Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

BLADDER

A vesicourachal diverticulum can be suggested by CT, US, or MRI by detecting a bladder outpouching in the appropriate location.

Infection

Infection leads to a pyourachus, located in the midline, deep to the rectus abdominis muscle.

Imaging reveals a fluid-filled midline cavity close to the anterior bladder wall. When infected, the cyst in effect becomes an abscess and the cyst wall gradually thickens. A characteristic CT finding of a pyourachus is a conicalshaped structure extending from the umbilicus to the bladder dome. Inflammatory changes in adjacent subcutaneous tissues, the rectus abdominis muscle, and mesenteric fat surround the infected urachus. Chronic infection results in a thickened cyst wall.

An infected urachal cyst can be drained percutaneously, although this is generally a temporary measure because of an increased reinfection rate. For these reasons most urachal cysts are resected. Also, if an infected urachal cyst is suspected in an adult, a necrotic (or infected) carcinoma should be in the differential diagnosis.

Cyst/Neoplasm

Some urachal cysts remain asymptomatic, and others serve as a nidus for infection, while a neoplasm develops in an occasional one. Some urachal cysts gradually enlarge. In general, if US or other imaging shows a midline cystic structure between the umbilicus and bladder not related to bowel, an urachal cyst should be suspected.

Occasionally dystrophic calcifications or osseous metaplasia develop in an urachal cyst wall. Metaplasia of urachal transitional epithelium can evolve into an adenoma and carcinoma. A majority of these carcinomas are adenocarcinomas, with an occasional transitional cell carcinoma, squamous cell carcinoma, sarcoma, or even a small cell carcinoma. In general, most carcinomas are detected late when the tumor has already spread. A not uncommon presentation is a suprapubic tumor, hematuria, mucusuria, pain, or discharge from the umbilicus. An occasional urachal adenocarcinoma metastasizes (6); a urachal mucinous carcinoma

is a less common cause of pseudomyxoma peritonei.

Imaging reveals a tumor involving the bladder apex, mostly extravesical in location and often growing along the urachus. Primary bladder carcinomas tend not to have these findings. Some mucin-producing urachal adenocarcinomas develop psammomatous calcifications, findings readily detected by CT. These mucinous adenocarcinomas can be solid, cystic, or mixed.

Ultrasonography should readily detect urachal cysts. If needed, CT confirms the diagnosis. Doppler US of an urachus adenocarcinoma revealed neovascularity and a low resistive index in the tumor (7).

Trauma

Spontaneous bladder rupture in the absence of trauma is rare but has occurred in a setting of previous radiation therapy, surgery, infection, or is idiopathic. Contrast extravasation may occur during voiding cystourethrography performed in a patient with an unused bladder. Most of these extravasations are self-limiting.

The risk of bladder rupture increases with bladder distention. Perforation of an empty bladder is generally associated with a penetrating injury, either extrinsic or a bone fragment.

After blunt pelvic trauma or in a setting of pelvic fractures, bladder or urethral injury is suggested by hematuria or inability to urinate. A small minority of patients with bladder rupture have only microscopic hematuria. A direct association exists between gross hematuria and bladder perforation, most being extraperitoneal, less often intraperitoneal, and least common being both intraand extraperitoneal. Pelvic fractures are present in a majority of patients with bladder perforation.

A retrograde urethrogram is generally obtained to exclude urethral injury, followed by a cystogram. At times extraperitoneal contrast extravasation is only seen on postdrainage radiographs. A cystogram should detect not only bladder rupture but also determine whether the rupture is intraor extraperitoneal (Fig. 11.2). During the cystogram an attempt should be made to identify a site of perforation. Subtle intraperitoneal leaks are difficult to

detect; the diagnosis is generally made by seeing contrast outline the loops of the bowel. Occasionally contrast absorbed from the peritoneal cavity and excreted by kidneys provides a clue to an intraperitoneal leak and thus a radiograph over the kidneys after a cystogram is useful.

