Clearing the air around spontaneous pneumorrhachis

INTRODUCTION

The Association of pneumorrachis with cancer is almost unknown, with only one case being reported previously in a patient with metastatic esophageal carcinoma. Even then, this patient had gas formation within an epidural metastatic deposit, as a likely explanation of the pneumorrachis. Our patient did not have any such deposits to the spine, and as such no obvious cause of the pneumorrachis could be determined.

CASE REPORT

A 16-year-old boy with Hodgkin lymphoma Stage IIA (early-stage unfavorable disease) was planned for chemotherapy with 6 cycles of adriamycin, etoposide, vinblastine, and dacarbazine. On day 28 of 1^st cycle of chemotherapy, he presented with complaints of cough associated with white-colored sputum and chest pain for 2 days. He also gave a history of nausea and retching. He gave no history of trauma or invasive procedure. There was no history of cigarette smoking or the use of recreational inhalants.

On physical examination, his respiratory rate was 22/min, heart rate of 145/min, blood pressure of 110/62, oxygen saturation of 100% on room air, and 98°F temperature. He appeared uncomfortable and coughed excessively but no signs of laborious breathing were observed. Non-contrast computed tomography scan of chest computed tomography (CT) performed for the assessment of infective focus in the chest demonstrated a patch of consolidation in the superior lingular segment of the left upper lobe with few nodules in bilateral lower lobes. These changes were radiologically deemed to be infective in etiology. Moreover, there were substantial pneumorrachis throughout the cervical, dorsal, and lumbar spinal canal with a mild component of pneumomediastinum demonstrated in Figures 1-3. However, no evidence of pneumothorax was seen. Pneumocephalus was ruled out by taking a plain brain CT. Considering the history of nausea, retching, and chest pain, oral contrast was given to the patient to rule out occult esophageal perforation. There was no extravasation of contrast from the esophagus. No apparent cause of pneumorrhachis was found on the CT scan.

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Figure 1:

(a) Axial computed tomography (CT) section at the level of oropharynx showing air in the pre-vertebral space. (b) Sagittal reformatted CT section showing air in the cervical segment of spinal canal.

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Figure 2:

(a) Axial computed tomography (CT) section at the level of lung apices showing air tracking through spinal nerve roots to the spinal canal. (b) Axial CT section showing pneumomediastinum and air lining vascular structures.

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Figure 3:

(a) Sagittal reformatted sections showing air in the spinal canal in the thoracolumbar level. (b) Follow-up image after 20 days shows complete reabsorption of intraspinal air.

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Diagnosis of spontaneous pneumorrhachis was made and since the patient was hemodynamically stable, he was kept under observation. He was treated with a course of oral broad-spectrum antibiotics and cough suppressants for respiratory tract infection. At the time of discharge, he was counseled to keep a close watch for symptoms such as sensory or motor weakness and to immediately report them to the treating physician. A repeat scan for the evaluation of pneumorrhachis was scheduled after 14 days or earlier if there were any neurological symptoms.

The patient did not develop any neurological symptoms, and on the follow-up scan after 2 weeks, complete resolution of the pneumorrhachis was seen. A comparison of previous CT and follow-up CT is shown in Figure 3b. (All the images taken from the CT scan were obtained using a 16-slice Siemens machine with 100 mAs and 120 kv).

DISCUSSION

Pneumorrhachis is a rare phenomenon and is characterized by the presence of air in the spinal canal.^[1] This finding has also been described as epidural pneumatosis, intraspinal pneumocele, spinal emphysema, pneumosaccus, and aerorhacia in the literature.^[2] Pneumorrhachis can be due to iatrogenic, traumatic, and non-traumatic causes.^[3]

The underlying pathophysiology is postulated to be increased intra-alveolar pressure (for example, excessive prolonged coughing, forceful vomiting, asthma, etc.^[4]), leading to rupture of alveoli, due to which air travels along the pulmonary perivascular interstitium and dissects along the fascial planes.^[5] As the pressure in the mediastinum is lower than the lung periphery, the air dissects toward the hilum of the lung and leads to pneumomediastinum. This sequence of events is described as the Macklin effect.^[6] Free entry of posterior mediastinal air into the epidural space through neural foramina can be explained by the lack of true fascial protection to the epidural space.^[5] Because of the low resistance from the loose connective tissues as compared with the rich vascular network present anteriorly, the dissected air preferably collects in the posterior epidural space.^[7]

Free air in the spinal canal can be localized as internal or external pneumorrhachis. Internal is intradural pneumorrhachis which means the air in the subdural or subarachnoid space and external means air in the extradural space.^[6] Intradural air is generally seen after trauma and represents severe injury.^[3]

Tracing the source of air in the spinal cord forms the basis of diagnostic workup once pneumorrhachis is spotted. This air can be due to surgical or invasive procedure, perforation of trachea or bronchus, rupture of the esophagus, bronchial asthma, post-intermittent positive pressure ventilation, extension of pneumoperitoneum, as a result of prolonged coughing, or can be spontaneous.^[8]

Concurrent pneumorrhachis with spontaneous pneumomediastinum and without pneumothorax is an extremely rare phenomenon.^[9] Rather pneumorrhachis is present in up to 10% of cases of spontaneous pneumomediastinum.^[6] Pneumorrhachis is mostly asymptomatic.^[6] Rarely, it can give rise to symptoms of cord compression, neurological deficits, or meningitis.^[6]

Since in majority of the cases, pneumorrachis is an asymptomatic phenomenon, its diagnosis is more likely to be on imaging, instead of on clinical findings.^[8] A CT scan is the best tool for diagnosis since it can depict a minute amount of air and can rule out other grim differential diagnoses leading to pneumorrhachis.^[1] However, even for CT, differentiating between intra- and extra-dural air is difficult.^[7]

Due to the rarity of the phenomenon, no clear guidelines exist for management. Most cases are treated with conservative measures as air is spontaneously reabsorbed by the blood.^[1] There is a theoretical benefit of introducing high-flow oxygen as it can increase the oxygen content of the entrapped gas, leading to more rapid absorption.^[10,11] Surgical intervention is needed in cases associated with persistent spinal fluid leak or entrapment of air in the spinal canal due to the formation of a one-way valve.^[12] Surgical intervention is also needed in thoracoarachnoid fistula and lung injuries.^[1]

In our patient with Hodgkin’s Lymphoma, the presence of cough most likely led to pneumorrhachis instead of underlying Hodgkin’s lymphoma. In cases of spontaneous pneumorrhachis, observation and control of cough, emesis, or asthma become important if it is present.^[4] A detailed review of available literature was done and is represented year-wise in the tabulated format in Tables 3-7.

CONCLUSION

Dominant pneumorrhachis in the absence of pneumothorax and the presence of only mild pneumomediastinum makes this case unique, discounting the theory proposed by Liao regarding positive alveolar pressure causing an alveolar rupture in cases of spontaneous pneumorrhachis being the predominant mechanism of air tracking into the mediastinum.