S9: embryology & obstructions Flashcards by Aashi Rawat

Where do the three separate kidney systems form from?

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

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Describe the pronephros

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

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Describe the mesonephros

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

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Describe the metanephros

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

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Describe the development of the renal functional unit

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

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Describe the ascent of the kidney

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

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What is a pelvic kidney?

Ascent of the kidney fails

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What is a horseshoe kidney?

Poles of the kidney fuse together

Can be caught further down by mesenteric artery

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What is an ectopic urethral orifice?

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

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Describe the urogenital sinus

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

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Describe development of the urethra in females

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

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Describe development of the urethra in males

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

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List causes of urinary retention

Calculi 
Pregnancy 
Benign prostatic hypertrophy 
Recent surgery
Drugs
Urethral strictures

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Compare acute and chronic urinary retention

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

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Describe management of acute urinary retention

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

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Describe management of chronic urinary retention

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

Describe post-obstructive diuresis

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

Describe hydronephrosis

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

What is the difference between hydronephrosis and hydroureter?

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)

Describe acute ureteric obstruction

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

Describe diagnosis of an upper urinary tract obstruction

Diagnosis with CT or USS – show structure, not function

Diuretic renography is a functional test

List ways to drain the upper urinary tract

Nephrostomy

JJ stent

Describe urolithiasis

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

Outline the 5 types of calculi

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

Describe the clinical presentation of stones

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

Describe the treatment for stones

``` 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 ```

Describe acute prostatitis

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

Describe chronic prostatitis

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

Describe chronic non-bacterial prostatitis

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

Describe benign prostatic hypertrophy

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

Describe complications of untreated BPH

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

Describe the treatment for BPH

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)

Why can DRE aid in detection of an enlarged prostate?

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