An Incidental Solitary Fibrous Tumour in the Retroperitoneum, Coexisting with Ipsilateral Atrophic Kidney

Solitary fibrous tumour (SFT) is a relatively uncommon spindle-cell neoplasm that most commonly arises in the pleura, but which may also arise from other serosal surfaces outside the pleura. However, SFT is now known to affect various serosal surfaces including pericardium, peritoneum, retroperitoneum nasal and paranasal sinuses, thyroid, cavernous sinus or pituitary fossa. The histologic features of this lesion may create diagnostic confusion with a variety of other spindle-cell tumours. To the best our knowledge, no cases with SFT have been previously noted in the retroperitoneum coexisting with atrophic kidney. Herein, we report the unique association of a solitary fibrous tumour in the retroperitoneum coexisting with ipsilateral atrophic kidney in a 60-year-old man and define histopatological findings of this tumour.