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Left kidney

The left kidney is a paired retroperitoneal organ of the urinary system, located on the posterior abdominal wall between T12 and L3 vertebral levels, slightly higher than the right kidney due to the absence of the large liver on the left. It measures approximately 11–13 cm in length, 5–7 cm in width, and 3–5 cm in thickness.

The left kidney is bean-shaped, with a convex lateral border and a concave medial border containing the renal hilum, where the renal artery enters, renal vein exits, and ureter begins. Internally, it consists of an outer cortex, an inner medulla (renal pyramids), and a renal pelvis, which collects urine before it drains into the ureter.

It is related anteriorly to the spleen, stomach, pancreas, left adrenal gland, and descending colon, and posteriorly to the diaphragm, quadratus lumborum, psoas major, and ribs 11–12. Clinically, the left kidney is important in conditions such as hydronephrosis, renal stones, renal cell carcinoma, trauma, and vascular anomalies.

Synonyms

  • Left renal organ

Function

  • Filters blood, removing metabolic waste and toxins

  • Regulates fluid balance, electrolytes, and acid-base homeostasis

  • Produces hormones: erythropoietin (EPO), renin, calcitriol

  • Maintains blood pressure regulation via the renin-angiotensin-aldosterone system (RAAS)

Nerve Supply

  • Derived from the renal plexus, with fibers from thoracic splanchnic nerves (T10–L1)

  • Sympathetic: controls vasoconstriction and renin secretion

  • Parasympathetic: minimal direct supply, via vagus nerve

Arterial Supply

  • Left renal artery, a direct branch of the abdominal aorta

  • Divides into anterior and posterior branches at the hilum → interlobar arteries → arcuate arteries → interlobular arteries

Venous Drainage

  • Left renal vein, which crosses anterior to the aorta beneath the superior mesenteric artery to join the IVC

  • Receives tributaries from the left gonadal vein, left suprarenal vein, and lumbar veins

MRI Appearance

T1-weighted images:

  • Renal cortex: intermediate signal

  • Medulla: relatively hypointense compared to cortex

  • Renal sinus fat: bright hyperintense

T2-weighted images:

  • Cortex: intermediate signal

  • Medulla: relatively hyperintense, differentiating corticomedullary structures

  • Fluid-filled collecting system appears bright

STIR:

  • Suppresses fat, making renal parenchyma and perinephric edema more conspicuous

  • Highlights inflammation, trauma, or tumors

T1 Fat-Saturated (Pre-contrast):

  • Renal cortex and medulla appear intermediate signal, clearly differentiated from suppressed perirenal fat

  • Useful for delineating renal margins

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Cortex enhances earlier and more intensely than medulla (corticomedullary differentiation)

  • Later phases: uniform enhancement

  • Detects renal tumors, perfusion defects, and vascular anomalies

MRV (Magnetic Resonance Venography):

  • Demonstrates left renal vein course across aorta

  • Shows tributaries (gonadal, adrenal, lumbar veins) and anomalies such as retroaortic left renal vein

  • Useful for evaluating nutcracker syndrome, thrombosis, or venous compression

CT Appearance

CT Pre-Contrast:

  • Kidney parenchyma appears as a soft tissue density (30–45 HU)

  • Useful for detecting renal stones, calcifications, hemorrhage

CT Post-Contrast:

  • Cortex enhances intensely in arterial phase, medulla in nephrographic phase

  • Excretory phase shows opacification of collecting system

  • Used for evaluation of tumors, infarcts, cysts, and hydronephrosis

CTV (CT Venography):

  • Provides detailed mapping of left renal vein and tributaries

  • Identifies compression, thrombosis, collateral formation, and anomalies

  • Crucial for transplant planning, vascular reconstruction, and varicocele evaluation

CT images

Left kidney CT axial image

CT images

Left kidney CT coronal image

MRI images

Left kidney MRI coronal image anatomy image -img-00000-00000

MRI images

Left kidney MRI sagittal image anatomy image -img-00000-00000