Case Presentation: A 26 year old female with a history of intravenous drug use (IVDU) presented to the hospital with a one week history of fevers, chills, and body aches. In the emergency department the patient was febrile to 38.4 Celsius with a grade III/VI holosystolic murmur heard best at the left lower sternal border. Initial workup revealed a leukocytosis to 32000 with a chest radiograph showing a multi-lobar pneumonia. Subsequently, an echocardiography revealed vegetations on the on both the mitral and tricuspid valves with associated severe mitral regurgitation and severe tricuspid regurgitation. Furthermore, a mobile vegetation on pulmonic valve which extended into both the right ventricle and the pulmonic artery during diastole was noted. Blood cultures persistently grew Methicillin Resistant Staphylococcus Aureus (MRSA) and the patient was treated with vancomycin and ceftaroline. After approximately three weeks of treatment she developed worsening neutropenia and recurrent  fevers. The patient underwent a computerized tomography (CT) chest which revealed pruning of the superior lobar pulmonary artery with dilatation of the intact portion, measuring approximately 1.8 cm with intraluminal gas bubbles within the pulmonary artery. These findings were consistent with a mycotic pulmonary artery aneurysm. The patient was transferred to another tertiary hospital for surgical correction of her pseudo-aneurysm with concurrent mitral and tricuspid valve replacement.

Discussion: Mycotic aneurysms are rare, accounting for less than 1% of all aortic aneurysms. Within the umbrella of mycotic aneurysms, pulmonary mycotic aneurysms are even rarer – occurring less frequently than intracranial, aortic and peripheral vasculature mycotic aneurysms. These pseudo-aneurysms are typically formed by one of two mechanisms: 1) invasion into the pulmonary artery from a surrounding focus of infection or 2) intraluminal septic emboli invasion into the vessel. Our patient had risk factors for both mechanisms as she had a multifocal pneumonia and infective endocarditis. Pulmonary mycotic aneurysms are most commonly associated with right heart endocarditis with an associated mortality rate as high as 80%. The most common organisms are staphylococcus and streptococcus; however, infections with mycobacterium and syphilis have also been described. Congenital anomalies, pulmonary hypertension, iatrogenic causes, and trauma are other risk factors associated with mycotic pulmonary aneurysms. For diagnosis, CT and magnetic resonance imaging (MRI) are the gold standard and centrally-located mycotic pulmonary aneurysms are more common than peripherally-located lesions. Early pharmacotherapy and surgical intervention is the mainstay of treatment. The type of surgical intervention is dependent on the location of the aneurysm. Proximal lesions are subject to aneusymorrhaphy or aneurysmectomy. Peripheral single lesions can be approached with wedge resection and lobectomy. Pneumonectomy can also be performed for peripheral or multiple unilateral lesions.  

Conclusions: The development of a pulmonary artery mycotic aneurysm is an uncommon complication of bacterial endocarditis. Due to the high mortality rate of this disease, early diagnosis with CT or MRI, pharmacotherapy, and surgical intervention is vital. This diagnosis must be considered in light of the current IVDU epidemic we now face.