White line of Toldt
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The white line of Toldt is a line formed at the junction of the lateral reflection of the posterior parietal peritoneum and the visceral peritoneum of the colon in the paracolic gutter. After the 270-degree counter-clockwise rotation of the intestinal tract during embryologic development, the transverse mesocolon is fused to the dorsal mesogastrium (these structures will go on to form the greater omentum and omental bursa). Following this, the ascending and descending mesocolons collide with and are fused with the retroperitoneum.
The white line represents the lateral extent of the Toldt fascia, which is interposed between the mesocolon and the retroperitoneum3. It represents an avascular plane used to mobilize the right and left hemicolon during surgical procedures such as a hemicolectomy. Mobilizing the colon in this manner is necessary for most procedures, such as resection, anastomosis, or ostomy creation.
Under normal conditions, from a radiological perspective, this may be continuous with the lateral margins of the perirenal fascia, the lateroconal fascia, but can represent the lateral margins of a potential space in retroperitoneal disease, such as necrotizing pancreatitis.