|ECR 2019 / C-1978|
|MRI of pelvic floor dysfunction: a practical review.|
Pelvic floor dysfunction (PFD) is a major medical and social problem. It is a common disorder that can seriously jeopardize a woman’s quality of life.
Weakening of the female pelvic floor is a prevalent and debilitating disorder. It results in abnormal descent of the urinary bladder, the uterovaginal vault, and the rectum, resulting in urinary incontinence, fecal incontinence, and pelvic organ prolapse. Pelvic floor weakening affects approximately 50% of women older than 50 years.
Pelvic floor weakness has many complex causes. The risk factors for PFD include pregnancy, multiparity, advanced age, menopause, obesity, connective tissue disorders, smoking, chronic obstructive pulmonary disease, and any other factors that result in a chronic rise in intraabdominal pressure.
Traditional imaging methods in assessment of pelvic floor weakness include urodynamics, voiding cystourethrography, ultrasonography of the bladder neck and anal sphincter, and fluoroscopic cystocolpodefecography.
To make a definite diagnosis of pelvic prolapse preoperatively, dynamic MR is an alternative to conventional fluoroscopic or sonographic examination, with the advantage of providing greater details, and thus helping the surgeon to have a good preoperative plan.
The pelvic floor is classically described as comprising three compartments: an anterior compartment containing the bladder and urethra, a middle compartment containing the vagina and uterus, and a posterior compartment containing the rectum(Fig. 1). The supporting structures of the female pelvis consist of a complex network of fascia, ligaments (fascial condensations), and muscles attached to pelvic bone. These structures form three contiguous layers from a superior to an inferior location: the endopelvic fascia, the pelvic diaphragm, and the urogenital diaphragm(Fig. 2).
The endopelvic fascia, the most superior layer of the pelvic floor, covers the levator ani muscles and pelvic organs in a continuous sheet. The endopelvic fascia provides three levels of fascial support (Fig. 3).
There are three groups of ligaments supporting the female urethra (Fig.4). These ligaments and anterior vaginal wall provide a hammock-like support and play an important role in maintaining urinary continence in women(Fig. 5). Therefore, a tear in the pubocervical fascia or periurethral ligament can lead to a cystocele, urethral hypermobility, or urinary incontinence.
In the middle compartment, elastic condensations of endopelvic fascia known as the paracolpium and parametrium provide support to the vagina, cervix, and uterus, preventing genital organ prolapse .
The posterior compartment contains an important anchoring structure for muscles and ligaments, called the perineal body or central tendon of the perineum, which lies within the anovaginal septum and prevents the expansion of the urogenital hiatus. The rectovaginal fascia is a portion of the endopelvic fascia that extends from the posterior wall of the vagina to the anterior wall of the rectum and attaches to the perineal body, preventing posterior prolapse(Fig. 6). A tear in the rectovaginal fascia can be inferred from the presence of an anterior rectocele or enterocele.
The pelvic diaphragm lies deep to the endopelvic fascia and is formed by the ischiococcygeus muscles and the levator ani, which is composed of the iliococcygeus, puborectalis, and pubococcygeus muscles. In healthy people these muscles continuously contract, providing tone to the pelvic floor and maintaining the pelvic organs in the correct position. The two most important components of the levator ani are the iliococcygeus and puborectalis muscles(Fig. 7).
The location of the urogenital diaphragm is caudal to the pelvic diaphragm and anterior to the anorectum. The urogenital diaphragm is composed of connective tissue and the deep transverse muscle of the perineum, which originates at the inner surface of the ischial ramus. It has multiple attachments to surrounding structures including the vagina, perineal body, external anal sphincter, and bulbocavernosus muscle(Fig. 8).
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