Teaching Case

Surveillance of a 65-year-old male for pT3N1 rectal carcinoma showed suspicious lung nodules. He underwent a CT-guided biopsy and four cores were taken. Upon completion, he complained of severe chest pain. He became diaphoretic and his oxygen saturations dropped to 92% on room air.

A suspicious lung nodule is noted in the right middle lobe on axial CT images (figure 1). The post lung biopsy CT reveals an air embolus within the right ventricle, peritumoural haemorrhage and a small pneumothorax (figures 2 and 3). A repeat CT scan thirty minutes later showed complete resolution of the air embolus. Our patient's symptoms were transient and fully resolved within minutes. He responded to conservative measures of 100% oxygen supplementation. Apart from the temporary drop in oxygen saturations, he remained haemodynamically stable throughout.

Air embolus is a rare and potentially fatal complication of CT-guided lung biopsies, reported in 0.02-0.07% of biopsies [1]. Air may gain access to the systemic circulation in one of three ways: 1) the needle tip may be placed into the pulmonary vein directly, 2) air introduced into the pulmonary arterial system may cross the microvasculature to the pulmonary venous system and 3) fistula may be created between an air-filled space and a pulmonary vein when a needle traverses both simultaneously.

Subsequent coughing, straining or valsava manoeuvre may cause air embolisation to occur. Air entering the pulmonary venous network embolises primarily to coronary and cerebral arteries. A mere 0.5-1 ml of air in the coronary arteries may cause cardiac arrest and just 2 ml of air in the cerebral arteries is sufficient to cause death [2].

Risk factors have been identified which increase the risk of air embolus occurring. Higher risks are incurred in patients undergoing procedures for cystic or cavitary lesions, patients with vasculitis or those on positive pressure ventilation [3]. Some reports have suggested that using larger needles increases the risk of embolisation; however emboli have also been reported with smaller gauge needles [4].

Systemic air embolus should be suspected if there is an acute deterioration in the cardiovascular or neurological status of the patient and may be confirmed by post-procedural CT scanning. As with our case, immediate treatment is with 100% oxygen therapy. Hyperoxygenation can replace the nitrogen contained within the embolus with oxygen and expedite its reabsorption by blood and surrounding tissues. This process may be aided by the use of hyperbaric oxygen therapy which has been shown to reduce mortality in cerebral embolism by 7% [5]. While hyperbaric oxygen therapy is the only definitive treatment for systemic air emboli, in reality it is not always readily available. Some authors suggest placing the patient in the left lateral decubitus or Trendellenburg position if an air embolus is detected in the left ventricle to reduce the risk of cerebral artery embolisation [2, 4]. Others suggest the prone position is more appropriate as blood flow will inevitably overcome any benefit to be gained from the positional buoyancy of the air embolus within the ventricle [6].

For this rare, but potentially life threatening condition, radiologists should take the necessary steps to minimise the occurrence of systemic air embolism and be familiar with the signs and symptoms of air embolism.