Teaching Case

A 19-year-old Caucasian male with no medical or surgical history presented at the emergency department for intermittent diffuse abdominal pain since 5 days. He complained of nausea, incoercible vomiting and loss of appetite. The patient was a known user of cannabis. Physical examination showed abdominal, thoracic and dorsal widespread subcutaneous emphysema.

Thoracic CT scan was performed because of the widespread extent of the subcutaneous emphysema. CT confirmed an extensive pneumomediastinum (Figure 1) but no pneumothorax. It also revealed a significant amount of air in the epidural space of the spinal canal from C6 to D12 (Figure 2). The patient was admitted for observation. The CT scan was repeated on the fifth day of hospitalization and showed an important decrease of the pneumomediastinum and subcutaneous emphysema. The component of air within the spinal canal had also decreased in volume. The patient was then discharged.

Background

The presence of air in the spinal canal is a known radiological finding. It was described for the first time in 1977 by Gordon and Hardman [1] as a traumatic pneumomyelogram in a patient with a skull base fracture. Over the years, few other cases reporting this finding have been published, dubbing it Pneumorrhachis (PR). Overall, fewer than 150 cases have been described in the literature as of 2018 [2]. A recent study by Behr et al. [2] however examined a population of 242 patients with pneumomediastinum and identified 14 patients with PR. A prevalence of 5.8% then gives rise to the notion PR may simply be underreported.

Clinical Perspective

The presence of air in the spinal canal is a finding that is usually associated with trauma. In absence of trauma, it is usually spontaneous and associated with pneumomediastinum as well as various conditions presenting with elevated intrathoracic pressure. When spontaneous, there exists a predilection for young illicit drug users (3,4,5). PR may be intradural or extradural. The former is associated with severe trauma, the latter being mostly spontaneous and innocuous [3]. Manoeuvres that raise intrathoracic pressure such as the Valsalva manoeuvre, create high intra-alveolar pressure. The distended alveoli may then rupture (the Macklin effect) [6]. Balachandran et al. hypothesized that due to the absence of fascial barriers between the posterior mediastinum and the retropharyngeal and epidural spaces, free air in the mediastinum and cervical soft-tissues may enter the paraspinal tissues and travel through neural foramina alongside the neurovascular bundle into the epidural space [7]. In our case, the pneumomediastinum probably occurred secondary to a Valsalva manoeuvre after forceful vomiting and/or attempts to maximize inhaled drug absorption (‘huffing’) [8].

Imaging Perspective

In general, the diagnosis of pneumomediastinum can be made on plain chest radiography if PR should be associated with increased severity of pneumomediastinum [9], CT should be the preferred diagnostic method of choice to assess pneumomediastinum as conventional imaging cannot detect PR, although treatment and outcome would probably remain unaffected.

Outcome

PR usually resolves spontaneously without neurologic sequelae. Conservative treatment is suggested, however, the accumulation of gas may cause intracranial and intraspinal hypertension causing hypotension [3]. Rarely PR may give rise to cord compression, requiring decompressive surgery [10].

Take-Home Message / Teaching Points

PR is an underreported sign that is commonly associated with pneumomediastinum. In the absence of trauma, PR is often associated with illicit drug use.