urinary system imaging and pathology

Question 1

what are the main components of the urinary system

Answer 1

kidneys
bladder
ureter
uretha

Question 2

what are the main functions of the urinary system

Answer 2

Removal of metabolic waste products from the body via the production of urine.

Regulation of electrolyte balance.

Osmoregulation to control the blood volume and body water contents.

Blood pressure homeostasis by altering water retention and thirst to change blood volume and keep blood pressure in a normal range.

Regulation of blood pH.

Question 3

Kidneys – Microscopic Structure

Answer 3

The renal pyramids contain the functional units of the kidney, the nephrons.

There are about 1 million nephrons in each kidney.

They filter the blood in order to produce urine which then is transported through the calyces which then transport the urine.

Question 4

what is nephron

Answer 4

each nephron is a long tubule that can be divided into 4 anatomically and functionally different regions
- bowmans capsule
- proximal convoluted tubule
- loop of henle
- distal convoluted tubule

Question 5

Bowman’s Capsule

Answer 5

The initial part of the tubule which is closed, expanded, and folded into a double-walled cuplike structure. It encloses a web like cluster of arterioles and capillaries called the glomerulus. The capsule and glomerulus together constitute the renal corpuscle.
The vessel which brings blood into the glomerulus is theafferent arteriole, whereas the vessel that carries the rest of the blood out that hasn’t been filtered out of the glomerulus is called theefferent arteriole.

Question 6

rest of nephron

Answer 6

Proximal Convoluted Tubule:
Twisting portion of the nephron close to the Bowman’s capsule.
Has a cuboidal epithelium containing microvilli.

Loop of Henle:
U-shaped section of the tubule that dips deep into the medulla of kidneys.

Distal Convoluted Tubule:
Has a smaller diameter to the proximal convoluted tubule and is composed of columnar epithelium which contains no microvilli.
It leads into the collecting duct, a straight tubule which collect urine to the ureters.

Question 7

Nephron

Answer 7

The columnar epithelium cells of the distal convoluted tubule are known as the macula densa and are in close proximity to the juxta glomerular cells which form part of the smooth muscle wall of the afferent arteriole.

Collectively the juxtaglomerular cells and the macula densa are known as the juxta glomerular apparatus which secretes endocrine hormones (renin) important to renal physiology and homeostasis.

Question 8

Formation of Urine

Answer 8

Urine is formed in the nephrons continuously by 3 process:

Glomerular filtration:
Takes place through the semi-permeable wall of the glomerulus and glomerular capsule.

Afferent arteriole that leads into the glomerulus has a larger diameter than efferent arteriole that leads away, producing increased pressure in the glomerulus which drives plasma small molecules through the walls of the capillaries and into the proximal capsule.

Water and small molecules pass through, some are re-absorbed later.

Large molecules, blood cells and plasma proteins (albumin) unable to filter and remain in capillaries.

Question 9

Formation of Urine (2)

Answer 9

Selective tubular reabsorption:
- Occurs along the entire length of the tubule.
- By the time it has reached the distal convoluted tubule, 95% of the water and solutes have been reabsorbed into the blood stream.
- 2 hormones control fluid and electrolyte balance:
Aldosterone - sodium reabsorption
Antidiuretic hormone (ADH) - water reabsorption

Tubular secretion:
- Substances not required are cleared by secretion into the convoluted tubules and excreted from body in the urine.
- Tubular secretion of hydrogen ions is important in maintaining homoeostasis.

Question 10

Formation of Urine (3)

Answer 10

renal corpuscle
generates the glomerular filtrate composed by water ions and small molecules

proximal convoluted tubule
reabsorbs sodium chloride potassium water glucose amino acids bicarbonate calcium and phosphate
secretes ammonium and creatinine

loop of henle - thin descending limb
reabsorbs water

loop of henle - thin ascending limb
reabsorbs sodium and chloride

distal convolted tubule
reabsorbs sodium and chloride

collecting duct
reabsorbs sodium chloride and water
secretes ammonium hydrogen ions and potassium

loop of henle - thick ascending limb
reabsorbs ammonium sodium chloride

Question 11

urine - chemical composition

Answer 11

95% of urine is water
5% is solutes
- urea
- breakdown of amino acids
- creatinine
- helps regenerate ATP more in skeletal muscles
-uric acid
- breakdown of purnines

