Overview
Definition:
The mesenteric root is the broad, fan-shaped mesentery that attaches the small intestine to the posterior abdominal wall
It traverses obliquely from the duodenojejunal junction at the ligament of Treitz on the left, down to the ileocecal junction on the right
Understanding its precise anatomy is crucial for safe surgical dissection and to prevent iatrogenic injury to vital mesenteric vessels and bowel segments.
Epidemiology:
Variations in mesenteric root length and branching patterns are common, occurring in up to 20-30% of individuals
These variations can influence surgical approaches, particularly in complex resections or reconstructive procedures
Congenital anomalies affecting the mesentery, though rare, can present with malrotation or intestinal atresia.
Clinical Significance:
Safe mobilization of the mesenteric root is paramount in various abdominal surgeries, including radical cancer resections (e.g., colorectal, pancreatic), aortic aneurysm repair, and bowel resections for ischemia or trauma
Injury to the superior mesenteric artery (SMA) or vein (SMV) can lead to catastrophic bowel infarction
Knowledge of the root's anatomy allows for controlled dissection, vessel preservation, and minimization of complications
This is a frequently tested area in surgical examinations.
Anatomy
Attachments:
The root attaches to the posterior abdominal wall, extending from the duodenojejunal flexure (left side, T2 vertebra level) obliquely downwards and to the right, to the ileocecal junction (right iliac fossa, approximately L3-L5 vertebral levels)
Its length varies but is typically around 15 cm.
Vasculature:
The superior mesenteric artery (SMA) and superior mesenteric vein (SMV) run within the mesentery
The SMA originates from the aorta at the level of L1 and descends, giving off branches supplying the jejunum, ileum, colon up to the splenic flexure, and pancreas
The SMV is formed by the confluence of veins draining the same territory and ascends parallel to the SMA
Identifying and preserving these vessels is a primary goal during mobilization.
Innervation:
The mesentery contains autonomic nerves (sympathetic and parasympathetic) and lymphatic vessels
These structures are often closely related to the mesenteric vessels and require careful dissection to avoid injury, which can lead to altered bowel motility or function.
Relations:
Anteriorly, the mesentery is related to loops of small intestine
Posteriorly, it crosses the ascending duodenum, right ureter, right psoas major muscle, and the inferior vena cava
The pancreas and the uncinome of the duodenum lie superiorly, and the terminal ileum and cecum inferiorly.
Surgical Mobilization Technique
Importance Of Dissection:
Meticulous dissection along avascular planes is essential
The goal is to free the small bowel from its mesenteric attachment while preserving the vascular supply
Failure to do so can result in ischemic injury to the bowel.
Dissection Planes:
Dissection typically proceeds along the avascular planes of the mesentery, using careful electrocautery or ligation of small vessels
The plane between the visceral peritoneum of the mesentery and the parietal peritoneum of the posterior abdominal wall is often utilized.
Cephalad Mobilization:
Beginning at the ligament of Treitz, the surgeon mobilizes the proximal jejunum and its mesentery from the posterior abdominal wall, working towards the right
This involves carefully dissecting the SMA and SMV from surrounding structures like the uncinome of the duodenum and the pancreas.
Caudal Mobilization:
Dissection continues downwards towards the ileocecal junction
Care must be taken to identify and ligate small arterial arcades and venous tributaries supplying the bowel
The terminal ileum and cecum are freed from their peritoneal attachments.
Vascular Considerations:
During mobilization, the SMA and SMV are often identified and may be temporarily occluded to control bleeding or facilitate dissection
However, prolonged occlusion must be avoided
Identification of major branches to specific bowel segments is crucial, especially in longer resections.
Variations And Anomalies
Common Variations:
The length of the mesenteric root can vary significantly
Some individuals may have a short, taut mesentery, increasing the risk of tension on the bowel or vessels during mobilization
The branching pattern of the SMA can also vary, with some arteries arising more proximally or having unusual courses.
Malrotation:
A congenital anomaly where the intestines fail to rotate normally during fetal development
This can lead to a narrow mesenteric base, predisposing to volvulus and intestinal obstruction
Surgical correction often involves derotation and widening of the mesenteric base.
Mesenteric Cysts And Tumors:
These can occur within the mesentery and may necessitate careful mobilization to excise without damaging vital structures
They can cause mass effect or obstruct lymphatic drainage.
Intestinal Atresia And Stenosis:
These conditions are often associated with abnormal mesenteric development, leading to vascular compromise or incomplete rotation
Surgical management requires meticulous attention to mesenteric anatomy.
Potential Complications
Vascular Injury:
Laceration or avulsion of the SMA or SMV can lead to immediate or delayed bowel ischemia, necessitating bowel resection or even leading to life-threatening complications
Accidental ligation of these vessels is a critical error.
Bowel Ischemia:
Excessive tension on the mesentery, inadequate mobilization, or injury to small mesenteric vessels can compromise blood supply to the bowel, leading to necrosis and perforation
This is a major cause of morbidity and mortality.
Nerve Injury:
Damage to autonomic nerves within the mesentery can result in altered bowel motility, ileus, or malabsorption
While often transient, severe damage can have long-term consequences.
Hemorrhage:
Injury to mesenteric vessels or their tributaries can cause significant intraoperative or postoperative bleeding, requiring transfusion and potentially re-operation.
Recurrent Hernia:
Inadequate repair of the mesenteric defect after mobilization can lead to internal hernias and subsequent bowel obstruction, particularly at the ligament of Treitz or ileocecal regions.
Prevention And Mitigation Strategies
Preoperative Imaging:
Advanced imaging like CT angiography can help delineate the mesenteric vasculature and identify anatomical variations or anomalies preoperatively, guiding surgical planning.
Meticulous Dissection:
Slow, deliberate dissection in well-defined avascular planes using appropriate surgical instruments
Employing magnification (loupes or microscope) can enhance visualization.
Identifying Vascular Structures:
Early identification and protection of the SMA and SMV and their major branches is paramount
Careful palpation and visualization of pulsatile vessels are key.
Controlled Mobilization:
Avoid aggressive or indiscriminate pulling on the mesentery
Mobilization should be performed systematically, freeing the bowel segment while maintaining vascular integrity.
Intraoperative Monitoring:
Monitoring bowel color, perfusion (e.g., using indocyanine green fluorescence), and pulsatility of vessels can help detect compromised blood supply early
Careful attention to estimated blood loss is also vital.
Key Points
Exam Focus:
Understanding the oblique course of the mesenteric root, its attachments, and the relationship of the SMA/SMV is critical
Common exam questions focus on vascular injury during mobilization, management of short mesentery, and anatomy relevant to radical resections.
Clinical Pearls:
Always start mobilization at the ligament of Treitz or ileocecal junction, depending on the direction of intended dissection
Never pull on the mesentery
dissect it
Identify the SMA and SMV early
Be aware of the "danger zone" near the origin of the SMA where the uncinome and superior border of the pancreas lie.
Common Mistakes:
Mistakes include aggressive traction causing vascular compromise, failing to identify major mesenteric vessels, inadequate mobilization leading to tension on the anastomosis, and not recognizing anatomical variations
Overlooking the potential for internal hernia formation after extensive mobilization.