RESUMEN
Germ Cell Tumours (GCTs) in children are uncommon, constituting approximately only 3% of all malignancies in children younger than 15 years of age. Primary extragonadal GCTs constitute only 1-5% of all GCTs and a retroperitoneal site is seen only in 4% of all extragonadal GCTs. Extragonadal GCTs arise from local transformation of primordial germ cells which have been misplaced during the migration of these cells through the midline dorsal mesentery in the fourth-sixth week of embryogenesis. GCTs in children show remarkable variability in age, site, presentation and histology. This is the case of a three-year-old male child who presented with a history of an abdominal swelling which was rapidly progressive in nature. Radiology showed a large retroperitoneal mass and lesions in the liver. Histopathology, immunohistochemistry and serum Alpha-fetoprotein (AFP) values confirmed a diagnosis of pure primary extragonadal yolk sac tumour.
