Imaging of Pulmonary Infarction

Pulmonary infarction in acute pulmonary embolism

Pulmonary infarction results from occlusion of the distal pulmonary arteries leading to ischemia, hemorrhage and ultimately necrosis of the lung parenchyma. It is most commonly caused by acute pulmonary embolism (PE), with a reported incidence of around 30%. Following an occlusion of the pulmonary artery, the bronchial arteries are recruited as primary source of perfusion of the pulmonary capillaries. The relatively higher blood pressure in the bronchial circulation causes an increase in the capillary blood flow, leading to extravasation of erythrocytes (i.e. alveolar hemorrhage). If this hemorrhage cannot be resorbed, it results in tissue necrosis and infarction. Different definitions of pulmonary infarction are used in literature (clinical, radiological and histological), although the diagnosis is nowadays mostly based on radiological characteristics. Notably, the infarcted area is only replaced by a fibrotic scar over a period of months. Hence and formally, the diagnosis of pulmonary infarction cannot be confirmed upon diagnosis of acute PE. Little is known of the impact and relevance of pulmonary infarction in acute PE, and whether specific management strategies should be applied to prevent and/or treat complications such as pain, pneumonia or post-PE syndrome. In this review we will summarize current knowledge on the pathophysiology, epidemiology, diagnosis and prognosis of pulmonary infarction in the setting of acute PE. We highlight the need for dedicated studies to overcome the current knowledge gaps.

Mucor pulmonary embolism in a patient with myelodysplastic syndrome

Mucormycosis is a life-threatening infectious disease that occurs most commonly in immunocompromised patients such as those with hematological malignancies. Its clinical symptoms and associated radiological findings vary and specific biomarkers and culture characteristics have not been defined. An 85-year-old man who had been treated for myelodysplastic syndrome and tuberculosis for several months presented with subacute fever and worsening left-side chest pain. Contrast-enhanced computed tomography images depicted massive tumor-like consolidation without enhancement, expanding from the left lower lobe. Emboli that did not respond to anticoagulants were detected in the left descending pulmonary artery. Despite intensive treatment he developed multiple organ failure and died 47 days after hospitalization. Gross pathology of a lung autopsy specimen revealed left lower pulmonary arterial emboli and pulmonary infarction, which was concluded to be the direct cause of death. The emboli were histopathologically identified as invasive mycelia in vessels. Mucor sp. was detected via real-time polymerase chain reaction and immunohistopathological analyses revealed that the mold in the blood vessels of lung tissue was partially positive for the mucor antigen. In the present case of Mucor sp. pulmonary emboli in a patient with myelodysplastic syndrome, radiographic findings were hard to distinguish from those typical of a lung abscess.

Laser-targeted photosensitizer-induced lung injury: noninvasive rat model of pulmonary infarction

Pulmonary infarction is a life-threatening lung injury that requires rapid and accurate diagnosis for proper treatment. Targetable and reproducible small-animal models that would allow experimental development and preclinical evaluation of diagnostic methods for detecting pulmonary infarction are critically missing. The authors report here a novel procedure to selectively induce pulmonary infarction by photodestructive laser-light irradiation in a targeted location within a specific lung compartment after administration of a photosensitizer. Histopathological analysis of the illuminated lung tissue revealed massive hemorrhage and vascular occlusion after acute injury localized to the site of irradiation. Collapse of alveolar structure, neutrophil influx, and necrosis were subsequently observed. Computed tomography (CT) scans showed evidence of abnormal density and airspace consolidation in the irradiated area of the lung, but not elsewhere in the lung compartment. Perfusion imaging using 99mTc-labeled macroaggregated albumin by single-photon emission computed tomography revealed diminished scintigraphic signal in the opaque area of infarcted lung tissue. The histological changes, CT findings, and perfusion characteristics of pulmonary infarction are mimicked using laser-irradiated, photosensitizer-mediated photodestruction to selectively induce chronic lung injury in a localized area. This small-animal model can be easily and readily used for targeted induction of pulmonary infarction in a designated area of lung compartment and offers the potential for use in evaluating novel diagnostic and therapeutic methods.