Question 12

urine - chemical composition

Answer 12

95% of urine is water
5% is solutes
- urea
- breakdown of amino acids
- creatinine
- helps regenerate ATP more in skeletal muscles
-uric acid
- breakdown of purnines

Question 13

urine - colour n pH

Answer 13

colour
- Urine varies in appearance, depending principally upon a body’s level of hydration.
- Normal urine is a transparent solution ranging from colourless to amber but is usually a pale yellow.
- In the urine of a healthy individual, the colour comes primarily from the presence of urobilin. Urobilin is a final waste product resulting from the breakdown of haeme from haemoglobin during the destruction of aging blood cells.

pH:
The pH normally is within the range of 5.5 to 7 with an average of 6.2.

Question 14

Micturition

Answer 14

When 300–400ml of urine is accumulated, the autonomic nerve fibres in the bladder wall that are sensitive to stretch are stimulated.

By conscious effort, reflex contraction of the bladder wall and relaxation of the internal sphincter can be inhibited for a limited period of time.

Question 15

Micturition

Answer 15

The Bladder Stretch Reflex
- A primitive spinal reflex in which micturition is stimulated in response to stretch of the bladder wall. It is analogous to a muscle spinal reflex, such as the patella reflex.
- During toilet training in infants, this spinal reflex is overridden by the higher centres of the brain, to give voluntary control over micturition.

Question 16

The Bladder Stretch Reflex

Answer 16

1 - sensory signals from stretch receptors of urinary bladder
2- motor signals from spinal cord cause contraction of walls of urinary bladder and relaxation of sphincter

Question 17

Micturition (2)

Answer 17

The Micturition Reflex:
Bladder fills with urine and the bladder walls stretch.
Sensory nerves detect stretch and transmit this information to the spinal cord.
Interneurons within the spinal cord relay the signal to the parasympathetic efferents (the pelvic nerve).
The pelvic nerve acts to contract the detrusor muscle, and stimulate micturition.

Question 18

Micturition Reflex

Answer 18

ureter

Question 19

Urinary System Imaging

Answer 19

Intravenous Urogram/Urography (IVU)
A radiographic study of the renal parenchyma, pelvicalyceal system, ureters and the urinary bladder.

Intravenous referring to a substance (contrast media) being administered into a vein.

Urogram/Urography referring to imaging of the urinary system.

Previously known as Intravenous Pyelogram (IVP)

Pyelogram refers to the images produced of the internal structure of the kidneys, the collecting systems, and the tubes leading from the kidneys to the bladder, the ureters.

Question 20

Urinary System Imaging (2)

Answer 20

Traditionally, IVU/IVP was done using plain radiography.
For many years, traditional IVU was the modality of choice for diagnosing urinary tract abnormalities.

This has now been replaced by CT:
CT Urogram (CTU) / CT Urography / CT IVU

Question 21

Plain Film IVU Procedure

Answer 21

control film -xr kub
injection of IV contrast
renal area 5 mins post injection
XR kub 15 mins post injection
XR kub post mictrurtion

Question 22

Plain Film IVU Procedure

Answer 22

control film -xr kub
injection of IV contrast
renal area 5 mins post injection
XR kub 15 mins post injection
XR kub post mictrurtion

Question 23

control KUB

Answer 23

Undertaken in all plain film IVUs.
Allows general survey of the urinary system.
Can demonstrate initial pathology, such as calcifications, stones etc.
Establishes correct radiographic technique/patient positioning.

Question 24

Nephrogram

Answer 24

Coned kidney view.
Taken immediately after injection of contrast (15secs).
Visualizes renal cortex/outline and other obvious abnormalities (mass).

Question 25

5 Minute Post Injection Renal View

Answer 25

Shows filling in the renal pelvis and calyces.
Determines symmetry of excretion of substances from kidneys.

Question 26

10 Minute Post Injection Renal View

Answer 26

Shows filling in the renal pelvis and calyces.
Distends calyces.
Determines symmetry of excretion of substances from kidneys.

Question 27

15 Minute Post Injection KUB

Answer 27

Demonstrates flow of urine to the bladder.
Assesses drainage of the upper tracts.
Whole length of ureters should be visible.

