Sonographic Determination of Type in a Fetal Imperforate Anus

The purpose of this study was to determine the type of an imperforate anus by using sonography in the prenatal period.

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.

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.

Although an imperforate anus is not always diagnosed prenatally, its type can be determined by prenatal sonography.