INTRODUCTION: The differential diagnosis of hypoxemia is broad, but all cases will fall within five commonly described mechanisms; hypoventilation, V/Q mismatch, right to left shunt, diffusion limitation, and reduced inspired oxygen. We present a case of a patient with hypoxemia that was ultimately diagnosed with a right to left shunt. This finding initially defied multiple diagnostic studies before the location was confirmed.
CASE PRESENTATION: A 24 year-old U.S. Marine presented with a history of progressive dyspnea and wheezing on exertion over three months. Prior to this he reported excellent exercise tolerance. His only past medical history was a gunshot to the chest in 1999 with right upper lobe wedge resection. His exam was notable for a well developed young man in no distress with a resting oxygen saturation of 90%. He had a normal chest x-ray and was referred to pulmonary medicine. He was diagnosed and treated for mild asthma with no improvement in symptoms. He was noted to desaturate to 87% upon ambulation. A room air ABG revealed a PaO2 of 61 mmHg. Noncontrast CT scan of the chest revealed post surgical changes only. A shunt study was positive and he was referred for a transthoracic echocardiogram with agitated saline. This study revealed nearly simultaneous opacification of both atria with bubbles, consistent with an intra-cardiac shunt. Cardiac function was otherwise normal. Subsequent transesophageal echocardiogram confirmed the bubble study results but revealed no septal defects. This suggested a pulmonary arteriovenous malformation. However, CT angiogram of the chest was negative. With the source of the right to let shunt unclear, a third echocardiogram with agitated saline was performed. Bubbles were visualized entering the left atrium via a pulmonary vein nearly immediately after injection, suggestive of a proximal pulmonary arteriovenous fistula (PAVF). Pulmonary angiogram confirmed this revealing a discrete 8 mm fistula between the right main pulmonary artery and the right upper pulmonary vein. After endovascular closure with a 10 mm Amplatzer septal occluder, the patient had resolution of symptoms and hypoxia.
DISCUSSION: Further history revealed the prior gunshot caused a pulmonary artery injury that required emergent repair. This trauma likely precipitated PAVF formation. PAVF are uncommon and most are hereditary1. Thoracic trauma is a rare cause with 6 prior cases reported from gunshots2, 3. Clinical presentation can be acute or occur decades after trauma. Our case is consistent with reports of late presentation3. CT angiogram is a useful diagnostic study for PAVF; our study was inadequately timed to diagnose a proximal PAVF. This case illustrates an important point about interpretation of contrast echocardiography. Traditionally we think of contrast appearance within the left atrium during the first 1-2 cardiac cycles as diagnostic of an intra-cardiac shunt. Our case demonstrates a proximal PAVF can also cause this result. Visualization of bubbles entering the pulmonary veins suggested this and pulmonary angiogram solidified the diagnosis.
CONCLUSIONS: This case illustrates the evaluation of a common clinical problem, the importance of a thorough history, and the value of persistence when the results of diagnostic tests do not match clinical suspicion. PAVF are uncommon but should be considered in the differential diagnosis of the patient with hypoxemia and a prior history of penetrating chest trauma.
Reference #1 Gossage JR, Kanj G. Pulmonary arteriovenous malformations. A state of the art review. Am J Respir Crit Care Med. 1998 Aug;158(2):643-61.
Reference #2 Dairywala IT, Lokhandwala J, Patrick H, Talucci R, Jain D. Severe refractory hypoxemia following a gunshot injury. Chest. 2005 Jan;127(1):398-401.
Reference #3 Khalil A, Parrot A, Hammoudi N, Korzec J, Fartoukh M, Carette MF. Severe refractory hypoxemia 16 years after a gunshot injury: Multidetector CT-angiography pattern and endovascular treatment. Circulation. 2010 Feb 9;121(5):e27-8.
DISCLOSURE: The following authors have nothing to disclose: Andrew Philip, Sean McKay, Joel Nations, Angeline Lazarus, Saira Aslam, Michael Ferguson
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