Surgical Anatomy

Several structures provide support for the posterior vagina and rectum:

1. The rectovaginal septum lies between the rectum and the vagina. It extends caudad from the posterior cervix and the uterosacral-cardinal complex to the perineal body centrally and the levator fascia laterally on each side. The rectovaginal septum is densest distally where it is composed of dense connective tissue. Its midportion contains fibrous tissue, fat, and neurovascular tissue. Proximally it is mostly composed of fat cells.

2. The pararectal “fascia” lies between the rectovaginal septum and the rectum. It originates from the pelvic sidewalls and divides into fibrous anterior and posterior sheaths, which envelop the rectum. It also contains blood vessels, nerves, and lymph nodes that supply the rectum.

3. The levator ani consists of the paired ileococcygeus, puborectalis, and pubococcygeus muscles. These function to maintain constant basal tone and a closed urogenital hiatus. They also provide a reflex contraction in response to increases in intraabdominal pressure. The puborectalis muscle acts as a sort of sling that causes the posterior vaginal wall to angulate about 45 degrees from the vertical.

4. The perineal body is the central point between the urogenital and anal triangles (Fig. 7-1). It contains interlacing muscle fibers from the bulbospongiosus and superficial transverse perineal muscles and the anterior portion of the external anal sphincter. There is also a contribution from the longitudinal rectal muscle and the medial fibers of the puborectalis muscle.

Figure 7-1 The perineal body is the central point between the urogenital and anal triangles. It consists mainly of interlacing muscle fibers from the bulbospongiosus muscle, the superficial transverse perineal muscle, and the external anal sphincter. There are also contributions from the longitudinal rectal muscle and the medial fibers of the puborectalis muscle.

Several critical components of pelvic floor relaxation are associated with rectocele formation. Loss of the normal horizontal axis of the levator plate and vagina, weakness of the urogenital and pelvic floor diaphragms, detachment of the levator ani from the central tendon of the perineum, and widening of the anogenital hiatus allow intraabdominal forces to be transmitted directly to pelvic organs without counteraction by normal underlying compensatory mechanisms. In addition, the rectovaginal septum becomes attenuated or disrupted, which allows intravaginal herniation of the rectum. Isolated breaks in the rectovaginal septum facilitate rectocele formation. There are several areas along the rectovaginal septum where breaks are commonly found (Fig. 7-2). The most common is a transverse separation immediately above the attachment of this septum to the perineal body, which results in a low or distal rectocele (seen just inside the introitus). A midline vertical defect is also very common and most likely represents a poorly repaired or poorly healed episiotomy. Rarely, one can see lateral separation on one side. Defects can occur in isolation or in combination. Identification of specific defects is important when one is considering performing a site-specific posterior repair. Therefore, each of these components of pelvic floor relaxation must be addressed at the time of rectocele or posterior vaginal wall repair. Identification of the specific pathophysiological features is critical when one is evaluating female patients with symptoms or signs of pelvic floor relaxation, including stress incontinence, cystocele, and/or uterine prolapse. Maintenance of the normal horizontal vaginal axis to allow compensatory mechanisms to be reestablished is an important goal of surgical repair of pelvic floor relaxation. Corrective surgery for posterior vaginal wall prolapse may include correction of the rectocele by reinforcement of the rectovaginal septum and prerectal and pararectal fasciae, repair of the levator muscle defect to restore the levator hiatus, restoration of the horizontal supporting plate of the proximal vagina, and repair of the perineum.

Figure 7-2 Illustration of the various sites where the rectovaginal septum can become disrupted. Shown are midline, lateral, and transverse (proximal and distal) breaks. More than one break in the septum can be present, and multiple breaks can be continuous with each other.

The indications for repair of the posterior compartment are not clearly defined for a patient with no symptoms attributable to the rectocele who is being evaluated for correction of apical and/or anterior compartment prolapse. Some surgeons advocate posterior compartment repair in all patients undergoing vaginal prolapse surgery, so that all areas of pelvic floor weakening are addressed. Other surgeons selectively repair the posterior compartment only in cases of defecatory dysfunction, most commonly outlet obstruction that is felt to be attributable to the rectocele or to posterior compartment prolapse extending beyond the hymen. These surgeons feel that the potential for morbidity associated with the repair of asymptomatic posterior prolapse (pain and dyspareunia) outweighs the benefit of complete “anatomical correction.” Furthermore, in selected cases of fecal incontinence secondary to an anal sphincter defect, transperineal anal sphincter repair may be combined with posterior compartment repair.

Preoperative Evaluation

History

Numerous symptoms related to bowel and sexual function have been attributed to posterior compartment prolapse, although few studies have adequately correlated surgical repair with definitive symptom improvement. Symptoms include sensation of a vaginal bulge or lump, incomplete evacuation of the bowel, constipation, fecal straining, the need for vaginal digitalization to facilitate defecation (splinting), and dyspareunia. Despite the association between constipation and the presence of a rectocele, many other factors can contribute to constipation. Furthermore, rectocele size does not directly correlate with symptoms.

Physical Examination

Assessment of the posterior vaginal compartment should be a routine component of the examination of any patient with incontinence or pelvic organ prolapse (see Chapter 1). This includes inspection for the presence of enterocele, rectocele, and perineal weakness. Generally, the posterior compartment is evaluated by displacing the anterior vaginal wall with half of a Graves speculum to allow complete visualization of the posterior wall during straining. Digital examination with one of the examiner’s fingers in the vagina and one finger in the rectum allows assessment of the rectovaginal septum, which is often quite attenuated with Pelvic Organ Prolapse Quantification (POP-Q) stage II and III rectoceles and may contain an enterocele sac. Physical examination may not reliably distinguish an enterocele from a high rectocele. Inspection of the rectovaginal septum for isolated breaks, typically found near its attachment to the perineal body or in the midline, is performed by placing a finger in the rectum and lifting up the posterior vaginal wall. Finally, inspection of the perineal body is performed to identify any defect associated with a widened introitus and a decreased distance between the anus and posterior vaginal fourchette. In cases of severe prolapse, combined defects of posterior vaginal wall support at the level of the pelvic floor and the perineum are often present.

The vaginal axis is assessed by digital examination. In a nulliparous woman with a well-supported pelvic floor, the proximal vagina will show a posterior curvature. In a patient with pelvic floor relaxation, the vaginal axis will be horizontal in the lithotomy position. Restoration of this important vaginal axis prevents further development or recurrence of pelvic organ prolapse. Increases in abdominal pressure will cause vaginal coaptation when the normal vaginal axis has been restored.

The final portion of the posterior compartment examination involves assessment of the anal sphincter, including resting tone, voluntary activity, and reflex activity. Defects in the external anal sphincter may be associated with symptoms of fecal incontinence. Digital examination is performed with the patient at rest, straining or coughing, and voluntarily contracting.