With the rapid progress in medical imaging technology, many conditions are being discovered incidentally on routine scans or imaging performed for other reasons. Fatty liver, or hepatic steatosis, is a common finding during abdominal ultrasound (US) scans, but can also be noted on computed tomography (CT) scans and magnetic resonance imaging (MRI). Fatty change is evident in the liver whenever there's higher production or mobilization of fatty acids or lower clearance of fatty acids, which may occur after hepatocellular injury. Common causes include obesity, alcohol use, diabetes mellitus, hepatitis, drugs (including chemotherapy regimens and steroid therapy), overeating and liver transplantation. The terms "fatty change" and "fatty liver" are preferred, since "fatty infiltration" isn't histologically correct. For most patients with this finding, no follow-up or change in management is required, apart from the initial blood work and counselling on the possible underlying cause for the condition, such as obesity or excess alcohol intake. Discovering fatty change can be significant, however, if the lesion mimics more serious liver disease, and further investigation may be required. The imaging characteristics of fatty change are usually easily identified on CT scans. In cases where the appearance on US and CT is nondiagnostic or equivocal, MRI can be helpful. With all imaging modalities, the hepatic vessels will be seen as normal through the region of fatty change, whereas most other pathologic lesions will displace the native vessels. In rare cases, image-guided liver biopsy may be needed to make the final diagnosis. If incidental fatty liver is discovered, blood work to assess synthetic liver function (bilirubin, international normalized ratio, albumin), aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase is recommended. If there's evidence of transaminitis, further blood work can be performed to rule out causes of hepatitis. For a significant transaminitis (2.5 times above normal values), consider a gastroenterology consult and possible liver biopsy. The concern is for nonalcoholic steatohepatitis (NASH), as roughly 5% of patients with this condition can go on to develop cirrhosis. This can usually be prevented by dealing with the underlying cause (obesity, diabetes, triglycerides, etc.). MM [References: Taveras JM, ed. Radiology: Imaging, Diagnosis, Intervention. J.B. Lippincott, Philadelphia, 2003; ch. 62: pp 1-16 Radiol Clin N Amer 1998;36:365-75.] (see our gastroenterologist's response to this question in the gastroenterology category)