  Robotic assistance has significantly improved the outcomes of open
microsurgery and rigid endoscopic surgery, however is yet to make an impact in
flexible endoscopic neurosurgery. Some of the most common intracranial
procedures for treatment of hydrocephalus and tumors stand to benefit from
increased dexterity and reduced invasiveness offered by robotic systems that
can navigate in the deep ventricular system of the brain. We review a spectrum
of flexible robotic devices, from the traditional highly actuated approach, to
more novel and bio-inspired mechanisms for safe navigation. For each
technology, we identify the operating principle and are able to evaluate the
potential for minimally invasive surgical applications. Overall, rigid-type
continuum robots have seen the most development, however, approaches combining
rigid and soft robotic principles into innovative devices, are ideally situated
to address safety and complexity limitations after future design evolution. We
also observe a number of related challenges in the field, from surgeon-robot
interfaces to robot evaluation procedures. Fundamentally, the challenges
revolve around a guarantee of safety in robotic devices with the prerequisites
to assist and improve upon surgical tasks. With innovative designs, materials
and evaluation techniques emerging, we see potential impacts in the next 5--10
years.
