Teaching Case

A 21-year-old girl was admitted for investigation of a sudden onset of chest pain, dyspnoea and cough. She had a previous history of severe asthma.
There was subcutaneous emphysema of the neck and upper part of the chest.
Lung auscultation revealed wheezes. The remainder of general and neurological examination was normal.

The admission chest radiograph showed signs of pneumomediastinum and extensive subcutaneous emphysema in the neck and upper thorax (figure 1).
To better delineate the extent of air dissection into the neck and mediastinum the patient underwent computed tomography, which confirmed the presence of pneumomediastinum and subcutaneous emphysema (figure 2a). It also depicted air dissecting the neural foramen into the epidural space of the spinal canal (pneumorrhachis) at the cervicothoracic region (figure 2b, c).
A follow-up CT showed considerable resolution of pneumomediastinum, subcutaneous emphysema and pneumorrhachis, with no evidence of mediastinitis.

Pneumorrhachis is the presence of air in the epidural space which can be seen in various situations, the most common causes being iatrogenic or traumatic. Pneumorrhachis secondary to spontaneous pneumomediastinum is rare, with less than 50 cases having been reported in the literature [1].
The typical patient is a male adolescent or young adult with bronchial asthma or a very recent history of hyperpnoea, illicit drug inhalation, vomiting, coughing or air travel. In all these cases, the primary aetiology suggested is alveolar rupture with secondary passage of air into the mediastinum [2].
It is well known that because of the absence of a fascial barrier between the posterior mediastinum and retropharyngeal space, the air may dissect along fascial planes from these spaces into the spinal canal through the neural foramina, which is not protected by a true fascial envelope. Our observation of air distending the cervical neural foramen supports this view.
Superiorly, the space is anatomically closed at the foramen magnum where the spinal dura attaches to the endosteal dura of the cranium, therefore air cannot extend intracranially [3].
Of 42 recently published cases of pneumomediastinum documented by CT, pneumorrhachis was observed in four (9.5%), suggesting that in spontaneous pneumomediastinum, pneumorrhachis is uncommon but not exceptional [4]. Pneumorrhachis is known to be a benign complication, and more importantly, in patients with spontaneous pneumomediastinum, pneumorrhachis is neurologically asymptomatic, as in our case, and self-limited in 98% of the cases [2].