Takashi Arakawa1, Si Eun Hwang2, Ji Hyun Kim3, Joerg Wilting4, José Francisco Rodríguez-Vázquez5, Gen Murakami6, Hong Pil Hwang7, Baik Hwan Cho7. 1. Fumon-in Clinic, Mashiko-cho, Tochigi, Japan. 2. Department of Surgery, Daejeon Sun Hospital, Daejeon, Republic of Korea. 3. Department of Anatomy, Chonbuk National University Medical School, Geonji-ro 20, Deokjin-gu, Jeonju, 561-712, Republic of Korea. 407kk@hanmail.net. 4. Department of Anatomy, School of Medicine, Georg-August-Universität Gőtingen, Gőttingen, Germany. 5. Department of Anatomy and Human Embryology, Institute of Embryology, Faculty of Medicine, Universidad Complutense, Madrid, Spain. 6. Division of Internal Medicine, Iwamizawa Asuka Hospital, Iwamizawa, Japan. 7. Department of Surgery & Biomedical Research Institute, Chonbuk National University Hospital, Jeonju, Republic of Korea.
Abstract
PURPOSE AND METHODS: The anal sinuses, small furrows above the pectinate line, sometimes form perianal abscesses in adults. We examined the pattern of fetal growth of the anal sinus and sphincters using 22 mid-term (8-18 weeks) and 6 late-stage (30-38 weeks) fetuses. RESULTS: In mid-term fetuses, the external and internal sphincters gradually increased in thickness, depending on specimen size (from 0.2 to 1.5 mm), whereas the anteroposterior diameter of the anal canal at the epithelial junction was relatively stable (0.5-1.0 mm) irrespective of specimen size. Anal canal diameter increased less than twofold between mid-term and late-stage fetuses, from 0.5-1.0 to almost 2 mm, whereas sphincter thickness increased over tenfold, from 0.2-1.5 to almost 3.5 mm. The anal sinus often showed balloon-like enlargement when the sphincter muscle bundles were tightly packed in mid-term, but not in late-stage fetuses. CONCLUSIONS: Large concentric mechanical stress from the sphincters in late-stage fetuses apparently prevented the anal sinus from expanding in a balloon-like manner. Conversely, to avoid anal stenosis, the growing sinuses maintained a luminal space of the anal canal in response to stress from rapidly growing sphincters. The inferiorly extending sinus usually provided temporal double canals separated by a thick column. In the presence of double lumens, anal canal duplication is likely to develop without any abnormalities of the anal epithelium and sphincters.
PURPOSE AND METHODS: The anal sinuses, small furrows above the pectinate line, sometimes form perianal abscesses in adults. We examined the pattern of fetal growth of the anal sinus and sphincters using 22 mid-term (8-18 weeks) and 6 late-stage (30-38 weeks) fetuses. RESULTS: In mid-term fetuses, the external and internal sphincters gradually increased in thickness, depending on specimen size (from 0.2 to 1.5 mm), whereas the anteroposterior diameter of the anal canal at the epithelial junction was relatively stable (0.5-1.0 mm) irrespective of specimen size. Anal canal diameter increased less than twofold between mid-term and late-stage fetuses, from 0.5-1.0 to almost 2 mm, whereas sphincter thickness increased over tenfold, from 0.2-1.5 to almost 3.5 mm. The anal sinus often showed balloon-like enlargement when the sphincter muscle bundles were tightly packed in mid-term, but not in late-stage fetuses. CONCLUSIONS: Large concentric mechanical stress from the sphincters in late-stage fetuses apparently prevented the anal sinus from expanding in a balloon-like manner. Conversely, to avoid anal stenosis, the growing sinuses maintained a luminal space of the anal canal in response to stress from rapidly growing sphincters. The inferiorly extending sinus usually provided temporal double canals separated by a thick column. In the presence of double lumens, anal canal duplication is likely to develop without any abnormalities of the anal epithelium and sphincters.
Authors: Tao Zhang; Hai Lan Zhang; Da Jia Wang; Xiao Bing Tang; Hui Min Jia; Yu Zuo Bai; Zheng Wei Yuan; Wei Lin Wang Journal: Int J Colorectal Dis Date: 2010-08-05 Impact factor: 2.571