Pelvis

The obstetric conjugate can be manually assessed by measuring the distance between the promontory and the inferior margin of the pubic symphysis (diagonal conjugate) using the middle finger minus 1.5 cm (0.6 in).

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In woman, the rectouterine pouch (pouch of DOUGLAS) is the most inferior recess of the peritoneal cavity. It can be accessed through the posterior fornix of the vagina. The pelvic fascia is the connective tissue between the peritoneal lining and the muscular walls and floor of the pelvis which contains nerves, blood vessels and lymphatics. The retropubic space (space of RETZIUS) behind the pubic symphysis and the retrorectal space are regions of the pelvic fascia containing loose connective tissue for the bladder and rectum to expand.

The muscles of the pelvic floor are actively contracted – together with the diaphragm and the abdominal muscles – to increase abdominal pressure during coughing, sneezing, forced expiration and weight lifting. Women more frequently suffer from pelvic floor insufficiency due to the extensive dilation of the levator hiatus during vaginal deliveries.

The puborectalis slings around the anorectal junction and pulls the rectum towards the pubic symphysis. This puborectalis loop is the basis for the perineal flexure of the rectum and maintains the anorectal angle .

The vesicouterine pouch is a peritoneal recess between the uterus and the urinary bladder. The rectouterine pouch (pouch of DOUGLAS, clin. term: cul-de-sac) posterior to the uterus is the most caudal extension of the peritoneal cavity in women and may collect fluids and pus in cases of inflammatory abdominal processes. The pouch of DOUGLAS can be accessed through the posterior fornix of the vagina. The close topographical relationship between the adnexa (ovary and uterine tube) and the appendix vermiformis of the colon explain why inflammations of the appendix (appendicitis) and of the uterine tube (salpingitis) may cause similar pain in the right lower abdominal quadrant.

The prostate gland is separated from the rectum only by the thin rectoprostatic fascia (DENONVILLIERS’ fascia) and the prostate can be assessed by digital rectal examination (DRE). Due to the high incidence of benign prostatic hyperplasia (BPH) and prostatic carcinoma , the digital rectal examination is part of a complete physical examination in men over 50 years of age.

The anal canal has three segments:

• Columnar zone: contains longitudinal folds (anal columns) formed by the underlying corpus cavernosum of rectum.

• Anal pecten: the stratified non-keratinized squamous epithelium creates a white zone in the mucosa; the superior border of this zone is referred to as pectinate line (clinical term: dentate line).

• Cutaneous zone: external skin, inconsistently limited by the anocutaneous line ).

Inspection of the mucosa of a prolapse allows the visual discrimination between a rectal (transverse folds) versus an anal (longitudinal folds) prolapse. Both result in fecal incontinence.

Above the anal valves, the anal sinuses are located as depressions in which proctodeal glands (anal glands) enter the anal canal. These glands may traverse the sphincter muscles and cause fistulas when inflamed and, thus, potentially facilitate the spread of the inflammation into the ischioanal fossa.

The anal sphincter muscles comprise:

• Internal anal sphincter (smooth muscle, involuntary sympathetic innervation): continuation of the circular muscular layer

• Corrugator ani (smooth muscle): continuation of the longitudinal muscular layer

• External anal sphincter (striated muscle, voluntary control via the pudendal nerve): has different segments (subcutaneous, superficial, deep parts)

• Puborectalis (striated muscle, voluntary control via direct branches of the sacral plexus and some contribution by the pudendal nerve): part of the levator ani; loops behind the rectum creating the perineal flexure. Essential to maintain the anorectal angle and for the storage of feces in the rectal ampulla.

The corpus cavernosum of rectum is primarily supplied by the superior rectal artery. Therefore, bleedings of hemorrhoids, which represent dilated rectal cavernous bodies, are arterial bleedings as shown by the bright red color.

Knowledge of lymphatic drainage pathways in the anorectal region is essential in cases of cancer in the anorectal region. Total mesorectal excision (TME) for rectal cancer removes pararectal lymph nodes within the mesorectum and spares the inferior hypogastric plexus and the presacral venous plexus located outside of the mesorectal fascia. The pectinate line inferior to the anal sinuses marks the border between the embryological hindgut (superior part of the anal canal) and the proctodeum (inferior part of the anal canal). Anal carcinoma proximal to the pectinate line metastasise to the pelvic nodes, distal carcinomas spread first to the inguinal nodes. Anal malignancies are staged according to their proximity to the anocutaneous line.

The internal openings of the ureters are usually closed. Contraction of the detrusor muscle for micturition firmly closes the ureteric openings to prevent reflux of urine into the ureters. Extreme dilation of the bladder wall compromises the ureteric closure mechanisms frequently causing a reflux of urine.

Suprapubic cystostomy : The empty bladder is positioned behind the pubic symphysis. Filled with urine, the bladder rises up to 10 cm (3.9 in) above the pubic symphysis pushing its peritoneal lining cranially towards the umbilicus. The bladder is then adjacent to the abdominal wall and can be accessed without opening the peritoneal cavity (suprapubic cystostomy) for cystoscopy or insertion of a suprapubic catheter.

The most common injury of the male urethra during transurethral catheterization occurs in the membranous part. The bends of the urethra have to be straight prior to inserting a catheter to avoid painful perforations of the membranous urethra or the prostatic urethra with consecutive profuse bleedings or extravasation of urine. The seminal colliculus (verumontanum) serves as anatomical landmark for the urinary sphincter during transurethral resection of the prostate (TURP) in cases of benign prostatic hypertrophy.

Because of the shorter length of the female urethra, ascending infections of the urinary bladder (cystitis) are more common in women than in men. Positioning of a transurethral catheter is easier in women due to the straight course of the shorter urethra. The urethral orifice in the vestibule is located ventral to the vagina.