Teaching Case

A 42-year-old man with no previous illness, was admitted for persistent cough, dyspnoea and headache several hours after recreational diving with rapid ascent.

The chest CT scan showed diffuse ground-glass attenuation involving the most anterior aspect of the upper lobes, the right middle lobe and the medial segments of the lower lobes. The periphery of the lung parenchyma was not involved. There was no thickening of the interlobular septa or consolidation. No pneumothorax, pneumomediastinum, pleural or pericardial effusion or lymphadenopathy. (Fig. 1)

The patient was treated with hyperbaric oxygen therapy. The follow up CT performed two weeks later demonstrated resolution of prior diffuse ground-glass attenuation areas (Fig. 2).

Decompression illness is the result of intra-or extravascular bubbles formed due to reduction of environmental pressure. It includes two pathophysiological syndromes: the arterial gas embolism and the decompression sickness [1, 2].
Arterial gas embolism occurs when expanding gas stretches and ruptures alveolar capillaries (pulmonary barotrauma) allowing alveolar gas to enter the arterial circulation [1].
Decompression sickness (DCS) starts with the formation of extravascular and intravascular bubbles when the sum of the dissolved gas tensions exceeds the local absolute pressure. In diving, this is possible by the increase in the tissue inert gas partial pressure that occurs when the gas is respired at high pressure. Supersaturation arises during decompression if the rate of ambient pressure reduction exceeds the rate of inert gas washout [1]. Both the arterial gas embolism and the decompression sickness, are precipitated by rapid ascent, related to the change from a high pressure state to a low pressure state [1, 2, 3].
Arterial gas embolism is presented as dry cough, retrosternal pain and dyspnoea (due to pulmonary barotrauma), and can also present as altered consciousness and confusion (related to cerebral air embolism) [1, 3]. On the other hand, DCS is divided in two types. Type I consists of joint pain and cutaneous presentations. Type II incorporates a myriad of cardiopulmonary and central nervous system manifestations. Symptoms might present with some delay; most cases(90%) will start within the first 3 hours [3]. Pain is the most frequently reported manifestation of DCS, particularly around larger joints, usually at periarticular location [1, 2, 3].
Due to its uncommon frequency and to the fact that most of the cases are clinically diagnosed, little is known about the radiological aspects of decompression illness. The differential diagnosis includes near-drowning and immersion pulmonary oedema [4, 5].
Pulmonary barotrauma is presented as diffuse ground-glass attenuation areas, while the immersion pulmonary oedema may add pleural effusion and/or interlobular septal thickening [3, 4]. Near-drowning is radiographically indistinguishable from pulmonary oedema from other causes [5].
The main treatment of decompression illness includes the administration of 100% oxygen at 1 atmosphere in a hyperbaric chamber, plus supportive care if needed [1, 3].
Take home messages: due to its specific treatment, although decompression illness is rare, it should be included in the differential diagnosis of diving accidents.
Written informed patient consent for publication has been obtained.