Anatomical Differences of Normal Kidney & Horseshoe Kidney Final Paper I do have paper that need to edit and transform it into APA style, citation , make t

Anatomical Differences of Normal Kidney & Horseshoe Kidney Final Paper I do have paper that need to edit and transform it into APA style, citation , make the paper clean no plagiarism Running head: ANATOMY OF THE NORMAL KIDNEY VS HORSESHOE KIDNEY
Normal Kidney & Horseshoe Kidney
The Anatomical Differences
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ANATOMY OF THE NORMAL KIDNEY VS HORSESHOE KIDNEY
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Anatomical anomalies of the kidneys such as renal fusions usually compromise the
normal physiology of the kidneys and it also lead to a wide array of complications. Main
purpose of this article is to differentiate the Normal Kidneys from Horseshoe Kidney.
Introduction and major functions: Kidneys support several important functions of
maintaining homeostasis in the body. The kidneys excrete end products of metabolism and
excess water from the body and reabsorbs amino acids and glucose into the body. These
functions are essential to control the concentration of different substances in the body, and
maintain the electrolyte and water balance in tissue fluids. The kidneys have endocrine
functions too, they produce and release erythropoietin, which affects red blood cell
formation; renin, which influences blood pressure; 1,25-di-hydroxycholecalciferol (the
metabolically active form of vitamin D)(9), which is involved in the control of calcium
absorption and mineral metabolism; and various other soluble factors with metabolic actions.
Appearance and situation: In the fresh state, the kidneys are reddish-brown bean-shaped
organs. They are situated posteriorly behind the peritoneum, on each side of the vertebral
column, and are surrounded by adipose tissue. Superiorly, they are level with the upper
border of the twelfth thoracic vertebra, and inferiorly, with the third lumbar vertebra. The
right is usually slightly inferior to the left, reflecting its relationship to the liver. The left is a
little longer and narrower than the right and lies nearer the median plane (Fig.1). The long
axis of each kidney is directed inferolaterally and the transverse axis posteromedially, which
means that the anterior and posterior aspects usually described are, in fact, anterolateral and
posteromedial. An appreciation of this orientation is important in percutaneous and endourological renal surgery (1).
Size and weight: In adults, each kidney is typically 11 cm in length, 6 cm in breadth and 3
cm in anteroposterior dimension. The left kidney may be 1.5 cm longer than the right; it is
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rare for the right kidney to be more than 1 cm longer than the left. The average weight is
150g (125-170g) in men and 135g (115-155g) in women (7). In thin individuals with a lax
abdominal wall, the lower pole of the lower right kidney may just be felt in full inspiration by
bimanual lumbar examination, but this is unusual. In the fetus and the newborn, the kidney
normally has 12 lobules; in the adult, these lobules are fused to present a smooth surface,
although traces of lobulation may remain and can mimic a renal mass on radiographic
imaging (1).
Important Relations, Right Kidney
Anteriorly: The suprarenal gland, the liver, the second part of the duodenum, and the right
colic flexure.
Posteriorly: The diaphragm; the costodiaphragmatic recess of the pleura; the 12th rib; and the
psoas, quadrates lumborum, and transversus abdominis muscles. The subcostal (T12),
iliohypogastric, and ilioinguinal nerves (L1) run downward and laterally.
Important Relations, Left Kidney
Anteriorly: The suprarenal gland, the spleen, the stomach, the pancreas, the left colic flexure,
and coils of jejunum
Posteriorly: The diaphragm; the costodiaphragmatic recess of the pleura; the 11th (the left
kidney is higher) and 12th ribs; and the psoas, quadratus lumborum, and transversus
abdominis muscles. The subcostal (T12), iliohypogastric, and ilioinguinal nerves (L1) run
downward and laterally. Note that many of the structures are directly in contact with the
kidneys, whereas others are separated by visceral layers of peritoneum (2).
ANATOMY OF THE NORMAL KIDNEY VS HORSESHOE KIDNEY
Figure 1: Relationships of the kidneys and ureters in the male retroperitoneum.
Figure 2: the CT image, showing the situation of both kidneys.
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Figure 3: Ultrasonogram showing the upper poles are normally oriented slightly more medially and posteriorly than the
lower poles
Figure 4: Left kidney, oblique vertical hemisection: normal macroscopic appearance of the renal cortex and renal
medulla and the major structures at the hilum of the kidney. In A, the fat body of the renal sinus and most of the major
vessels at the hilum has been removed, and the renal pelvis has not been opened. In B, the renal pelvis has been opened to
reveal the interlobar arteries. (Grays Anatomy.)
