urinary tract radiology 1 word

د. نجلاء حنون lec.1

Radiology of urinary tract
The radiological examinations of the urinary tract are :
1.KUB( plain x-ray )
2.Ultrasound.
3.Intravenous urography (IVU).
4. Computed tomography(CT) .
5.Radionuclide examinations.
6. Magneticresonance imaging (MRI).
7. Arteriography .
8. Studies requiring catheterization or direct puncture of the collecting systems.
Imaging technique
Ultrasound
The following are the main uses of ultrasound:
• To investigate patients with symptoms thought to arise from the urinary tract.
• To demonstrate the size of the kidneys and exclude hydronephrosis in patients with renal failure.
• To diagnose hydronephrosis, renal tumours, abscesses and cysts including polycystic disease.
• To assess and follow-up renal size and scarring in children with urinary tract infections.
• To assess the bladder and prostate.
Normal renal ultrasound
At ultrasound, the kidneys should be smooth in outline. The parenchyma surrounds a central echogenic region, known as the central echo complex (the renal sinus), consisting of the pelvicaliceal system, together with the surrounding fat and renal blood vessels . In most instances, the normal pelvicaliceal system is not visible within the renal sinus. The renal cortex generates homogeneous hypoechoic texture that are of equal or less echogenicity than those of the adjacent liver or spleen , and the renal pyramids are seen as triangular hypoechoic areas adjacent to the renal sinus.
The normal adult renal length, measured by ultrasound,is 9–12 cm. Renal length varies with age, being maximal in the young adult. There may be a difference between the two kidneys, normally of less than 1.5 cm. A kidney with a bifid collecting system is usually 1–2 cm larger than a kidney with a single pelvicaliceal system. Minor changes in size occur in many conditions .
Normal ureters are not usually visualized due to overlying bowel gas.
The urinary bladder should be examined in the distended state: the walls should be sharply defined and barely perceptible .The bladder may also be assessed following micturition, to measure the post micturition residual volume of urine.


Urography
Urography is the term used to describe the imaging of the renal tract using intravenous iodinated contrast medium.
There are 2 types :
1.The traditional intravenous urogram ( IVU )
2. CT urography .

CT has the advantage of being

- highly sensitive for the detection of stones including those that may be radiolucent on plain film.
-allows the characterization of renal lesions and the detection of ureteric lesions.
-demonstrates the surrounding retroperitoneal and abdominal tissues.
-CT overcomes the overlap of superimposed tissues, which can cause difficulty when interpreting traditional IVU.

The principles of both techniques are similar. Firstly, ‘non-contrast’ imaging of the renal tract is required, in order to identify all renal tract calcifications. In some case, where the clinical question relates to renal calculi, the non contrast CT may be sufficient (known as the ‘CT KUB’).
the non-contrast study is followed by the injection of iodinated contrast medium. Images are obtained at specific time intervals in order to demonstrate the nephrogram (contrast within the kidneys parenchyma ) and the urogram (contrast within the PCS, ureters and bladder). CT IVU may be reformatted in the coronal plane in order to have a similar appearance to traditional IVU .

The main indications for urography ( Intravenous urography or CT urography) are :

• When detailed demonstration of the pelvicaliceal system and ureters are required.
• In suspected ureteric injury, e.g. following pelvic surgery or trauma.
• Assessment of acute ureteric colic
Indication of CT scan of urinary tract :
• Investigation of renal calculi.
• Investigation of haematuria.
• Characterization of a renal mass.
• Staging and follow-up of renal carcinoma.
• To delineate renal vascular anatomy (e.g. suspected renal artery stenosis or prior to live related kidney donation).
• To diagnose or exclude renal trauma.


IVU study
-Plain film in intravenous urogram: it used to Identify all calcifications. Decide if they are in the kidneys by relating them to the renal outlines , calcification seen in the line of the ureters or bladder must be reviewed with post contrast scans, to determine whether the calcification lies in the renal tract. Note that calcification can be obscured by contrast medium and stones are missed if no plain film is taken.
The major causes of urinary tract calcification include calculi , diffuse nephrocalcinosis, localized nephrocalcinosis (e.g. tuberculosis or tumours) and prostatic calcification.
Look at the other structures on the film. Include a review of the bones and other soft tissues, just as you would on any plain abdominal film.
-Films taken after injection of contrast medium Kidneys
1 .Check that the kidneys are in their normal positions . The left kidney is usually higher than the right.
2 .Identify the whole of both renal outlines. If any indentations or bulges are present they must be explained.
• Local indentations . The renal parenchymal width should be uniform and symmetrical, between 2 and 2.5 cm. Minor indentations between normal calices are due to persistent fetal lobulations. All other local indentations are scars.
• Local bulges of the renal outline. A bulge of the renal outline may be due to a mass or a cyst, which often displaces and deforms the adjacent calices. An important normal variant causing a bulge of the outline is the so called ‘splenic hump’ .
3 .Measure the renal lengths. The normal length of the adult kidney at IVU is between 10 and 16 cm. These figures are higher than those for renal size measured on ultrasound mainly due to radiographic magnification of the image

