What are the causes of fatty liver and diagnosis?

Fatty liver. Several, from alcohol, diabetes, with high cholesterol & hypertension &obesity (metabolic syndrome), severe weight loss, diverticulosis, toxins such as phosphorus or mushroom poisoning, drugs such as Methotrexate & glucocorticoids, hepatitis c & HIV infection.
Dx w/ CT/US or Bx. I agree with the above answer. I would also add that fatty liver is frequently seen or suggested on ultrasound, ct or MRI study and occiaionaof the abdomen. The appearance on ct is quite typical, particularly in cases of significant fatty changes. When the diagnosis is in doubt or when clinically warranted, a liver biopsy may be performed for pathologic diagnosis.