K
Kidneys
The kidneys are paired retroperitoneal organs situated on the posterior abdominal wall, approximately from T12 to L3 vertebral levels. Their surface projection lies mainly in the upper lumbar and hypochondriac regions, with the right kidney positioned slightly lower than the left because of the liver.
RegionSurface Anatomy
SystemUrinary System
The kidneys are paired, bean-shaped retroperitoneal organs situated on the posterior abdominal wall. Their relatively fixed position makes their projection onto the body surface an important part of abdominal and posterior trunk surface anatomy.
Each kidney lies on either side of the vertebral column, generally extending from approximately the T12 to L3 vertebral levels. The right kidney usually lies slightly lower than the left because of the large right lobe of the liver.
Surface landmarks are useful for understanding the position of the kidneys during physical examination, diagnostic imaging, renal procedures, and posterior surgical approaches.
General Surface Projection
The kidneys project mainly into the hypochondriac and lumbar regions of the posterior abdomen.
Because they lie retroperitoneally, they are positioned deep to the posterior abdominal wall rather than freely within the peritoneal cavity.
Vertebral Levels
The kidneys usually extend approximately from the level of T12 to L3, although their exact positions vary with body habitus, respiration, age, and individual anatomy.
The left kidney is generally positioned slightly higher than the right.
| Feature | Right Kidney | Left Kidney |
|---|---|---|
| General level | Approximately T12 to L3, slightly lower | Approximately T12 to L3, slightly higher |
| Reason for relative position | Displaced inferiorly by liver | No equivalent large superior organ |
| Rib relationship | Primarily 12th rib | 11th and 12th ribs |
Right Kidney
The right kidney lies slightly inferior to the left kidney because of its relationship with the liver.
Its upper pole is positioned deep to the posterior abdominal wall and lower thoracic region, while its lower pole extends into the upper lumbar region.
Left Kidney
The left kidney is generally positioned higher than the right.
Its superior pole extends farther superiorly and is related posteriorly to both the 11th and 12th ribs.
Posterior Surface Projection
From the posterior body surface, each kidney projects onto the lower thoracic and upper lumbar regions lateral to the vertebral column.
The long axis of each kidney is oblique, with the superior pole lying somewhat closer to the midline than the inferior pole.
Relationship to the Ribs
The kidneys are partly protected posteriorly by the lower ribs.
The right kidney is crossed posteriorly by the 12th rib, while the left kidney is related to both the 11th and 12th ribs.
Twelfth Rib
The 12th rib is an important posterior landmark for both kidneys.
It crosses the posterior surface of each kidney, although the relationship is more extensive on the higher left side.
Eleventh Rib
The 11th rib is related to the superior posterior surface of the left kidney.
The right kidney generally lies too low to have the same relationship with the 11th rib.
Renal Hilum
The renal hilum is the medial indentation through which the renal vessels, renal pelvis, lymphatics, and nerves enter or leave the kidney.
The hila face predominantly medially and somewhat anteriorly because of the orientation of the kidneys on the posterior abdominal wall.
Surface Level of the Renal Hilum
The renal hila lie approximately near the transpyloric plane, which passes through the body of the L1 vertebra.
The left renal hilum is typically near this level, while the right hilum may lie slightly lower.
Transpyloric Plane
The transpyloric plane is a horizontal surface anatomical plane located approximately midway between the jugular notch and pubic symphysis.
Posteriorly, it crosses approximately the L1 vertebral body and is a useful reference for the renal hila and several other upper abdominal structures.
Long Axis of the Kidney
The long axis of each kidney is not perfectly vertical.
The superior poles lie closer to the vertebral column than the inferior poles, producing a slight inferolateral orientation.
Anterior Surface Projection
From the anterior abdominal wall, the kidneys project deeply into the upper lateral abdomen.
They are overlapped by multiple intraperitoneal organs, so their anterior surface projection does not correspond to an easily palpable external outline.
