Kidney Anatomy
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Direct answer
Retroperitoneal, bean-shaped and paired, each kidney measures about 11 by 6 by 3 centimetres, weighs 150 grams, and lies obliquely from T12 to L3 — the right sitting about 1.3 centimetres lower because the liver pushes it down. From within out it is wrapped by its true capsule, perirenal fat, and the renal (Gerota's) fascia, which is open inferiorly so that infection and urine can track downward toward the pelvis. At the hilum the renal vein, artery and ureteric pelvis pass from front to back in the order vein-artery-ureter (VAU), the left vein being long (it crosses in front of the aorta, receiving the left suprarenal and gonadal veins) and the right artery being long (it passes behind the inferior vena cava). Five segmental arteries — apical, upper, middle, lower and posterior — make the kidney a segmental organ, and the posterior branch divides before the hilum, creating the relatively avascular Brodel's line on the posterior surface.
What you must remember
- Levels and landmarks: T12 to L3; the twelfth rib crosses the posterior surface obliquely; the lower pole of the right kidney is palpable in thin subjects on deep inspiration only if enlarged.
- Anterior relations, right: liver, second part of duodenum (over the hilum — mobilised surgically by Kocher's manoeuvre), hepatic flexure; left: stomach, pancreas, spleen, splenic flexure, jejunum — the left kidney is the "surgical kidney" approached more easily.
- Hilum order front to back: renal vein, renal artery, renal pelvis — "VAU"; lymphatics and nerves accompany them; on the right the artery lies behind the IVC.
- Fascial compartments: perirenal fat within Gerota's fascia, closed above and open below toward the iliac fossa — perinephric abscess points to the lumbar (Petit's) triangle or pelvis.
- Segmental supply: apical, upper, middle and lower anterior segmental arteries plus a posterior branch; none anastomose significantly, so ligation of a branch infarcts its segment — the basis of segmental (partial) nephrectomy.
- Congenital trio: horseshoe kidney (lower poles fused, isthmus caught under the superior mesenteric artery at L4, prone to stasis and stones), ectopic kidney, and PUJ obstruction (the commonest cause of hydronephrosis in children and young adults).
- Referred pain: renal pelvis and ureter T10–L2, so colic travels loin to groin, then to the scrotum or labium as the stone nears the bladder.
Following a stone down the ureter
Renal colic is referred pain mapped segmentally. A stone in the renal pelvis irritates T10–L2 afferents and pain sits in the loin and flank; as it negotiates the ureter, the spasm drives the pain diagonally from loin to groin "as if electrically connected". Three constrictions are the anatomical trapdoors where stones impact: the pelviureteric junction, the pelvic brim where the ureter crosses the bifurcation of the common iliac vessels (or the iliac vessels), and the vesicoureteric junction — the narrowest point, where a stone produces the strangest referred symptom of all, urgency and pain at the tip of the penis or labia via the pudendal nerve S2–S4, because the ureteric and bladder afferents converge. A stone at the vesicoureteric junction with a fever is an emergency, since an obstructed infected system becomes urological sepsis within hours.
Where students slip
The usual casualties are symmetry and hilum order. "Which renal vein is longer and why?" — the left, which must cross the midline in front of the aorta beneath the superior mesenteric artery to reach the IVC; the right artery is the longer one, passing behind the vena cava. Getting this backwards is a distinction-losing error, since it also explains the nutcracker syndrome and the left gonadal vein's drainage into the left renal vein (varicocele logic). The second trap: the hilum faces anteromedially, so from behind the artery is encountered first — a fact only surgeons quoting the lumbar approach volunteer. Third, the renal angle between the twelfth rib and erector spinae is the spot hammered in Murphy's kidney punch.
Frequently asked questions
Why is the right kidney lower than the left?
The large right lobe of the liver pushes it down about 1.3 centimetres, so the right kidney lies from L1 rather than T12 downward.
What is the order of structures at the renal hilum from front to back?
Renal vein, renal artery, then the renal pelvis (ureter) — VAU — with branches of the renal artery usually lying between vein and pelvis.
Why does a horseshoe kidney fail to ascend fully?
Its isthmus of fused lower poles is trapped beneath the origin of the superior mesenteric artery at about the L4 level, halting normal ascent from the pelvis.
What is Brodel's line and its surgical use?
A relatively avascular plane on the posterior surface between the territories of the anterior and posterior segmental arteries; incisions along it (anatrophic nephrolithotomy) minimise bleeding.
Which veins drain into the left renal vein and what clinical syndrome results from its compression?
The left suprarenal and left gonadal veins; compression between the aorta and superior mesenteric artery produces the nutcracker syndrome, with left flank pain, haematuria and left varicocele.