The fatty casts are casts that contain lipid droplets sequestrated in a hyaline matrix. Because of the maltese cross interference pattern, when viewed under polarized light, the fatty casts are easy to identify. Fatty casts can appear under two types. In the first type, the embedded fat droplets are parsed in the hyaline matrix. This type should be reported as a hyaline fatty cast. In the second type, the droplets are within oval fat bodies. This type should be reported as oval fat body cast. The oval fat body casts are associated with the nephrotic syndrome. The urinary context will be one of a high proteinuria. If the specimen has a dipstick reaction positive for blood, then, the presence of blood casts is expected.
The clinical significance of the hyaline fatty casts is unknown. These casts were found twice in apparently healthy persons. We haven't found any explanation or outcome in the literature about this situation. On the otherhand, this figure is frequent and considered as moreless significant in feline.(http://128.253.82.7/block3/ua-sed/fatty.htm)