Anterior Relations of the Right Kidney
The anterior surface of the right kidney is related to several abdominal structures, including:
- Right suprarenal gland
- Liver
- Second part of the duodenum
- Right colic region
- Small intestinal loops
Anterior Relations of the Left Kidney
The anterior surface of the left kidney is related to structures including:
- Left suprarenal gland
- Stomach
- Spleen
- Pancreas
- Left colic region
- Jejunal loops
Posterior Relations
The posterior surfaces of the kidneys are related to the diaphragm and muscles of the posterior abdominal wall.
Important muscular relationships include the psoas major, quadratus lumborum, and transversus abdominis.
Diaphragm
The upper portions of both kidneys lie against the diaphragm.
This relationship explains why the kidneys move slightly with respiration and why posterior approaches near the upper poles must account for the pleural cavity.
Psoas Major
The psoas major lies medial to the posterior surface of each kidney.
Its relationship contributes to the oblique orientation of the kidneys and is important in posterior abdominal imaging and surgery.
Quadratus Lumborum
The quadratus lumborum forms part of the posterior muscular bed of each kidney.
It lies posterior to the kidney and is separated from it by fascial and fatty layers.
Transversus Abdominis
The transversus abdominis is related to the lateral portion of the posterior renal surface.
Together with psoas major and quadratus lumborum, it contributes to the muscular posterior relations of the kidneys.
Costovertebral Angle
The costovertebral angle is the angle formed posteriorly between the 12th rib and the vertebral column or paraspinal region.
It is an important clinical surface landmark because the kidneys lie deep to this region.
Costovertebral Angle Tenderness
Tenderness elicited by percussion over the costovertebral angle may occur with pathology affecting the kidney or surrounding structures.
The finding is not anatomically specific by itself and must be interpreted with the rest of the clinical examination.
Renal Mobility with Respiration
The kidneys move with respiration because of their relationship with the diaphragm and surrounding tissues.
During inspiration, they generally descend slightly as the diaphragm moves inferiorly.
Retroperitoneal Position
The kidneys are primary retroperitoneal organs.
They lie behind the parietal peritoneum on the posterior abdominal wall and are surrounded by layers of fat and renal fascia.
Renal Fascia
The kidneys and surrounding perirenal fat are enclosed by renal fascia.
This fascial organization helps maintain renal position while still allowing limited movement with respiration and changes in body position.
Perirenal Fat
Perirenal fat surrounds the kidney within the renal fascial compartment.
It cushions the organ and contributes to its support within the retroperitoneum.
Pararenal Fat
Pararenal fat lies external to the renal fascia, particularly posteriorly and posterolaterally.
These fatty layers separate the kidneys from surrounding abdominal wall structures and influence their appearance on cross-sectional imaging.
Relationship to the Suprarenal Glands
The suprarenal glands lie superior and somewhat medial to the upper poles of the kidneys.
Although closely related, each suprarenal gland is separated from the kidney by connective tissue within the fascial compartment.
Relationship to the Ureters
At each renal hilum, the renal pelvis narrows to become the ureter.
The ureters descend retroperitoneally from the kidneys toward the pelvis, generally following a course over the psoas major muscles.
Surface Anatomy in the Nine Abdominal Regions
The kidneys project predominantly into the hypochondriac and lumbar regions.
| Region | Renal Relationship |
|---|---|
| Right hypochondriac | Upper portion of right kidney |
| Right lumbar | Major portion of right kidney |
| Left hypochondriac | Upper portion of left kidney |
| Left lumbar | Major portion of left kidney |
| Epigastric | Medial renal structures may approach this region deeply |
Surface Anatomy in the Four Quadrants
The right kidney lies predominantly deep within the right upper quadrant, while the left kidney lies predominantly within the left upper quadrant.
Their inferior poles can extend toward the level of the lower upper quadrants depending on individual anatomy.
Palpation of the Kidneys
Normal adult kidneys are usually difficult to palpate because of their deep retroperitoneal position.
The lower pole of the right kidney may sometimes be palpable in thin individuals, particularly during deep inspiration, because the right kidney lies slightly lower.
