T1 pseudohyperintensity on fat-suppressed magnetic resonance imaging: a potential diagnostic pitfall.

Magnetic resonance imaging findings in 2 patients with misleading T1 hyperintensity seen only on fat-suppressed images are presented; one with a renal cell carcinoma that was misinterpreted as a hemorrhagic cyst and the other with an ovarian serous cystadenocarcinoma that was misinterpreted as a complicated endometrioma. The apparent T1 hyperintensity on fat-suppressed images in these cases was likely due to varying perception of image signal dependent on local contrast, an optical effect known as the checker-shadow illusion. T1 pseudohyperintensity should be considered when apparently high T1 signal intensity is seen only on fat-suppressed images; review of non-fat-suppressed images may help prevent an erroneous diagnoses of blood-containing lesions.