The
Clinical Approach to the Acutely Ill Patient- imaging
Imaging 4
Sonography
4
Plain
Abdominal Films 5
Intravenous
Pyelography 5
Computed
Tomography 5
Magnetic
Resonance Imaging 6
Chest
X-Ray 6
Imaging
Sonography
History,
physical examination and laboratory tests are usually completed by various
imaging procedures. In Europe, the easiest test to access is commonly
sonography; in the US it is probably CT. Sonography allows the evaluation of
the size and position of the kidneys, parenchymal width, and the detection of
masses, calculi (especially over 3 mm) and calcifications. Moreover, it is
possible to diagnose urinary tract dilatation and assess the grade of
hydronephrosis. In the lower urinary tract, sonography can show bladder tumors,
clots, and bladder stones. Finally, after micturition the residual volume can
be calculated.
Emergency
indications for formal renal ultrasound include renal colic, renal failure,
acute renal infection, urinary retention, and the detection of complications in
renal transplant patients, as well as the exclusion of important nonurologic
differential diagnoses such as spleen or liver rupture. However, because of the
overwhelming diagnostic advantages of CT, renal ultrasound is likely the second
best choice for imaging calculi in suspected colic, except in children and
pregnant women.
Emergency
vascular evaluation by Doppler or duplex sonography is indicated in the acute
scrotum to detect testicular torsion: the ultrasound finding of decreased or
absent testicular flow achieves a sensitivity of up to 90% and a specificity of
over 98%. Emergency duplex sonography is also applicable for the detection of
renal venous thrombosis (as a second choice after CT in patients who are
pregnant or allergic to iodinated contrast) and perfusion disorders complicating
renal transplantation, trauma, or urologic surgery.
Plain
Abdominal Films
Include
information about the size and position of the kidneys, of the psoas shadow
(poor identification may be a manifestation of retroperitoneal hematoma from a ruptured
aortic aneurysm), and of intestinal gas distribution (e.g., postoperative
ileus) and can aid the search for calculi and organ calcification, free
intraabdominal gas, and bone pathology. For more than half a century, the plain
abdominal film was the only tool available to detect urolithiasis. However,
because of its limited accuracy for the direct detection of stones, it is
indicated only in follow-up of conservatively managed urolithiasis, of
fragmentation results after lithotripsy (in combination with sonography), and
for missed calculi after ureterorenoscopy (Grosse et al. 2005). Its advantages include
availability, rapidity, and the ease of image evaluation even by a
nonradiologist. Its only secondary effect is a small degree of radiation
exposure, which is generally not a contraindication except in pregnant women
and perhaps young children.
Intravenous
Pyelography
Secretory
function of each kidney, the presence of delay in filling of the renal pelvis
(found in urinary obstruction), the post-void residual volume, and can describe
the genitourinary anatomic pathology. Until 1995, IVP was the mainstay in the
diagnosis of renal colic, but it has since been supplanted by helical CT. Its
drawbacks are its generally lower sensitivity, the risk of forniceal rupture because
of osmotic diuresis from contrast in the presence of occluding calculi, and the
relatively long time to obtain the several images required for a complete IVP
study. In some hospital systems, although the patient may be billed more for a
CT scan than for an
IVP
(say US $ 2,000 for a noncontrast CT of the abdomen and pelvis versus US $ 650
for an IVP), the actual cost to the institution is much lower for CT. The specificities of IVP and helical CT for
urolithiasis appear to be similar.
Further
disadvantages of IVP include the potential to mask stones through the secreted
contrast product, the risks of iodinated contrast (including allergic reaction up
to anaphylaxis), and an eventual induction of thyrotoxicosis in patients with
clinically silent hyperthyroidism. The possibility of impaired renal function from
IVP dye and the contraindication to injection in those with significant renal
insufficiency cannot be forgotten. It is not without its benefits, however, and
there
are
some situations in which IVP is actually preferred, as in the need for precise
anatomic planning before complex URS or percutaneous nephrolithotomy.
Computed
Tomography
Computed
tomography is the gold standard in most urologic emergencies, including
urolithiasis and renal trauma in the context of polytrauma. It is also useful
in the exclusion of postoperative complications such as hemorrhage, abscess, or
ileus, or differential diagnoses such as abdominal aortic aneurysm. The use of
the nonenhanced helical CT to detect urolithiasis has been established since
the ninetees (Liu et al. 2000; Miller et al. 1998) and has now mostly displaced
IVP (Dalla Palma 2001). The sensitivity, depending on calculus size, amounts to
nearly 100%. CT detects even nonradiolucent calculi, with the exception of
stones composed of the protease- inhibitor indinavir (used to treat HIV). It
can also predict the chances of spontaneous calculus discharge by its accurate
size measurement and by the inverse correlation of the intensity of perinephric
stranding with spontaneous discharge (Sandhu et al. 2003a, b). Generally,
exposure to radiation from CT is higher than with IVP, although newer low-dose
nonenhanced helical CT protocols achieve radiation doses in the same range as
IVP with comparable accuracy to standard CT imaging (Hamm et al. 2002).
CT
urography (CT scan without, then with, contrast, followed by delayed images
showing the urinary excretion phase) reaches an accuracy of 100% in the
detection of urolithiasis and it permits assessment of the retroperitoneum and
renal vessels, facilitating the differentiation from other causes of acute
flank pain. Its major drawbacks are its long duration, high radiation dose, and
the necessity for contrast with the attendant potential secondary effects.
In
the hemodynamically stable trauma patient, CT is the gold standard, as it
accurately defines the location and severity of injuries, allowing a
conservative surgical approach if appropriate. It also provides a view of the
entire abdominal viscera, retroperitoneum and pelvis.
Hemodynamic
instability still mandates immediate operative exploration in patients with
suspected renal trauma. Intraoperatively, a single-shot IVP can be obtained to
image renal injury.
In
the setting of hemodynamic stable polytrauma patient, CT cystography is an
excellent alternative to conventional retrograde cystography (Deck et al. 2000),
when necessary. Also, it allows the diagnosis of ureteral lesions resulting in
contrast extravasation. In cases of persistent strong suspicion with negative
CT, IVP or retrograde ureteropyelography (Lynch et al. 2005) should be adopted.
To
detect urethral injury, the recommended imaging method is still retrograde
urethrography
(Lynch
et al. 2005).
Magnetic
Resonance Imaging
Because
of its excellent anatomic accuracy, MRI has become irreplaceable in modern uroradiology,
but most indications concern oncology and only rarely is it used to evaluate
urologic emergencies.
An
exception worth mentioning is the evaluation of penile rupture (when history
and examination are unclear).
In
MRI urography, the T2-weighted sequences are used to create an accurate
anatomic representation of the urogenital organs and for the detection and
analysis of hydronephrosis and hydroureters independent of renal function.
T1-weighted contrast-enhanced MRI allows the analysis of excretory renal
function and the evaluation of urinary outflow in the upper urogenital
tract.
MRI urography is particularly useful in the diagnosis of congenital
disturbances in children. The avoidance of iodinated contrast also makes MRI
the primary choice in patients allergic to contrast material.
Chest
X-Ray
Basal
pneumonia with low posterior intercostal pain mimicking pyelonephritis) or
complications of urologic disorders (e.g., lung metastases in testicular
cancer), chest-x-ray should also be considered.