Bimanual Examination
Clinical renal palpation may use a bimanual technique, with one hand placed posteriorly in the flank and the other on the anterior abdominal wall.
Deep inspiration can cause the kidney to descend slightly toward the examining hands.
Renal Percussion
Direct percussion does not outline the kidneys reliably because they are deep and overlapped by other tissues.
Clinical percussion over the posterior renal angle is used primarily to assess tenderness rather than determine exact renal dimensions.
Imaging and Surface Projection
Ultrasonography, CT, and MRI demonstrate the actual renal position much more accurately than external landmarks alone.
Surface anatomy remains useful for orienting examinations and procedures, but individual variation should always be expected.
Clinical Significance
Renal Enlargement
An enlarged kidney may extend beyond its usual surface projection and become more readily palpable.
Causes can include hydronephrosis, cystic disease, tumors, and other renal abnormalities.
Nephroptosis
Nephroptosis refers to excessive downward displacement of a kidney, particularly when moving from a supine to an upright position.
This alters the expected renal surface projection and may affect the orientation of the renal vessels and ureter.
Renal Ectopia
A congenitally ectopic kidney may fail to ascend to the normal upper lumbar position during development.
A pelvic kidney, for example, has a completely different surface projection from a normally positioned kidney.
Horseshoe Kidney
In a horseshoe kidney, the lower poles are usually fused by an isthmus.
The fused kidneys typically lie lower than normal because ascent is limited during development, altering their expected abdominal projection.
Renal Pain
Pain arising from the kidney may be perceived in the flank or posterior abdominal region.
Ureteric pain can radiate inferiorly as visceral afferent pathways associated with the urinary tract are activated.
Renal Biopsy
The posterior surface projection of the kidney is clinically important during percutaneous renal biopsy.
Image guidance is used to identify a safe route and reduce the risk of injury to the pleura, major vessels, and adjacent abdominal structures.
Pleural Relationship
The upper poles of the kidneys lie close to the diaphragm and pleural reflections.
This is particularly important during posterior procedures directed toward the superior renal region because an excessively superior approach can enter the pleural cavity.
Surface Projection Compared with Spleen
| Feature | Kidney | Spleen |
|---|---|---|
| Position | Retroperitoneal | Intraperitoneal |
| Posterior rib relationship | Lower ribs, especially 12th | Approximately ribs 9 to 11 |
| Mobility | Limited respiratory movement | Moves with diaphragm |
| General region | Hypochondriac and lumbar | Left hypochondriac |
Key Surface Anatomy Features
| Feature | Key Point |
|---|---|
| Position | Posterior abdominal wall, retroperitoneal |
| Approximate vertebral levels | T12 to L3 |
| Higher kidney | Left |
| Right kidney rib relationship | 12th rib |
| Left kidney rib relationship | 11th and 12th ribs |
| Hilum level | Approximately L1/transpyloric plane, right slightly lower |
| Main abdominal regions | Hypochondriac and lumbar |
| Posterior clinical landmark | Costovertebral angle |
| Respiratory movement | Descend slightly during inspiration |
| Orientation | Superior poles closer to midline than inferior poles |
Anatomical Importance
The kidneys have a relatively predictable surface projection because they are retroperitoneal organs anchored to the posterior abdominal wall. They generally extend from approximately T12 to L3, with the left kidney positioned slightly higher than the right.
Their relationships with the lower ribs, vertebral column, transpyloric plane, diaphragm, and posterior abdominal muscles provide useful landmarks for understanding renal position. The right kidney's lower position reflects the presence of the liver, while the higher left kidney is related posteriorly to both the 11th and 12th ribs.
These surface relationships have practical importance in physical examination, imaging, renal biopsy, surgery, and interpretation of flank symptoms. However, respiratory movement, body habitus, developmental variation, and renal pathology can all alter the expected projection of the kidneys.
Published on September 26, 2026
Last updated on September 26, 2026
Last updated on September 26, 2026