Contrast enhanced ultrasound of renal masses

Table 1 Rare renal tumors according to the current WHO classification[76]

Entity	Dignity	Clinical meaning
Renal cell tumors
RCC associated with neuroblastoma	Malignant	Long term survivors of childhood neuroblastoma
Nephroblastic tumors
Nephroblastoma	Malignant	Malignant embryonal neoplasm; 1:8000 children, 98% < 10 yr; if treated excellent prognosis = Wilm’s tumor
Nephrogenic rests and nephroblastomatosis	Malignant potential	Nephrogenic rests in 1% of infant autopsies; possible transformation into nephroblastoma
Mesenchymal tumors in children
Ossifying renal tumor of infants	Benign	12 cases reported, mostly in children < 18 mo
Clear cell sarcoma	Malignant	Typically bone metastasis, metastases can develop late
Rhabdoid tumor	Malignant	Highly invasive; 80% ≤ 2 yr; 2 yr survival rate < 20%
Congenital mesoblastic nephroma	Malignant	Excellent prognosis when completely excised; recurrence rate 5%; metastases in rare cases
Mesenchymal tumors in adults
Leiomyoma	Benign	Arises typically from the renal capsule; incidental tumors < 10 mm, but sometimes large
Hemangioma	Benign	No mitosis and nuclear pleomorphism
Lymphangioma	Benign	Presenting as a peripelvic or renal sinus mass. Some cases may develop secondary to inflammatory lower urinary tract diseases; cystic
Juxtaglomerular cell tumor	Benign	Benign rennin-secreting tumor → hypertension; about 70 tumors described; typically < 3 cm
Renomedullary interstitial cell tumor	Benign	Common autopsy findings in adults; > 1 tumor in 50%; < 5 mm
Intrarenal Schwannoma	Benign	Common benign tumor of peripheral and auditory nerves
Cystic nephroma	Benign	Cystic; female >> male
Mixed epithelial and stromal tumor	Benign	Complex renal neoplasm; contains large cysts
Neuroblastoma	Benign
Solitary fibrous tumor	Malignant potential	Frequent painless hematuria; confused with RCC
Paraganglioma/phaeochromocytoma	Malignant potential
Leimyosarcoma (incl. renal vein)	Malignant	The most common renal sarcoma; 5-yr survival rate 35%; chemotherapy is ineffective
Osteosarcoma	Malignant
Angiosarcoma	Malignant	Rare, aggressive; poor prognosis; strong male predominance, androgen factor possible; rapid metastases
Hemangiopericytoma	Malignant
Malignant fibrous histiocytoma	Malignant	Pararenal and retroperitoneal extension
Synovial sarcoma	Malignant	Characterized by a specific translocation: t (X; 18)(p11.2; q11); recurrence is commonly seen
Renal carcinoid tumor	Malignant	Association with horseshoe kidney; carcinoid syndrome < 10%; cystic, calcification
Neuroendocrine carcinoma	Malignant	Poorly differentiated epithelial NPL with neuroendocrine differentiation; poor prognosis; necrotic mass
Primitive neuroectodermal tumor (Ewing sarcoma)	Malignant	Inhomogeneous, often replacing the entire kidney; hemorrhage, necrosis
Plasmocytoma, Lymphoma and Leukemia
Lymphoma	Malignant	Typically secondary renal lymphomas; primary renal lymphoma very rare
Plasmocytoma	Malignant	Occurs as a manifestation of a disseminated multiple myeloma
Leukemia	Malignant	Interstitial infiltration of leukemic cells can be called extramedullary leukemia in the kidney
Germ cell tumors
Teratoma	Benign
Choriocarcinoma	Malignant	Difficult to differentiate from high grade urothelial carcinomas; mostly metastases from testicular germ cell tumors

RCC: Renal cell carcinoma; NPL: Neoplasia; >>: Much more frequent or predominantly seen in female.