Clinical Differentiation between a Normal Anus, Anterior Anus, Congenital Anal Stenosis, and Perineal Fistula: Definitions and Consequences-The ARM-Net Consortium Consensus

Abstract

In the past, an anteriorly located anus was often misdiagnosed and treated as an anorectal malformation (ARM) with a perineal fistula (PF). The paper aims to define the criteria for a normal anus, an anterior anus (AA) as an anatomic variant, and milder types of ARM such as congenital anal stenosis (CAS) and PF. An extensive literature search was performed by a working group of the ARM-Net Consortium concerning the subject "Normal Anus, AA, and mild ARM". A consensus on definitions, clinical characteristics, diagnostic management, and treatment modalities was established, and a diagnostic algorithm was proposed. The algorithm enables pediatricians, midwives, gynecologists, and surgeons to make a timely correct diagnosis of any abnormally looking anus and initiate further management if needed. Thus, the routine physical inspection of a newborn should include the inspection of the anus and define its position, relation to the external sphincter, and caliber. A correct diagnosis and use of the presented terminology will avoid misclassifications and allow the initiation of correct management. This will provide a reliable comparison of different therapeutic management and outcomes of these patient cohorts in the future.

Keywords: ARM-Net Consortium; anal position index; anal stenosis; anorectal malformation; anterior anus; perineal fistula.

Figure 1

(a) Picture of a normal anus in a female infant. (b) Picture of an anterior anus in a female infant. Note the proximity of the anal opening to the external genitalia. (c). Picture of a non-stenotic perineal fistula. The sphincter muscle complex does not encircle the anal opening along the anterior margin.

Figure 2

The algorithm shows the diagnostic pathway that leads to diagnosing a normal anus, anterior anus with or without stenosis, congenital anal stenosis, and perineal fistula (stenotic or non-stenotic). * The anal caliber is measured according to the equation presented by el Haddad and Corkery [21].

Figure 3

API measurement in females (a) and males (b). API is calculated by dividing the distance between the fourchette (a) or scroto-perineal fold (b) to the center of the anus with the distance between fourchette (a) or scroto-perineal fold (b) to the tip of the coccyx marked on a transparent tape or flexible ruler. Anterior displacement is diagnosed when the API is <0.34 in females and <0.43 in boys (overall mean minus 2 standard deviations as presented by Sharma et al. [40]). API = anal position index.

Figure 4

Picture of a female newborn with AA and a perineal groove. The patient also has Pierre-Robin syndrome.