Sudol-Szopinska, Iwona, Małgorzata Konodziejczak, and Wiesław Jakubowski. 2002. “Anal Ultrasound in Patient With Leukoplakia of the Anal Canal. Case Report”. Radiology and Oncology 36 (3). https://www.radioloncol.com/index.php/ro/article/view/1393.