After Hemispherectomy: What Fills the Cranial Cavity?

Post-Hemispherectomy Space Filling

After removal of one cerebral hemisphere (for intractable epilepsy), the empty cranial space is filled by:

1. Cerebrospinal Fluid (CSF): Expands to occupy most of the volume; ventricles enlarge (hydrocephalus ex vacuo).
2. Soft Tissue Expansion: Remaining hemisphere shifts medially; meninges (arachnoid, pia) and glial scar fill gaps.
3. Limited Neuroplasticity: Remaining cortex assumes some functions (especially in young children).
4. Skull Remodeling: Over years, inner table may resorb, outer table may thin; cranial asymmetry reduces.

Outcomes

• Seizure freedom: 70–85%.
• Hemiparesis: Permanent but often improves with rehab.
• Cognitive: Depends on age at surgery (younger = better plasticity).
• Shunt may be needed if communicating hydrocephalus develops.