Segmental Arteries

1. Overview

Segmental arteries are the first intrarenal branches of the renal artery, supplying blood to distinct anatomical segments of the kidney. These arteries are end arteries, meaning they do not form collateral circulation with adjacent segments, making their integrity crucial for the perfusion of specific renal zones. Their precise distribution is fundamental to surgical and imaging approaches involving the kidney.

2. Location

Segmental arteries originate from the renal artery just after it enters the renal hilum, and they branch within the renal sinus. Their pathway includes:

• Arising posterior to the renal vein and anterior to the renal pelvis at the hilum.

• Entering the renal sinus where they divide into lobar arteries, then further into interlobar arteries.

• Distributed in a segmental pattern within the renal parenchyma, supplying specific anatomical zones of the kidney.

The number of segmental arteries varies slightly, but typically there are 5 major branches, each supplying a renal segment:

• Superior (apical) segmental artery

• Anterosuperior segmental artery

• Anteroinferior segmental artery

• Inferior segmental artery

• Posterior segmental artery

3. Structure

Segmental arteries are classified as muscular arteries, and they share a typical three-layered structure:

• Tunica intima: Endothelial lining supported by internal elastic lamina.

• Tunica media: Contains smooth muscle responsible for regulating blood flow via vasoconstriction or dilation.

• Tunica adventitia: Connective tissue layer with autonomic nerve fibers and vasa vasorum.

Each artery follows a fairly fixed course and does not significantly anastomose with neighboring segmental arteries, reinforcing their end-artery status.

4. Function

The segmental arteries function to:

• Distribute blood flow: Directly supply specific anatomical segments of the kidney.

• Enable targeted perfusion: Allow regional control of renal perfusion, which is critical during surgical interventions.

• Support renal filtration: Deliver blood to glomerular arterioles for filtration in the nephron.

5. Physiological Role(s)

Segmental arteries contribute to multiple physiological processes by enabling:

• Efficient renal perfusion: Deliver consistent blood flow across different regions of the renal parenchyma.

• Filtration regulation: Maintain appropriate pressure and volume delivery to glomerular capillaries via their downstream branches (afferent arterioles).

• Response to systemic changes: Capable of vasoconstriction or vasodilation in response to neural or hormonal signals (e.g., sympathetic input, angiotensin II).

6. Clinical Significance

End-Artery Behavior and Infarction

Because segmental arteries are end arteries, occlusion (e.g., due to embolism, thrombosis, or trauma) leads to segmental renal infarction. This results in:

• Flank pain

• Hematuria

• Elevated lactate dehydrogenase (LDH)

Imaging shows a wedge-shaped area of hypoperfusion or necrosis.

Surgical Relevance in Nephrectomy

Understanding segmental arterial anatomy is crucial during:

• Partial nephrectomy: Surgeons may selectively clamp a segmental artery to preserve as much functional kidney tissue as possible.

• Renal transplantation: Precise knowledge of segmental supply helps plan vascular anastomoses.

Angiographic and Interventional Procedures

Segmental arteries are visualized in renal angiography and can be targeted in:

• Embolization procedures: For treatment of renal tumors or trauma-related bleeding.

• Endovascular interventions: To manage aneurysms or arteriovenous malformations.

Anatomical Variants

In some individuals, accessory renal arteries may give rise to additional segmental arteries. These variants are important in:

• Kidney transplantation

• Imaging interpretation

• Preoperative planning for urological or vascular procedures

Renovascular Hypertension

Segmental artery stenosis can reduce perfusion to specific renal segments, triggering renin release and potentially contributing to secondary hypertension. This condition is diagnosed via Doppler ultrasound, CT angiography, or MRI.