There are several important clinical features that must be elicited on perineal examination, such as the presence or absence of the anus, the presence of vaginal and urethral openings, the presence and exact position of the fistula, the size of the anal dimple and midline groove, and the presence of a presacral mass. Due to the VACTERL condition, a full and detailed examination of the entire child is mandatory after the discovery of an ARM. Particular stress must be placed on the examination of the spine, the pelvis, the esophagus, and the cardiovascular system to ensure a life-threatening abnormality has not been overlooked because of an absent rectum.
In order to identify anomalies correctly, a detailed understanding of the normal anatomy of the perineum is required. On inspection of the perineum the position of the anus or its absence should be noted. The normal position of the anus in a girl is one third of the distance from the coccyx to the fourchette. If the anus is present and in the correct position the passage of a soft catheter greater than 2 cm into the rectum and the presence of meconium passage rules out atresia. The parasagittal muscle fibers are located on either side of the midline of the normal anal position. These fibers are responsible for the midline but
tock groove. The higher the fistula in the urethra, the fewer the parasagittal fibers present, hence the flatter the perineum appears. The midline groove between the buttocks and the anal dimple also becomes less prominent the higher the fistula (Fig. 9.1).
Anal stenosis is a subjective diagnosis that is frequently made following a "tight" digital examination. The normal size of the anus is described as 1.3 + (3 x birth weight in kg) in millimeters.
In the presence of an anal membrane, the anus is usually in the normal position. However, a thin epithelial lining is present overlying the opening. Meco-nium can be seen bulging behind the membrane.
In boys, the midline raphae and the scrotum need to be examined for a fistulous opening. The urethral meatus is assessed for the presence of meconium staining, which occurs with rectourethral fistula (Fig. 9.2). A damp clean swab can be left at the me-atus to assess for meconium staining and microscopy should be performed on the urine. The presence of meconium or squamous epithelium in the urine indicates a fistula into the urinary system. Other lesions that can occur include a midline subepithelial tract along which meconium can be milked or a midline skin tag described as a "bucket handle". On occasion a thin membrane (called the anal membrane) obstructs the meconium, which can be seen behind it.
In females a key step is determining the number of orifices present. The presence of the hymen and the small size of the newborn perineum can make this quite challenging and leads to significant confusion. Three frequently made errors are failure to diagnose the presence of a single orifice only (cloaca) and failure to visualize the vestibular fistula or to label ves-
fibular fistulas as vaginal. Careful inspection with a good light source is necessary to avoid these pitfalls. If the size of the introitus appears smaller than in a normal female, the possibility of a cloacal anomaly is very high. On probing a rectovestibular fistula with a fine forceps, the probe will pass posteriorly and backwards. The probe in a rectovaginal fistula will pass only upwards and this has long been stated as a method of differentiating between the two.
Rosen et al. in 2002 assessed the incidence of rec-tovaginal fistula and demonstrated the importance of the correct initial diagnosis. A review of 617 patients over a 20-year period revealed that only 6 (1%) had a true rectovaginal fistula. Of a total of 139 patients who were referred after a previous repair, 42 had a diagnosis of rectovaginal fistula. The diagnosis was incorrect in all cases. Twelve patients had a rectovestibular fistula, and 30 had a cloaca with a persistent urogenital sinus requiring a second complete repair .
In the rare female with a perineal groove anomaly, the anus is not stenotic but there is a mucosal strip extending through a slightly bifid perineal body to the introitus. In the "perineal canal" variant of an H-fistula in girls the anus is patent (± stenosis). Deep in the fourchette is a fistulous orifice and mucosal-lined canal running through the perineal body to the anterior wall of the anal canal.
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