Gas in the Spinal Canal (Pneumorrhachis)

This was a puzzle on call a while back. An intoxicated man, found down, was brought in and sent to us for head and cervical spine CT. The head was negative, but the cervical spine CT showed two tiny pockets of gas in the anterior epidural space at the level of C4-C5 and C5-C6 on the right. What I finally settled on was that gas introduced into the venous system during IV access had made it to the epidural venous plexus just in time for the CT of the cervical spine. Another possibility was that gas from vacuum disc phenomenon had escaped into the epidural space with disc herniation. The patient was stable and clinical suspicion for a traumatic etiology (see below) was low, so he was monitored while he detoxified and released. If there had been clinical suspicion, a more thorough workup would have been indicated.

The differential diagnosis of gas in the spinal canal is wide:

• Disc degeneration
• Epidural abscess
• Iatrogenic: e.g., thoracostomy tube placement, IV access
• Blunt chest trauma: Gas from pneumothorax or pneumomediastinum (tracheal or esophageal rupture), when associated with a tear of the spinal meninges, can track into the spinal canal. A case of traumatic lung herniation into the epidural space has also been reported.
• Blunt pelvic trauma: Gas from the gastrointestinal tract, when associated with a tear of the spinal meninges, can track into the spinal canal
• Strenuous exercise
• Skull fracture: Source may be gas the sinuses, mastoid air cells, or outside world.

References

• Hwang WC, Kim HC. CT demonstration of spinal epidural air after chest trauma. Eur Radiol. 2000;10(2):396-7.
• McIntosh SE, Salcedo-Dovi H, Cortes V. Air in the spinal canal associated with trauma. J Emerg Med. 2006 Jul;31(1):33-5.