Histologic (hematoxylin and eosin stain) findings of synchronous primary carcinoid tumor and primary adenocarcinoma arising within mature cystic teratoma of horseshoe kidney. (A) Teratomatous component with multilocular cystic spaces. Original magnification ×20. (B) Teratomatous cyst lined by mucinous columnar enteric-type or colonic-like epithelium with muscular wall. Original magnification ×200. (C) Teratomatous cyst lined by ciliated epithelium with muscular wall. Original magnification ×600. (D) Teratomatous cyst wall composed predominantly of smooth muscle. Original magnification ×100.