The internal structure is divided into the outer renal cortex, inner renal medulla, and
renal pelvis. The outer renal cortex is surrounded by the renal capsule and contains numerous
blood vessels that connect to the nephrons (basic functional and structural unit of the kidney).
The inner renal medulla is arranged into several pyramid-shaped lobes (renal pyramids),
ANATOMY OF THE NORMAL KIDNEY VS HORSESHOE KIDNEY
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which are separated by the cortical tissue that collects into the ducts known as calyces. It
contains a dense network of nephrons structure such as glomerulus, Bowman’s capsule, and
renal tubules to allow blood filtration. The renal pelvis (hilum) is a concave part of the beanshaped kidney that allows blood vessels and nerves to enter and exit the kidney (9) .
Vascular Supply and Lymphatic drainage:
Arteries: The renal artery arises from the aorta at the level of the 2nd lumbar vertebra. Each
renal artery usually divides into five segmental arteries that enter the hilum of the kidney.
They are distributed to different segments or areas of the kidney. Lobar arteries arise from
each segmental artery, one for each renal pyramid. Before entering the renal substance, each
lobar artery gives off two or three interlobar arteries (Fig. 5). The interlobar arteries run
toward the cortex on each side of the renal pyramid. At the junction of the cortex and the
medulla, the interlobar arteries give off the arcuate arteries, which arch over the bases of the
pyramids (Fig. 6). The arcuate arteries give off several interlobular arteries that ascend in the
cortex. The afferent glomerular arterioles arise as branches of the interlobular arteries.
Veins: The renal vein emerges from the hilum in front of the renal artery and drains into the
inferior vena cava.
Lymph Drainage: Lymph drains to the lateral aortic lymph nodes around the origin of the
renal artery.
Nerve Supply: The nerve supply is the renal sympathetic plexus. The afferent fibers that
travel through the renal plexus enter the spinal cord in the 10th, 11th, and 12th thoracic
nerves.(2)
Coverings: The kidneys have the following coverings (Fig. 5):
1-Fibrous capsule: This surrounds the kidney and is closely applied to its outer surface.
2-Perirenal fat: This covers the fibrous capsule.
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3-Renal fascia: This is a condensation of connective tissue that lies outside the perirenal fat
and encloses the kidneys and suprarenal glands; it is continuous laterally with the fascia
transversalis.
4-Pararenal fat: This lies external to the renal fascia and is often in large quantity. It forms
part of the retroperitoneal fat. The perirenal fat, renal fascia, and pararenal fat support the
kidneys and hold them in position on the posterior abdominal wall.
Renal Structure: Each kidney has a dark brown outer cortex and a light brown inner
medulla. The medulla is composed of about a dozen renal pyramids, each having its base
oriented toward the cortex and its apex, the renal papilla, projecting medially (Fig. 5). The
cortex extends into the medulla between adjacent pyramids as the renal columns. Extending
from the bases of the renal pyramids into the cortex are striations known as medullary rays.
The renal sinus, which is the space within the hilum, contains the upper expanded end of the
ureter, the renal pelvis. This divides into two or three major calyces, each of which divides
into two or three minor calyces (Fig. 5). Each minor calyx is indented by the apex of the renal
pyramid, the renal papilla.
Figure 5: A. Right kidney, anterior surface. B. Right kidney, coronal section showing the cortex, medulla, pyramids, renal papillae, and
calyces. (snell’s clinical anatomy)
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The renal artery branches from the lower part of the aorta to provide blood supply
carrying oxygen and nutrients to the kidneys, whereas the renal vein takes away filtered
blood from the kidneys to the inferior vena cava. Furthermore, renal pelvis serves as the exit
point for the ureters, a muscular tube that empties urine from the kidney into the urinary
bladder from where it is excreted from the body via the urethra (9).
Figure 6: Anterior relations of both kidneys. Visceral peritoneum covering the kidneys has been left in position. Brown areas indicate where
the kidney is in direct contact with the adjacent viscera. (snell’s clinical anatomy)
Figure 7: MRA (magnetic resonance angiography) shows the normal renal blood supply.
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Figure 8: A resin corrosion cast of human kidneys. Ureters, pelves and calyces are yellow; aorta, renal arteries and their branches are red(1).
