Mri for my sister shows 4days old massive edema surrounding a 4cm liquid mass .is the open brain surgery is the best thing if the tumor normal or not?

Surgery necessary: Your post is a little unclear so if i misstate the facts please repost. You describe a 4 cm liquid mass with massive surrounding edema. Certainly a mass with surrounding edema is worrisome for a malignant brain tumor. However, most would describe a brain tumor as solid mass on scans. Other possibilities include brain abscess that might look liquid. Surgery would establish correct diagnosis.

possibly biopsy: Hard to really say without seeing the mri, but an open surgery might be best if the mass is in accessible locations. Alternatively, a biopsy or aspiration using computer guidance might be another option if the mass is in eloquent areas or very deep. Talk to your neurosurgeon.

The "massive edema" is troubling, and raises concerns of a brain abscess, but also perhaps a metastasis from a remote cancer. This is clearly an indication for, at the very least, a brain biopsy, to initiate appropriate therapeutic planning.