Urinary Diversions and Neobladders Workup

Prior to urinary diversion, assessment of the patient's renal function is important. Most consider a minimum creatinine clearance of 60 mL/min necessary prior to performing continent diversion. A minimum of renal function is necessary because of the increased renal demand created by continent urinary diversion. Because of the increased contact time of urine with bowel segments, previously eliminated renal products are reabsorbed and must again be reexcreted.

Laboratory studies for patients with urinary diversion should be primarily directed toward excluding infection and assessing metabolic status, specifically metabolic acidosis because of concerns discussed in Pathophysiology. The following laboratory studies are suggested:

• Arterial blood gas (if significant metabolic acidosis is expected)
• Acid-base disturbance graph
• Acid-base nomogram (may be found at via the National Center of Emergency Medicine Informatics at www.ncemi.org/etools/datafiles/acid-base_disturbance_graph.gif)
• Complete blood cell count
• Urinalysis and urine culture (if indicated)
• Electrolytes, BUN, and creatinine

Ultrasonography is as follows:

• Ultrasonography is a desirable method for imaging the upper urinary tracts because it requires no nephrotoxic agents.
• Ultrasonography is most useful if findings are completely normal or if no change from prior multiple studies is demonstrated upon comparison.
• Keep in mind that the appearance of hydronephrosis or hydroureteronephrosis does not always indicate obstruction. Surgeons commonly perform "nonrefluxing" ureteral anastomoses, which may result in an ultrasonographic image similar to that of an obstruction. One must consider if a "physiologic" antegrade study is indicated in conjunction with ultrasonography to definitively rule out obstruction.
• Mild-to-moderate hydronephrosis in a patient with urinary diversion is not unusual, especially with a noncontinent conduit.
• Remember that ultrasonography offers no information on the physiologic drainage of the urinary system.

Intravenous pyelography is as follows:

• Most urologists are comfortable with the anatomical information obtained from an intravenous pyelography (IVP). Depending on the evaluating physician's preference, IVP is an excellent method of imaging the integrity and drainage of the upper urinary system.
• The major drawback of this test is with a patient who is either allergic to intravenous contrast or is azotemic; however, in the absence of these two limitations, this is the study of choice for evaluating a patient for a urinary diversion procedure.

Nuclear scan is as follows:

• Mercaptotriglycylglycine or diethylenetriamine pentaacetic acid is an excellent imaging agent for assessing renal function and drainage.
• Drainage is better assessed with the addition of a Lasix injection after accumulation of tracer in the collecting systems.
• The main drawback to nuclear imaging is the lack of information obtained regarding the precise location of obstruction or integrity of the urinary tract.

CT scanning is as follows:

• Noncontrast CT scanning is most useful for demonstrating the presence of urinary calculi; if absent, performing a contrast-enhanced study alone or after noncontrast images is probably more useful for assessing drainage, function, and integrity.
• CT scanning is extremely valuable for assessing a ruptured continent urinary reservoir or for determining the presence of fistulous communication of the urinary tract with the gastrointestinal or genital tracts.

MRI is as follows:

• MRI is rarely indicated in an evaluation for urinary diversion. The most likely indication is to rule out recurrent cancer in a patient who has equivocal CT scan findings.
• The other potential use for MRI is using gadolinium for imaging the drainage of a tract in a patient who is azotemic or allergic to intravenous contrast.

Cystography is as follows:

• Distension of the continent reservoir with contrast is indicated when the patient is thought to have a ruptured segment. The reservoir must be assessed in at least two views, and the conduit must be adequately distended.
• Redundant folds of bowel are not uncommon after a continent diversion has been fashioned. With this in mind, ensuring that those redundant folds are adequately distended is important for excluding rupture. A good rule of thumb is to ask the patient how much urine is normally obtained with each void or catheterization.
• Cystography to rule out a rupture is best performed under real-time imaging, thereby allowing the reservoir to be monitored throughout the entire distension phase.

Urodynamic studies are as follows:

• Urodynamic studies of continent bowel segments have been performed and reported in the medical literature.
• Few clinical indications exist for urodynamic studies, with the exception of treating a patient with a continent urinary diversion and unrelenting incontinence.

To determine the etiology for which urinary diversion is required, CT scanning, MRI, ultrasonography, IVP, and urodynamic studies play specific roles in helping determine the presence of malignancy, urinary tract obstruction, or urine storage abnormalities. All of these conditions may be harmful to the patient's future renal function.

Abnormal histologic findings are uncommon in diversion procedures because the pathologic bladder specimen is removed. Rarely, a biopsy is performed on the intestinal segments that have replaced the bladder. For further information on the histopathologic findings of bladder tumors, refer to Bladder Cancer.