Rectal Anatomy

The analysis of the anatomy of the distal portion of the large intestine and of the sigmoid colon at the level of the third sacral vertebra is continuous with the distal portion of the large intestine: the rectum.

The longitudinal musculature that at the colonic level is arranged in three bands, the taeniae, at the colorectal junction expands again to form a continuous layer of longitudinal musculature [1]. The haus-tra disappear and the distal portion of the intestine appears as a smooth, almost cylindrical tube. The regular mucosal folds are missing, however the rectum may show some folds (Fig. 1). One of these is usually located 8-10 cm above the anum (Kohlrausch fold) and below it the rectal lumen dilates to form the rectal ampulla. The rectum approaches the anterior surface of the posterior pelvic wall and has a peritoneal covering extending on to its lateral and anterior surface and reflecting onto adjacent organs below the Kohlrausch fold (Fig. 1). In women the peritoneal recto-uterine reflection forms the pouch of Douglas; in men the peritoneal reflection between the rectum and prostate is obliterated and forms Denonvilliers fascia. A thin rectovaginal septum separates the rectum from the vagina. The rectum is about 12-15 cm long and is divided into three portions: upper, middle and lower. The upper rectum extends from the recto-sigmoid junction (readily recognised by the surgeon because the taeniae have disappeared, but lacking a precise radiologic reference) to the middle rectal valve (Kohlrausch valve) located on the right lateral margin of the ampulla at the level of the peritoneal reflection. Thus, the upper rectum is intraperi-toneal [2]. The mid and lower rectum are extraperi-toneal. On the left lateral margin two valves may be present (Houston's valves). The lower valve represents the superior limit of the lower rectum while the superior limit of the mid-rectum is Kohlrausch valve (Fig. 1).

The anal canal is 3-4 cm long and is located between the rectum superiorly and the perianal skin inferiorly [3]. Its superior limit is defined by the inter nal anal sphincter and by the ano-rectal angle, delimited by the levator ani muscle, while for anatomists the ano-rectal junction corresponds to the pectinate line following the level of the anal valves [4].

The pelvic cavity is grossly cone-shaped and the muscle and bone segments constitute the walls and the pelvic floor [5]. Anteriorly the walls are represented by the pubis and laterally by the internal obturator muscles, posteriorly by the sacrum and the pyramidal muscles.

The internal obturator muscle originates from the pubis and the obturator membrane, reaches the lesser ischiatic foramen to leave the pelvic cavity and insert onto the greater trochanter. The pelvic floor is exclusively muscular, it supports the intrapelvic viscera and has the shape of a roof. The steepest point corresponds to the anal orifice. The pelvic floor essentially consists of the levator ani, extending from the horizontal portion of pubis lateral to the aponeurosis of internal obturator muscles. Between the anteromedian fibres of these muscles there is a triangular gap covered with the urogenital diaphragm through which the urethra and the vagina pass into the perineum. Posterior to the urogenital diaphragm, the fibres of levator ani muscle cross, delimiting the anal orifice, and reach the sacrococ-cygeal raphe.

The levator ani muscle is oblique to reach the steepest point of the floor, thus transverse CT scans section it almost perpendicularly. Only coronal MR scans visualise the muscle completely [6]. Posteriorly, the pelvic floor is composed of the ilio-coccygeus muscle continuous with the levator ani. Outside the 'pelvic cone', posteriorly, the posterior group muscles (greatest, middle and least gluteal muscle) trans-versally located between the sacrum, the wing of ilium and the femur, attach the lower limb to the pelvis together with the muscles of the anterolateral group of the leg extending longitudinally between the iliac spine and proximal femur. Outside the pelvic cone there are the pectinate and external obturator muscles transversally located between the pubis and the posterior aspect of femur.

What Houston Valv Rectum

Fig. 1. Anatomy of the rectum: scheme. At about 8-10 cm from internal anal sphincter, on the right lateral wall there is a Kohlrausch valve (2) corresponding to the peritoneal fold. It represents the upper limit of mid-rectum. On the left lateral wall there are the inferior (1) and superior (3) Houston valves. Inferior Houston valve (1) represents the upper limit of the lower rectum while the recto-sigmoid junction (4) is not definitely recognised on imaging. It is located 10 cm from the anus

Fig. 1. Anatomy of the rectum: scheme. At about 8-10 cm from internal anal sphincter, on the right lateral wall there is a Kohlrausch valve (2) corresponding to the peritoneal fold. It represents the upper limit of mid-rectum. On the left lateral wall there are the inferior (1) and superior (3) Houston valves. Inferior Houston valve (1) represents the upper limit of the lower rectum while the recto-sigmoid junction (4) is not definitely recognised on imaging. It is located 10 cm from the anus

Was this article helpful?

0 0
Dealing With Erectile Dysfunction

Dealing With Erectile Dysfunction

Whether you call it erectile dysfunction, ED, impotence, or any number of slang terms, erection problems are something many men have to face during the course of their lifetimes.

Get My Free Ebook


Post a comment