Systemic air embolism and decompression illnes in a scuba diver.

Clinical History

A 27-year-old woman arrived at our emergency department with loss of consciousness after two dives at the depth of 40 meters during the morning. After cardiopulmonary resuscitation, the patient underwent a non-enhanced cerebral and chest CT scan in order to exclude pneumothorax before the hyperbaric oxygen therapy(HBOT).

Imaging Findings

Chest CT shows small gas endovascular bubbles, localized in retroclavear position, posterior to the sternal manubrium bilaterally and in the main pulmonary artery. Other gas bubbles were incidentally detected on the lower slices of thoracic CT, into the inferior vena cava and in some portal branches for the left hepatic lobe. At the CT performed 3 days later, only some small gas bubbles in the inferior vena cava at the level of the renal veins still persist.

At the neuroimaging, CT shows an area of low attenuation in the cortical regions of parietal lobes bilaterally, in the right cerebellar medium peduncle involving the omolateral cerebellar lobe and in the right basal ganglia. Other findings are loss of gray white matter differentiation and effacement of cerebral sulci. Brain and spine MRI confirm cerebral ischemic lesions and shows areas of hyperintensity on DWI and T2WI, involving also the spinal cord at T8-T9 levels.

Discussion

The decompression illness (DCI) includes all clinical events induced by a fast reduction in environmental pressure, sufficient to form nitrogen gas bubbles previously present in the tissues or blood in a soluble phase. After a deep dive, if the rise is too fast, the bubbles are formed too rapidly and the body fails to eliminate them; the air bubbles are then trapped in tissues and blood, causing ischemic damage [1]. Venous and portal gas embolism (VGE) is frequently found in the venous circulation after diving activities and is usually asymptomatic [2]; but when excessive quantities of gas (over 50 ml) enter into the venous system, cardiovascular collapse can be caused [3]. Every VGE has the potential to evolve into an arterial gas embolism (paradoxical embolism): patent foramen ovale, increased venous return (coughing or Valsalva maneuver), increased pulmonary artery pressure, intrapulmonary shunts, and pulmonary barotrauma [1-3]. Once a bubble is in the arterial side the obstruction of small functional end-arteries is more serious in coronary and cerebral circulation[4]. Mechanisms of damage are multiple: arterial occlusion, venous infarction and in situ nitrogen direct toxicity [1]. Main radiological findings are the presence of air bubbles of various sizes in the vascular bed, both arterial and venous, and in the parenchymal organs. In our case there were no bubbles in the arterial circulation, but their presence is indirectly documented by severe neurological symptoms. In fact, CT and MR findings suggest hypoxic injury: arterial occlusion determines especially the cerebral lesions while venous occlusion may play a main role in spine lesion [1]. Other described DCI lesions are acute kidney injury and hepatobiliary injury [5, 6]. Radiological investigations are not routinely reported in the assessment of decompression illness, mainly if there were a delay hyperbaric therapy (mandatory in case of arterial gas embolism, neurological or cardiovascular symptoms) [7, 8]. The literature reports that imaging may help to support the diagnosis of DCI [9], to discriminate between the two types of DCI if clinic is not clear (Type I with symptoms involving skin, skeletomuscular system, or lymphatic system, and Type II with neurological symptoms) [10] or to exclude other causes of venous and portal gas embolism, which may have differential diagnosis (non-related acute coincidental illness) [7]. Immediately the patient underwent HBOT, where the ambient pressure is raised and air is 100%O2. The aim is immediate reduction in bubble volume, increasing the diffusion gradient for inert gas and oxygenation of ischemic tissue [4]. Eight days later the patient was awakened from coma and started rehabilitation.

Differential Diagnosis List

Final Diagnosis

Systemic air embolism and decompression illness.

URL:	https://eurorad.org/case/14140
DOI:	10.1594/EURORAD/CASE.14140
ISSN:	1563-4086