Horseshoe Kidney: also known as ren arcuatus (in Latin), renal fusion or super kidney, is
a congenital disorder (2). The term “horseshoe” refers to the fusion of both kidneys across the
midline by an isthmus of either functioning renal parenchyma or fibrous tissue. Horseshoe
kidneys are found in 1 in 400 individuals. A transverse bridge of renal tissue, the isthmus,
which usually but not invariably contains functioning renal substance, connects the two renal
masses. The isthmus lies between the inferior poles, most commonly anterior to the great
vessels. The ureters curve anterior to the isthmus and often have a high insertion into the
renal pelvis (See Fig. below A, B). The blood supply to horseshoe kidneys is variable. One
vessel to each moiety is seen in 30% of horseshoe kidneys, but multiple anomalous vessels
are common; the isthmus may be supplied by a vessel directly from the aorta or from
branches of the inferior mesenteric, common iliac or external iliac arteries. In view of this
variable arterial anatomy, angiography or CT scanning with vascular reconstruction is very
helpful when planning renal surgery on horseshoe kidneys. Horseshoe kidneys can have an
associated congenital pelviureteric junction obstruction in up to 30% of cases. Anomalous
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vessels crossing the ureter and the abnormal course of the ureter as it passes over renal
substance may also cause obstruction. Horseshoe kidneys have an increased incidence of
stone disease, probably as a consequence of areas of inefficient drainage.(1)
Figure 9: A, Horseshoe kidney. Note the ureters pass anterior to the isthmus. Note also the relatively high insertion of the ureters into the renal pelvis.
B, Late phase post-contrast axial CT scan showing a horseshoe kidney. Both lower poles are directed medially and fused by an isthmus (arrowed). Note that the
renal pelvis (seen here filled with contrast) are directed anteriorly. (Grays Anatomy 41st Ed 2015.)
Horseshoe kidney is the most common fusion anomalies of the kidneys. The term
“horseshoe” refers to the fusion of both kidneys across the midline by an isthmus of either
functioning renal parenchyma or fibrous tissue. More than 90 percent of all cases involve the
fusion between lower (inferior) poles of the kidneys. Other cases of renal fusion occur in
either upper (superior) pole or both upper and lower poles (7). Fusion in the midline leads to
the formation of U-shaped horseshoe kidney, whereas lateral fusion forms L-shaped
horseshoe kidney (3).
Signs and symptoms: Although often asymptomatic, the most common presenting symptom
of patients with a horseshoe kidney is abdominal or flank pain. However, presentation is
often non-specific (5). Approximately a third of patients with horseshoe kidneys remain
asymptomatic throughout their entire life with over 50% of patients having no medical issues
related to their renal fusion when followed for a 25 year period (5) . As a result, it is estimated
that approximately 25% of patients with horseshoe kidneys are diagnosed incidentally with
ultrasound or CT imaging (5)
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Pathophysiology: Kidneys are normally located in the retroperitoneal space between the T12
and L3 vertebrae after ascending from the pelvis during development to rest underneath
the adrenal glands (5). In patients with this condition, the horseshoe kidney ascent is
commonly arrested by the inferior mesenteric artery due to the central fusion of the kidneys
(12)
. However, this is present in only 40% of cases, and, in 20% of cases, the fused kidney
remains in the pelvis (5). Its ascension may also be restricted by its own renal artery (13).
Additionally, during normal development, the kidneys undergo a 90 degree medial rotation
while ascending. However, due to the renal fusion, this rotation is impaired resulting in
abnormal placement of the ureters. This in turn can lead to urinary stasis and drainage issues
(5)
. Furthermore, approximately 70% of kidneys in normal individuals are supplied by a
single renal artery with the remaining 30% having embryonic collateral or accessory arteries
(5)
. With horseshoe kidneys, the majority is supplied by derivatives of the abdominal
aorta or common illiac arteries depending on the final position of the kidneys (5) (8).
Etiology: There have been several proposed factors that may contribute to the development
of a horseshoe kidney. Different exposures to the developing fetus such as different
teratogens (e.g. thalidomide, ethanol, ACE inhibitors, cocaine, gentamycin, corticosteroids,
NSAIDs, and vitamin A) have been hypothesized (5) (14) (15). Impairment of a developing
embryo’s nephrogenic cell migration or abnormal migration of the kidneys due to fetal
structural abnormalities is another potential factor (5) (14). However, no definitive genetic
cause has been identified (5) (15).
Diagnosis: Horseshoe kidneys are commonly diagnosed incidentally on abdominal imaging.
The diagnosis can be made with many different imaging modalities such as ultrasound,
intravenous pyelogram, CT, and MRI (5).
Common features that can be found on imaging include:
ANATOMY OF THE NORMAL KIDNEY VS HORSESHOE KIDNEY
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Midline symmetrical fusion (present in 90% of cases) or lateral asymmetric fusion
(present in 10% of cases) of the lower poles (16) .
