Invasion by Fat.
—Young1 described 11 cases of invasion of the kidney by fat, or replacement lipoma. In the first case, invasion by fat occurred in the absence of infection, pyuria and nephrolithiasis. In all cases there was an increase in perirenal fat, which was firmer than normal and surrounded the pelvis, entering the hilus around the vessels and pelvis and following the infundibula into the kidney. The pelvis was always embedded in fat, and in some cases was completely obliterated. In 2 cases, not associated with lithiasis, atrophy of the kidney had progressed to a remarkable degree. In the other cases, atrophy of the renal substance had occurred around the fatty replacement.Young stated that replacement lipomatosis is related to the process commonly known as autonephrectomy. Most extensive fatty invasion has occurred in completely obstructed kidneys. Atrophy of renal substance might be secondary to replacement by fat