Answer to the letter to the editor: “A case of cervical pneumorrhachis induced by the combination of pneumomediastinum and root avulsion injuries” concerning “Pathogenesis, diagnosis and management of pneumorrhachis” (by M. Oertel et al.)

Abstract

We greatly appreciate the interest the authors have shown in our article on pathogenesis, diagnosis and management of pneumorrhachis [3]. The pathophysiology and aetiologies of pneumorrhachis are known to be multifold with intraspinal air being almost always associated with further air distributions in other parts of the body [3]. Nevertheless, the occurrence of pneumorrhachis secondary to pneumomediastinum has rarely been reported and the coexistence of spinal and mediastinal emphysema with nerve root avulsion injuries is an exceptional finding. Only one case of pneumorrhachis associated with pneumomediastinum and root avulsion of nerve plexuses was previously described [1]. The authors now have added a case of traumatic secondary cervical pneumorrhachis induced by a combination of pneumothorax, pneumomediastinum, subcutaneous emphysema, and cervical nerve root avulsion injuries. Similar to the case described by Harris et al. [1], traumatic avulsion of spinal nerve roots with tearing of associated nerve sheaths may have allowed air to enter the intraspinal subarachnoid space following thoracic injury with pneumomediastinum. Alternatively, spreading of mediastinal air may have occurred through fascial planes of the posterior mediastinum along the nerve plexuses and great vessels into the spinal epidural space behind the driving pressure of the pneumothorax and pneumomediastinum. It is well documented that air may dissect due to a one-way valve mechanism between the paraspinal soft tissues along the pleura into the spinal canal via the neural foramina and along the vascular and neural sheaths thereby producing pneumorrhachis [3]. Another potential pathway described whereby mediastinal air may reach the intraspinal space is by means of embolization of air through the intercostal and mediastinal veins into the paravertebral and vertebral vein plexuses and subsequently into the epidural intraspinal canal [2]. These findings indicate, that the differentiation between spinal epidural and subarachnoidal air and their coincidence could be helpful in diagnosis and treatment of the pathophysiologic mechanism and aetiologies causing pneumorrhachis. The present case is not only interesting because it adds a less common mechanism of air introduction into the spinal space to the long list of pathogenesis and causes of pneumorrhachis. It also makes clear that the diagnosis of pneumorrhachis especially in the trauma setting calls for a search for underlying pathologies and potential pathways of air entry into the spinal canal including occult meningeal lacerations with associated leakage of cerebro-spinal fluid or spinal and neural injuries.