Analysis of safe entry zones into the brainstem

Area of Science:

• Neurosurgery
• Surgical Anatomy

Background:

• Intra-axial brainstem surgeries present significant challenges.
• Numerous "safe entry zones" (SEZs) for brainstem lesions exist in literature, but evidence is often limited.

Purpose of the Study:

• To systematically review and categorize the clinical evidence supporting proposed safe entry zones (SEZs) for intra-axial brainstem lesions.
• To assess the level of evidence for different SEZs based on published clinical case numbers.

Main Methods:

• A comprehensive literature search was conducted using PubMed/MEDLINE for English-language publications.
• Publications were included if they described SEZs for brainstem lesions, with cadaveric studies included but clinical case counts treated as zero.
• Evidence levels were defined as "case report" (≤5 cases), "limited evidence" (>5 to <25 cases), and "credible evidence" (≥25 cases).

Main Results:

• Twenty-five of 32 publications were included, identifying 21 distinct SEZs across the midbrain (6), pons (9), and medulla (6).
• Ten SEZs had "case report" level evidence, and 7 had "limited evidence."
• Only 4 SEZs were supported by "credible evidence."

Conclusions:

• The majority of proposed SEZs for intra-axial brainstem lesions lack robust clinical evidence.
• While many SEZs originate from anatomical studies, few have progressed to higher levels of clinical validation.
• Selecting the optimal surgical approach for brainstem lesions remains a complex, case-dependent decision.