When Pneumonia Is Not Pneumonia: T-cell Acute Lymphoblastic Leukemia Presenting With Mediastinal Mass, Airway Compression, and Pericardial Effusion in a 4-Year-Old.

Pediatric leukemia may initially present in a way that mimics common respiratory infections, particularly when fever, cough, chest pain, and radiographic findings are observed. This overlap may obscure the diagnosis of malignancy, especially when the initial imaging is interpreted as community-acquired pneumonia. T-cell acute lymphoblastic leukemia (T-ALL) is commonly linked with anterior mediastinal masses that may result in airway compression, atelectasis, pleural or pericardial effusions, and cardiopulmonary instability. We describe a previously healthy four-year-old boy who presented with two weeks of fever and dry cough associated with chest pain. He was initially treated with high-dose amoxicillin for presumed pneumonia, but symptoms persisted, prompting the emergency department (ED) visit. On examination, the patient exhibited mild tachycardia and cervical and right axillary lymphadenopathy, while the systemic examinations, including respiratory, cardiac, and abdominal examinations, were unremarkable. Laboratory evaluation showed leukocytosis with circulating blasts, anemia, elevated inflammatory markers, and markedly elevated lactate dehydrogenase. Repeat imaging showed mediastinal enlargement and a potential mass, suggesting a possible leukemia in the presence of blast cells, and necessitated transfer to a higher center within the hospital network that offered subspecialty services. A CT of the chest showed a large anterior mediastinal mass, left mainstem bronchus narrowing, left lower lobe atelectasis, and a large pericardial effusion. Echocardiography demonstrated a moderate to large circumferential pericardial effusion with early signs of tamponade physiology. Flow cytometry of peripheral blood proved T-ALL. The patient was admitted to the pediatric intensive care unit and given tumor lysis prophylaxis, empiric cefepime for fever in the setting of functional neutropenia, corticosteroids for tumor debulking, and pericardiocentesis before initiation of leukemia-directed therapy. Suspicion of malignancy and urgent evaluation should be considered in patients with persistent pneumonia-like symptoms, mediastinal widening, lymphadenopathy, cytopenias or blasts, elevated lactate dehydrogenase, or failure to improve with appropriate antibiotics.