Interlobar Arteries

1. Overview

Interlobar arteries are critical vessels in the renal vasculature that transport oxygenated blood from the renal artery deeper into the kidney. They lie between the renal lobes and serve as conduits between the larger segmental arteries and the arcuate arteries. Their role is essential in maintaining blood flow to both the cortex and medulla, ensuring proper glomerular filtration and tubular function throughout the nephron.

2. Location

Interlobar arteries are located within the renal columns, which are extensions of cortical tissue between the renal pyramids. They originate from the segmental arteries, which arise from the renal artery shortly after it enters the hilum of the kidney. Each interlobar artery ascends vertically through a renal column toward the corticomedullary junction, where it branches into arcuate arteries that run transversely along the base of the renal pyramids.

3. Structure

Interlobar arteries are medium-sized muscular arteries with typical three-layered wall architecture:

• Tunica intima: A thin inner endothelial layer with a basement membrane.

• Tunica media: Contains multiple layers of smooth muscle cells that allow vasoconstriction and vasodilation to regulate renal perfusion.

• Tunica adventitia: Outer connective tissue layer containing vasa vasorum, collagen, and sympathetic nerve fibers.

These arteries travel in a straight, column-like fashion between lobes, eventually arching at the corticomedullary junction to form arcuate arteries.

4. Function

The primary function of the interlobar arteries is to:

• Deliver blood: Carry oxygenated blood from the segmental arteries to the arcuate arteries at the corticomedullary boundary.

• Supply renal lobes: Serve as the main blood vessels for individual renal lobes (one pyramid plus overlying cortex).

• Facilitate glomerular perfusion: Provide the upstream blood flow required for afferent arterioles to supply the glomeruli.

5. Physiological Role(s)

Interlobar arteries contribute to several important physiological processes:

• Renal hemodynamics: They regulate blood pressure and volume entering the renal cortex through downstream branches.

• Segmental perfusion: Ensure each renal lobe receives sufficient oxygen and nutrients for nephron activity.

• Support autoregulation: Their tone can be adjusted in response to systemic signals, helping to maintain a stable glomerular filtration rate (GFR) across a range of blood pressures.

6. Clinical Significance

Ischemic Kidney Injury

Blockage or narrowing (stenosis) of interlobar arteries can reduce perfusion to specific lobes, leading to focal ischemia, tubular damage, or infarction. Such localized injury may occur due to:

• Atheroembolic disease

• Thrombosis or embolism

• Vasculitis

Hypertension-Related Damage

Long-standing hypertension can cause arteriolosclerosis and thickening of interlobar arteries, reducing their lumen diameter. This leads to:

• Nephrosclerosis

• Reduced GFR

• Progressive chronic kidney disease (CKD)

Renal Artery Stenosis

Though more commonly affecting the main renal artery, segmental or interlobar artery involvement can also impair renal perfusion and stimulate renin release, contributing to secondary hypertension.

Imaging Relevance

Interlobar arteries can be visualized via:

• Color Doppler ultrasound: Used to assess renal perfusion patterns.

• CT angiography (CTA): Reveals vascular anatomy and any stenosis or aneurysm.

In renal transplant assessment, proper alignment and function of interlobar arteries is crucial for graft viability.

Surgical and Transplantation Considerations

During renal surgery or transplantation, understanding the segmental and interlobar arterial supply helps avoid ischemic damage. Injuries to interlobar arteries during procedures can cause segmental infarction or bleeding complications.

Renal Infarction

In cases of interlobar artery occlusion, wedge-shaped infarcts may form in the kidney cortex and medulla. Symptoms include sudden-onset flank pain, hematuria, and elevated LDH levels. Diagnosis is typically made via CT scan or contrast imaging.