SAFE ENTRY ZONES TO BRAINSTEM

Safe entry zones to brainstem - Rationale

Ø  The brain stem is densely composed of important neural structures such as nuclei and neural tracts.

Ø  Causes of morbidity following brainstem surgery-

o   Direct damage during removal of the lesion,

o   Selection of an entry route into the brain stem, and

o   The direction of brain stem retraction

Ø  In most cases, the optimal surgical route can be established by use of the 2-point method, in which an imaginary line drawn from the center of the lesion to the point nearest the surface of the brain defines the least disruptive approach † Where critical neural structures are sparse and no perforating arteries are present.

Safe entry zones to brainstem

Suprafacial triangle

„ MLF medially

„ VII nerve caudally

„ SCP & ICP laterally

†  The brain stem can be retracted either laterally or rostrally with relative safety.

Infrafacial triangle

„ MLF medially,

„ Striae medullares caudally,

„ Facial nerve laterally

The brain stem can be retracted only laterally.

Safe entry zones to brainstem Anterolateral aspect

Midbrain- Lateral mesencephalic sulcus

Pons- Peritrigeminal area

Medulla- Retro-olivary sulcus