40 CHAPTER 2 Urological investigations
Radiological imaging of the urinary tract
Ultrasound
Ultrasound is a noninvasive method of urinary tract imaging. While it provides good images of the kidneys and bladder, anatomical detail of the ureter is poor and the mid-ureter cannot be imaged at all by ultrasound because of overlying bowel gas.
Uses of ultrasound
Renal
•Assessment of hematuria
•Determination of nature of renal masses—can differentiate simple cysts (smooth, well-demarcated wall, reflecting no echoes; benign) from solid masses (almost always malignant; cystic masses with solid components or multiple septae or calcification may be malignant) and from those casting an “acoustic shadow” (stones) (Fig. 2.1)
•Can determine the presence or absence of hydronephrosis (dilatation of the collecting system) in patients with abnormal renal function (Fig. 2.2)
•Allows ultrasound-guided nephrostomy insertion in patients with hydronephrosis and renal impairment or with infected, obstructed kidneys
Bladder
•Measurement of post-void residual urine volume
•Allows ultrasound-guided placement of a suprapubic catheter
Prostate: transrectal ultrasound (TRUS)
•Measurement of prostate size (where gross prostatic enlargement is suspected on the basis of a DRE, and surgery, in the form of open prostatectomy, is contemplated)
•To assist prostate biopsy (allows biopsy of hypoechoic or hyperechoic lesions)
•Investigation of azoospermia (can establish the presence of ejaculatory duct obstruction)
Urethra
•Can image the urethra and establish the depth and extent of spongiofibrosis in urethral stricture disease
Testes
•Assessment of the patient complaining of a lump in the testicle (or scrotum)—can differentiate benign lesions (hydrocele, epididymal cyst) from malignant testicular tumors (solid, echo poor or with abnormal echo pattern)
•When combined with power Doppler can establish the presence or absence of testicular blood flow in suspected torsion
•Assessment of testicular trauma (rupture is indicated by abnormal echo pattern, due to blood within the body of the testis; surrounding
RADIOLOGICAL IMAGING OF THE URINARY TRACT 41
hematoma may be seen—blood within the scrotal soft tissues that has escaped through a tear in the tunica albuginea and the visceral and parietal layers of the tunica vaginalis; hematocele—blood contained by an intact parietal layer of the tunica vaginalis)
•Investigation of infertility—varicoceles and testicular atrophy may be identified
Figure 2.1 An acoustic shadow cast by a stone within the kidney.
Figure 2.2 Hydronephrosis. Urine in dilated calyces appears black (hypoechoic).
42 CHAPTER 2 Urological investigations
Uses of plain abdominal radiography (KUB X-ray—kidneys, ureters, bladder)
Plain abdominal radiography is for detection of stones and determination of their size and (to an extent) their location within the kidneys, ureters, and bladder (Fig. 2.3).
For renal calculi, a calcification overlying the kidneys is intrarenal if it maintains its relationship to the kidney on inspiratory and expiratory films (i.e., if it moves with the kidney). If in doubt as to whether an opacity overlying the outline of the kidney is intrarenal or not, get an ultrasound (look for the characteristic acoustic shadow within the kidney), intravenous pyelography (IVP), or computed tomographic urography (CTU).
Sensitivity for detection of renal calculi is on the order of 50–70% (i.e., the false-negative rate is between 30% and 50%; it misses ureteric stones when these are present in 30–50% of cases). CTU or IVP, which relate the position of the opacity to the anatomical location of the ureters, are required to make a definitive diagnosis of a ureteric stone. However, once the presence of a ureteric stone has been confirmed by another imaging study (CTU or IVP), and as long as it is radio-opaque enough and large enough to be seen, plain radiography is a good way of following the patient to establish whether the stone is progressing distally, down the ureter.
Plain radiography is not useful for following ureteric stones that are radiolucent (e.g., uric acid) or small (generally a stone must be 3–4 mm to be visible on plain X-ray), or when the stones pass through the ureter as it lies over the sacrum. The ability of KUB X-ray to visualize stones is also dependent on the amount of overlying bowel gas.
Plain tomography (a plain X-ray taken of a fixed coronal plane through the kidneys) can be useful, but is rarely done with the availability of ultrasound and CT.
Opacities that may be confused with stones (renal, ureteric) on plain radiography include calcified lymph nodes and pelvic phleboliths (round, lucent center, usually below the ischial spines).
Look for the psoas shadow—this is obscured where there is retroperitoneal fluid (pus or blood) (Fig. 2.4).
USES OF PLAIN ABDOMINAL RADIOGRAPHY 43
Figure 2.3 Small staghorn calculus on KUB X-ray.
Figure 2.4 Leaking abdominal aortic aneurysm (AAA) on plain X-ray; the right psoas shadow cannot be seen because of retroperitoneal hemorrhage.