The kidneys and ureters
Prof.Abdulrazzaq Al-Salman
Embryology:
A bud from the lower end of the mesonephric (wolffian) duct grows
backwards behind the peritoneum to the sacral region. The stalk of the
bud forms the ureter and its dilated upper extremity, the renal pelvis. The
primitive pelvis bifurcates repeatedly to form first the calyces and, after
several subsequent divisions, the collecting ducts. The renal parenchyma
is derived from the metanephros, which is the most caudal of a series of
embryonic renal masses:the primitive pronephros regresses as its function
is supplanted by the mesonephros, which in turn is succeeded by the
metanephros. The continuity of the glomerular apparatus and nephric
tubules formed within the metanephros is established through connection
with the collecting ducts. each kidney ascends the posterior abdominal
wall to reach its normal position in the loin.
Surgical anatomy:
The parenchyma of each kidney usually drains into seven calyces,three
upper, two middle and two lower calyces. Each of the three segments
represents an anatomical and physiologically distinct unit with its own
blood supply.
CONGENITAL ABNORMALITIES OF THE KIDNEY
Absence of one kidney
The prevalence of unilateral renal agenesis is about 1:1400 and it is
usually discovered incidentally. If the mesonephric duct has failed to bud,
the ureter will be absent. Alternatively, the ureter and renal pelvis are
present but the kidney is absent.
Renal ectopia
In approximately 1:1000 people the kidney does not ascend.Ectopic
kidneys are usually found near the pelvic brim and are usually left sided.
Horseshoe kidney
When the medial subdivisions of the mesonephric bud meet and fuse, the
normal ascent of the kidneys is impeded by midline structures. The result
is a pair of ectopic kidneys, usually fused at their lower poles, lying in
front of the fourth lumbar vertebra and great vessels. Horseshoe kidney is
found in 1:1000 necropsies and is commoner in men. Horseshoe kidneys
are liable to disease, possibly because the ureters angulate as they pass
over the fused isthmus. This may lead to urinary stasis with consequent
infection and nephrolithiasis. If not recognised, a pelvic kidney may
cause diagnostic confusion during surgery. The most frequent appearance
on the urogram shows the lower pole calyces on both sides being directed
towards the midline.
Unilateral fusion: (synonyms: crossed dystopia, cross fused renal
ectopia) is rare but the urogram appearance is striking. Both kidneys are
in one loin and are usually fused. The ureter of the lower kidney crosses
the midline to enter the bladder on the contralateral side.
Congenital cystic kidneys :(synonym: polycystic kidneys) are hereditary
and potentially lethal, and can be transmitted by either parent as an
autosomal dominant trait. Thus, the risk of an offspring inheriting the
condition can be as high as one in two depending upon the penetrance of
the gene. The disease is not usually detectable on standard imaging until
the second and third decades of life and does not usually manifest itself
clinically before the age of 30 years.
Pathology
The kidneys are huge: the cysts distort the renal capsule. The renal
parenchyma is riddled with cysts of varying size containing clear fluid,
thick brown material or coagulated blood. There may be a congenital
cystic disease of the liver.
Clinical features in the adult
The condition is slightly more common in women than men.
There are six clinical features:
• an irregular upper quadrant abdominal mass; enlargement
The bilateral knobbly enlargement is unmistakable.
• loin pain; felt as dull loin ache, is thought to be caused by the weight of
the organ dragging upon its pedicle or by stretching of the renal capsule
by the cysts.
• haematuria; Rupture of a cyst into the renal pelvis .
• infection; Pyelonephritis is common because of urinary stasis.
• hypertension; present in up to 75% of patients.
• uraemia: develop as functioning renal tissue is replaced progressively
by cysts.
Imaging
Renal imaging shows multiple cysts in both kidneys and sometimes
cysts in the liver and other organs. Blood and debris in the cysts may
mimic the heterogeneity of a cystic adenocarcinoma.
Simple cysts are usually solitary and have smooth thin walls and
homogeneous contents .Doubt about the diagnosis can be resolved by
cytological examination of cyst fluid obtained by fine-needle aspiration.
Polycystic kidneys have a typical appearance on urography: the renal
shadows are enlarged in all directions; the renal pelvis is compressed and
elongated; and the calyces are stretched over the cysts (‘big, bizarre and
bilateral’)(Spider leg appearance) .
