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Background
Nonneoplastic entities that clinically and radiologically mimic tumors can lead to diagnostic confusion and delay appropriate therapy.

Educational Goals / Teaching Points
We describe pitfalls in oncologic imaging, review tumor mimics, posttreatment changes, and discuss various problem-solving tools.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Confounders at primary diagnosis include inflammatory, infective, and vascular disorders. In a patient presenting with focal neurologic deficit, seizures, or abnormal behavior, there may be several causes other than a neoplasm leading to the clinical presentation. These include demyelination, infections such as fungal, parasitic, tuberculosis and neurocysticercosis, and sarcoidosis. MRI would be the preferred imaging modality in conjunction with blood, serological, and CSF examination. MR spectroscopy helps by providing molecular information about the lesion. Bone tumors are a commonly mistaken entity in the setting of osteomyelitis, bone cysts, fracture, scurvy and osteogenesis imperfecta. On imaging, chronic osteomyelitis can closely mimic aggressive tumors such as Ewing’s sarcoma. Imaging must be reviewed in the appropriate clinical context, and plain radiographs should be correlated with findings on MRI before arriving at the diagnosis. Abnormal perfusion, such as arterioportal shunting in the liver, can lead to transient attenuation or intensity differences that must not be mistaken for neoplasm. Other pathologies in the liver that cause diagnostic confusion include abscesses, focal hepatic steatosis, and cysts. A combination of ultrasound, contrast-enhanced CT, multiphase MRI, or contrast-enhanced ultrasound (CEUS) may be necessary to characterize the lesion. Infarcts, cysts and perfusion abnormalities mimic tumors in the spleen, whereas adrenal hemorrhage can be mistaken for an adrenal mass. A hypertrophied column of Bertin can mimic a renal mass, CEUS can help make the distinction. Sludge and stones in the renal collecting system may cause diagnostic confusion. Intrapulmonary nodes or granuloma may mimic lung metastases. Multimodality imaging along with short-term follow-up in the right clinical setting will clinch the diagnosis. In a patient with cancer, it is essential to identify complications of therapy and differentiate posttreatment changes from residual or recurrent disease. Radiotherapy-induced organ injury varies from edema and necrosis to fibrosis leading to architectural distortion. Postchemotherapy infections, bone marrow changes, and thymic rebound hyperplasia are common. In the immediate posttherapy setting, the distinction from residual tumor is challenging as metabolic activity may be high owing to inflammation, reducing the accuracy of nuclear imaging techniques. Diffusion-weighted imaging (DWI) can help in problem-solving, as the tumor would restrict while inflammation would facilitate diffusion. Dynamic-contrast enhanced MRI is another useful tool to distinguish neoplasm from nonneoplastic entities.

Conclusion
Multimodality serial imaging and close follow-up are quintessential in the management of such patients.