Journal of Endometriosis ( 2010 ; : 1) 19-25 2 © 2010 Wichtig Editore - ISSN 2035-9969 19 Review INTRODUCTION Sixty years ago Fallon wrote in the JAMA that “Four per cent of the last 225 patients with ‘external’ endometrio- sis who were seen at this clinic were less than 20 years old. Four per cent is a small figure, but there are grounds for suspecting that it is less than the true one. And it is a significant, even a large percentage when weighed against the common belief that youth does not have endometrio- sis” (1). In fact, although endometriosis is recognized to be a common cause of chronic pelvic pain for women in their reproductive periods, its occurrence in adolescents has long been underestimated. Adolescent endometriosis is not rare. The Endometriosis Association’s 1998 regis- try of 4000 adult women demonstrated that two-third of them had experienced their first pelvic symptoms before 20 years of age and 21% had pain before 15 years of age (2). Documented rates in adolescent patients undergoing laparoscopy for chronic pelvic pain range from about 25% to 45% (3). Since the adolescent patient with endometrio- sis may pose a certain challenge, several overviews have focused on the issues surrounding disease presentation, diagnosis and management strategies in the young popu- lation (4-7). Few papers have highlighted the differences in adolescent and adult types of endometriosis. In this article, distinctive characteristics of adolescent and young endo- metriosis are considered in order to outline pathogenetic and scientific concepts that might be useful in explaining the wide array of clinical presentations and the variable manifestations of the adult disease as well. Peculiar aspects of endometriosis in adolescents Massimo Candiani 1 , Stefania Ronzoni 2 , Davide Gentilini 3 , Iacopo Tandoi 1 , Edgardo Somigliana 4 , Paola Viganò 5 1 Department of Obstetrics and Gynecology, IRCCS San Raffaele Hospital, Milan - Italy 2 Department of Obstetrics and Gynecology, DMSD San Paolo Hospital, Milan - Italy 3 Istituto Auxologico Italiano, Milan - Italy 4 Pope John’s Hospital, Aber - Oyam District - Uganda 5 CROG: Center for Research in Obstetrics and Gynecology, Milan - Italy ABSTRACT: Although documented rates of endometriosis in adolescent patients undergoing laparos- copy for chronic pelvic pain range from about 25% to 45%, adolescent endometriosis has received lim- ited attention in terms of research activity and follow-up studies. In this manuscript, distinctive charac- teristics of adolescent and young endometriosis have been considered in order to define pathogenetic and scientific concepts that might be useful in clarifying some aspects of the adult disease as well. Some highlights relative to the cellular origin of the disease can be derived from reported cases before menarche, from the appearance of endometriotic lesions in teenagers (mostly stage I-II endometrio- sis), and from the relative infrequency of ovarian endometriotic cysts in this population. Adolescents and young patients might be also particularly useful for studying the natural course of the disease. To this end, clinical manifestations and recurrence patterns of the disease in adolescent patients need to be elucidated. Differences in clinical aspects of the disease between the adult and young populations are presented. Risk of recurrence and potential risk factors involved in the reappearance of the disease in teenagers are completely unknown. (Journal of Endometriosis 2010; 2: 19-25) KEY WORDS: Adolescence, Endometriosis, Pathogenesis, Pelvic pain