Radiological and Pathological Features of Cyst Formation in Idiopathic Multicentric Castleman Disease

HIGHLIGHTS: What are the main findings? Pulmonary cysts in idiopathic Castleman disease (MCD) emerged from the area of ground-glass attenuation (GGA) on HRCT, and the cysts did not regress by treatment. The pathological evaluation showed a high degree of plasma cell infiltration and loss of elastic fibers around the cyst wall. What are the implications of the main findings? The loss of elastic fibers may be an important factor in cyst formation in idiopathic MCD. Introducing anti-inflammatory therapy, such as tocilizumab, before pathologic loss of elastic fibers occurs might prevent irreversible cyst formation in MCD. ABSTRACT: Introduction: Idiopathic multicentric Castleman disease (MCD) has been reported to form lung cysts at a relatively high rate. However, the radiological and pathological features of cystic formation in MCD are unclear. Methods: To clarify these questions, we retrospectively investigated the radiological and pathological findings of cysts in MCD patients. Eight consecutive patients who underwent surgical lung biopsies in our center from 2000 to 2019 were included. Results: The median age was 44.5 years, with three males and five females. On the initial computed tomography, cyst formation was found in seven patients (87.5%). All of the cysts were multiple, round, and thin walled, accompanying ground-glass attenuation (GGA) around cysts. In six patients (75%), cysts increased during their clinical courses, and the new cysts had emerged from GGA, although GGA was improved by treatment. In all four cases, whose pulmonary cysts could be pathologically evaluated, a marked plasma cell infiltration around the cyst wall, and loss of elastic fibers of the alveolar wall were observed. Conclusions: Pulmonary cysts emerged in the area of GGA pathologically consistent with plasma cell infiltration. Cysts in MCD may be formed by the loss of elastic fibers due to marked plasma cell infiltration and may be considered irreversible changes.