RADIOLOGICAL ANATOMY OF THE URINARY SYSTEM :
Kidneys :
Kidneys lie retroperitonealy in the paravertbral gutter of the posterior abdominal
wall , their upper poles more medial and posterior than lower poles .They are 12cm
long , 6 cm width , 3.5cm thick
Their size approximately that of 3 and 1/2 vertebrae on XR .
Each kidney consist of outer cortex an inner medulla
Extensions of cortex centrally as columns (of Bertin ) separate the the medulla into
pyramids which extending into the calyces and called papillae
Minor calyces combines to form two - three major calyces which in turn form
renal pelvis
The renal pelvis may be intrarenal or extrarenal
The gap between renal substance and renal pelvis called renal sinus
The renal hilum : lie medially , that of the Rt at the level of L1 vertebra and that of
the Lt at L1-l2 level .The renal pelvis lie anteriorly , the renal vein posteriorly and
the artery in between
Lymphatic vessels and nerves also enter renal hilum
Relations of the kidneys :
Posteriorly :
Upper third :diaphragm , 12th rib , plura
Lower third :psoas , quadrtus lumborum and transverse abdominis muscle
Superiorly : Adrenal glands
Anteriorly :
RK : liver , second part of duodenum , ascending colon ,& small intestine
LK : stomach , pancreas+its vessels , spleen , splenic flexure of colon & small
intestine
Blood supply of the Kidney :
Renal arteries arise from the aorta at L1L2 level
Rt renal artery longer and lower than the Lt renal artery and passes posterior to the
IVC
Each artery divided into three branches , two anterior to the renal pelvis supply
anterior part of the kidney and one posterior supply its posterior part
These arteries further subdivided into segmental , interlobar , arcuate (at the base of
pyramids ) and interlobular arteries
Venous drainage :
The renal veins drain directly to the IVC .The LT renal vein is longer and passes
anterior to the aorta to reach IVC .Inferiorphrenic , adrenal and gonadal veins also
drain to LRV
Fascial spaces around kidneys ;
A true fibrous capsule surrounds the kidneys, which is surrounded by perinephrenic
fat that separate kidneys from adrenal glands and other organs .
Fibroareollar tissue around this fat called renal fascial which has anterior lamella
called Gerotas fascia and posterior lamella called Zuckerkandel fascia
The renal fascia encloses the perinephric space
The adrena gland lies with in perinephric space separated from the kidneys by fat
Below this space is open
The fat with in perinephric space has septa that can lead to the accumulation of
urine , blood or pus that escape into this space
The space between anterior pararenal fascia and posterior peritoneum called anterior
pararenal space which contains pancreas , duodenum and ascending and descending
colon
Posterior to the renal fascia and anterior to the posterior abdominal muscles is the
posterior pararenal space
Radiological features of the kidneys :
Plain XR
*Perirenal fat makes all or part of the kidney outline visible
*Real size 11-15cm on XR or approximately 3 and 1/2 vertebral body heights
*Usually LT kidney bigger than RT , but difference of 2cm abnormal
*In children kidneys relatively bigger : about 4 vertebral body heights
*The kidneys move with change in position and respiration
*Gases in the stomach , colon or the duodenum this may overlie renal outlines so
this minimize by bowel preparation prior to take XR
IVU
-Rena outline can be in nephrographic phase of IVU in most cases
-can identify size of the kidneys and fetal lobulation
-splenic hump is prominence of mid portion of the lateral border kidney and is
normal variant
-calyseal system cap identified in urographic phase. They are connected to the renal
pelvis by infundibulae which may be short or long
-the papillae are conical and indent the calyces with surrounding sharp fornices
-several papillae may indent a single calyx called complex calyx which is more
common at the upper pole
-renal vessels can cause filling defect at the renal pelvis because passing close to it
which is less obvious in well filled collecting system
-renal pelvis bifid in 10 % of cases
-prominent renal sinus fat cause thinning and elongation of infundibulae on IVU.
US;
-renal size usually less than that on XR, upper normal limit length is = 12cm
-cortex is distinguishable from less echogenic medulla , difference more marked in
young infant
-fat in the renal sinus , very echogenic and lucent area in it due to renal pelvis ay be
the first sign of hydronephrosis
-the renal pedicle can be seen
-relationship of both kidneys to the liver , pancreas and spleen can be see
CT
-the kidneys are seen on slices fromT12 - L3 vertebral levels
-at the hilum the kidney measures 5cm transverse and 4 cm sagittaly , renal
pranchyma is 1.5 cm thick
-both posterior and anterior relationships can be seen on non contrast studies
-perinephric fat more obvious medial to the lower pole of he kidney and is a favored
site of accumulation of blood , urine or pus (in perinephric abcess )
-on non contrast study the renal substance homoenous , after IV contrast , cortex first
opacified , then medulla and pyramids making possible to distinguish between them
-renal vessels as seen after contrast administration
MRI
- not as good as US for assessment of masses less than 3cm diameter but useful
for imaging renal vessels including tumor staging
- renal cortex and medulla have different SI
- fat visible in the renal sinus and the renal pelvis not visible unless dilated
- renal vessels well seen , MRI especially useful to assess renal artery stensis and
tumor or thrombus at the renal vein
Arteriography
-less used nowadays
-aortography especially used to assess accessory renal artery which is present in 20%
of aortograms and more common in horse shoe and ectopic kidneys
-in selective studies upper pole supplied by anterior and posterior branches and
lower pole by anterior branch .
Others
Renal venography , interventional , scintograhy