Diagnostic procedures and clinico-radiological findings of acute fibrinous and organizing pneumonia: a systematic review and pooled analysis

An Integrated Radiologic-Pathologic Understanding of COVID-19 Pneumonia

This article reviews the radiologic and pathologic findings of the epithelial and endothelial injuries in COVID-19 pneumonia to help radiologists understand the fundamental nature of the disease. The radiologic and pathologic manifestations of COVID-19 pneumonia result from epithelial and endothelial injuries based on viral toxicity and immunopathologic effects. The pathologic features of mild and reversible COVID-19 pneumonia involve nonspecific pneumonia or an organizing pneumonia pattern, while the pathologic features of potentially fatal and irreversible COVID-19 pneumonia are characterized by diffuse alveolar damage followed by fibrosis or acute fibrinous organizing pneumonia. These pathologic responses of epithelial injuries observed in COVID-19 pneumonia are not specific to SARS-CoV-2 but rather constitute universal responses to viral pneumonia. Endothelial injury in COVID-19 pneumonia is a prominent feature compared with other types of viral pneumonia and encompasses various vascular abnormalities at different levels, including pulmonary thromboembolism, vascular engorgement, peripheral vascular reduction, a vascular tree-in-bud pattern, and lung perfusion abnormality. Chest CT with different imaging techniques (eg, CT quantification, dual-energy CT perfusion) can fully capture the various manifestations of epithelial and endothelial injuries. CT can thus aid in establishing prognosis and identifying patients at risk for deterioration.

Case report: Corticosteroid-resistant acute fibrinous and organizing pneumonia with myelodysplastic syndrome

Acute fibrinous and organizing pneumonia (AFOP) is a lung disease with an unusual pathological pattern. The definitive diagnosis of AFOP relies on pathological evidence of intra-alveolar fibrin exudate, lymphoplasmacytic infiltrate, and the absence of a hyaline membrane. Furthermore, its etiology is difficult to confirm, and corticosteroids are usually effective. Herein, we report the case of a young male who presented with high fever, hemocytopenia, and consolidation in both lungs. The initial misdiagnosis was community-acquired pneumonia. Subsequently, a lung biopsy revealed abundant fibrin and fibroblast exudates in the alveolar spaces, indicating AFOP. In addition, bone marrow biopsy and karyotype analysis demonstrated that the patient simultaneously had myelodysplastic syndrome (MDS) and hemophagocytic lymphohistiocytosis. In this case, the AFOP was considered secondary to MDS; however, the disease did not respond to glucocorticoid treatment or chemotherapy. Hence, AFOP should be considered in patients with underlying hematological diseases, and early identification and diagnosis are important. Furthermore, the management of patients with severe AFOP requires further investigation.

Update on cryptogenic organizing pneumonia

Cryptogenic organizing pneumonia (COP) is a form of idiopathic interstitial pneumonia that results from the pulmonary reaction to various unidentified injuries. Secondary organizing pneumonia is diagnosed when the triggering factor has been identified; it is mainly caused by infections, toxic substance exposure, drugs, connective tissue diseases, malignancies, autoimmune diseases, bone marrow, or organ transplantation, and radiotherapy. There has been an increase in the number of reports of drug-induced organizing pneumonia (OP). New biological therapies, interferon, monoclonal antibodies, anti-interleukin antibodies, and PD1/PDL-1 inhibitors may induce this specific pulmonary reaction. The classical form of COP is usually subacute and does not manifest as severe disease. Patients maintain sufficient respiratory function, and treatment with steroids is usually effective. Several specific forms of OP (e.g., the cicatricial variant or acute fibrinous type) have distinct clinical and histological features, require higher doses of immunosuppressive drugs, and have a worse prognosis. In the era of administering steroid-sparing therapies for the treatment of interstitial lung diseases, connective tissue dases, and other conditions, it is important to emphasize this type of therapy for patients with COP.