The Evaluation of FDG PET/CT Scan Findings in Patients with Organizing Pneumonia Mimicking Lung Cancer

Abstract

Objective: Organizing pneumonia (OP) is a rare lung condition that is characterized by the presence of polypoid tissues due to fibroblastic plugs within respiratory bronchioles, alveolar ducts and sacs. The three main radiologic patterns of OP include typical, solitary-focal and infiltrative forms. The maximum standardized uptake value (SUVmax) on positron emission tomography-computed tomography (PET/CT) may be high in benign conditions such as OP as well as malignant diseases. The aim of our study was to investigate PET-CT characteristics of OP in patients mimicking lung cancer.

Methods: The clinical and radiologic characteristics of 50 patients who were referred to our hospital for PET/CT evaluation due to suspicion of lung malignancy, and who were pathologically diagnosed as OP between 2009 and 2013 were retrospectively reviewed.

Results: The mean age of the patients was 58.2 years. Ninety-six percent of patients (48) were male. Radiologic evaluation revealed 27 (54%) focal involvement, 10 (20%) consolidation with air-bronchogram (typical), 1 (2%) infiltrative and 12 (24%) other types of involvement (multiple nodules and cavitary lesions). The mean SUVmax value of the lesions on PET/CT was calculated as 6.5. Mediastinal lymph node involvement (at least one station) was detected in 76% of our study group with a mean SUVmax value of 3.27.

Conclusion: OP may cause false positive results on PET/CT. However, PET/CT results may be used as a guide for invasive procedures that should be performed when there is suspicion of malignancy.

Figure 1. CT and PET-CT scans of a patient with focal lesionA) A focal lesion 3 cm in diameter with irregular borders radiating to the pleural surface in the right lower lobe. B) SUVmax of the lesion on PET/CT was 5.09. Trans-thoracic fine needle biopsy was insufficient for diagnosis, thus, it was surgically removed. The pathology of the lesion was reported as organizing peumonia

Figure 2. PET/CT scans of a patient with multiple nodules and cavitary lesionA) A cavitary lesion 2.5 cm in diameter in the superior segment of left lower lobe (SUVmax: 7.04). There is low metabolic activity in the left hilar lymph node (SUVmax: 3.38). B) Bilateral multiple nodules, the largest 2.5 cm in diameter (SUVmax: 3.93). The patient underwent trans-thoracic fine needle biopsy, which was reported as organizing pneumonia after pathologic evaluation

Figure 3. CT and PET-CT scans of a patient with mediastinal massA) A mediastinal lesion of 6.2x4x5 in size, extending to the paramediastinal area from the apical region of the left lung on Thorax CT. B) SUVmax of the lesion on PET/CT was 10.59. The center of the mass was hypo-metabolic. C) High metabolic activity in subcarinal (SUVmax: 6.96), right hilar (SUVmax: 3.32-4.07) and left hilar (SUVmax: 4.12) mediastinal lymph nodes. The pathology of the specimen obtained via trans-thoracic fine needle aspiration biopsy revealed organizing pneumonia