Question 28

Post Micturition KUB/Bladder View

Answer 28

Assesses bladder emptying/urine retention.
Assesses drainage of the upper tracts.
Demonstrates urine reflux and prostatic enlargement.
Full length KUB but bladder views also done.

Question 29

CT Urogram

Answer 29

Same principle as a plain IVU ie. to visualise the collecting systems, ureters and bladder with intravenous contrast.

Done in a single acquisition as opposed to the multiple and more dynamic traditional IVU.

Visualisation of other structures in the abdomen is also better with CTU than with traditional IVU.

Some protocol variations, however a split bolus is generally used:
The total amount of IV contrast is administered in phases rather than as a whole all at once.

Question 30

Scanning/Injection Protocol

Answer 30

Pre-Contrast Scan
Injection of 1st bolus
Wait 5 mins
Injection of 2nd bolus
Wait 2 mins
Scan

Question 31

Unenhanced Phase/Pre-Contrast

Answer 31

Demonstrates KUB anatomy in full prior to contrast administration.
Helps detect calcification/fat in kidneys.
Sets baseline Hounsfield Units (HU) which may help detect malignancy.

Question 32

Arterial/Corticomedullary Phase

Answer 32

About 30 seconds post-contrast injection.
Maximum opacification of renal arteries.
Contrast in the cortical capillaries, peritubular spaces and then with optimally enhanced renal cortex.
This phase is not always performed, depending on the clinical indications or hospital protocol.

Question 33

Nephrographic/Portal-Venous Phase

Answer 33

About 80 seconds post-contrast.
Homogenous enhancement of the renal parenchyma and medulla.
Best stage for identifying lesions.

Question 34

Delayed/Excretory Phase

Answer 34

Ranges from 3 to 15 minutes post-contrast.
Defines relationships between centrally located masses and collecting system.
Defines calyx and renal pelvis involvement.
Helps determine emptying of urinary system into bladder.
Usually done routinely/depending on clinical indications.

Question 35

Post-Processing

Answer 35

Coronal/Sagittal Planes
Maximum Intensity Projection (MIP)
3D

Question 36

IVU vs CTU

Answer 36

IVU
Longer exam requiring several radiographs to be taken at intervals.
Poor diagnostic accuracy in diagnosis and characterisation of parenchymal lesions.
It has little diagnostic role to detect the cause of obstruction in absence of radio-opaque stones along the course of the urinary tract.

CT Urogram
CTU has become the gold standard and the most useful diagnostic tool for various renal and urinary tract abnormalities including complex congenital anomalies, trauma, infection and tumours.
The “one-stop-shop” use of CTU in different anomalies including vascular, parenchymal, and urothelial evaluation has a great impact in management of patients.
However, CT still has disadvantages over IVU including its high cost and the higher radiation dose but it is more effective than IVU.

Question 37

Clinical Indications/Pathologies

Answer 37

Renal calculi
Renal colic (pain)
Macroscopic/Microscopic haematuria (blood in urine)
Renal obstruction/Hydronephrosis
Renal Cysts/Polycystic Kidneys
Recurrent UTI (Urinary Tract Infection)
Renal trauma
Review of complex congenital abnormalities
Prospective renal transplant
Renal Cell Carcinoma (RCC)
Transitional Cell Carcinoma (TCC)

Question 38

Pathologies

Answer 38

Renal Calculi (Kidney Stones) / Urolithiasis / Nephrolithiasis refers to the presence of calculi anywhere along the course of the urinary tract (ureteric/bladder calculi).
Fairly common and often associated with severe pain (renal colic).
Can be as small as a grain of sand or as large as a pearl.
Most are calcium based but they can also be struvite or uric acid based.

Question 39

Renal Calculi

Answer 39

Imaging:
Plain film: limited as although most stones are radio-opaque (calcium based) some are radio-lucent (uric acid based).
Ultrasound: frequently used as the first investigation of the urinary tract but not as sensitive as CT. Stones often produce acoustic shadowing.
CT: nearly all stones are visible on a CT KUB (non-contrast) although they can vary in density.

Question 40

Haematuria

Answer 40

Occurs when blood enters the urinary collecting system and is excreted in the urine.