Treatment: As kidney failure develops, a low-protein diet will help to
postpone the inevitability of renal replacement therapy. Infection,
anaemia, hypertension and disturbances of calcium metabolism
also need appropriate treatment by a nephrologist.Surgery to uncap the
cysts (Rovsing’s operation) is rarely indicated because few now accept
that this can preserve renal function by relieving pressure on the
parenchyma .
CONGENITAL ABNORMALITIES OF THE RENAL PELVIS AND
URETER
Duplication of a renal pelvis:
Duplication of a renal pelvis is found in about 4% of patients. It is
usually unilateral and left sided. The small upper renal pelvis drains the
upper group of calyces; the larger lower renal pelvis drains the middle
and lower groups of calyces.
Duplication of a ureter:
Duplication of a ureter is found in about 3% of urograms. The ureters
often join in the lower third of their course and have a common ureteric
orifice. When the ureters open independently into the bladder the ureter
from the upper pelvis opens distal and medial to its fellow.
Clinical features
Duplication of the renal pelvis or ureter is often a chance finding on
renal imaging, but infection, calculus formation and pelviureteric
junction obstruction are more common than in normal kidneys. One of
the moieties may be dysplastic and non-functioning. When the two
ureters open separately, both may be abnormal in function, position or
both.
In children, this may result in a refluxing lower pole ureter and an upper
pole ureter terminating in a ureterocele. In such cases, the duplex kidney
is at risk of infection and/or obstruction.
In the female, an ectopic ureter opens either into the urethra below the
sphincter or into the vagina. The diagnosis can often be made from the
history alone and is confirmed by urography. A girl or woman who voids
normally but who has dribbled urine for as long as she can remember
probably has an ectopic ureteric orifice. The orifice is difficult to see
because it is guarded by a valve: it may help to give an intravenous
injection of a dye such as indigocarmine to colour the urine leaking from
it.
In the male patient, the aberrant opening is above the external urethral
sphincter so the patient is continent. The ureteric orifice at the apex of the
trigone, the posterior urethra, in a seminal vesicle or in an ejaculatory
duct is likely to be functionally abnormal, and infection is common.
Treatment
Asymptomatic duplication of the kidney is harmless and does not
require treatment.
If one moiety is severely diseased or atrophic,partial nephrectomy is
usually simple and effective.
A refluxing ureter may need reimplanting.
An ectopic ureter in the female frequently drains hydronephrotic and
chronically infected renal tissue, which is best excised. Rarely, the
incontinence can be cured and renal function preserved by implanting the
ectopic ureter into the bladder or contralateral ureter .
Congenital megaureter:
Congenital megaureter is a rare oddity that may be bilateral and
associated with other congenital anomalies. Functional obstruction
at the lower end of the ureter may lead to progressive dilatation and
infection.
The ureteric orifice appears normal and a ureteric catheter passes easily.
Reflux is not a feature of the untreated condition but is almost inevitable
if the ureteric orifice is opened endoscopically.
Spontaneous improvement can occur but infection or deteriorating
function will require refashioning and reimplantion of the affected ureter.
Post-caval ureter:
The right ureter passes behind the vena cava instead of lying to the right
of it. If this causes obstructive symptoms, the ureter can be divided and
rejoined in front of the cava using a long oblique anastomosis without
tension. Unusually, the retrocaval portion of the ureter is fibrotic and
must be excised.
Ureterocele:
Ureterocele is a cystic enlargement of the intramural ureter, which is
thought to result from congenital atresia of the ureteric orifice. Although
present from childhood, the condition is often unrecognised until adult
life. The ‘adder head’ on excretory urography is typical. Usually the cyst
wall is composed of urothelium only and the diagnosis is confirmed by
the cystoscopic appearance of a translucent cyst enlarging and collapsing
as urine flows in from above.
Treatment
should be avoided unless there are symptoms arising from
infection and/or stone formation. Ureterocele is most common in women;
occasionally, the cyst may cause obstruction to the bladder outflow by
prolapsing into the internal urethral opening.
Endoscopic diathermy incision is usually all that is required for treatment
of a symptomatic ureterocele, although a micturating cystogram is
advisable to detect postoperative urinary reflux.
In advanced unilateral cases with hydronephrosis or pyonephrosis,
nephrectomy may be appropriate.
Summary