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Neuroradiology Case of the Week

Case 359

October 2008

Jonathan R. Wood, BS and P-L Westesson, MD, PhD, DDS

Clinical Presentation: A 66-year-old man was transferred from an outside hospital for management of aspiration pneumonia which required intubation and mechanical ventilation. After treatment in the medical ICU for approximately 2 months, he developed labile blood pressures. A head CT was ordered to evaluate for an intracranial process along with a chest CT to evaluate for interval change in his pneumonia.

Imaging Findings:
Head CT showed no acute intracranial hemorrhage, midline shift, or extra-axial fluid collection. Old lacunar infarcts were present in the basal ganglia bilaterally and the right corona radiata. There was decreased attenuation of the periventricular white matter. Fluid was present in the sphenoid sinuses and the mastoid air cells were opacified. There was diffuse subcutaneous emphysema at the skull base.
Chest CT demonstrated interval decrease in bilateral lung opacities with pulmonary interstitial emphysema. There was an extensive pneumomediastinum tracking superiorly and inferiorly with involvement of the anterior abdomen.

Diagnosis: Cervical subcutaneous emphysema in association with a spontaneous pneumomediastinum

Discussion: Cervical subcutaneous emphysema is the presence of gas in the fascial spaces underneath the cervical skin and is commonly caused by iatrogenic injury such as mechanical ventilation, surgery, and endoscopy. Ventilation can cause injury by traumatic intubation or barotrauma. The most common surgeries that have reportedly caused subcutaneous emphysema are adenotonsillectomies, dental surgery, and other procedures in the pharynx, trachea, and esophagus [1].
     Barotrauma is a well known cause of cervical subcutaneous emphysema as well as the presence of air in the retropharyngeal space. Rupture of either alveoli or a subpleural bleb allows air into the pulmonary interstitium where it dissects along the pulmonary vasculature and into the mediastinum. In the mediastinum there are two common pathways for air to extend into the neck. First is the anatomic communication between the mediastinum and a potential space in the deep neck, commonly referred to as the danger space. The danger space is continuous from the diaphragm at the inferior to the base of the skull superiorly. The anterior wall is formed by the alar fascia and the posterior wall by the prevertebral fascia. The lateral walls of the danger space are formed by the fusion of the alar and prevertebral fascia at the transverse vertebral processes. Contents in the mediastinum can extend up the danger space, into the retropharyngeal space, and then into the parapharyngeal space. The second anatomic communication is a direct connection between the mediastinum and the anterior visceral space contained within the deep cervical fascia. Air can extend through the anterior visceral space into the subcutaneous tissue of the neck. Air in the cervical subcutaneous tissue or retropharyngeal space is indicative of a possible pneumomediastinum that needs to be investigated.
     Common symptoms of spontaneous pneumomediastinum are acute onset retrosternal pain radiating to the back or shoulders, sore throat, dysphagia, odynophagia, and generalized neck pain. Respiratory symptoms are uncommon without coexisting pulmonary disease. Mediastinal crepitus (Hamman's sign) is pathognomonic for mediastinal emphysema and other common signs are decreased cardiac dullness to percussion and cervical subcutaneous emphysema [3].
     Esophageal rupture, known as Boerhaave's syndrome, is commonly confused with spontaneous pneumomediastinum because of their similar clinical presentations early in the disease. It is important to distinguish these two entities because Boerhaave's syndrome is a potentially fatal medical emergency while a spontaneous pneumomediastinum is self-limited. The distinction between these two syndromes can be made radiographically. Mediastinal emphysema from a spontaneous pneumomediastinum is usually located at the level of the lung hili and superiorly. Mediastinal emphysema from Boerhaave's syndrome tends to be located posteriorly and inferiorly beneath the parietal pleura and left hemidiaphragm. Spontaneous perforation of the esophagus also can cause a reactive pneumonitis in the posterior basilar left lower lobe causing retrocardiac opacification and silhouetting of the aorta. A unilateral left pleural effusion is also commonly seen. The diagnosis can be confirmed by a contrast medium swallow which will show extravasation of contrast into the pleural cavity in Boerhaave's syndrome. Initially a water-soluble contrast should be used since barium can cause severe mediastinitis and possibly increase morbidity and mortality [5].

References:

1. Joanes V, Gallego JM. Extensive craniofacial subcutaneous emphysema after evacuation of a chronic subdural haematoma. Acta Neurochir (Wien). 2003 Aug;145(8):713-4; discussion 714. [PubMed]
2. Cavuslu S, Oncul O, Gungor A, Kizilkaya E, Candan H. A case of recurrent subcutaneous emphysema as a complication of endotracheal intubation. Ear Nose Throat J. 2004 Jul;83(7):485-8. [PubMed]
3. Granich MS, Klotz RE, Lofgren RH, Partlow RC Jr, DiGregorio LI. Spontaneous retropharyngeal and cervical subcutaneous emphysema in adults. Arch Otolaryngol. 1983 Oct;109(10):701-4. [PubMed]
4. Levine PA. Hypopharyngeal perforation. An untoward complication of endotracheal intubation. Arch Otolaryngol. 1980 Sep;106(9):578-80. [PubMed]
5. Rogers LF, Puig AW, Dooley BN, Cuello L. Diagnostic considerations in mediastinal emphysema: a pathophysiologic-roentgenologic approach to Boerhaave's syndrome and spontaneous pneumomediastinum. Am J Roentgenol Radium Ther Nucl Med. 1972 Jul;115(3):495-511. [PubMed]