S9: embryology & obstructions

Question 1

Where do the three separate kidney systems form from?

Answer 1

Organisation of intermediate mesoderm
3 systems develop sequentially
Disappearance of one system marks the onset of development of the next developmental stage
1st appears in the cervical region – the pronephros

Question 2

Describe the pronephros

Answer 2

First kidney system, never functions in humans
Important because of its duct – pronephric duct extends from the cervical region to the cloaca and drives the development of the next developmental stage

Question 3

Describe the mesonephros

Answer 3

Mesonephric tubules develop caudal to the pronephric region
Mesonephric tubules plus mesonephric duct = embryonic kidney
-mesonephric duct has important role in the development of the repro system in the male
-sprouts the ureteric bud which induces development of the definitive kidney
No water conserving function -> need to upgrade

Question 4

Describe the metanephros

Answer 4

Undifferentiated intermediate mesoderm, caudal to the mesonephros 
Ureteric bud induces development of the true kidney, metanephros in this tissue 
Ureteric bud (releases growth factors) contacts metanephric blastema -> bud expands and branches -> renal pelvis, minor & major calyces

Question 5

Describe the development of the renal functional unit

Answer 5

Ureteric bud drives the development of the definitive kidney
Collecting system is derived from the ureteric bud itself
The excretory component is derived from intermediate mesoderm under the influence of the ureteric bud

Question 6

Describe the ascent of the kidney

Answer 6

Metanephric kidney first appears in the pelvic region
Undergoes an apparent caudal to cranial shift, crossing the arterial fork formed by vessels returning blood from the fetus to the placenta
Swaps position with the gonads

Question 7

What is a pelvic kidney?

Answer 7

Ascent of the kidney fails

Question 8

What is a horseshoe kidney?

Answer 8

Poles of the kidney fuse together

Can be caught further down by mesenteric artery

Question 9

What is an ectopic urethral orifice?

Answer 9

Splitting of the ureteric bud
Partial or complete
Symptomatic consequence is ectopic urethral opening

Question 10

Describe the urogenital sinus

Answer 10

Created from hindgut by urorectal septum
UGS is continuous with umbilicus – urachus closes to become median umbilical ligament
Superior part connects to umbilicus
Majority differentiates to form the urinary bladder
Inferior part develops into the urethra – sex differences in structural development of the urethra

Question 11

Describe development of the urethra in females

Answer 11

Mesonephric ducts (MD) reach urogenital sinus (UGS)
Ureteric bud sprouts from MD
UGS begins to expand & MD begins to regress
MD regression continues, ureteric bud opens into UGS

Question 12

Describe development of the urethra in males

Answer 12

Mesonephric ducts (MD) reach urogenital sinus (UGS)
Ureteric bud (UB) sprouts from MD
Smooth musculature begins to appear, UGS begins to expand
UB & MD make independent openings in UGS

Question 13

List causes of urinary retention

Answer 13

Calculi 
Pregnancy 
Benign prostatic hypertrophy 
Recent surgery
Drugs
Urethral strictures

Question 14

Compare acute and chronic urinary retention

Answer 14

Acute – painful inability to void, residual volume 300-1500ml
Chronic – painless, may still be voiding, residual volume 300-4000ml

Question 15

Describe management of acute urinary retention

Answer 15

Catheterise and record residual urinary volume
History, examination, urine dip, U&Es
Treat any obvious cause
BPH – alpha blocker, may trial without catheter after 1-2 weeks

Question 16

Describe management of chronic urinary retention

Answer 16

Catheterise and record residual volume
History, examination, urine dip, U&Es
High pressure -> abnormal U&Es, hydronephrosis, repeat episodes can cause permanent renal scarring and CKD
Low pressure -> normal renal function, no hydronephrosis
Plan for long-term catherization or intermittent self-catherization

Question 17

Describe post-obstructive diuresis

Answer 17

Following resolution of urinary retention through catherization
Kidneys can often over-diurese -> can lead to worsening AKI
Urine output should be monitored for 24 hours post catheterisation – patients with high urine volumes should be supported with IV fluids

Question 18

Describe hydronephrosis

Answer 18

Dilation of the renal pelvis and calyces (build-up of urine) due to obstruction at any point in the urinary tract causing increased pressure and blockage:
1) Unilateral – upper urinary tract obstruction
2) Bilateral – lower urinary tract obstruction
Progressive atrophy of the kidney develops from the back pressure from the obstruction and is transmitted to the distal parts of the nephron
GFR declines and if obstruction is bilateral, the patient goes into renal failure

Question 19

What is the difference between hydronephrosis and hydroureter?

