"Two is not enough" - Impact of the number of tissue samples obtained from stereotactic brain biopsies in suspected glioblastoma.

Objective: Stereotactic procedures are performed in many neurosurgical departments in order to obtain tumor tissue from brain lesions for histopathological evaluation. Biopsies can be performed frame-guided and frame less. Some departments use a biopsy needle (cylinder probe), others a forceps for repetitive smaller tissue samples. Although the applied techniques are somehow different, it is still unclear how many tissue samples have to be taken to establish reliably a final diagnosis based on histopathological and genetic examinations. Only precise histopathological diagnosis results in adequate therapy.

Methods: We included 43 consecutive patients who underwent stereotactic biopsy of a suspected glioblastoma between 02/2013 and 07/2015. All patients showed contrast enhancing tumors in the MRI. The patients underwent stereotactic biopsy with the Leksell frame attached to their head. All stereotactic procedures were performed in the presence of a neuropathologist. Target and Entry Points were calculated with BrainLab iplan software (BrainLab iplan 1.0, Munich, Germany). First the two samples 5mm before the Target (pre-target) and the "Targetpoint" itself were analyzed (group 1), then a histopathological evaluation of all samples was performed (group 2).

Results: Mean number of extracted samples was 14. Using classical hematoxylin-eosin stainings, in group 1 histopathological diagnosis was correct in only 30 cases accounting for 73%. Contrariwise a final diagnosis was made in 100% in group 2.

Conclusion: If only two tissue samples were evaluated in this group of patients with suspected glioblastoma, a correct diagnosis was possible in only 73% of the cases. We conclude that two samples are not enough to establish a final diagnosis even in a subgroup of suspected glioblastoma.