The extensive differential diagnosis of a paediatric abdominal mass may be considerably narrowed by considering the clinical information and radiographic characteristics. Less than half of abdominal masses are surgical and, of these, nearly all are retroperitoneal, and usually renal. A neonatal abdominal mass is usually benign, retroperitoneal and renal, caused in particular by hydronephrosis and multicystic dysplastic kidney. The commonest neonatal benign and malignant tumours are mesoblastic nephroma and sacrococcygeal teratoma respectively. In the older child abdominal masses are most likely to be malignant retroperitoneal tumours, especially neuroblastoma and Wilm's tumour. The commonest benign mass in this age group is appendix abscess. The initial radiological investigation is a plain abdominal film. In the neonate, where the most likely cause is a benign cystic mass, ultrasound is the preferred subsequent investigation. In the older child, where the risk of malignancy is higher, it may be justifiable to use CT in preference to ultrasound. The spectrum of abdominal masses in paediatric practice is diverse, but a knowledge of the statistical distribution, clinical features and imaging characteristics allows the formulation of a focused differential.

hydronephrosis; teratoma; neuroblastoma; Wilm’s appendix mass