Epidural gas presenting as Spinal Space occupying lesion- A review of 8 paper since 1994

Introduction:
Among unusual abnormalities of the lumbar spine reported since the introduction of Computed Tomography (CT), the presence of gas lucency in the spinal canal, known as vacuum phenomenon, is often demonstrated (7). The finding of gas within the vertebral disc space (vacuum phenomenon) is relatively common. This disorder often presents major diagnostic and therapeutic challenges, especially in the presence of multiple degenerative changes and chronic back pain in elderly patients. Kloc W (8) describes pathophysiology and diagnostics of gaseous degeneration associated with the herniated disc. Degenerative spine disease, gaseous degeneration of the intervertebral disc and epidural gas can be disclosed by imaging studies. The presence of epidural gas is attributed to gaseous disc degeneration. This pathology may cause radicular pain similar to sciatic pain produced by disc herniation. Surgery might be indicated in these cases.
The initial reports on epidural gas (6):
The authors Cheng TM et al (1994) described two patients with presentations and findings that have not been previously described in the literature. Both patients had histories of upper lumbar back and leg pain. Degenerative spine disease, gaseous degeneration of the intervertebral discs, and epidural gas in the lateral recesses were noted on imaging studies. However, because both patients had undergone prior epidural diagnostic and therapeutic procedures, the epidural gas in the lateral recesses could be attributed either to gaseous disc degeneration or to the previous intraspinal procedures. One patient was found to have a large, far lateral extruded disc fragment that contained air. The nerve root in the second patient was impaled by an unusual combination of a small extruded disc fragment as well as an air-filled sac that was surrounded by the walled-off fragment's capsule and which freely communicated with the gaseous degenerated disc space. Cheng TM et al discussed the suspected mechanism of root compression. The possibility of disc herniation should be seriously considered in cases of nerve root compression in which epidural gas is present, especially those associated with gaseous degenerated discs.
Epidural gas pseudocyst (4,7):
Epidural gas pseudocyst compressing a nerve root in patients with a lateral disc herniation has rarely been reported. Salpietro FM et al reported a case of a 44-year-old man who experienced violent low back pain and monolateral sciatica, exacerbated by orthostatic position, one week before admission. A lumbosacral spine CT showed the presence of vacuum phenomenon associated with a degenerated disc material and a capsulated epidural gas collection with evidence of root compression.
A microsurgical interlaminar approach was carried out and, before the posterior longitudinal ligament was entered, a spherical "bubble" compressing the nerve roots was observed. The capsulated pseudocyst was dissected out, peeled off and excised en bloc. A large part of the posterior longitudinal ligament and the lateral disc herniation were removed. Postoperatively the patient was completely free of symptoms.
Salpietro FM et al have associated the mechanism of exacerbation of pain was probably due to the increased radicular compression in the upright posture and, besides the presence of a lateral disc herniation, could be related to a pneumatic squeezing of gas from the intervertebral space into the well capsulated sac by the solicitated L4-L5 motion segment. Histological study of the wall of the pseudocyst showed the presence of fibrous tissue identical to the ligament. They concluded that, in case of a lumbar disc herniation, it is recommended to perform a complete microdiscectomy and an accurate removal of the involved portion of posterior longitudinal ligament in order to prevent pseudocystic formations.
CT in detecting intra-spinal gas (5):
Tsitouridis I et al of Radiology Department, Papageorgiou General Hospital, Greece reported Disc-like herniation in association with gas collection in the spinal canal.
Gas production as a part of disk degeneration can occur but rarely causes nerve compression syndromes. Few cases have been reported in which lumbar intraspinal epidural gas cause nerve root compression symptoms. We present 12 cases of gas collection in the spinal canal that were presented to the orthopaedic out-patient department with symptoms of low back pain and sciatica. CT showed the presence of free epidural gas collections adjacent to or over the affected nerve roots. Relief of symptoms was noted with the change of positions, lying down or sleeping. In this study, we conclude that the presence of lumbar intraspinal epidural gas that causes radicular compressing phenomena, can be easily detected with the use of CT.
Recurrent radiculopathy caused by epidural gas after spinal surgery (3):
Vacuum phenomenon (gas accumulation in an intervertebral disc) is relatively common. Gas can also spontaneously enter and collect in the epidural space, but symptomatic epidural gas after spinal surgery is very rare.
Sasani M et reported primary disorders in the 4 new cases were disc extrusion at L2-L3 (Case 1), disc degeneration and herniation at L4-L5 (Case 2), stenosis of the lumbar spinal canal (Case 3), and disc herniation at L5-S1 with spinal canal stenosis (Case 4). The corresponding surgeries performed were L2-L3 microdiscectomy, L4-L5 microdiscectomy with instrumentation, right unilateral hemilaminotomy with complete instrumentation, and L5-S1 microdiscectomy.
All 4 patients developed unexpected postoperative complaints of low back and radicular pain. Each was investigated with computed tomography and magnetic resonance imaging. The images revealed epidural gas collections compressing the thecal sac and/or nerve roots.
Epidural gas after lumbar surgery is very rare but can cause unexpected postoperative back or radicular pain. Combined computed tomography and magnetic resonance imaging should be used to identify the problem and rule out other disorders. This is a iatrogenic complication that raise concern among the spinal surgeons. However Sasani M et reported combined computed tomography and magnetic resonance imaging should be used to identify the problem and rule out other disorders. Conservative treatment should be the first-line approach but surgery is often necessary if this does not resolve the problem.
Association of Intradural disc herniation and epidural gas: more than a informal association? (1,2)
Hidalgo-Ovejero AM et al alerted spine surgeons to this potential association between Intradural disc herniation and epidural gas. According to Hidalgo-Ovejero AM et al this association is found in 2% of the patients with intraspinal gas.
Hidalgo-Ovejero AM et al concluded potential presence of an intradural disc herniation must always be considered when performing an open discectomy on a patient whose CT scan study shows the presence of epidural gas. This association is particularly striking given the relative rarity of intradural herniations and intraspinal gas. In the event that no clear disc herniation was found, an intradural examination may be indicated to justify clinical signs and symptoms or previous radiologic studies.

References:
1. Spine. 1998 Jan 15;23(2):281-3.
2. Spine. 2004 Oct 15;29(20):E463-7
3. Spine. 2007 May 1;32(10):E320-5.
4. J Neurosurg Sci. 2002 Jun;46(2):93-5; discussion 95.
5. Eur J Radiol. 2005 Oct;56(1):1-4
6. J Neurosurg. 1994 Sep;81(3):453-8.
7. J Neurosurg Sci. 2002 Jun;46(2):93-5; discussion 95.
8. Chir Narzadow Ruchu Ortop Pol. 1998;63(2):117-22; discussion 123-4.