Well-Differentiated Neuroendocrine Tumor

Primary well-differentiated neuroendocrine tumor of the kidney (previously known as carcinoid) is an exceedingly rare tumor. About 20% of cases arise in patients with horse-shoe kidneys. Some cases are associated with renal teratoma or polycystic kidney disease. The average age at presentation is about 50 years. Presenting symptoms usually include back/flank pain, hematuria, fever, weight loss, and enlarging abdominal mass. About one-third of cases are asymptomatic and discovered incidentally. Neuroendocrine syndromes are uncommon. The tumor is usually solitary, well-demarcated, solid, and yellow-tan in appearance. Mean size is about 8 cm. One-third show cystic component. About 50% of cases are confined to the kidney. Involvement of perinephric fat and renal vein is seen in 30% and 10% of cases respectively.