48 CHAPTER 2 Urological investigations
Other urological contrast studies
Voiding cystourethrography (VCUG) (Fig. 2.8)
VCUG is used to identify the presence of vesicoureteric reflux during filling and emptying of the bladder and presence and site of obstruction in the outlet of the bladder and within the urethra, particularly in patients with neuropathic bladder problems (e.g., spinal cord injury). This study is helpful for delineating the proximal extent of urethral strictures.
Cystography
This study consists of retrograde filling of the bladder, via a catheter, with contrast. It is used to identify vesicocolic and vesicovaginal fistulae and bladder rupture (extraperitoneal and intraperitoneal).
Urethrography (Fig. 2.9)
Retrograde filling of the urethra with contrast is used to identify the site and length of urethral strictures (Fig. 2.10) or presence, extent, and site of urethral injury (in pelvic fracture, for example).
Ileal loopogram
Retrograde filling of an ileal conduit with contrast is used to establish the presence of free reflux into the ureters (a normal finding; absence of free reflux suggests obstruction at the ureteroileal junction due to ischemic stenosis or recurrent TCC in the ureters at the ureteroileal junction) and the presence of TCCs in the ureters or renal pelvis (an occasional finding in patients who have had a cystectomy for bladder TCC with ileal conduit urinary diversion).
Retrograde pyelography
This study consists of retrograde instillation of contrast into the ureters by a ureteric catheter inserted into the ureter via a cystocope (rigid or flexible). It provides excellent definition of the ureter and renal pelvis for detection of ureteric and renal pelvic TCCs or radiolucent stones in patients with persistent hematuria in whom other tests have shown no abnormality.
Retrograde pyelography is also used to diagnose the presence and site of ureteric injury (obstruction, ureteric leak) in cases of ureteric injury (e.g., after hysterectomy or caesarean section).
OTHER UROLOGICAL CONTRAST STUDIES 49
Figure 2.8 VCUG showing bilateral ureteric reflux.
Figure 2.9 Normal urethrogram.
Figure 2.10 A urethrogram showing a bulbar urethral stricture.
50 CHAPTER 2 Urological investigations
Computed tomography (CT) and magnetic resonance imaging (MRI)
Computed tomography
CT is widely used for investigation of urological symptoms and disease. It can detect very small differences in X-ray absorption values of tissues, providing a very wide range of densities (and therefore differentiation between tissues) when compared with plain radiography.
The computer calculates the absorption value (attenuation) of each pixel and reconstructs this into an image. The attenuation values are expressed on a scale from –1000 to +1000 Hounsfield units (water = 0, air = –1000, bone = +1000).
More recently, advances in computing power have enabled the data to be reformatted so that images can be produced in sagittal and coronal planes as well as in the more familiar horizontal plane (Figs. 2.11 and 2.12).
“Plain” CT scans (without contrast) can detect calcification and calculi within the urinary tract. Administration of intravenous contrast is used to evaluate the nature of solid renal lesions and determine the nature of soft tissue masses (e.g., to differentiate bowel from lymph nodes in cancer staging CTs).
“Spiral” or “helical” CT is very rapid scanning while the table on which the patient is lying is moved though the scanner. A large volume of the body can be imaged in a single breath hold, thus eliminating movement artifact. This is particularly useful for identifying suspected ureteric stones in patients with acute flank pain.
Uses of CT
Renal
•Investigation of renal masses—characterizes solid from cystic lesions; differentiates benign (e.g., angiomyolipoma) from malignant solid masses (e.g., renal cell carcinoma)
•Staging of renal cancer (establishes local, nodal, and distant spread)
•Assessment of stone size and location (within the collecting system or within the parenchyma of the kidney)
•Detection and localization of site of intrarenal and perirenal collections of pus (pyonephrosis, perinephric abscess)
•Staging (grading) of renal trauma
•Determination of cause of hydronephrosis
Ureters
• Locates and measures size of ureteric stones
Bladder
• Bladder cancer staging (establishes local, nodal, and distant spread)
Uses of MRI
•Staging of pelvic cancer—bladder and prostate cancer staging (establishes local, nodal, and distant spread). As with CT, edema and fibrosis cannot be reliably distinguished from tumor within the bladder
CT AND MRI 51
wall, leading to overstaging of cancer. Again, as with CT, microscopic disease cannot be identified, leading to understaging of cancer.
•Localization of undescended testes
•Identification of ureteric stones, where ionizing radiation is best avoided (e.g., pregnant women with flank pain)
Figure 2.11 Coronal CT image of abdomen showing the left kidney, aorta, and IVC.
Figure 2.12 Coronal CT image of abdomen, showing the left kidney and paravertebral muscles.