Sonographic Determination of Type in a Fetal Imperforate Anus.

Objectives-The purpose of this study was to determine the type of an imperforate anus by using sonography in the prenatal period. Methods-This retrospective study evaluated the fetal anus in all pregnant women, including low-and high-risk populations, between February 2010 and November 2013. High-type imperforate anuses were diagnosed by prenatal sonography when the anal sphincter muscles and anal canal mucosa were not visible. Low-type imperforate anuses were prenatally suspected when at least 1 of the following was present: (1) a small anus; (2) no visible anal mucosa; or (3) close location of the genitalia by the anus without a visible perineal body, particularly in a female fetus. Results-Among the 9499 fetuses, 41 were prenatally suspected of having an imperforate anus, and 32 were confirmed to have this disorder. During the same study period, there were 11 false-negative cases, for a diagnostic sensitivity rate of 74%. All 9 fetuses who were confirmed to have a normal anus were prenatally suspected of having a low-type imperforate anus. Among the 32 fetuses with a confirmed imperforate anus, 19 were confirmed to have a high or intermediate type and 13 to have a low type. The type in 3 fetuses was incorrectly determined prenatally. Conclusions-Although an imperforate anus is not always diagnosed prenatally, its type can be determined by prenatal sonography.