Intravenous urography is inadequate to evaluate bladder trauma. Likewise, US is not a substitute for a cystogram in a setting of trauma, although US may detect a hematoma or fluid in the peritoneal cavity. Magnetic resonance is generally precluded during the immediate posttrauma period by monitoring logistics in a strong magnetic field.

Many of these trauma patients undergo contrast CT to evaluate for pelvic and abdominal trauma. The presence of pelvic fractures and pelvic fluid is associated with bladder rupture, but a bladder perforation cannot be excluded on this study without full bladder distension. In some centers CT cystography, performed after retrograde instillation of contrast, has replaced conventional cystography. Another option is to clamp the patient’s Foley catheter prior to scanning and add a 5-minute or so delay after intravenous (IV) contrast injection to allow for bladder distention. Thin, contiguous slices through the bladder are necessary for this

study. Preliminary evidence suggests that CT cystography achieves similar accuracy to that of conventional cystography (8), but the practical choice between these two studies is not settled. Also, extravasated contrast detected on a CT cystogram performed after IV contrast injection does not necessarily represents bladder rupture—renal injury can lead to similar findings.

Whether children with pelvic trauma should first undergo a cystogram or CT is debatable, and the role of a CT cystogram in children is not clear.

Extraperitoneal urine and contrast extravasation is into the prevesical space of Retzius; fluid can dissect along the tissue fascial planes and extend into the scrotum or dissect laterally into the hip, resulting in such curiosities as a hip arthrogram becaming evident due to extraperitoneal bladder rupture and an acetabular fracture.

In general, extraperitoneal bladder rupture is managed by catheter drainage, while intraperitoneal rupture is explored surgically. Most extraperitoneal bladder ruptures resolve without surgery. The key to successful management is continuous bladder drainage.

Shotgun pellets have passed spontaneously during voiding.

BLADDER

Wall Thickening

Infection/Inflammation

Cystitis

General Imaging Findings

Lower urinary tract infection is considerably more common in women than men. Most attacks clear with antibiotic therapy and recur only in a minority. Imaging is generally reserved for those women not responding to antibiotics, frequent reinfections, atypical presentation, or known risk factors, including hematuria, suspected upper urinary tract infection, past history of stones, infection, or reflux.

If imaging is deemed necessary for suspected upper tract involvement, IV urography is generally the first preferred test. A minority of authors recommend a conventional radiograph combined with US. Some bladder abnormalities are detected on an IV urogram, although voiding cystography provides more information, including the presence of vesicoureteral reflux. Urethral diverticula are also detected with voiding cystography, although at times a specific double-balloon urethrogram and other studies are necessary for their detection (urethral diverticula are discussed in Chapter 12).

While mild cystitis has no abnormal radiographic findings, with progressively more severe involvement focal mural thickening evolves, intraluminal tumors may develop, and occasionally an irregular outline become evident. Initially bladder capacity tends to be normal, but with progressive inflammation the lumen contracts.

In adults, the presence of bladder wall thickening and irregularity can be secondary to either inflammation or neoplasm, and in many patients a biopsy is necessary to narrow the diagnosis. Not all bladder polyps are neoplastic; occasionally cystitis results in inflammatory polyps. These inflammatory tumors can be differentiated from other spindle cell proliferations by immunohistochemical means.

Most so-called congenital hourglass bladders are found in adult males and are associated with bladder inflammation. Imaging simply reveals an hourglass outline.

T1-weighted MRI reveals two distinct layers in a cystitis-thickened bladder wall: a hyperintense inner and an isointense outer layer. T2-

weighted MRI reveals four distinct layers: (1) hypointense inner epithelium, (2) hyperintense lamina propria, (3) hypointense muscle layer, and (4) isointense outer layer representing muscle and connective tissue.

Interstitial Cystitis

Interstitial cystitis is more of a syndrome than a specific disease. Etiology is unknown but is often multifactorial in origin. Helicobacter pylori probably is not a cause of this condition. A relationship has been suggested between interstitial cystitis and collagenous colitis. The vast majority affected are women.