•
Position of fused kidneys is lower than normal with incomplete medial rotation (16).
•
Renal pelvis and ureters are positioned more anteriorly and ventrally cross the isthmus (16)
(17).
•
Isthmus that may be positioned below the inferior mesenteric artery (16) .
•
Variant arterial supply that can originate from the abdominal aorta or common illiac
arteries (5) (8) (16) .
•
Lower poles of kidney that extend ventromedially and may be poorly defined (18).
The difference: The horseshoe kidney differs from the normal kidneys in terms of location,
orientation, and vasculature. Normally, the upper poles of the kidneys are oriented slightly
more medially and posteriorly than the lower poles; thus, allowing the organs to take their
position in the abdomen below the adrenal glands. However, the ascent of horseshoe kidney
positions the lower poles more medially where the kidneys sit lower in the abdomen and
pelvis than normal. It is shown that the inferior mesenteric artery (IMA) at L3 tethered over
the isthmus holds hack the horseshoe kidney’s ascent into the abdomen (5). The fusion
prevents normal renal rotation, in which the ureters normally cross in front of the isthmus as
they descend to the urinary bladder. Reverse renal axis leaves the ureters with a high insertion
point into the renal pelvis by passing anteriorly over the isthmus located just below the IMA
as they descend to the urinary bladder (3).
Renal vascular supply is also variable with horseshoe kidneys. The vascular supply
involves multiple blood vessels arising from the aorta, iliac artery, and IMA. Accessory renal
arteries may arise from the aorta adjacent to the main renal artery, distal to the ostium of the
main artery, or from the iliac artery. When multiple arteries occur, each renal artery supplies
ANATOMY OF THE NORMAL KIDNEY VS HORSESHOE KIDNEY
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blood to a specific region of the kidney; thus, occlusion of one artery may cause infarction to
the corresponding region due to lack of collateral perfusion. However, multiple renal veins
interconnect within the kidney and directly or indirectly drain to the inferior vena cava (8).
Various radiological imaging modalities demonstrate significant differences of the
normal anatomy of the kidney seen in horseshoe kidneys. Intravenous urogram (IVU) and
plain radiographs help reveal abnormal features of an altered renal axis associated with
horseshoe kidney (Fig. 11). The kidneys normally follow the axis of the psoas muscles, with
the lower poles lying at a more lateral position than the upper poles (4). However, the axis in
the horseshoe kidney is reversed as indicated in the plain radiograph below (Fig. 10).
figure 10: Plain radiograph of the abdomen showing a reversed axis. The kidneys appear symmetrical in midline fusion of the left lower
renal pole.
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Figure 11: The IUV shows the lower pole calyx of the right kidney lying medial to the ureter. Some degree of malrotation is also present in
both kidneys and renal pelvis appears enlarged.
Figure 12: Axial CT image of the abdomen showing a horseshoe kidney
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Figure 13: A: shows a left ureteropelvic junction (UPJ) obstruction in the upper calyceal group, whereas B indicates a
reduction of renal parenchyma (10).
This contrast-enhanced axial CT image shows fused kidneys at different levels of
malrotation, with a parenchymal isthmus at the lower poles (Fig.14).
Figure 14: The axial contrast-enhanced T1-weighted MRI image shows parenchymal tissue isthmus of the horseshoe lying anterior to the
spine.
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MRI illustration, Showing the connection between the presence of isthmus and reversed renal
axis lead to variation in renal vascular supply in horseshoe kidneys. Multiple blood vessels
can be seen arising from aorta, iliac artery, and inferior mesenteric artery (MRA)(Fig.15).
Figure 15: MRI illustration, Showing the connection between the presence of isthmus and reversed renal axis lead to variation in renal
vascular supply in horseshoe kidneys.
Figure 16: This is a traverse ultrasonogram of the abdomen showing a soft-tissue hypoechoic mass (isthmus), which is anterior to the spine
and aorta and fusing the lower renal poles.
Clinical presentation: About one-third of the patients with horseshoe kidney remain
asymptomatic but the incidence cases are often detected during routine radiological
assessments (3). Physical examinations may show the presence of a midline lower-abdominal
mass associated with obstruction, stones, infection, or tumors. Subsequently, patients with
normal and horseshoe kidneys may present common clinical signs associated with
gastrointestinal problems such as abdominal pain, abdominal distention, and nausea (5).
However, patients with horseshoe kidneys are affected by a wide range of
genitourinary and extragenitorurinary pathologies. Most of the complications of horseshoe
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kidneys include lithiasis, ureteropelvic junction obstruction, and renal infections…
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