Introduction: Different kinds of pediatric renal tumors are known, the commonest of which is Wilms' tumor or nephroblastoma; other less common tumors are nephroblastomatosis, rhabdoid malignant tumor, clear cell sarcoma, congenital mesoblastic nephroma and multilocular cystic nephroma. However, the diagnostic imaging features of all these neoplasms are very similar. Ultrasonography (US) and Computed Tomography (CT) have currently a preminent role in the diagnostic evaluation of these conditions, compared to conventional radiology. The use of Spiral Computed Tomography (spiral CT) has definitely improved the efficacy of CT and we report on the advantages of this technique in both diagnosing and staging pediatric renal tumors.
Material and methods: We examined 11 children with renal masses, 5 boys and 6 girls, whose age ranged 3 days to 10 years. All of them were submitted to US and CT; an abdominal plain film was previously obtained in 5 cases. Five patients were examined with conventional CT scaning, while the other 6 patients were submitted to spiral CT. CT examinations were always performed before and after i.v. administration of nonionic contrast medium (3 mL/kg). Contrast medium injection was performed manually in most cases; a mechanical injector was used only for older children, with 1 mL/s injection rate. Volume scan started at the end of manual or mechanical injection, or in some cases with a 70-second delay from the beginning of the mechanical injection. Spiral CT examinations were performed with 5-mm collimation thickness, 10 mm/s table speed (pitch = 2), 5-mm reconstruction intervals. In 4 of 6 cases studied with spiral CT a simple sedation of the patients was necessary.
Results: In 4 patients the abdominal plain film provided diagnostic information based on indirect signs such as bowel loops displacement by the tumor; it showed also some calcifications within the lesion in 1 of these cases and it was negative in 1 case. US allowed to detect the tumor and to evaluate its site, size and morphology in all patients. However, this technique is inaccurate in detecting abdominal lymph nodes involvement and failed to show two small cortical lesions in the contralateral kidney. CT always allowed to confirm the renal origin of the tumor, clearly showing the mass morphology and size and its intra- and extrarenal spread; moreover this technique evaluated the densitometric pattern of the mass before and after contrast medium administration. Compared to conventional CT, the spiral technique improved the enhancement of the lesion and abdominal vessels; the latter were better studied using multiplanar reconstructions (MPR). Furthermore, spiral CT detected a peritumoral pseudocapsule in 3 cases, a 5-mm lesion of the contralateral kidney in 1 case and abdominal lymph nodes involvement in 1 case. Angiography was performed in 2 patients to assess the presence of hemorrhagic components within the lesion and the possibility of preoperative embolization.
Discussion: CT is currently the technique of choice in the diagnosis and staging of renal masses in children, since it allows to recognize lesion site, size and densitometric patterns and provides an excellent visualization of surrounding structures (vessels and lymph nodes). Spiral CT further improves the examination quality, reducing the sedation time and requiring lower radiation doses. The use of MPR improves the depiction of great vessels and permits to detect venous thrombosis. Finally, synchronous lesions in the contralateral kidney and metastases to the liver and lungs are more easier to show.