Pulmonary inflammatory pseudotumor: 18F-FDG PET/CT imaging features of 8 patients

1473 Objectives An inflammatory process producing a pulmonary pseudotumor is also known as pulmonary inflammatory pseudotumor (PIP), inflammatory myofibroblastic tumor, fibrous histiocytoma, xanthogranuloma and plasma cell granuloma. The variable histologic appearance of these lesions accounts for different appellations mentioned above. To date, 18F-FDG PET/CT imaging characteristics of PIP are limited to sporadic case reports. We present a series of 8 PIP cases with their imaging features and discuss the patterns most useful to raise the potential diagnosis of benign pulmonary lesion. Methods We report eight pathologically proven PIP patients with 18F-FDG PET/CT imaging. The clinical presentation and 18F-FDG PET/CT imaging characteristics of this rare and benign entity are described. Results The patient cohort age ranged from 31 to 77 years. PIP had anatomic and functional imaging characteristics mimicking malignancy. Half of the cases had unifocal nodular/mass-like lesions and the other half presented with multifocal or confluent masses unilaterally or bilaterally. Their SUV encompassed borderline abnormal uptake intensity and flagrantly hypermetabolic behavior. 18F-FDG PET/CT evaluation was initiated in all cases for the staging of a presumed lung malignancy detected by CT or after pulmonary lesion enlargement from serial imaging monitoring. While the lesion size and maximum SUV varied greatly in this cohort, the most commonly encountered PIP features are (1) the pleural-based patterns abutting the chest walls and/or mediastinum and (2) the predominantly absent hypermetabolic mediastinal nodal disease (except for 2 cases with borderline 18F-FDG avidity and histologically proven benign reactive nodes). Conclusions Based on this small series, even though there were no definitive discriminatory clinical or 18F-FDG PET/CT imaging features to distinguish PIP from malignancy, lesions abutting the pleura/mediastinum with absence of obvious hypermetabolic mediastinal nodal disease may raise the possibility of PIP in a differential diagnosis of lung lesions concerning patients with low pre-test probability for malignancy. References 1. Narla LD, Newman B, Spottswood S, Narla S, Kolli R. Inflammatory Pseudotumor. Radiographics 2003; 23:719-729. 2. Dong A, et al. Inflammatory Myofibroblastic Tumor, FDG PET/CT Findings with Pathologic Correlation. Clinical Nuclear Medicine 2014; 39(2):113-121. 3. Agrons GA, Rosado-de-Christenson ML, Kirejczyk WM, Stocker JT. Pulmonary Inflammatory Pseudotumor: Radiologic Features. Radiology 1998; 206:511-518. 4. Patnana M, Sevrukov AB, Elsayes KM, Viswanathan C, Lubner M, Menias CO. Inflammatory pseudotumor: the great mimicker. AJR Am J Roentgenol 2012;198 (3): W217-27. 5. Fornell-Perez R, Santana-Montesdeoca J, Garcia-Villar C, Camacho-Garcia MC. Two Types of Presentation of Pulmonary Inflammatory Pseudotumors. Archivos De Bronconeumologia 2012;48(8):296-299. 6. Kim TS, Han J, Kim GY, Lee KS, Kim H, Kim J. Pulmonary Inflammatory Pseudotumor (Inflammatory Myofibroblastic Tumor), CT Features with Pathologic Correlation. J Comput Assist Tomogr 2005;29:633-639. Table: Characteristics of 8 cases of pulmonary inflammatory pseudotumors. Figure 1: (A & B) PET/CT images of unilateral hypermetabolic pulmonary inflammatory pseudotumors, (C) PET/CT images of bilateral hypermetabolic pulmonary inflammatory pseudotumors.