Contribution of 3D Modeling in Surgical Management of Pediatric Retroperitoneal and Pelvic Tumors

Inclusion Criteria: Children: * Children between 3 months and less than 18 years old * Children with a pelvic tumor requiring an MRI for a possible surgical intervention * Children with a retroperitoneal tumor requiring a CT scan or MRI with a view to surgical intervention * Children with no contraindication for a CT scan and/or 3T MRI * Children whose parents do not object to their participation in the study Other participants: * Operating surgeon agreeing to participate in the study * Caregiver agreeing to participate in the study * External surgeon agreeing to participate in the study Exclusion Criteria: Children : * Contraindication to MRI: metallic ocular foreign body, pacemaker, mechanical heart valve, old vascular clips on cerebral aneurysm * Need for an MRI under general anaesthesia * Contraindication for a CT scan with injection: renal failure, allergy to iodinated contrast products * Patients having participated in a therapeutic clinical trial involving a new molecule within 30 days before inclusion * Emergency situation