Pulmonary hyalinizing granuloma presenting with mixed imaging features in CT and FDG PET: A case report.

A 52-year-old man was referred to our hospital for further evaluation after suspicious pulmonary shadows were detected on a routine health checkup. Chest CT revealed multiple nodular and mass-like lesions with mixed characteristics in both lungs, along with interlobular septal thickening and lymphadenopathy. FDG-PET demonstrated variable degrees of uptake across the lesions. A surgical biopsy of a mass in the left lower lobe yielded a pathological diagnosis of pulmonary hyalinizing granuloma (PHG). PHG is an extremely rare benign pulmonary condition of unknown etiology, that can be associated with various diseases. Histologically, the nodules are characterized by dense, eosinophilic hyalinized collagen arranged in concentric lamellae, frequently exhibiting a whorled or layered pattern. Radiologic findings typically include multiple bilateral pulmonary lesions; however, cavitation and calcification are rarely observed and are considered non-specific. Definitive diagnosis requires histological confirmation. In this case, no underlying or associated systemic diseases were identified histologically; however, the presence of interlobular septal thickening was atypical for previously reported PHG findings, raising the suspicion of a coexisting disease with lymphatic involvement. Close clinical and radiological follow-up is warranted to monitor for potential comorbid conditions.