Calices

The calices should be evenly distributed and reasonably symmetrical. The shape of a normal calix is ‘cupped’ and when it is dilated it is described as ‘clubbed . The normal ‘cup’ is due to the indentation of the papilla into the calix. Caliceal dilatation has two basic causes: destructionof the papilla or obstruction .

causes of dilated calcies

1: Due to obstruction, with dilatation down to a specific point
of hold-up

Within the lumen

• Calculus
• Blood clot.
• Sloughed papilla.
Within the wall of the collecting system.
• Intrinsic pelviureteric junction obstruction.
• Transitional cell tumour.
• Infective stricture (e.g. tuberculosis or schistosomiasis)
Extrinsic compression
• Retroperitoneal fibrosis.
• Pelvic tumour, e.g. cervical, ovarian or rectal carcinoma.
• Aberrant renal artery or retrocaval ureter.
2:Due to papillary atrophy or destruction
• Reflux nephropathy.
• Papillary necrosis.
• Tuberculosis.


pelvis and ureters
The normal renal pelvis and pelvi-ureteric junction are funnel shaped. The ureters are usually seen in only part of their length on any one film of IVU because of obliteration of the lumen by peristalsis. Dilatation of the renal pelvis and ureter may be secondary to obstruction but there are other causes (e.g. congenital variant or secondary to vesicoureteric reflux). Filling defects within the pelvis and ureters should be identified. The three common causes are tumours, calculi or blood clots. Congenital variations of the renal collecting system are relatively common .

Bladder

The bladder is a centrally located structure that should have a smooth outline. It often shows normal smooth indentations from above owing to the uterus or the sigmoid colon, and from below by muscles of the pelvic floor . After micturition the bladder should be empty, apart from a little contrast trapped in the folded mucosa.

Computed tomography urography

CT is initially performed without intravnous contrast medium (non-contrast CT or ‘CT KUB’) to identify calcification .Images are then obtained following the administration of a rapid bolus of intravenous contrast medium. The time at which images are obtained following contrast administration depends on the indication ,these time phases include:
(i) The early renal cortical enhancement phase.
( ii)The homogeneous nephrogram phase; and
(iii)The delayed urographic phase, obtained several minutes later to demonstrate contrast within the collecting systems. With the multidetector CT (MDCT) systems, images may be reformatted in the coronal or sagittal plane for surgical planning .

Magnetic resonance imaging

Magnetic resonance imaging gives similar anatomical information to CT, with the advantage of being able to obtain scans directly in multiple planes. It is generally used in selected circumstances , including :
-To demonstrate renal artery stenosis .
- Inferior vena caval extension of renal tumours.
- To clarify problems not solved by ultrasound or CT.
-To assess the extent of bladder or prostate cancer prior to consideration for surgery.
Calcification is not visible on MRI, which is one of the main disadvantages of the technique for renal tract imaging.

Normal magnetic resonance imaging

As with CT and ultrasound, the renal contours should be smooth. Corticomedullary differentiation is best seen on T1-weighted images and immediately following intravenous contrast enhancement with gadolinium .
The renal collecting systems, ureters and bladder are best seen on T2-weighted images, as the fluid returns a high signal intensity . A heavily T2-weighted image may be used to acquire an magnetic resonance urogram ( MR- urogram).


Some normal variants are well demonstrated on MRI:
-Fetal lobulation & a column of Bertin (which is normal renal parenchyma that may look mass-like) .
The renal vasculature is best demonstrated following intravenous gadolinium and may be displayed in three dimensions.
Special techniques
Retrograde and antegrade pyelography
The techniques of retrograde and antegrade pyelography (the term pyelography means demonstrating the pelvicaliceal system and ureters) involve direct injection of contrast material into the pelvicaliceal system or ureters through catheters placed via cystoscopy (retrograde pyelography) or percutaneously into the kidney via the loin (antegrade pyelography).

The indications are limited to those situations where the information cannot be achieved by less invasive means, e.g. IVU, CT or MRI to confirm a possible transitional cell carcinoma in the renal pelvis or ureter.

Voiding cystourethrogram (micturating cystogram) and videourodynamics

In voiding cystourethrography, the bladder is filled with iodinated contrast medium through a catheter and films are taken during voiding. The entire process is observed fluoroscopically to identify vesicoureteric reflux.
The bladder and urethra can be assessed during voiding to demonstrate strictures or urethral valves .

Videourodynamic examination

Combines voiding cystourethrography with bladder pressur measurements, which necessitate bladder and rectal pressure lines.
It is indicated in the investigation
- Patient with incontinence to distinguish detrusor instability from sphincter weakness (stress incontinence).
-In elderly men with obstructive symptoms, to differentiate true
obstruction from bladder instability
- In patients with a neurogenic bladder.


Urethrography

The urethra is visualized during voiding cystourethrography.For full visualization of the male urethra, however, an ascending urethrogram with contrast medium injection via the external urethral meatus is necessary .
The usual indications for the examination are:
- The identificationof urethral strictures
- To demonstrate extravasation from the urethra or bladder neck following trauma.

Renal arteriography

Renal arteriography is performed via a catheter introduced into the femoral artery by the Seldinger technique . Selective injection are made into one or both renal arteries .
It is mainly used:
- To confirm the CT or MRI findings of vascular anatomy prior to renal surgery.
-To confirm renal artery stenosis prior to percutaneous balloon angioplasty.