Haematuria can derive from the kidneys, ureters, bladder, prostate (in men), or urethra.

Macroscopic (frank) haematuria is considered >1 mL of blood in the urine which can be pink, red, or dark brown.
Microscopic haematuria may be either symptomatic (persistent urge to urinate, pain/burning with urination and strong-smelling urine) or asymptomatic.

Question 41

Haematuria

Answer 41

The role of imaging is to identify the source of the haematuria and will usually include an US and CT urogram

Question 42

Renal Cysts

Answer 42

Fluid-filled sacs found in the kidney.
They can be classified as either simple or complex.

Simple cysts:
Have a well-defined outline and homogeneous features.
Very common in older patients.

Complex cysts:
More complicated structures.
Thick walls, septations, calcification and heterogeneous enhancement on imaging.
Classified using the Bosniak classification.
Have a risk of malignancy.

Question 42

Renal Cysts

Answer 42

Fluid-filled sacs found in the kidney.
They can be classified as either simple or complex.

Simple cysts:
Have a well-defined outline and homogeneous features.
Very common in older patients.

Complex cysts:
More complicated structures.
Thick walls, septations, calcification and heterogeneous enhancement on imaging.
Classified using the Bosniak classification.
Have a risk of malignancy.

Question 43

Hydronephrosis

Answer 43

Occurs when a kidney swells due to urine failing to properly drain from the kidney to the bladder (swelling most commonly affects only one kidney but it can involve both).
Hydronephrosis isn’t a primary disease. It’s a secondary condition that results from some other underlying disease.
Kidney stone
Congenital blockage
Blood clot
Scarring of tissue (from injury or previous surgery)
Tumour
Enlarged prostate (noncancerous)
Pregnancy
Urinary tract infection
It is structural issue and is the result of a blockage or obstruction in the urinary tract.

Question 44

Renal Cell Carcinoma (RCC)

Answer 44

Most common type of malignant renal cancer.
Originates in the lining of the proximal convoluted tubule.
8th most common adult malignancy, representing 2% of all cancers.
Usually treated by partial or complete removal of the affected kidney.
Most common sites of metastasis are (in order): the lungs, the bones, lymph nodes, the liver, adrenals and the brain.

Question 45

Renal Cell Carcinoma (RCC)

Answer 45

Imaging is essential in accurately staging renal cell carcinomas and in pre-operative planning.

Ultrasound:
Not as sensitive or specific as CT or MRI.
Has a widely varying sonographic appearance. It may appear solid or partially cystic, and may be hyper, iso, or hypoechogenic to the surrounding renal parenchyma.

CT:
During the corticomedullary phase of enhancement, 25-70 seconds after administration of contrast, renal cell carcinomas demonstrate variable enhancement.
In general small lesions enhance homogeneously, whereas larger lesions have irregular enhancement due to areas of necrosis.
The nephrogenic phase (80-180 seconds) is the most sensitive phase for detection of abnormal contrast enhancement.
Renal cell carcinoma typically causes hypervascular metastases, best appreciated on arterial phase imaging of the upper abdomen.

Question 46

Renal Cell Carcinoma (RCC)

Answer 46

MRI:
Excellent at imaging the kidneys and locally staging tumours but is also able to suggest the likely histology on the grounds of T2 differences.
Also useful for imaging the renal vein and IVC tumour thrombus.

Question 47

Other Anomalies

Answer 47

Horseshoe Kidney:
Most common type of renal fusion anomaly (congenital).
They render the kidneys susceptible to trauma.
Risk factor for the development of renal calculi and transitional cell carcinoma of the renal pelvis.

Question 48

Other Anomalies

Answer 48

Duplex Kidney:
A duplex/duplicated collecting system, one of the most common congenital renal tract abnormalities.
It is characterised by an incomplete fusion of upper and lower pole sections resulting in a variety of complete or incomplete duplications of the collecting system.
While considered an anatomical variant, duplex collecting systems may be complicated by vesicoureteric reflux and obstruction/hydronephrosis.

Question 49

Other Anomalies

Answer 49

Pelvic (Ectopic) Kidney:
Located in the pelvis instead of the abdomen.
Occurs when a kidney does not ascend from its original location in the pelvis to its final location during foetal development.
Typically, the kidney functions normally despite being in the wrong location.