There are many articles about the role of preoperative MRI in determining the type and level of anorectal malformation that can be helpful in planning and predicting the prognosis and also investigating the spinal and urethral anomalies that indirectly affect the management of disease and operation (2). MRI also has a role in these patients for demonstration of the status of sphincter muscle complex, the symmetry of the sphincter, and perirectal fibrosis (10, 11).
Sonography is usually used to determine the level of the disorder (low and high) indirectly based on the distance between location of anoplasty and pouch of rectum. Although this approach is not very determinative and there are a lot of diagnostic overlaps in this field (1, 7-9).
In review articles, we found only one paper about the detection of the passage of rectum from levator ani muscle in the transverse view of infra-coccygeal plane that could be helpful for differentiation of high and low groups (10). In the study, infra-coccygeal US was sited inferior to the coccyx and posterior to the anus for conducting the approach. Transverse images of the anorectal area were obtained by scanning. Sedation was not used during the procedure. Similar to our study, cases underwent colostomy. After that, a definitive repair pull-through was operated.
The pre-operative exact localization of anal pit and especially sphincter muscle complex with sonography can be helpful for surgeons to select less invasive approaches that determine the future fecal continence of the patient (12).
In this study, with accurate ultrasound investigation of the perineal region, we noticed two sonographic findings that can be helpful in patients with imperforate anus to determine the proper path of the anal canal for pull-through operation. These findings were multi-layered view of anal pit and sphincter muscle complex.
Multi-layered view of anal pit is exactly similar to gut signature and is determined as a peripheral hypoechoic layer with two central parallel echogenic lines. This view was probably the result of fetal anal pit as a result of non-ruptured anal membrane and/or non-route formation. This view was not seen in patients with recto-vestibular fistula. Although it had 3-4 mm diameter, in cloacal anomaly patient, it had about 10 mm anterior-posterior diameters in sagittal plane that was probably due to fetal merge of anal and vaginal orifices.
In most of patients, the anal pit was not straight and it had a parasagittal position and a slightly curved with eccentric attachment to the center of the sphincter muscle complex. These can explain the pathophysiology of the disease.
Anal sphincter and muscle complex was seen as a circular muscular tissue bulk that surrounds the echogenic mucus of the gastrointestinal tract. It was visible on the coronal plane at depth of subcutaneous fat of the perineal area with 2 - 3.6 mm thickness. This complex was visible in all of our 10 patients.
In addition, the result of this study shows that the distance between the rectal pouch and the skin without attention to the muscle sphincter is unreliable and can make serious pitfalls and unaware complications. In all patients, the distance between the rectal pouch and skin through the anal pit and muscle complex (11 mm) was longer than the shortened distance between the rectal pouch and the skin (3 - 8 mm, mean: 4.7 mm).
In lithotomy position, it is important to notice that the multi-layered view of the anal pit and anal sphincter complex was only visible in the coronal view and was invisible in the routine sagittal and transverse view, then it may be ignored and not noticed in studies. Therefore, we believe sonography is mandatory in both sagittal and coronial views. In the review of articles, we did not encounter a similar publication about the use of these findings in patients with imperforate anus, although there are many articles about the use of sonography in determining the anal sphincter complex in adults with various diseases (13, 14).
This is a preliminary cross sectional study with a low number of patients. In addition, the frequency of the ultrasonic probe device was our study limitation. Exact examination of the perineal region with high-frequency probes (14 to 20 MHz) with a high number of patients can provide better and more reliable results.
The multi-layer view of anal pit and the muscular bulk of anal sphincter complex are the two important sonographic findings that can better differentiate the level of anal malformation and act as an indicator for the location of anal sphincter pull through in patients with imperforate anus.
LEAVE A COMMENT HERE: