Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

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diagnostic. In distinction to enterovesical fistulas, the presence of gas within the bladder is uncommon with a vesicovaginal fistula.

mal delivery (38). Not all manifest with vaginal urinary leakage; an occasional one results in hematuria.

Enterovesical

The most common cause of enterovesical fistulas in adults is sigmoid diverticulitis. Less often encountered are colon and bladder malignancies, Crohn’s disease, pelvic radiation, trauma, and infection by actinomycosis, tuberculosis, lymphogranuloma venereum, or an adjacent abscess, such as neglected appendicitis.

Indirect signs of a fistula include gas within the bladder and an irregular outline to the bladder wall. With some fistulas cystoscopy is noncontributory.

A suspected fistula is studied by cystography or barium enema; either study demonstrates most fistulas, although occasionally only one or the other outlines a fistula. A rare clinically suspected fistula is not detected with imaging; some of these become evident a week or so later. As a last resort, the Bourne test should be considered; following a nondiagnostic barium enema, a horizontal x-ray beam radiograph is obtained of a centrifuged urine sample. The sample may contain sufficient barium to be visible on the radiograph. The need for a Bourne test is rare and it is now mostly of historical interest.

Computed tomography and MRI outline some bladder fistulas. Gadolinium-enhanced T1-weighted MR images are superior in showing a fistula compared to precontrast images. If a fistula is accessible, contrast injection into the fistula and fistulography or MRI should define it.

Occasionally Tc-99m–diethylenetriamine pentaacetic acid (DTPA) renography shows radioactivity in the sigmoid colon with an enterovesical fistula.

Uterovesical

These fistulas are rare. In a collection of five uterovesical fistulas all were secondary to a prior cesarean section and all presented with intermittent hematuria (37); hysterosalpingography revealed some of these fistulas. In another collection of 10 such fistulas, 60% were secondary to cesarian section and 40% to prior abnor-

Diverticula

Bladder diverticula form when mucosa herniates through overlying muscle. A purist would thus describe them as pseudodiverticula, a term not generally used. Some diverticula have smooth muscle fibers within the wall. Fibrosis develops in some secondary to chronic inflammation. Diverticula may be single or multiple, small or large. Most diverticula have a wide neck. At times a diverticulum is larger than the remainder of the bladder. Very large diverticula tend to have a relatively smooth outline.

Diverticula may be primary developmental in origin or acquired secondary to another abnormality. An increased prevalence occurs in patients with Ehlers-Danlos syndrome and prune belly syndrome. They develop because of outflow obstruction, stasis, or prior surgery. An occasional one is associated with urinary retention or undergoes spontaneous rupture.

Diverticula close to the ureterovesical junction were described by Hutch in patients with a neuropathic bladder. These diverticula are believed to develop due to weakening of the detrusor muscle in this region and are associated with vesicoureteral reflux. If the ureter inserts into a diverticulum, the appearance mimics a ureterocele. Or, a Hutch diverticulum simply obstructs an adjacent ureter by its bulk.

A bladder diverticulum can be diagnosed by US if a communication with the main bladder lumen can be identified. Ultrasonography reveals an occasional bladder diverticulum as a complex pelvic tumor apparently separated from the bladder, leading to diagnostic confusion.

Endoscopic therapy of bladder diverticula has been performed with varying success.

The prevalence of neoplasms within a bladder diverticulum is greater than in a normal bladder, probably because of chronic inflammation and stasis. The most common neoplasm is a transitional cell carcinoma. Occasionally a sarcoma, squamous cell carcinoma, or even an adenocarcinoma develops in a diverticulum.

Most malignancies are detected late and are associated with a poor prognosis.

Ultrasonography reveals a diverticular neoplasm as an intraluminal, hyperechoic, nonshadowing tumor that does not change with a change in patient position.A cystogram may not detect the diverticulum, and a diverticular tumor is thus missed. Computed tomography and MRI outline an intraluminal soft tissue tumor. An MRI in oblique planes can identify the diverticular neck and establish that a tumor is indeed within the diverticulum. Localized tumor infiltration is seen as focal diverticular wall thickening. Occasionally associated calcifications are detected.

Herniation

Clinical

A cystocele is a bladder hernia, although many authors use this term in a narrower sense to describe bladder prolapse into the vagina. In women, a common type of cystocele consists of an abnormal bulge by the bladder into the anterior vaginal wall due to weakness in the pubocervical fascia. The appearance of such a cystocele, with bladder outline below the symphysis pubis, is familiar to most radiologists. These cystoceles become more prominent with the patient upright. Many are associated with generalized pelvic floor laxity and stress incontinence (incontinence is discussed in the next section).

