Mesenteric sinuses
In the lower floor of the abdominal cavity, there are two major spaces separated by the root of the mesentery of the small intestine: the right and left mesenteric sinuses. Anteriorly, their superior parts are very often covered by the greater omentum, which must be considered during surgical explorations.
The right mesenteric sinus (sinus mesentericus dexter) is an anatomically closed space. Its boundaries form a distinct contour:
- Superiorly, the sinus is limited by the transverse mesocolon (mesocolon transversum).
- On the right, it is bounded by the ascending colon (colon ascendens).
- On the left and inferiorly, the boundary is formed by the mesentery of the small intestine (mesenterium) as well as the terminal segment of the ileum.
The main topographical feature of the right sinus is that it is completely isolated from the lesser pelvic cavity. Communication with the pelvis is absent due to the terminal segment of the small intestine and its mesentery, which create a dense natural barrier.
The left mesenteric sinus (sinus mesentericus sinister) is significantly larger than the right one in its anatomical dimensions. It is located to the left and inferior to the root of the mesentery of the small intestine. Loops of the small intestine lie within this extensive space.
- Superiorly, like the right sinus, it is bounded by the transverse mesocolon.
- On the left, its wall is formed by the descending colon.
- On the right, the boundary is formed by the mesentery of the small intestine.
Unlike the isolated right space, the left sinus has wide communication with the lesser pelvic cavity.
Paracolic gutters of the abdominal cavity
Along the lateral borders of the ascending and descending colons lie the paracolic gutters. They serve as pathways of communication between various regions of the abdominal cavity and the pelvis.
The right paracolic gutter (canalis lateralis dexter) runs in the space between the right lateral abdominal wall and the ascending colon. Its anatomical communications:
- Superiorly, the gutter passes into the posterior part of the right subphrenic space.
- Inferiorly, it opens into the right iliac fossa.
It is important to note that the length and depth of the right gutter are highly variable. In some cases, additional ligaments are present between the ascending colon and the lateral abdominal wall. They can divide a single gutter into several isolated compartments, changing its configuration.
The left paracolic gutter (canalis lateralis sinister) is formed between the left lateral abdominal wall and the descending colon. Its boundaries and communications have fundamental differences from the right one:
- Superiorly, the pathway is closed by the phrenicocolic ligament (lig. phrenicocolicum). This barrier reliably separates the left gutter from the spleen bed as well as from the left subphrenic space.
- Inferiorly, the gutter passes absolutely freely first into the left iliac fossa and then descends directly into the lesser pelvis.
Topography in the horizontal position
To understand operative surgery, it is extremely important to know where the deepest points of the described spaces are located when the patient's torso is in a horizontal position. It is in these areas that fluid will accumulate first.
In the mesenteric sinuses, the deepest places are their upper corners. The general description of the sinuses notes that the deepest place is the upper right corner. Meanwhile, for the left sinus (sinus mesentericus sinister), the deepest point specifically is its upper left corner.
As for the left paracolic gutter, in a person lying on their back, its deepest part is projected strictly at the level of the end of the eleventh (XI) rib.
Briefly: answers to topical questions
What anatomical structures form the boundaries of the left mesenteric sinus?
The left mesenteric sinus (sinus mesentericus sinister) is located to the left and inferior to the root of the mesentery of the small intestine. Its boundaries are formed by the following anatomical structures:
- Superiorly — transverse mesocolon.
- On the left — descending colon.
- On the right — mesentery of the small intestine.
The left mesenteric sinus widely communicates with the lesser pelvic cavity.
What major blood vessels run in the root of the mesentery of the small intestine?
The superior mesenteric vessels run in the root of the mesentery of the small intestine. Between the leaves of the peritoneum within the fatty tissue are located:
- Superior mesenteric artery (a. mesenterica superior) — runs along with its branches.
- Venae comitantes — accompany the arterial bed.
In addition to major blood vessels, nerves, lymph nodes, and lymphatic vessels also run in the root of the mesentery.
To avoid confusing the communications of the spaces, remember: the right sinus is "locked" inferiorly by the terminal ileum, while the left sinus and the left paracolic gutter are freely "open" inferiorly, directly into the lesser pelvis.
Class and exam questions
Which of the mesenteric sinuses communicates with the lesser pelvis?
The left mesenteric sinus (sinus mesentericus sinister) has wide communication with the lesser pelvic cavity. The right sinus is completely isolated from it.
What bounds the left paracolic gutter superiorly?
It is bounded by the phrenicocolic ligament (lig. phrenicocolicum). It reliably separates the gutter from the spleen bed and the left subphrenic space.
Where is the deepest point of the left paracolic gutter located in a recumbent patient?
In the horizontal position of the torso, the deepest part of this gutter is located at the level of the end of the 11th rib.
What is the contents of the left mesenteric sinus?
Loops of the small intestine are located inside the left mesenteric sinus. Anteriorly, its superior part is frequently covered by the greater omentum.
What else to study on this topic
- Topography of the root of the mesentery of the small intestine and its influence on the size of the sinuses
- Ligaments dividing the right paracolic gutter into isolated compartments
- Relation of the greater omentum to the superior parts of the mesenteric sinuses
- Communications of the right paracolic gutter with the subphrenic space
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