Pure primary renal yolk sac tumour in an adult: extremely rare clinical finding.

We present a rare case of an extragonadal retroperitoneal yolk sac tumour in an adult male, who presented with severe abdominal pain to his local hospital. Imaging revealed a large retroperitoneal soft tissue mass with no evidence of metastases. Initial biopsy demonstrated poorly differentiated carcinoma, favoured to be renal cell carcinoma. The patient underwent surgical resection following re-presentation with severe abdominal pain and significant interval enlargement of the mass. Laparotomy revealed a renal tumour that had ruptured through the left mesocolon into the peritoneal cavity. Postoperative histopathological examination revealed a yolk sac tumour involving the kidney, perinephric fat, renal sinus fat, renal hilar lymph node and colonic mesentery. Immunohistochemical staining for alpha-fetoprotein and glypican 3 was positive in the tumour cells without evidence of other germ cell elements, confirming the diagnosis of a pure yolk sac tumour. To our knowledge, this is an extremely rare case of a primary pure yolk sac tumour arising from the kidney in an adult.