In men, a common site for bladder hernias is into the inguinal canal; in women, femoral canal hernias are more common. In men most inguinal hernias are direct and more often on the right.

Unless large or obstructed, most bladder hernias are asymptomatic. Some men have twophase micturition that improves when pressure is exerted on the scrotum. Clinically, some men with a bladder hernia are suspected of prostatism but no bladder outlet obstruction is found. Complications include bladder incarceration or even infarction in a strangulated hernia. A massive inguinoscrotal bladder hernia can lead to acute renal insufficiency.

Complete bladder inversion through the urethra is very rare (39); a cystogram through

ADVANCED IMAGING OF THE ABDOMEN

an orifice posterior to the extruded mass yielded a bladder volume of 20mL.

Imaging

A bladder groin hernia, regardless of type, is identified by IV urography or cystography; in some patients a hernia becomes evident only when they are upright or prone, or if a delayed radiograph is obtained. With suspicion of a bladder groin hernia, video urodynamic imaging with the patient standing is helpful. The presence of lateral displacement of the distal ureter, a small visualized bladder volume, and incomplete bladder base visualization suggest a bladder hernia. Most appear as widemouthed bladder protrusions into the inguinal region. Bilateral inguinal bladder hernias are not uncommon.

Technetium-99m–methylene diphosphonate (MDP) bone scintigraphy detects a bladder groin hernia through increased inguinal region activity that changes with a change in patient position. Bone scintigraphy will also detect bladder herniation into the scrotum.

Incontinence

Urinary incontinence is considerably more common in women, and most incontinence classifications pertain to women.

Women

Clinical

Urinary incontinence is related to pelvic organ prolapse and other pelvic floor abnormalities and is discussed in more detail in Chapter 12. In young girls presenting with incontinence, an ectopic ureter inserting below the urethral sphincter or even into the vagina should be suspected.

Urinary incontinence is traditionally divided into three subtypes: stress, urge, and mixed. Stress incontinence occurs in a setting of increased intraabdominal pressure and insufficient urethral resistance. Urge incontinence consists of an inability to inhibit bladder contractions. At times urge incontinence is precipitated by coughing or straining and the two

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types of incontinence overlap. Mixed incontinence is common and probably consists of several variants. Most classifications are based on stress incontinence, although some women with urge incontinence or a mixed type are also undoubtedly included. One classification sof stress urinary incontinence is based on endorectal US findings of urethral hypermobility, bladder neck incompetence, intrinsic urethral sphincter incompetence, and whether a cystocele is present or not. At times the urethral sphincter does not function normally because of prior surgery and fibrosis or a spinal cord lesion.

Urethral hypermobility results in an excessive change in urethral axis with straining and leads to urinary incontinence. Senior radiologists probably remember performing chain cystograms to help detect stress incontinence, a study that has been supplanted by newer imaging modalities.

Imaging

Voiding cystourethrography (VCUG) has been used to evaluate stress incontinence, yet this examination appears to be of limited value. It detects less than two-thirds of stress incontinence; false positives include women with detrusor instability and urge incontinence. Previously taught measurements of posterior vesicourethral angle change, urethral descent, urethral inclination and presence of a urethrocele on straining, detected on a VCUG, have been questioned in their ability to predict stress incontinence, yet some of these findings are now being resurrected with MRI studies.

Perineal US can be performed after injecting a hyperechoic contrast agent transurethrally. With the patient upright, contrast outlines the inferior part of the bladder. Stress incontinence is associated with the presence of a cystocele, a funnel-like opening of the proximal urethra, an increase in the retrovesical angle, and bladder neck descent. By evaluating bladder neck mobility relative to the symphysis pubis, perineal US achieved a sensitivity of only 78% and a specificity of 77% in detecting stress incontinence (40), and the authors concluded that perineal US is not sensitive enough to be used for predicting stress incontinence. Nevertheless, perineal US appears superior to the lateral view chain urethrogram if bladder

neck mobility is studied during a Valsalva maneuver.

Depth and width of proximal urethral dilation during coughing and Valsalva maneuver are readily assessed by perineal US. Bladder neck descent occurs both in continent and incontinent women. The urethra dilates during coughing and Valsalva maneuver both in incontinent and some continent women and dilation per se does not imply incontinence.

