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Nuclear Medicine

E2788. Nononcologic Findings in PET/CT

Olsen A,  Puri S,  Rubens D,  Jones L,  Weiss S,  Strang J. University of Rochester Medical Center, Rochester, NY

Address correspondence to A. Olsen (a.b.olsen@gmail.com)

Background Information: PET is a cornerstone of oncologic imaging, and represents an important modality for staging many cancers. There are several reasons why apparent uptake of FDG may not correlate to malignancy. Although PET is most commonly used for staging, it may also provide diagnostic information about other conditions such as infections, inflammation, or treatment-related effects. Further, PET imaging may support a benign etiology when other modalities are suggestive of malignancy. Recognizing the PET appearance of these nonmalignant entities can play an important role in appropriately guiding patient care.

Educational Goals/Teaching Points: The objective of this exhibit is to review common and uncommon examples of nonmalignant FDG uptake in PET imaging, and to give examples of mimics of malignancy as they appear on PET. A wide range of cases will be reviewed. Infectious cases include MAI sacroiliitis, BCG epididymitis/prostatitis, splenic abscess, ruptured appendicitis, and cholecystitis. Inflammatory cases include dermatomyositis, Erdheim-Chester disease, sclerosing mesenteritis, retroperitoneal fibrosis, and Crohn disease. Treatment-related cases include pleurodesis-related uptake, bone marrow biopsy site uptake, radiation therapy related changes, and drug-induced hepatitis. Anatomic/physiologic cases include consolidation in an anomalous pulmonary segment, focal hepatic fat mimicking metastases, and focal hepatic uptake in the setting of SVC obstruction (hot spot sign). Benign lesions to be reviewed include soft-tissue hemangioma and adenomas of the liver, pancreas, and bowel. Miscellaneous cases to be reviewed include pulmonary calcinosis, Paget disease, pulmonary infarction, attenuation correction related artifact, and arterial FDG injection.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: Routine PET imaging may reveal anatomical variants and nonmalignant pathology (including benign lesions) which can mimic malignancy. Additionally, some medications and other treatments may result in elevated FDG uptake resulting from complications or normal response to treatment. Attenuation correction can also result in falsely elevated standard uptake values (SUVs) in the setting of misregistration, which is common near the diaphragm. Ultimately, failure to recognize the cause of unusual FDG uptake may result in overdiagnosis or overstaging of malignancy, or may result in delayed diagnosis and treatment of important nonmalignant pathology.

Conclusion: Although most PET evaluations offer a relatively straightforward assessment of a malignancy’s true extent, problematic cases of atypical FDG uptake can arise from infectious, inflammatory, medication-related or anatomic/physiologic causes. The radiologist’s ability to differentiate malignancy from its mimics can help limit overstaging and overdiagnosis of malignancy, and expedites appropriate treatment of the underlying pathology mimicking malignancy, thus reducing patients’ exposure to risk from potentially unnecessary diagnostic procedures or inappropriate treatments.