In addition to the specific risks of pluripotential cells and their derivatives, introducing cells into the postnatal and mature CNS has its own set of risks, that include heterotopic neuronal differentiation with functional disruption and epileptogenesis, as well as the structural disruption and mass effect that may accompany exuberant cell expansion. Both tissue- and hESC-derived neural stem cells have been reported to have escaped to the spinal canal and ventricular system (Amariglio et al., 2009; Steward et al., 2014), adventitious growths that auger a high risk of obstructive hydrocephalus or, in the spinal cord, syringomyelia (Steward et al., 2014; Tuszynski et al., 2014). Cells escaping to the subarachnoid space might similarly be associated with surface venous compression and consequent cerebral edema, as well as with disruption in CSF flow and metabolic waste clearance (Iliff et al., 2012).
