1 INTRODUCTION

Pneumorrachis is a rare condition. We report two cases of radiculopathy caused by spontaneous pneumorrachis. Patients complain for back pain. The radiological findings showed the intra spinal gas comprising the nerve root. Conservative treatment was sufficient to improve symptom.

Pneumorrachis is a rare phenomenon defined as the presence of intraspinal air. It can be caused by various etiologies, mainly trauma, and medical procedures such as spine surgery or epidural anesthesia. Less common causes of pneumorrachis include spinal infection, tumoral, or degenerative disk diseases. It is usually an asymptomatic and incidental imaging finding. However, it can seldom lead to radicular or spinal nerve compression.¹

We report herein two cases of spontaneous pneumorrachis due to degenerative disk disease and discuss the mechanism, diagnosis, and management of this rare condition.

2 CASE 1

A 78-year-old woman presented with a 1-year history of progressive low back mechanical pain associated with low right limb paraesthesia. She has no history of trauma or spinal surgery. The lumbar spine range of motion was limited (Schober's test = 10 mm) and the Leri test was positive. The neuromuscular examination was unremarkable. Biochemical investigations were normal (Table 1).

The plain X-ray of the spine showed disk space narrowing at L4-L5 and L5-S1. Computed tomography (CT) visualized a degenerated L4-L5 disk with a vacuum phenomenon as well as a moderate protrusion at L5-S1 space. A gas bubble was noticed in the right lateral recess at L4-L5 with probable evidence of right L4 root compression (Figure 1).

The patient was treated conservatively with analgesics combined with spine rehabilitation.

3 CASE 2

A 61-year-old, retired sheet metal worker, with chronic low back pain presented with a 2-month history of left sciatica that irradiated to the foot in the L5 dermatome. Past medical history was unremarkable. There was no paraesthesia, weakness, or bowel or bladder dysfunction. Physical examination demonstrated a full range of motion. Motor and sensory functions were normal and the straight leg-raising test was positive in the left. Biological tests showed hemoglobin level at 13 g/dl, white blood cell count 7600 elements/mm³, C-reactive protein and erythrocytes sedimentation rate at 5 mg/L and 17 mm; respectively.

Radiographs showed degenerative changes in the lumbar spine. CT scans demonstrated a foraminal disk protrusion with intradiscal gas compressing the left L5 nerve root (Figure 2). The patient improved on conservative management or symptomatic treatment (Table 2).

4 DISCUSSION

In addition to trauma causes, other air sources may be found as epidural infection with gas-producing organisms, air introduction via lumbar puncture, or spinal surgery. Relatively rare, the presence of epidural gas in the degenerative spine was reported in a few cases of literature, secondary to vacuum phenomenon.

The vacuum phenomenon is a radiological finding defined as the presence of gaseous collection in the intervertebral disk space resulting from the movement of the spine, especially extension and traction.² It is a common finding that has been detected or reported in 46% of patients aged over 40 years.³

The intradiscal gas diffuses from the extra-cellular fluid into areas of subatmospheric pressure and it cannot be reabsorbed because the degenerated disk is avascular. Some authors have discussed the role of disk aging in the genesis of the gas.^{2, 4} This would be due to dehydration and the decrease in the proportion of proteins in the disk.⁵ The gas is composed of 90%–92% nitrogen along with oxygen, carbon dioxide, and other trace gases.^{2, 6}

The vacuum phenomenon has been mostly observed in L5-S1 disk with decreasing frequency at a higher lumbar level.⁷

Whereas the vacuum phenomenon is a common finding, the presence of gaseous collection within the spinal canal is unusual. The gas formation is often associated with a disk herniation such as in our second case, but it can also be found free within the spinal canal as in the first case.^{8, 9}

In most previous cases, the gas-containing cyst has been noticed at the level of an intervertebral disk with a vacuum phenomenon suggesting that the gas is originated from the intervertebral disk.¹⁰

Interestingly, the gas can migrate to the spinal canal within a degenerated nucleus pulposus, resulting in a gas-containing disk herniation. Otherwise, the gas that fills the disk is expulsed in the spinal canal by a “valve-pump” mechanism through ruptures in the annulus fibrosus and collects under pressure within a fibrous capsule or a pseudo-capsule.⁶

The histological study of a few cases of free gas noticed that the gas cyst was surrounded by the posterior longitudinal ligament (PLL) suggesting that air coming from the disk was trapped between the PLL and the bone. Furthermore, no recurrence has been observed after the PLL removal.^{11, 12} Damierre et al. reported the case wherein gas aspiration was failed due to the persistence of pseudo capsules. Surgical removal of membrane proved identical PLL tissue of capsule and improved patient pain.¹¹

Mostly asymptomatic, only a few cases of intraspinal gas can cause compressive radiculopathy. The clinical features are similar to those of common sciatica. Moreover, we can notice an exacerbation of the pain at the change of positions reflecting the free movements of the air in the epidural space.¹³ Furthermore, only a few cases reported neurological symptoms as lower extremity paresthesia and paralysis. An acute cauda equina syndrome and cervical myelopathy have been reported.^{14, 15}

On standard spine x-rays, we often notice degenerative modifications of the spine and sometimes a vacuum phenomenon.¹³

CT scan is currently the imaging tool of choice to diagnosis pneumorrachis showing the degenerative modifications of the spine with a vacuum phenomenon and, at the same level, the intraspinal gas collection with a density from −200 to −900 Hounsfield units.¹⁶ On MRI, gas is seen in low signal on the T1 and T2 weighted sequences.¹⁶

For the management of intraspinal gas, most authors recommend conservative therapy including bed rest, analgesics, non-steroidal anti-inflammatory drugs, myorelaxant drugs, and epidural glucocorticoid injections.¹⁶ Intraspinal gas may disappear spontaneously.^{17, 18} In our cases, we noticed an improvement without using invasive procedures.

Some authors reported the efficacy of the CT-guided aspiration of the gas cyst.^{19, 20} However, in some cases, intraspinal gas recurred with a relapse of the radicular syndrome.^{10, 11} Indeed, this procedure does not modify the local environment, and the origin of the air remains.

Surgery is the preferred treatment for patients who failed to respond to conservative therapy. The procedure combines gas evacuation with a disk curettage to prevent recurrence.^{12, 21-25}

5 CONCLUSION

Pneumorrachis caused by degenerative disk disease is a rare condition that can rarely lead to a radicular syndrome. Its prevalence increases with age and it may be due to two mechanisms: a gas-containing disk herniation or an intraspinal free gas. CT scan is the preferred imaging technique. The treatment is conservative at first. CT-guided needle aspiration can be suggested despite the risk of relapse. Surgery remains the treatment of choice in case of neurological signs or recurrence under conservative treatment.

CONFLICT OF INTEREST

None declared.

AUTHORS CONTRIBUTIONS

HLF, KM, DBN, and WT: analyzed and interpreted the patient data and provided advice for treatment. DK ensured the clinical follow-up of the patient. LBA wrote the manuscript; and all authors: read, revised, and approved the final manuscript.

CONSENT

Written informed consent was obtained from the two patients for the publication of this case report.