Spinal anesthesia is similar to epidural in that it is placed, with a needle, in the same approximate location of the lower spine. However, with spinal anesthesia the needle is passed beyond the epidural space into the spinal fluid space, allowing an even deeper intensity of regional anesthesia in a distribution that is similar to that achieved with epidural anesthesia.
A spinal technique uses a single injection. With an epidural, a catheter is ususally placed into the epidural space which allows mutlipe injections and/or an infusion of medication to be given.
A spinal anesthetic is the anesthetic technique used most frequently for patients having cesarean sections (assuming they don't already have an epidural catheter in place). A spinal anesthetic is also sometimes given when an epidural catheter is being placed. This is called a combined spinal-epidural technique.
Potential complications with spinal anesthesia are essentially the same as those listed in the epidural anesthesia section.