(Publicado en Spine 19: 2210-2212. 1994).

Introduction and Summary of Background data: Intradiscal gas is associated with tumors, infection, traumatisms, therapeutic and diagnostic spinal procedures, deposit illnesses and disc degeneration. However, the existence of gas within the spinal canal has been published previously on 29 ocasions, of which 14 where associated with disc herniations.

Material: In our study 19 more cases of intraspinal gas will be presented, corresponding to discal hernias, 6 of which have required surgical treatment up till now.

The association of disc herniation with gas and intradural herniation frecuently appears in literature, although this fact has not been proved in our group.

In our experience the presence of herniated disc with gas in the canal is seen more frecuently in cases of chronic patients and advanced age.

Conclusion: It should be indicated that intrahernial gas is much more common than is reflected in literature. We believe, moreover, that this is a finding which goes unnoticed, and there should be awareness of its association with intradural hernias.

(KEY WORDS: Herniated Disc, Vacuum Phenomenon, Intradiscal gas)

Intradiscal gas has been associated with tumors, infections, traumatisms, discal injection procedures or procedures carried out in the canal for therapeutic or diagnostic reasons, deposits of calcic pyrophosphate, alcaptonuria, and in particular, with disc degeneration (17)(20). Analyses of intradiscal gas have revealed that it was 90-92 % nitrogen, combined mainly with oxygen and carbon dioxide (8).

The frequency of the phenomenon of intradiscal vacuum has been seen in up to 20.8 % asymptomatic patients (11) when simple radiology was used, and in up to 46 % of cases when the diagnostic medium used was the scanner (17).

However, the existence of gas within the spinal canal has been seen on 29 occasions from the world´s literature (1-5)(7)(9)(11)(13)(14)(18)(19)(21-24), of which 14 were associated with proven disc herniations (1-3)(5)(7)(9)(11)(13)(14)(18)(19) (TABLE No. 1).

In this study 19 more cases of intraspinal gas due to disc herniation will be presented.

See table No. 2.

FIGURES No. 1, 2, 3, 4

The finding of gas in the disc is something frequent in clinical practice, and it is a proven fact in the literature. The existence of gas in spinal canal, due in most cases to disc herniation, is a fact rarely found in the literature (TABLE No. 2). Nevertheless, in spite of this we contribute 19 cases to the literature on intraspinal gas due to disc herniations, which were treated succesfully in 6 cases by laminectomies or laminotomies with exeresis of the disc. In the remaining cases up till now surgical treatment has not been necessary.

It has been confirmed radiologically that the phenomenon of vacuum increases with extension and decreases with flexion of the rachis (16)(17) due to the negative pressure which is produced with hyperextension of the rachis.

Although DICKSON (6) indicates that the presence of gas within the medullar canal is pathognomonic of a disc herniation is not exact, and besides this possibility the gas within the spinal canal can be produced by a leak of gas of the facet joint (11), or of the disc (2)(5)(11)(22)(24) without a "true" disc herniation. Moreover in some cases the gas can be found within a intraspinal synovial cyst of the facet joint (12)(15)(21)(23) or forming a pseudocyst in relationship with the disc space (4).

GULATI (11) makes a difference between spinal gas associated to a disc herniation and gas produced by other causes. In the former case the gas is found only in the position where the herniation is situated being surrounded by soft disc material, while in the latter case the gas can be found surrounding the epidural space.

On three ocassions of those published cases there were intradural disc herniations (1)(5)(14), and given the low number of this type of hernias, the frequency of association between intradural disc herniation and intraspinal gas is worthy of note.

For GERSHOM (10), GULATI (11) and MORTENSEN (18) the cases correspond to chronic patients, more to cases of canal stenosis than to acute herniated disc, and in most cases they were related to patients of advanced age. This data accords in general terms with ours, mainly as regards development time. In all but six cases the disc herniation was to be found in the L5-S1 space.

Surgery was necessary in 6 of our cases, producing relief of symptoms. The other patiens have improved for the time being with NSAIDs and physical treatment. In patients who were not operated on the existence of infection or a tumor was ruled out through additional examinations.

In all cases operated on, a great quantity of nucleus material was found within the herniation, something which for MORTENSEN (18), only occurred in 2 out of his 4 cases. On the other hand ELSTER (7) reported a vacuum phenomenon in the cervical spine canal associated with a herniated disc confirmed at the surgery time, but he was not able to confirm the existence of disc material surrounding the gas on computed tomography; so this fact does not exclude that the gas lies within a disc herniation.

We consider that intraspinal gas is much more frequent than published, and it´is associated in most cases with disc herniations. This finding has no clinical consequences, although one must appreciate its probably association with intradural disc hernias. Our opinion is that intrahernial gas is not infrequent, although it goes unnoticed in the vast majority of radiological studies and principally in scanner.

