% vs. 33%, p=0.04). Risk of tumour residual was also significantly higher when vessel encasement or prepontine extension was observed.

Conclusions Infratentorial ependymomas can be preoperatively classified as lateral-type or midfloor-type tumours. This correlates well with operative findings. Lateral-type tumours have significantly increased risk of residual tumour compared to midfloor- type tumours and this may influence intensity of imaging surveillance.