The epidural space contains fat, blood vessels and lymphatics.
Steroid injections into the epidural space can inadvertently reach the blood vessels.
The significant is twofold. First the patient is unlikely to get clinical relief of their pain since the injection went into the blood vessels instead of the intended target: the nerve root and disc.
The second is more concerning. Injection of steroids into the artery can result in stroke and death. Dawley recently demonstrated the arterial injection of steroids lead to cerebral hemorrhage by obstructing the microvasculture as well as the toxicity of the steroid.
I have previously blogged on the mounting concerns over steroid injections.