Thoracic actinomycosis usually results from aspiration of infective materials in the oropharynx. The organism produces proteolytic enzymes that allow the infection to cross fascial planes. Therefore, if appropriate therapy is not instituted, pulmonary actinomycosis commonly spreads from an early pneumonic focus across lung fissures to involve the pleura and chest wall, with eventual fistula formation and drainage containing sulfur granules. Although the aggressive nature of the infiltration and frequent presentation of hemoptysis have been well described (5
), actinomycosis involving the pulmonary vasculature has rarely been documented. Only one case of mycotic pulmonary aneurysm due to actinomycosis has been reported in the medical literature (1
); however, to our knowledge, imaging findings, including the CT appearance of a mycotic aneurysm associated with actinomycosis, have not been reported.
Aneurysms of any type affecting the pulmonary arteries are very rare compared with aortic, intracranial or other major vascular locations. They may occur in association with congenital cardiovascular anomalies, infection, trauma, generalized vasculitis or pulmonary hypertension (7
). Of these conditions, infection is the major cause of pulmonary aneurysms. Mycotic or infectious pulmonary aneurysms are most commonly caused by pyogenic microorganisms, including Staphylococcus and Streptococcus; however, treponemal, mycobacterial, but rarely fungal organisms, including Aspergillus and Candida species, have been reported (1
). Tuberculosis and syphilis, once the major causes of mycotic pulmonary aneurysms, are now better controlled since the introduction of antibiotics (7
The proposed pathologic mechanisms of mycotic pulmonary aneurysm include direct involvement of an adjacent pulmonary artery from a focus of suppurating pulmonary infection, as in tuberculosis, ischemic injury to the pulmonary arterial wall as a result of infection of the vasa vasorum, as in syphilis, and direct extension into a vessel wall from an intraluminal septic thromboembolus or the blood itself, as in bacterial endocarditis (2
). Among these mechanisms, the first was thought to be the most likely to be responsible for the development of the pulmonary aneurysm in our case. Both true and false aneurysms have been found in the mycotic aneurysm. Virulent organisms produce severe destruction of all layers of the arterial wall, resulting in the formation of a false aneurysm, whereas indolent organisms tend to cause a true aneurysm, as the arterial wall is less severely damaged (8
The radiographic appearance of a mycotic pulmonary aneurysm includes well- or ill-defined pulmonary nodules or focal parenchymal consolidation, which are frequently nondiagnostic and indistinguishable from those of infectious or neoplastic conditions (9
). Rapid change in the contour of a nodule may occasionally suggest a mycotic aneurysm, but as in our patient, a mycotic aneurysm associated with necrotizing pneumonia can be difficult to diagnose. Although pulmonary angiography was previously the gold standard of diagnosis, CT and MRI have recently become important alternatives. Both contrast-enhanced CT and MR imaging clearly show the vascular nature of a mass like lesion resulting from a pulmonary aneurysm. In our patient, CT disclosed a hyperenhancing nodule, connected with a pulmonary vessel within the parenchymal lesion of low attenuation. The density of the enhancing nodule had the same attenuation as the enhancing vessels, which was virtually diagnostic of a pulmonary aneurysm.
Experience in the management of mycotic pulmonary aneurysms is limited as their diagnosis is rare. Their management is usually surgical, and involves aneurysmectomy, lobectomy, aneurysmorrhaphy or banding (2
). In addition, as in our patient, alternative nonsurgical therapeutic procedures, including occlusion of aneurysm with steel coils or detachable balloons, have been reported (3
In summary, a case of a mycotic pulmonary aneurysm occurring in association with necrotizing pneumonia, caused by Actinomyces, where the patient was successfully treated with transcatheter intervention with steel coils is reported.