Posterior fossa ependymomas: new radiological classification with surgical correlation.
OBJECTIVE
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 pre-operative 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 lateral-type 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 midfloor-type 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 pre-operatively 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.
U-King-Im
Jean Marie
JM
Department of Diagnostic Imaging, Hospital for Sick Children and the University of Toronto, 555 University Ave, Toronto, ON, Canada.
Taylor
Michael D
MD
Raybaud
Charles
C
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D004806:Ependymoma / Q000145:classification* / Q000473:pathology / Q000601:surgery; D005260:Female; D006801:Humans; D007223:Infant; D015192:Infratentorial Neoplasms / Q000145:classification* / Q000473:pathology / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male