Kidneys

Surface anatomy and relationships

• Appearance
  • Kidneys in children have more prominent fetal lobulations, which generally disappear by the first year of life.
  • The adult kidney’s lateral contour might have a focal renal parenchymal bulge (dromedary hump), which is more common on the left side and of no pathological significance
• Dimensions
  • Each kidney measures 10-12cm in length, 5.5-7.5cm in width, and 2.5-3cm in thickness
• Weight
  • Each adult male kidney weighs ≈125-170g; the kidney is 10-15g smaller in females
• Position
  • Varies based on (3):
    1. Phase of respiration (inspiration vs. expiration)
    2. Body position
    3. Presence of anatomic anomalies
  • Supine end-expiration position:
    • Right kidney
      • Between the top of L1 to bottom of L3 vertebra
      • 1-2cm lower than the left kidney (liver causes inferior displacement)
      • Upper pole at level of the 12th rib
      • Lower pole between the L3-L4 vertebrae
    • Left kidney
      • Between T12 and L3 vertebrae
      • Related to the 11th and 12th ribs
      • Upper pole at level of the 11th rib
      • The tail of the pancreas lies in close proximity to the upper pole of the left kidney and left adrenal gland
    • Both renal hila ≈at the level of L1
  • Pleural cavity
    • The inferior limit of the pleural cavity may lie anywhere between the 10th and 12th ribs.
      • Access through the 10th or 11th intercostal space (above the 11th or 12th rib) requires careful mobilization of the lower edge of the pleura to avoid entering it
      • Access through the 9th intercostal space (above the 10th rib) inevitably requires entry into the pleural cavity
      • Clinical implication: Percutaneous access above the 11th rib (10th intercostal space) is associated with increased risk for injuring pleura and even lungs. Therefore, when possible, subcostal (below the 12th rib) or the 11th intercostal (between the 11th and 12th ribs) access should be achieved
  • The posterior surface is adjacent to the quadratus lumborum muscle and the diaphragm.
  • The anteromedial surface is adjacent to the psoas major.
  • Longitudinal axes are oblique
    • The upper poles more medial and posterior than the lower poles = Lower poles Lateral Anterior = Lower LANTern
    • The medial aspect is rotated anteriorly at ≈30°
  • The parietal peritoneum bridging the upper pole of the right kidney to the liver forms the hepatorenal ligament; excessive downward traction of the right kidney may cause capsular tear of the liver and may lead to hemorrhage.
  • The parietal peritoneum bridging the upper pole of the left kidney to the spleen forms the splenorenal ligament; excessive downward traction of the spleen may cause capsular tear of the spleen and may lead to hemorrhage.

Transversalis fascia and posterior pararenal space

• See CW11 Chapter 33

Anterior pararenal space and inner stratum

• Can be developed to gain access to the kidney anteriorly when followed medially from the white line of Toldt
  • The white line of Toldt is formed at the lateral border of the fusion of the colonic mesentery with the posterior parietal peritoneum

Perirenal space

• Contains
  • Adrenal
  • Kidney
  • Ureter
  • Perirenal fat
  • Renal vascular pedicle
  • Gonadal vessels
• The perirenal fat is finer and lighter yellow in color compared with the coarser yellow-orange pararenal fat.
• The perirenal space has a conelike shape that is open at its inferior extent in the extraperitoneal pelvis.
  • There is some controversy regarding the medial and inferior extents of the perirenal space. Historically, it was assumed that there was no communication between the right and left perirenal spaces. However, based on in vivo cases and cadaveric injection studies, there may be some communication across the midline below the level of the renal hilum

Gerota fascia (perirenal/renal fascia)

• Named after the Romanian anatomist Dimitrie D. Gerota (1867-1939)
• Encloses perinrenal space
• Closed superiorly and laterally, and open inferiorly
  • Superiorly, the Gerota fascia is continuous with the diaphragmatic fascia on the inferior surface of the diaphragm
  • The anterior and posterior laminae merge laterally to form the lateroconal fascia, which functions to separate the anterior and posterior pararenal spaces. It can be visualized radiographically on computed tomographic (CT) scan and continues anterolaterally deep to the transversalis fascia.
    • The lateroconal fascia then fuses with the peritoneum lateral to the colon to form the white line of Toldt.
  • Clinical implication: Perinephric fluid collection can tract inferiorly into the pelvis without violating the Gerota fascia
• Continues medially to fuse with the contralateral side
  • Envelops the aorta and IVC
• Extends inferiomedially along the abdominal ureter as a periureteral fascia
• Surrounded by a layer of condensed fat called paranephric fat
• Must be opened to access the kidneys, adrenals, or abdominal ureters
  • To access the kidneys transperitoneally, the colon needs to be mobilized from the white line of Toldt

Renal hilum

• Structures (from anterior to posterior) (4) VAUA:
  • Renal Vein
  • Renal Artery
  • Renal pelvis/Ureter
  • Posterior segmental Artery
• To access
  • Right renal hilum, the second part of the duodenum and head of pancreas may need to be mobilized medially to expose the IVC
  • Left renal hilum, the tail of the pancreas and the spleen (with the splenic vessels) need to be mobilized

