Mesoblastic Nephroma Etiology: hamartoma of kidneyUS: enlarged solid reniform shaped mass in renal fossaClinical: most common solid renal mass up to 3 months of age Radiology Cases of Mesoblastic Nephroma Transverse (above) and sagittal (below) US images shows an enlarged solid reniform shaped mass in the right renal fossa. Surgery Cases of Mesoblastic Nephroma Surgical image shows an extremely large right renal tumor displacing the cecum into the left lower quadrant.