The pelvic floor is comprised of three compartments based on function and location, labeled anterior, middle, and posterior compartments. The anterior compartment encompasses the urethra, the middle includes the vagina, and the posterior has the rectum. The levator ani is the main muscle group that encircles and supports the pelvic inlet and pelvic floor. The muscles of the levator ani are the puborectalis, pubococcygeus, and iliococcygeus, which work together to counteract gravity and keep pelvic organs in position, while also facilitating defecation, urination, and childbirth. The external and internal anal sphincters, encased by the levator ani muscles, are the primary muscles responsible for maintaining fecal continence and defecation. Detrusor muscles in the wall of the bladder and the urethral sphincter muscles work together to maintain urinary continence and permit urination.

The major abnormalities of the pelvic floor result from damage or weakening of the sphincters and levator ani muscles and include urinary incontinence, fecal incontinence, and prolapse of the bladder, uterus, or rectum. Damage to the anal sphincter may result from childbirth or rectal surgery and can lead to fecal incontinence, often years afterward. Weakening of the levator ani muscles may also result from childbearing, but also occurs with advancing age, and can lead to urinary incontinence and bladder prolapse. Sonography has proven useful for assessing the degree of displacement of pelvic organs in patients with symptoms of recurrent urinary tract infections, urgency, frequency, urinary incontinence, pain, dysuria, voiding dysfunction, prolapse, vaginal pain, fecal incontinence, and dyspareunia.

Masses or cysts may arise in the walls of the urethra or vagina. These include urethral diverticula, Bartholin and Gartner duct cysts, vaginal endometriosis, and leiomyomata, among others. Sonography of the perineum and pelvic floor provides information about the origin, size, and composition of such lesions, to assist in making the diagnosis.

Imaging the pelvic floor is best accomplished with 2D scanning at the introitus or using 3D volume reconstruction of views of the urethra, vagina, and rectum. The vaginal probe is placed on the perineum, not inside the vagina. The transverse plane demonstrates a cross section of the components of the pelvic floor, including the urethra, vagina, rectum, and surrounding muscles (Figure 33.1.1).

Evaluation of a patient with urinary incontinence, involves scanning longitudinally to image the urethra while the patient is relaxed and with Valsalva. When there is urinary incontinence and a cystocele, the bladder shifts caudally and rotates posteriorly into the vagina, findings that are exacerbated with Valsalva. The urethra becomes oriented perpendicular to the perineum (Figure 33.1.2). The urethra in women treated for incontinence surgically, such as with a urethral sling placed along the posterior length of the urethra, will be oriented more normally, supported by the sling (Figure 33.1.3).