Gross and microscopic anatomy

• The kidney is divided into cortex and medulla
• Renal Medulla
  • More centrally located
  • Divided into 8-18 striated renal pyramids
    • The base of the pyramids is positioned at the corticomedually boundary
    • Each renal pyramid terminates centrally in a papilla, and each papilla is cupped by an individual minor calyx
      • A group of minor calyces join to form a major calyx. The major calyces combine to form the renal pelvis
• Renal Cortex
  • ≈1 cm in thickness
  • Covers the base of each renal pyramid peripherally
  • Extends downward between the individual pyramids to form the columns of Bertin
• The cells lining the collecting ducts are cubical to columnar and are more resistant to damage than those of the renal tubules.
• The calyces, pelvis, ureters, bladder, and urethra are lined by transitional epithelium/urothelium

Radiologic anatomy of the renal parenchyma

• Ultrasound
  • In adults, the normal kidneys have smooth margins and are isoechoic to the liver. However, both renal cortices and pyramids are usually hypoechoic to the liver, spleen, and renal sinus
  • Increasing echogenicity correlates to the severity of pathologic changes in renal parenchyma.
• CT
  • The renal parenchyma is homogeneous on unenhanced CT
  • CT angiography is currently the gold standard to assess renal arteries
• MRI
  • T1-weighted sequences show the renal cortex much brighter than the renal medulla, whereas the cortex is slightly less intense than the medulla on T2-weighted sequences

Renal vasculature

• Each kidney is commonly supplied by a single renal artery, which arises directly from the abdominal aorta, and a single renal vein usually drains directly to the IVC

Arterial supply

• Summary of branching:
  • Main renal artery -->
  • Anterior vs. posterior branch -->
  • Segmental arteries -->
  • Lobar arteries -->
  • Interlobar arteries -->
  • Arcuate arteries -->
  • Interlobular arteries -->
  • Afferent arteriole -->
  • Glomerulus -->
  • Efferent arteriole
• Anterior and posterior branch of main renal artery
  • Anterior branch
    • Supplies the anterior aspect, comprising ≈2/3 of the total kidney
    • Divides into segmental arteries (4):
      1. Apical
      2. Upper
      3. Middle
      4. Lower
  • Posterior branch
    • Supplies the posterior aspect, comprising ≈1/3 of the total kidney
    • Becomes the posterior segmental artery
    • Represents the first and most consistent branch, which separates from the renal artery before it enters the renal hilum
    • A small apical segmental branch may originate from this posterior branch, but it arises most commonly form the anterior division
• Segmental arteries
  • End arteries that do not anastomose significantly with other segmental arteries.
    • Clinical implication: Occlusion or injury to a segmental branch will cause segmental renal infarctions.
  • The posterior segmental artery from the posterior division passes posterior to the renal pelvis while the others pass anteriorly pass anterior to the renal pelvis
    • Clinical implication: If the posterior segmental branch passes anterior to the ureter, UPJO may occur
    • There is a longitudinal avascular plane (line of Brodel) between the posterior and anterior segmental arteries just posterior to the lateral aspect of the kidney through which incision results in significantly less blood loss
      • Posterior calyces along the line of Brodel are preferred
• Variations to renal vascular occur in 25-40% of kidneys
  • Accessory renal arteries are seen in 25-28% of patients and are considered the sole arterial supply to a specific portion of the renal parenchyma
    • Clinical implication: presence of accessory renal artery may contraindicate laparoscopic donor nephrectomy
  • Blood supply to an ectopic kidney originates from adjacent vessels

Venous drainage

• Correlates closely with the arterial supply, with the exception that venous drainage has extensive collateral communication. unlike the arterial supply
• 3-5 segmental renal veins eventually unite to form the renal vein
• The right and left renal veins lie anterior to the right and left renal arteries and drain into the IVC.
• The right renal vein is 2-4 cm, the left renal vein is 6-10 cm.
• The longer left renal vein receives the left adrenal vein and the left gonadal (testicular or ovarian) vein.
  • The left renal vein also may receive a lumbar vein, which could be easily avulsed during surgical manipulation of the left renal vein.
• The left renal vein traverses the acute angle between the superior mesenteric artery anteriorly
  • Nutcracker syndrome most often refers to compression of the left renal vein between the superior mesenteric artery and aorta
  • Insert figure
  • Anomalies of the renal veins are less common than those of the renal arteries

Pelvicalyceal system

• The upper pole of the kidney usually contains 3 calyces, and less commonly 2, whereas 3-4 calyces could be identified at the interpolar region and 2-3 calyces at the lower pole
• The renal pelvis usually has a capacity of 3-10 mL of urine

Questions

1. Describe the arterial branching of the renal artery.

Answers

1. Describe the arterial branching of the renal artery.

References

• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 21
• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 33