Dendriform pulmonary ossification in fibrosing interstitial lung disease with primary biliary cholangitis.

Dendriform pulmonary ossification (DPO) is a rare condition characterised by branching bone formation within the lung parenchyma, often associated with fibrotic interstitial lung disease (ILD). We report an asymptomatic man in his 80s with primary biliary cholangitis who presented with bilateral lower-lobe fibrosis and subpleural micronodules on high-resolution CT, initially suggesting granulomatous ILD. Transbronchial lung cryobiopsy revealed fibrosis with intra-alveolar ossification and subsequent bone window high-resolution CT confirmed branching calcified structures, establishing the diagnosis of DPO. This case highlights the importance of considering DPO in fibrotic ILD with subtle nodular findings and demonstrates the utility of transbronchial lung cryobiopsy in the differential diagnosis.