Saturday, April 14, 2012

The Clinical Approach to the Acutely Ill Patient imaging


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.


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