Imaging of the kidney and ureters



Imaging of the kidney and ureters Week 22 LOs

(Syllabus)

1. Understand the concepts and associated principles, functional and clinical applications of medical imaging of the upper urinary tract (kidneys and ureters)

There are multiple investigations from which to choose to image the urinary tract. Each has particular attributes and so depends on the question that one wants answered and the suspected diagnosis.

Renal Ultrasound

• quick, non-invasive, first and often only method of imaging used

• shows renal size and position, dilatation of collecting system (suggesting obstruction), distinguish tumours and cysts, and show other abdominal, pelvic and retroperitoneal pathology

• disadvantage is that it is operator dependent and printed images convey only a fraction of the information gained by performing/watching the investigation on real time

Intravenous urography (IVU)

• has largely been replaced by ultrasound for routine renal imaging, but provides excellent definition of the collecting system and ureters

• better than ultrasound for examining renal papillae, stones and urothelial malignancy

• radiographs are taken at intervals following IV administration of an iodine-containing compound that is excreted by the kidney

• early image (I minute after injection) = nephrogram phase of renal perfusion in patients with adequate renal arterial supply

• followed by contrast filling the collecting system, ureters and bladder

• disadvantages: need for injection, time requirement, dependence on adequate renal function for good images, and risk of exposure to contrast medium (nephrotoxicity, allergy)

Pyelography

• A pyelogram is an X-Ray image of the renal pelvis

• Antegrade pyelography

o insertion of fine needle into the pelvicalyceal system under ultrasound or radiographic control

o contrast is injected to outline the collecting system, and particularly to localize obstruction

• Retrograde pyelography

o performed by inserting catheters into the ureteric orifices at cystoscopy (examination of the bladder performed prior to contrast injection up the ureters)

Renal arteriography and venography

• arteriography - to investigate suspected renal artery stenosis or haemorrhage

• also used for renal tumours

• venpgraphy – performed by placing a catheter into the IVC via the femoral vein and is used to diagnose renal vein thrombosis (a complication of nephritic syndrome) or extension of a renal tumour

• both techniques entail exposure to contrast medium

Computed tomography (CT)

• useful for characterizing mass lesions within the kidney, or combinations os cysts with masses

• gives clearer definition of the retroperitoneal anatomy and, unlike ultrasound, is aided by ↑ fat (outlines tissues and organs)

• Spiral CT:

o is a rapid sequence technique, with images obtained immediately following a bolus IV injection of contrast media to outline vascular structures

o produces high quality images of main renal vessels and can produce renal and adrenal images at the same time

Magnetic Resonance Imaging (MRI)

• excellent resolution and distinction between different tissues and options for non-invasive arterial imaging

Summary

|Test |Particularly useful for |Cost |

|Plain abdominal X-Ray |radio-opaque calculi |+ |

|Plain renal tomogram1 |renal size and outline |+ |

|Intravenous pyelogram2 |renal size, outline and function (nephrogram) |++ |

| |Renal pelvis, ureter and bladder (excretory phase) | |

|Retrograde pyelogram |bladder visualization by cystoscopy, ureter and renal pelvis |++++ |

|Antegrade pyelogram |obstructed renal pelvis and ureter |+++ |

|Ultrasonography |renal cysts, size and pelvis |++ |

|Dynamic isotope scan2 |renal blood flow, differential function and outflow |++ |

|Static isotope scan2 |renal size and scars |++ |

|CT |renal mass lesions, non-radio-opaque calculi |++++ |

|Spiral CT |renal artery anatomy | |

|Magnetic Resonance Imaging |renal mass lesions |++++ |

|Magnetic resonance angiography |renal arterial flow | |

1. Tomography is imaging by sections or sectioning, e.g. CT and PET scans

2. ‘Dynamic’ isotopes (e.g. DTPA) are filtered and excreted by the kidney, whereas ‘static’ isotopes (e.g. DMSA) are taken up by renal cells

• in the investigation of loin pain and macroscopic haematuria, adequate info can usually be obtained from simple investigations

• 90% of renal calculi are radio-opaque so the plain abdominal X-Ray is often a useful first test

• ultrasonography is cheap and non-invasive and provides useful information about renal size, renal mass lesions (in particular cysts), and renal pelvic and uretic dilatation

[pic]

These figures show an X-ray with contrast dye (intravenous pyelogram, or IVP) of the kidneys, ureters, and bladder. Figure 1 shows a normal flow from the kidneys, through the ureters, to the bladder (white arrows). Figure 2 shows a kidney stone blocking the normal flow of urine in the ureter on the right.

Contrast enhanced CT scan through the kidneys in nephrogram phase (showing corticomedullary differentiation).  This is approximately 100 seconds following contrast administration and would show renal lesions well.

Contrast enhanced CT scan through the kidneys in excretory phase (showing excretion of contrast into the collecting system).  This is approximately 8 minutes following contrast administration and would show urothelial lesions well, such as transitional cell carcinoma, stones, blood clots. (urothelium = the specialized epithelium that lines the urinary tract)

Renal Ultrasound. Sagittal view of normal left kidney showing normal cortex (C) and echogenic (bright) renal sinus fat (F).

3D reconstructed image from CT scan of the abdomen and pelvis known as CT IVP (intravenous pyelogram).  This 3D reconstruction is performed through the right kidney (K) and follows the normal ureter (arrows) all the way to the ureter's insertion into the bladder.

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