Lymphocytic Interstitial Pneumonia Presenting as hilar mass with Obstructive Atelectasis: A Case Report and Literature Review

Abstract Background Lymphocytic Interstitial Pneumonia (LIP) is a rare benign lymphoproliferative disorder characterized by diffuse infiltration of lymphocytes and plasma cells in the pulmonary parenchyma. It is commonly associated with autoimmune diseases. Chest CT showed multiple bronchial cysts and diffuse interstitial infiltration in most cases. Due to its nonspecific clinical manifestations, it is often misdiagnosed or overlooked. Definitive diagnosis requires pathological biopsy.Case presentation A 65-year-old male was admitted due to cough for one month. Chest CT revealed left hilar mass with left upper lung lingular segment consolidation and atelectasis (measuring approximately 3.5 cm). the pathological showed hyperplasia of alveolar epithelium with extensive interstitial infiltration of lymphocytes and plasma cells, along with histiocyte proliferation in alveolar spaces, suggestive of LIP. After treatment with corticosteroids, the patient's symptoms improved, and follow-up imaging showed radiographic resolution of the lesions.Conclusions To our knowledge, our case may be the first reported case of LIP presenting as a hilar mass on chest CT. This atypical radiological manifestation underscores the importance of differentiating LIP from malignant tumors in clinical practice.