The purpose of the present study is to compare the characteristics, i.e. efficacy, duration, safety and hospital stay, of a frameless fiducial-less brain biopsy method with those of the standard frame-based stereotactic technique.

Inclusion criteria: adult patients with cerebral lesions: 1) for whom no conclusive diagnosis could be settled in a noninvasive manner; and 2a) who also had surgically inaccessible lesions (or involving eloquent areas), or multifocal lesions, or lesions for which the probable diagnosis is a contraindication for craniotomy, or 2b) were too ill or too old for open craniotomy.

Type of Intervention: standard frame-based stereotactic brain biopsy technique or frameless fiducial-less method using an optical based navigation system and a mini frame apparatus - trajectory guide.

The purpose of the present study is to compare the characteristics, i.e. efficacy, duration, safety and hospital stay, of a frameless fiducial-less brain biopsy method with those of the standard frame-based stereotactic technique, in order to apply a technique friendlier to the patient, more comfortable for the surgeon and more flexible concerning the overall hospital's function.

Inclusion criteria: adult patients with cerebral lesions: 1) for whom no conclusive diagnosis could be settled in a noninvasive manner; and 2a) who also had surgically inaccessible lesions (or involving eloquent areas), or multifocal lesions, or lesions for which the probable diagnosis is a contraindication for craniotomy, or 2b) were too ill or too old for open craniotomy.

Type of Intervention: standard frame-based stereotactic brain biopsy technique or frameless fiducial-less method using an optical based navigation system and a mini frame apparatus - trajectory guide.

The following parameters will be assessed: diagnostic yield, histological - cytological evaluation of the biopsy specimens, cerebral lesions' location, lesions' maximum diameter, duration of: the overall procedure, the preparatory steps overall, the preparation inside the OR, operation ("skin-to-skin"), the time spent inside the OR overall, neurologic morbidity, new abnormal findings in the postoperative head CT scan, length of hospitalization.

Inclusion Criteria: Patients: 1) for whom no conclusive diagnosis could be settled in a noninvasive manner; and 2 who also had surgically inaccessible lesions (or involving eloquent areas), or multifocal lesions, or lesions for which the probable diagnosis is a contraindication for craniotomy.

Exclusion Criteria: 1) Pediatric patients, 2) Coagulation abnormalities, 3) destructive comorbidities and very short life expectancy.