Interstitial cystitis is a severe and debilitating bladder disorder manifesting by pelvic pain and urinary frequency. No diagnostic test is available for this condition and it is diagnosed by exclusion. Urodynamic studies, including a voiding cystourethrogram, are necessary to exclude other conditions. Thus in patients initially believed to have interstitial cystitis, urethral abnormalities such as periurethral fibrosis, urethral diverticula, and chronic urethritis are common; eventually only four of 23 patients in one study were believed to suffer from interstitial cystitis (9).

Therapy is difficult. Some women with intractable interstitial cystitis undergo enterocystoplasty, but even some of these continue being symptomatic. Some require an ileal loop diversion. Of interest is that some subsequent ileal loop biopsies also show histologic changes of interstitial cystitis. Intravesical bacillus Calmette-Guérin (BCG) therapy has led to improvement in some patients (10).

An anterior vaginal hernia (enterocele) developed in 11% of women who underwent cystectomy and urethrectomy for intractable interstitial cystitis (11); clinically, these hernias mimic a midline cystocele except they contain bowel.

Hemorrhagic Cystitis

In some patients hemorrhagic cystitis and interstitial nephritis are associated with the use of nonsteroidal antiinflammatory drugs (NSAIDs). Cyclophosphamide therapy is also implicated, at times resulting in massive bleeding. Radiation cystitis, secondary to pelvic radiation therapy, also manifests as hemorrhagic

Figure 11.3. Hemorrhagic cystitis due to Cytoxan therapy. Computed tomography reveals a thick-walled bladder containing blood clots, debris, and gas. (Courtesy of Patrick Fultz, M.D., University of Rochester.)

cystitis. Bladder wall edema and inflammation resolves in some patients, while in others it progresses to a small, shrunken bladder. Of interest is that hyperbaric oxygen therapy appears helpful in radiation cystitis (12); hematuria subsides and symptoms improve.

The CT and MR appearance of hemorrhagic cystitis varies depending on timing (Fig. 11.3). Active and very recent bleeding has T1and T2-weighted imaging characteristics of fluid. Slightly older blood becomes hyperintense on T1and hypointense on T2-weighted images, findings reflecting intracellular methemoglobin due to subacute intramural hemorrhage.

Eosinophilic Cystitis

Eosinophilic cystitis is a histologic diagnosis characterized by massive eosinophilic infiltration. Etiology in most patients is unknown, although remission in some patients undergoing steroid therapy suggests an allergic condition. One should keep in mind, however, that occasionally a chronic infection results in eosinophilic cystitis. Partial cystectomy and a pseudoneoplastic condition or reaction to suture material can also lead to eosinophilic cystitis.

Eosinophilic cystitis can be subdivided into three clinical entities having different presentations and treatments (13):

Group I consists of young adults and children with a background of atopy or

parasitic infestation who have micturition difficulties or hematuria. They respond to steroids.

Group II consists mostly of middle-aged women with chronic, recurrent cystopathy. They respond poorly to therapy.

Group III consists of elderly patients with chronic bladder irritation or other type of injury. They usually do not require therapy.

Some of these patients have eosinophilia and eosinophiluria. A minority progress to fibrosis and a small, retracted bladder, similar to that seen with interstitial or tuberculous cystitis. Ureteral involvement and hydronephrosis necessitate surgery.

Imaging findings in eosinophilic cystitis are nonspecific. Some patients develop an intraluminal tumor. Spontaneous bladder rupture is a rare complication of eosinophilic cystitis.

Emphysematous Cystitis

Emphysematous cystitis almost always implies infection, with the most common infection being due to Escherichia coli. Many of these patients are diabetics. Occasionally emphysematous pyelonephritis coexists with emphysematous cystitis. Some of these patients have gas in the bladder and develop pneumaturia, thus suggesting an enterovesical fistula. Untreated, the condition evolves into bladder gangrene.

