Decreased MEPs during subcutaneous dissection for untethering surgery of a “true” lipomyelomeningocele: aggravated traction of the spinal cord by release of the sac from the original nest

Purpose It is well known that the preoperative enlarged sac in occult spinal dysraphism, in which the spinal cord is attached to its dome, can be associated with neurological deficits by aggravation of spinal cord traction. We experienced a similar phenomenon during the early stage of untethering surgery for “lipomyelomeningocele in a strict sense (LMMC).”