An alternative technique is endorectal US in a standing position, the bladder filled with saline, and the test performed at rest and during a Valsalva maneuver; those with stress incontinence have a larger pubovesical angle during both resting and straining than controls; however, considerable overlap exists. Endorectal US shows the midurethral cross-sectional area to be significantly smaller in women with stress incontinence than in those without, a difference due to a significantly smaller peripheral striated muscle component in those with stress incontinence (41); this peripheral striated muscle surrounded the urethra completely in 36% of women without stress incontinence, but only in 5% of those with severe incontinence. The urethropelvic ligament thickness was significantly thinner in those with stress incontinence. The clinical application of these findings in formulating therapy remains to be established.

Endovaginal US measures the distance from the bladder neck to the symphysis pubis. Various displacement criteria with and without stress have been suggested to detect urinary stress incontinence, none achieving popularity.

Magnetic resonance imaging is acquiring a primary role in evaluating stress incontinence, although technical limitations exist with horizontal bore MR units; ideally, the study should be performed with the patient in the upright position. Sagittal T2-weighted MRI identifies a cystocele as a posteriorly bulging bladder into the vagina. High resolution endovaginal MR provides detailed dynamic pelvic floor visualization during straining when using T2weighted single-shot fast spin echo (FSE) sequences without contrast. Levator ani thinning is associated with stress urine incontinence (42). Varying degrees of protrusion, including prolapse, are identified. Stress incontinence is associated with a greater vesicourethral angle and larger retropubic space than found in continent women. Both bladder floor descent and

cervical descent is greater in incontinent than in nulliparous women, but symptoms do not always correlate with the amplitude of bladder floor descent (43).

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tinence. These consist of self-detachable crosslinked silicone balloons and a biocompatible filler material. This technique is most effective in treating intrinsic sphincter deficiency.

Therapy

A vesicourethropexy (Marshall-Marchetti operation) has a high early postoperative success rate, which decreases with time. Postoperative imaging identifies an elevated bladder base. A similar bladder elevation is also occasionally seen due to large degenerative bony spurs at the symphysis pubis.

A number of bulking agents, including autologous fat, polytetrafluoroethylene, and bovine collagen have been injected to treat stress incontinence but most are associated with either side effects or limited long-term results. Periurethral collagen (glutaraldehyde crosslinked bovine collagen) injection has become popular therapy for symptomatic urinary stress incontinence since gaining United States Food and Drug Administration approval. The agent is injected under local anesthesia. It appears to be biocompatible with little evidence of a foreignbody or immunologic reaction. Collagen is partially reabsorbed within several years. A follow-up of 24 months after periurethral collagen injection in women with severe urinary incontinence resulted in a continent rate of 33%, with 39% improved and 28% considered to be failures (44). Complications include urinary urgency and incontinence, at times irreversible, hematuria, and urinary retention. Urinary tract infection after collagen injection is uncommon.

Comparing posttherapy transvesical and endovaginal US, the endovaginal approach reveals collagen in more patients; collagen is identified as circumscribed masses at the bladder base having varying echogenicity. Magnetic resonance imaging identifies collagen as hyperintense foci within the urethral wall; neither visualized collagen volume nor its position are related to clinical outcome.

Periurethral silicone implants in women with intrinsic sphincter deficiency resulted in a subjective success rate of 80% at 6 weeks and 60% at 1 year (45).

Implantable microballoons have also been used as therapy for female urinary incon-

Men

Continence after prostatectomy is maintained by an intact sphincter. Urinary stress incontinence after prostatectomy is generally due to sphincter dysfunction, such as scarring or decreased contractions, findings evaluated with endourethral US.

Transurethral collagen injection is used to treat urinary incontinence after radical prostatectomy. Collagen injection in men with incontinence result in a low continence rate: 20% to 24% in several studies; the success of the cure by collagen injection is influenced by the severity of the pretreatment incontinence, detrusor overactivity, and other factors. Endorectal US in men after collagen injection reveals hypoechoic masses adjacent to the bladder.

Children

Urinary incontinence is a common pediatric urologic problem. In infants the reflexcontrolled bladder matures to normal bladder function during the first several years of life as the bladder sphincter grows and central nervous control of micturition matures. Sufficient anatomic maturation is necessary before neurologic control is established.

Collagen injection for incontinence has achieved mixed results in children. One study reported that 5% of children became continent and 25% improved, and the authors questioned the high collagen injection cure rates previously reported for urinary incontinence in children (46).

Immunosuppression

Acute hemorrhagic cystitis is occasionally reported after a kidney transplant, probably due to an adenovirus infection.

Immunosuppressed renal transplant patients are more prone to developing a bladder lymphoma than the general population.