Cystoscopy reveals bladder mucosal vesicles. Computed tomography readily detects emphysematous cystitis or emphysematous pyelonephritis. Conventional radiographs may miss small amounts of intraluminal air unless films with a horizontal x-ray beam are obtained. Ultrasonography reveals a thickened hyperechoic bladder wall and acoustic shadowing

within the lumen.

Fungal Cystitis

Fungal infection of the lower urinary tract is seen in patients with a neurogenic bladder, prolonged antibiotic therapy, or prolonged use of an indwelling catheter. Occasionally the condition evolves into emphysematous cystitis, especially in diabetics.

When extensive, Candida cystitis results in a “fungus ball,” which on rare occasion can result in bladder outlet obstruction.

BLADDER

Figure 11.4. Bladder tuberculosis in a patient with previous renal tuberculosis. Computed tomography shows a thick walled shrunken bladder and a nodule projecting from the wall (arrows). The ureters are dilated. (Courtesy of Egle Jonaitiene, M.D., Kaunas Medical University, Kaunas, Lithuania.)

Tuberculous Cystitis

Bladder tuberculosis is usually associated with renal involvement. This chronic infection results in an interstitial cystitis and an eventual spastic, small capacity, thick-walled bladder. Clinical presentation tends to mimic interstitial cystitis. A rare tuberculous cystitis results in a spontaneous bladder perforation.

Cystography reveals a polypoid bladder outline, ulcerations, and infiltration of the ureterovesical junctions, with the latter evolving into ureteral obstruction or vesicoureteral reflux. Calcifications develop in some bladders but are not commonly detected with conventional radiography. Any intraluminal septations are best seen with either CT or US. Extensive granulomas result in a polypoid appearance. The overall appearance mimics a malignancy (Fig. 11.4).

Schistosomal Cystitis

Schistosomiasis (bilharziasis) is endemic in Africa and western Asia, and infection occurs by contact with water containing cercariae emitted from snails. Schistosoma haematobium develops in portal veins and migrates against the blood flow in the portal vein, the inferior mesenteric vein, and probably from hemorrhoidal veins

into bladder veins, where adults deposit eggs. The eggs then pass through the bladder wall and are eliminated in urine.

Initially involved are bladder trigone and adjacent ureteral segments, distinguishing schistosomiasis from tuberculosis; the kidneys are primarily involved with the latter, and the ureters are secondarily affected.

Hematuria is a typical and often the only clinical presentation. Neither urinary tract infections nor urinary stones are more common than in the general population.

The bladder wall gradually assumes an irregular outline and hydroureters develop. At times a biopsy yields eosinophilic cystitis. Some patients develop granulomatous bladder polyps. Fibrosis and hyperplastic changes evolve into squamous metaplasia, predisposing these patients to subsequent carcinoma. An early onset of chromosomal aberration is found even in histologically benign-appearing mucosa. Carcinomas in bilharziasis are common and occur at a relatively early age. Tumors range from nodular to infiltrating.

A classic conventional radiographic finding of bladder schistosomiasis is bladder wall calcification, and in endemic areas in the appropriate clinical setting, little else is in the differential diagnosis. These calcifications are better defined with CT. They range from being barely visible, to those having a thin, rim-like appearance, to marked calcification of the entire bladder wall. Ureteral calcifications appear as distal ureteral linear, parallel lines mimicking vascular calcifications.

Urography reveals thickened folds and a shrunken bladder lumen. An enlarged prostate elevating the bladder base is common. In some countries the ready availability of US has made this modality the imaging choice in following these patients.

Actinomycosal Cystitis

Bladder actinomycosis is uncommon. Infected individuals tend to develop extensive fistulas and fibrosis; at times the appearance mimics that of a bladder tumor.

Granulomatous Cystitis

A granulomatous cystitis,often seen in children, is part of eosinophilic cystitis and is often