Renal Columns

1. Overview

Renal columns (also called columns of Bertin) are extensions of the renal cortex that project between the medullary pyramids within the kidney. These structures help maintain the integrity and organization of the renal parenchyma and serve as passageways for blood vessels traveling between the outer cortex and inner medulla. While not involved in urine formation themselves, they play a key structural and vascular role in renal physiology.

2. Location

Renal columns are located within the kidney, specifically:

• Between adjacent renal pyramids in the medulla.

• Extending inward from the cortex toward the renal sinus.

They are visible on cross-section as lighter-colored cortical tissue that interrupts the darker renal pyramids. Despite their location within the medullary region, they are part of the cortex histologically and functionally.

3. Structure

Renal columns are composed of cortical tissue, and their structure resembles the surrounding cortex. They include:

• Renal connective tissue: Providing structural support to neighboring lobes.

• Proximal and distal convoluted tubules: Located within the columns, though in smaller numbers compared to the outer cortex.

• Interlobar arteries and veins: Pass vertically through the columns to supply and drain the renal lobes.

There is no involvement of collecting ducts or loops of Henle, which are confined to the renal pyramids.

4. Function

The renal columns primarily serve structural and vascular functions:

• Structural partitioning: Separate renal pyramids and define renal lobes.

• Conduits for blood flow: House interlobar arteries and veins traveling to and from the cortex and medulla.

• Stabilization of kidney architecture: Maintain the compact structure of the kidney during filtration and urine transport.

5. Physiological Role(s)

Although not involved in active urine processing, renal columns contribute to several key physiological processes:

• Support cortical function: By physically anchoring and connecting cortical tissue deeper into the kidney.

• Facilitate blood distribution: Allow essential vascular communication between the renal cortex (site of glomerular filtration) and medulla (site of concentration mechanisms).

• Assist in nephron integrity: By stabilizing nephron components and preventing displacement during kidney expansion and contraction.

6. Clinical Significance

Hypertrophied Renal Column

A hypertrophied column of Bertin refers to an enlarged renal column that may mimic a renal mass on imaging. Key features include:

• Benign anatomical variant

• Normal renal parenchyma histologically

• Seen as a wedge-shaped area with the same echogenicity as the cortex

It can be differentiated from a tumor using ultrasound, CT, or MRI based on enhancement patterns and continuity with the cortex.

Surgical Landmarks

During partial nephrectomy or other renal surgeries, renal columns serve as safe planes to access renal vessels or collecting structures while minimizing damage to nephrons.Renal Pathologies

Although rare, infections (e.g., pyelonephritis) or infarcts can involve renal columns. In some cases:

• Inflammatory changes may extend through the column to the cortex

• Ischemia may be seen along interlobar vessels running in the columns

Pediatric and Fetal Kidneys

Renal columns are more pronounced in fetal and neonatal kidneys, often resulting in lobulated kidney surfaces. This is a normal finding and typically smooths out with age, though in some adults, it may persist as persistent fetal lobulation.

Imaging Relevance

On imaging:

• Ultrasound: Renal columns appear isoechoic to the cortex and help distinguish renal pyramids.

• CT/MRI: Used to evaluate structural abnormalities, tumors, or vascular flow through the columns.