Spinal cord seeding is prevalent in ependymoma as these tumours are well known to disseminate throughout cerebrospinal fluid. Infratentorial tumours have a higher chance of seeding than supratentorial tumours.
The incidence of subarachnoid seeding has been found to vary with both tumour grade and tumour location:
Table 7. Percentage of tumours that display seeding
| Tumour Properties |
|
% of Tumours with Seeding |
| Location |
Supratentorial |
8% |
| |
Posterior Fossa |
15% |
| Grade |
High Grade |
20% |
| |
Low Grade |
9% |
It should be noted that reports of clinical seeding tend to underestimate its true incidence because routine myelograms are often not performed.
30-50% of tumours extend into the cervical spinal canal. Downward extension through the cisterna magna and the cervical spinal canal through the Foramen of Magendie may occur. Tumour growth frequently extends to the C2 level, but has been documented to extend down to C5.