1- ANDA S, DALE LG, VASSAL J: Intradural disc herniation with vacuum phenomenon: CT diagnosis. Neuroradiol. 29, 407, 1987.

2- AUSTIN RM, BANKOFF MS, CARTER BL: Gas collections in the spinal canal on computed tomography. J. Comput. Assist. Tomogr. 5: 522, 1981.

3- CHAFETZ N, GENANT HK: Computed tomography of the lumbar spine. Orthop. Clin. North. Am. 14: 147, 1983.

4- DEMIERRE B, RAMAMDAN A, HAUSER H: Radicular compression due to lumbar intraspinal gas pseudocyst: Case report. Neurosurg. 22: 731, 1988.

5- DILLON WP, KASSEF LG, KNACKSTEDT VE, OSBORN AG: Computed tomography and differential diagnosis of the extruded lumbar disc. J. Comput. Assist. Tomogr. 6: 969, 1983.

6- DICKSON RA: Spinal Surgery. Science and practice. Ed. BUTTERWORTHS. LONDON 1990, 96.

7- ELSTER A, JENSEN K: Vacuum phenomenon within the cervical spinal canal: CT demonstration of a herniated disc. J. Comput. Assist. Tomogr. 8: 533, 1984.

8- FORD LT, GILULA LA, MURPHY WA, GADO M: Analysis of gas in vacuum lumbar disc. A.J.R. 128: 1056, 1977.

9- FRIES JW, BODEELY DA, VIJUNGCO JG, YEAGER VL, GAFFEY WR: Computed tomography of herniated and extruded nucleous pulposus.J. Comput. Assist. Tomogr. 6: 875, 1982.

10- GERSHON-COHEN J, SCHRAER H, DKIAROF DM and cols.: Dissolution of the intervertebreal disc in the aged normal: The phantom nucleous pulposus. Radiology 62: 383, 1954.

11- GULATI AN, WEINSTEIN ZR: Gas in the spinal canal association with the lumbosacral vacuum phenomenon: CT findings. Neuroradiol. 20: 191, 1980.

12- JACKSON MD, ATLAS SW, MANI JR, NORMAN D: Intraspinal synovial cysts: MR imaging. Radiology 170: 527, 1989.

13- KAISER MC, CAPESIUS P, VEIGA-PIRES JA, BRUCH JM: Recognition of gas containing disc herniation on lateral CT-scoutview. Neuroradiology 29: 98, 1987.

14- KAISER MC, SANDT G, ROILGEN A, CAPESIUS P, POOS D, OHANNA F: Intradural disk herniation with CT appearance of gas collection. AJNR 6: 117, 1985.

15- KIELY MJ: Neuroradiology case of the day. Lumbar synovial cyst. AJNR 160: 1336, 1993.

16- KNUTSSON F: The vacuum phenomenon in the intervertebral discs. Acta Radiol. 23: 173, 1942.

17- LARDE D, MATHIEU D, FRIJA G, GASTON A, VASILE N: Spinal vacuum phenomenon: CT diagnosis and significance. J. Comput. Assist. Tomogr. 6: 671, 1982.

18- MORTENSEN WW, THORNE RP, DONALDSON III WF: Symptomatic gas-containing disc herniation. Report of four cases. Spine 16: 190, 1991.

19- ORRISON WW, LILLEAS FG: CT demonstration of gas in a herniated nuleous pulposus. J. Comput. Assist. Tomogr. 6: 807, 1982.

20- RESNICK D, NIWAYAMA G, GUERRA J, VINTON V, USSELMAN J: Spinal vacuum phenomena: Anatomial study and review. Radiology 139: 341, 1981.

21- SCHULZ EE, WEST WL, HINSHAW DB, JOHNSON RJ: Gas in a lumbar extradural juxtaaricular cyst: Sign of synovial origin. AJR 143: 875, 1984

22- SIMONETTI G, MARTINO V, SANTILLI S, CHIAPETTA F: Lumbar root compression by a gas containing cyst in the extradural space. Case report. J. Neurosurg. Sci. 36: 101, 1992.

23- SPENCER RR, JAHNKE RW, HARDY TL : Case report. Dissection of the gas into a intraspinal synovial cyst from contiguous vacuum facet. J. Comput. Assist. Tomogr. 7: 886, 1983.

24- TEPLICK JG, TEPLICK SK, GOODMAN L, HASKIN ME: Pitfalls and unusual findings in computed tomography of the lumbar spine. J. Comput. Assist. Tomogr. 6: 888, 1982.

Figure 1 and 2. Computed tomographic scans of the case Nº 10 demostrating gas in the spinal canal

Figure 3. Computed tomographic scan of the case Nº 9

Figure 4. Computed tomographic scan of the case Nº 8

TOTAL 29 14

* CASES WITH INTRADURAL DISC HERNIATIONS

** THE ONLY CASE OF CERVICAL DISC HERNIATION