A small hole, usually about 15 to 20mm in diameter, which is drilled through the skull, using either a hand-held bit and brace or, more often these days, an electrically or pneumatically powered drill. Several different types of neurosurgical procedures can be carried out through a burr hole, including placement of shuntA shunt shifts one object, or volume of fluid (or gas or electrical current), from one place to another. In the context of neurosurgical practice we are considering cerebrospinal fluid, which is diverted from the ventricles of the brain, or the spinal theca, into another part of the body, most often the peritoneal cavity. catheters and passage of a ventriculoscopeAn optical, surgical instrument that is passed through the brain substance, via a burr hole in the skull, and into the ventricles of the brain. Abnormal tissues may be biopsied (sampled), internal channels may be created to by-pass obstructions, or shunt tubing may be positioned – or sometimes removed..