Abstract Background Dendriform pulmonary ossification (DPO) is a rare, chronic form of heterotopic bone formation within the lung interstitium, most often associated with chronic inflammation, cardiac disease, or diffuse lung injury. On high-resolution CT, its branching subpleural calcifications may mimic reticulation or early fibrosis, leading to misdiagnosis as interstitial lung disease (ILD). Awareness of this entity is critical to avoid unnecessary immunosuppression, invasive biopsy, and patient anxiety. Case Presentation A 61-year-old woman with hypertension, hypothyroidism, and sickle cell anemia was referred to the pulmonology clinic after a CT chest in 2023 revealed scattered subpleural ground-glass and reticulonodular opacities concerning for early fibrotic ILD. When compared with a 2017 CT, there was no evidence of traction bronchiectasis, honeycombing, or architectural distortion, only stable peripheral nodular calcifications. Multidisciplinary review determined that the pattern was inconsistent with ILD but warranted surveillance. Repeat high-resolution CTs in 2024 and 2025 demonstrated persistent branching calcified opacities along subpleural and interlobular septal lines without progression, consistent with dendriform pulmonary ossification. The patient remained asymptomatic, denying dyspnea, cough, or sputum production. Pulmonary function testing revealed normal spirometry (FVC 73% predicted, FEV1 79% predicted, FEV1/FVC 87%) and preserved diffusion capacity (DLCO 88%), unchanged over two years. Results Radiographically, the key distinguishing feature was subpleural dendritic calcification mimicking reticulation but lacking parenchymal distortion. The absence of fibrosis, traction bronchiectasis, or honeycombing supported the diagnosis of DPO. Over eight years of serial imaging, the findings remained stable, and the patient continues annual HRCT and PFT surveillance with no pharmacologic intervention. Conclusion This case highlights dendriform pulmonary ossification as a rare but important radiologic mimic of fibrotic ILD. Initial concern for early interstitial fibrosis prompted further evaluation, but longitudinal stability and the characteristic branching calcified pattern revealed a benign ossific process. Recognizing this distinct imaging signature, particularly the dendritic subpleural distribution without architectural distortion, can prevent unnecessary immunosuppressive therapy and reassure both patients and clinicians of its indolent course. This abstract is funded by: none
Mahmood et al. (Fri,) studied this question.