In retinoblastoma, after enucleation, which tissue is sectioned to find out systemic metastasis

C i.e. Optic nerve Enucleation is indicated in large retinoblastoma with diffuse involvement (due to poor prognosis & high risk of recurrence) & normal fellow eye (so aggressive chemotherapy is inappropriate). It should be done with minimal-manipulation and it is imperative to obtain 8-12 mm piece of optic nerve Q to rule out any spread of tumor to brain.