From imaging clue to diagnosis: Pseudomonas putida pneumonia with the reversed halo sign-navigating diagnosis and treatment.

A 69-year-old female was admitted with a four-day history of unexplained fever. Lung examination revealed coarse breath sounds, and laboratory tests showed elevated inflammatory markers. She had no identifiable environmental or occupational exposure, and initial screening for common respiratory pathogens was negative. Chest computed tomography (CT) scan demonstrated patchy ground-glass opacities and reticular shadows distributed along the bronchovascular bundles in the right upper lobe and dorsal segments of both lower lobes, with lesions showing the reversed halo sign (RHS). Initial empirical antibiotic therapy was ineffective. Subsequent bronchoalveolar lavage (BAL) culture yielded heavy growth of Pseudomonas putida, with negative fungal and tuberculosis nucleic acid testing. Based on antimicrobial susceptibility testing, the treatment regimen was adjusted to a combination of ceftazidime and amikacin. Following this targeted therapy, the patient's symptomatic improvement occurred while imaging abnormalities persisted, indicating a clinical-radiological dissociation. The patient was discharged after a 15-day hospital stay. This case highlights the following: (1) In community-acquired pneumonia with atypical imaging features (such as the RHS) that is refractory to conventional therapy, the differential diagnosis should be expanded to include environmental opportunistic pathogens like P. putida; (2) The RHS is a non-specific imaging finding, and its diagnostic significance must be interpreted in conjunction with lesion distribution, dynamic changes, and the complete clinical context; (3) Obtaining microbiological evidence through minimally invasive techniques such as BAL is crucial for shifting from empirical to precise targeted therapy, thereby improving patient prognosis.