Magnetic resonance imaging of focal organizing pneumonia: differential diagnosis with peripheral lung carcinoma

Background Computed tomography (CT) is the most common way to evaluate focal organizing pneumonia (FOP); however, sometimes it is difficult to differentiate FOP and peripheral lung carcinoma (PLC). Purpose To clarify the MRI manifestation of FOP and the value of MR in the differential diagnosis of FOP and PLC in comparison to CT. Material and Methods Chest MR (3D T1WI, T2WI TSE, DWI) and CT images of 72 patients (50 men: mean age=64.7 years; 22 women: mean age=64.9 years; 36 FOPs and 36 PLCs) were retrospectively analyzed. Two experienced radiologists reviewed all CT and MR images and graded CT and MR findings completely independently. The apparent diffusion coefficient (ADC) value was measured by the two radiologists independently. Paired sample t-test and Fisher's exact test were used to compare the ADC values and MR features between the two groups. Finally, the ROC curve was used to evaluate the diagnostic efficiency of MR. Results The ADC value of FOP was larger than PLC (P < 0.05). Necrosis, abscess cavity, broad contact with the pleura, and focal pleural effusion were more common in FOP (P < 0.05). PLC patients showed more (P < 0.05) irregular margins, pleural indentation, and lymphadenopathy. ADC value can be used to differentiate FOP and PLC, and the cutoff value is 1048 x 10-6mm2/s. The sensitivity, specificity, AUC and accuracy of diagnosis of CT, MR was (61.1%, 88.9%, 0.820, and 75%) vs (72.2%, 97.2%, 0.950, and 93.1%), respectively. Conclusion Compared with CT, MR can increase radiologists' confidence in the differential diagnosis of FOP and PLC.