RENAL VARIANTS DIAGNOSTIC RADIOLOGY
Category: Diagnostic Radiology
Abstract :
Duplex kidneys These occur in a spectrum of degrees, from two separate organs
with separate collecting systems and duplex ureters, to a mild degree of
separation of the PCS at the renal hilum. The latter is more difficult to
recognize on ultrasound, but the two moieties of the PCS are separated by a zone
of normal renal cortex which invaginates the kidney, a hypertrophied column of
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Duplex kidneys
These occur in a spectrum of degrees, from two separate organs
with separate collecting systems and duplex ureters, to a mild degree of
separation of the PCS at the renal hilum. The latter is more difficult to
recognize on ultrasound, but the two moieties of the PCS are separated by a zone
of normal renal cortex which invaginates the kidney, a hypertrophied column of
Bertin (see below).
If duplex ureters are present (a difficult diagnosis to make
on ultrasound unless dilatation is present) then a ureterocoele related to the
upper moiety should be sought at or adjacent to the bladder. This may cause
dilatation of the affected moiety. The main renal artery and vein may also be
duplicated, which can occasionally be identified using colour or power
Doppler.
Ectopic kidneys
The kidney normally ascends from the pelvis
into the renal fossa during its course of development. During this ‘migration’
it rotates inwards so that the renal hilum faces medially. A failure of this
mechanism causes the kidney to fall short of its normal position, remaining in
the pelvis, that is, a pelvic kidney. Usually it lies on the correct side,
however occasionally it can cross to the other side, lying inferior to its
normally placed partner—crossed renal ectopia. Frequently it may fuse with the
lower pole of the other kidney, crossed fused renal ectopia, resulting in what
appears to be a very long, unilateral organ.
Horseshoe kidneys
In the
horseshoe kidney, the kidneys lie one on each side of the abdomen but their
lower poles are fused by a connecting band of renal tissue, or isthmus, which
lies anterior to the aorta and IVC. The kidneys tend to be rotated and lie with
their lower poles medially. It may be difficult to visualize the isthmus due to
bowel gas anterior to it but a horseshoe kidney should always be suspected when
the operator is unable to identify the lower poles of the kidneys confidently.
When the isthmus can be seen, it is important not to confuse it with other
abdominal masses, such as lymphadenopathy. CT is occasionally performed because
of this but normally clarifies the findings.
Extrarenal pelvis
Not
infrequently, the renal pelvis projects outside the kidney, medial to the renal
sinus. This is best seen in a transverse section through the renal hilum. It is
frequently ‘baggy’, containing anechoic urine, which is prominently demonstrated
on the ultrasound scan. The importance of recognizing the extrarenal pelvis lies
in not confusing it with dilatation of the PCS, or with a parapelvic cyst or
collection.
Hypertrophied column of Bertin
The septum of Bertin is an
invagination of renal cortex down to the renal sinus. It occurs at the junctions
of original fetal lobulations and is present in duplex systems (see above),
dividing the two moieties. Particularly prominent, hypertrophied columns of
Bertin may mimic a renal tumour. It is usually possible to distinguish between
the two as the column of Bertin does not affect the renal outline and has the
same acoustic characteristics as the adjacent cortex. Colour or power Doppler
can be helpful in revealing the normal, regular vascular pattern (as opposed to
the chaotic and increased blood flow pattern of malignant renal tumours). If
doubt persists, particularly in a symptomatic patient, CT will differentiate
tumour from a prominent column of Bertin; an isotope scan can also be helpful in
demonstrating normally functioning renal tissue.
Renal humps
These are
areas of renal cortex, which form a bulge in the renal outline. Like the
hypertrophied column of Bertin, a hump may mimic a renal mass. Careful scanning
can usually solve the dilemma as the cortex remains constant in thickness. The
most usual manifestation is the splenic hump on the left kidney, which is a
flattening of the upper pole with a lateral prominence just below the margin of
the spleen. Humps are basically a variation in the shape of the kidney rather
than an area of hypertrophied tissue.
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