INTERESTING IMAGES The computed tomography features of multifocal nephroblasto- matosis S Andronikou MBBCh (WIts), FCRadDiag (SA), FRCR (London) eWelman MBChB E Kader MBChB Department of Paediatric Radiology, University of Gape Town and Institute of Child Health, Red Cross War Memorial Children's Hospital, Rondebosch, Cape Town Corresponding author SAndronlkou Department of Paediatric Radiology, Red Cross War Memorial Children's Hospital, Gape Town, 7700 Tel: (021) 658-5422. Fax: (021) 658-5101. E-mail: docsav@mweb.co.za Nephroblastomatosis re- fers to persistent metanephric blastemal (nephrogenic) rests found within the kidneys after 34 weeks' gestation. Autopsy stud- ies have shown that they occur in up to 1% of children under 3 months of age. They are consid- ered premalignant owing to their strong association with Wilm's tumours. Even though unifocal and diffuse disease occurs, multifocal nephroblastomatosis is the most common type encoun- tered. Lesions are located prima- rily at the periphery, but may oc- cur anywhere within the kidney. Effective management of these children requires identifi- cation of both the nephro- blastomatosis and the Wilm's tu- mours. Imaging is critical, as sur- gical biopsy may be complicated by the multiplicity and small size of the lesions, as well as the risk of peritoneal seeding. 48 SA JOURNAL OF RADIOLOGY. February 2001 Multifocal nephroblastomatosis has multiple smooth foci in the pe- riphery of the renal cortex. These le- sions are lenticular or ovoid, usually 5-20 mm in size and sharply demar- cated. The kidneys are large and their contour is lobulated, often with signifi- cant bulges. In contrast, diffuse nephroblastomatosis produces a thick uniform peripheral rind of abnormal tis- sue in an enlarged kidney with preser- vation of the renal shape and contour. At computed tomography (CT), the density of the lesions resembles normal cortex. These lesions are poorly vascularised and after contrast admin- istration are markedly hypodense when compared with normal renal cortex. The centrally located normal Figures la and lb: Pre- and post-contrast CT of the kidneys. On the pre-contrast image, the left kidney is enlarged more than the right, but both demonstrate a homogeneous density. After contrast administration, the cheracteristic centrally located enhancing normal parenchyma resembling "stag antlers" (arrows) Is well demonstrated against the non-enhancing peripheral mult/focal nephrogenic rests (crosses). topage49 mailto:docsav@mweb.co.za The computed tomography features of multifocal nephroblastornatosis frompage48 renal tissue shows characteristic dis- tortion resembling "stag antlers" after contrast administration. The most characteristic feature of the nephro- genic rests is their homogeneous ap- pearance. In comparison, Wilm's tu- mours are often heterogeneous both pre- and post-contrast administration. Size and shape are unhelpful features in differentiation. Lymphoma may produce homogeneously enlarged kid- neys that may initially appear identi- cal to diffuse or multifocal nephroblastomatosis, but will not demonstrate the central "stag antlers". CT is considered to have similar potential to gadolinium-enhanced MRI in the diagnosis of nephroblastomatosis with regard to identification and differentiation from Wilm's tumour. In our personal ex- perience, however, MRI has a greater sensitivity for the detection of small lesions. References Goske MJ, Mitchell C, Reslan WA. Imaging of patients with Wilms' tumor. Sem Ural Oneal 1999; 17: 11-20. Rohrschneider WK, Weirich A, Rieden K, Darge K, Trëger J, Graf N. US, CT and MR imaging characteristics of nephroblastomatosis. Pediatr Radial 1998; 28: 435-443. Figures 28 and 2b: Before and after chemotherapy. Typical homogeneous peripheral nephrogenic rests with central "stag antler" configuration of the contrast-enhancing normal parenchyma. The post-chemotherapy CT scan shows a reduction in the size of the nephroblastomatosis, with expansion of the previously compressed normal parenchyma. 49 SAJOURNAL OF RADIOLOGY· February 2001