Table 2.

Summary of less common adult unilateral renal masses

Mass	Distinguishing features
Multilocular cystic renal tumor	Bimodal age distribution, young boys and middle-aged women
	Large, multiseptated, cystic mass separated by thick, enhancing septations
Renal medullary carcinoma	Predominance in black patients with sickle cell trait
	Aggressive, infiltrating neoplasm arising from the medulla
Collecting duct carcinoma	Aggressive neoplasm arising from the medulla
Metanephric adenoma	Produces erythropoietin and is associated with polycythemia in 12% of cases
	Benign neoplasm related histologically to Wilms tumor
Leiomyoma	Commonly found in women in the 2nd to 5th decade of life
	Hypervascular
	Benign
Hemangioma	Demonstrates early intense enhancement on the arterial phase that persists on the delayed phase
	Hyperintense on T2-weighted MR images
Lymphangioma	Well-defined uni-or multiloculated mass arising from the renal sinus or perinephric space; locules do not enhance
	Communicating cysts with lymphoid cells in their septa
Sarcoma	Different histologic subtypes: leiomyosarcoma, angiosarcoma, rhabdomyosarcoma, etc.
	Nonspecific imaging characteristics
Renomedullary interstitial tumor	Benign tumors arising from renomedullary interstitial cells
	Commonly found on autopsies as small lesions, but clinically are rare and not seen
Carcinoid	Neuroendocrine tumor that can manifest with carcinoid syndrome on liver metastasis
	Somatostatin receptor scintigraphy can aid in staging, but not often in locating the renal tumor
Small cell carcinoma	Resembles its counterparts arising from the trachea-bronchial tree
	Aggressive behavior
Juxtaglomerular apparatus tumor	May produce elevated renin, associated with hypertension