A teratoid cyst containing nephrogenic tissue in a woman with a horseshoe kidney.

A 21 year old woman presenting with flank pain and vomiting was found to have a cystic lesion associated with a horseshoe kidney. The inner aspect of the cyst wall consisted of connective tissue intermingled with colonic-type epithelium. Within the cyst wall there were multiple foci of immature and incompletely differentiated renal elements, together with fragments of urothelium, smooth muscle, bone, and neuroendocrine tissue. No immature renal blastema were found. This lesion is unique and labelled as a teratoid cyst containing nephrogenic tissue.