Answer 19

Hydronephrosis = obstruction at the pelviureteric junction
Hydroureter = obstruction at the ureter (eventually developing hydronephrosis)
Bladder distension with hypertrophy = obstruction of the bladder neck/urethra (eventually leads to hydroureter and hydronephrosis)

Question 20

Describe acute ureteric obstruction

Answer 20

Renal colic, caused by calculus but can also be blood clots or sloughed papilla
Usually, a unilateral problem
Leads to acute renal failure if bilateral – anuria/oliguria
Pyonephrosis can develop – infected, obstructed kidney & failure to promptly decompress may lead to death from sepsis and permanent loss of renal function

Question 21

Describe diagnosis of an upper urinary tract obstruction

Answer 21

Diagnosis with CT or USS – show structure, not function

Diuretic renography is a functional test

Question 22

List ways to drain the upper urinary tract

Answer 22

Nephrostomy

JJ stent

Question 23

Describe urolithiasis

Answer 23

Risk factors: men, Caucasians
Dehydration increases the concentration of the urine & is a predisposing factor
Can form anywhere in the urinary tract – 3 most common sites: pelviureteric junction, pelvic brim & vesicoureteric junction
CT scan gold standard for diagnosing stones

Question 24

Outline the 5 types of calculi

Answer 24

Calcium oxalate stones – associated with hypercalcaemia, primary hyperparathyroidism & hyperoxaluria
Mixed calcium phosphate and calcium oxalate stones – associated with alkaline urine
Magnesium ammonium phosphate stones – associated with urea splitting bacteria
Uric acid stones – associated with gout and myeloproliferative disorders
Cystine stones – patients with inherited cystinuria

Question 25

Describe the clinical presentation of stones

Answer 25

Renal stones – continuous dull ache in the flank
Ureteric stones – classical renal colic, typically radiates from loin to groin, patient appears sweaty, pale, restless with nausea & vomiting
Bladder stones – strangury: the urge to pass something that will not pass
Recurrent and untreatable UTIs, haematuria or renal failure
May be asymptomatic

Question 26

Describe the treatment for stones

Answer 26

Stones < 4-5mm pass spontaneously, larger stones might require surgical intervention 
Extracorporeal shock wave lithotripsy (ESWL): shock waves are used to fragment the calculi into small pieces which will then pass out in the urine 
Ureteroscopic destruction/removal of stones 
Percutaneous nephrolithotomy (PCNL): endoscopic removal of the stone 
Open surgical removal
Prevention of further stones: high fluid intake & correction of any underlying metabolic abnormality

Question 27

Describe acute prostatitis

Answer 27

Pathogens: E.coli, proteus and staph species & sexually transmitted pathogens (chlamydia & gonorrhoea)
Inflammation can be focal or diffuse
Patients present with malaise, rigors, fever, difficulty in passing urine, dysuria & perineal tenderness
Rectal exam = soft, tender & enlarged prostate

Question 28

Describe chronic prostatitis

Answer 28

Results from inadequately treated infection
Can occur because some antibodies cannot penetrate the prostate effectively, often a history of recurrent prostatic and UTIs
Some patients are asymptomatic & will present with no preceding acute phase
Difficult to diagnose & treat – confirmed by histological examination and positive culture from sample of prostatic secretion

Question 29

Describe chronic non-bacterial prostatitis

Answer 29

Results in enlargement of the prostate
Often no history of recurrent UTIs
Usual pathogen is C. trachomatis – typically sexually active men are affected
Histological examination shows fibrosis as a result of chronic inflammation

Question 30

Describe benign prostatic hypertrophy

Answer 30

Non-neoplastic enlargement of the prostate gland, can eventually lead to bladder outflow obstruction
Cause is unknown but may be related to levels of male sex hormones
Presentation: difficulty/hesitancy in starting to urinate, poor stream, dribbling postmicturition, frequency & nocturia
DRE – prostate is firm, smooth and rubbery

Question 31

Describe complications of untreated BPH

Answer 31

Can present with acute urinary retention, which is accompanied by a distended and tender bladder & desperate urge to pass urine
Patient may have progressive bladder distension, leading to chronic painless retention and overflow incontinence
Can lead to bilateral upper tract obstruction and renal impairment – patient presenting in CKD

Question 32

Describe the treatment for BPH

Answer 32

Medical treatment
1) Alpha-blockers: relax smooth muscle at bladder neck and within prostate
2) Finasteride (5a-reductase inhibitor): prevents the conversion of testosterone to the most potent androgen dihydrotestosterone
Surgical treatment
1) Transurethral resection of the prostate (TURP)

Question 33

Why can DRE aid in detection of an enlarged prostate?

Answer 33

Posteriorly, the prostate lies next to the rectum with its anterior surface against the pubis
Can easily be felt