Pathology report:

Tissue origin: Right kidney.
Gross description: Specimen Type: Radical nephrectomy Laterality: Right Kidney Size: Kidney dimension: 7.5 x 6 x 3.5 cm Weight: 105 grams Tumor Site: Lower area Tumor Size: 5 x 4 x 4.5 cm Tumor Characteristics: Solid and cystic with necrosis. Focality: Unifocal Adrenal gland: Not seen. Macroscopic Extent of Tumor Gerota's fascia: Intact Renal Sinus: Renal sinus involvement by tumor not identified Renal vein invasion: Absent Renal Capsule Grossly Intact: Yes. 
Microscopic features: Histologic Type: Nephroblastoma, regressive type. Necrosis: Present (99% of tumor). Nephrogenic Rests: Absent. Anaplasia: Absent Margins: Margins uninvolved by tumor. Renal Sinus: Not involved. Regional Lymph Nodes: Four lymph nodes, free of tumor (0/4) Adrenal Gland: Free of tumor.
Comment(s): Most of the tumor shows chemotherapy-induced changes (necrosis, fibromyxoid and sclerotic stroma with hemorrhage and hemosiderin-laden macrophages). Only rare microscopic foci of epithelial elements within muscular stroma and rare blastemal cells are seen.

Diagnosis: Right kidney, radical nephrectomy: Nephroblastoma, regressive type.  

• horseshoe kidney is the most common type of congenital fusion anomaly of kidneys in children. 

• Wilms tumor is the most common intra-abdominal solid mass lesion in children.

• Wilms tumor has increased incidence in horseshoe kidneys.

Case courtesy Dr. Fatena Ajlouni, Consultant Radiologist. King Hussein Cancer Center. Amman. Jordan.