Overview
Definition:
Superior Mesenteric Artery (SMA) injury refers to damage to the main artery supplying blood to the small intestine, most of the large intestine, and parts of the pancreas
This can result from blunt or penetrating trauma, leading to bowel ischemia, hemorrhage, and potentially fatal outcomes if not promptly managed.
Epidemiology:
SMA injuries are relatively uncommon, accounting for a small percentage of all visceral artery injuries
They are more frequently seen in penetrating trauma (stab wounds, gunshot wounds) than blunt trauma
High-energy blunt trauma, such as from motor vehicle accidents, can cause shear forces leading to intimal tears or even complete transection.
Clinical Significance:
SMA injuries are a surgical emergency due to the critical role of the SMA in bowel perfusion
Inadequate blood supply leads to mesenteric ischemia, which can rapidly progress to bowel infarction, sepsis, multiorgan failure, and death
Prompt diagnosis and definitive management are crucial for patient survival and preservation of bowel viability.
Clinical Presentation
Symptoms:
Severe abdominal pain, often out of proportion to physical findings
Nausea and vomiting
Hematemesis or melena (if injury is proximal or associated with duodenal injury)
Abdominal distension
Signs of hypovolemic shock: tachycardia, hypotension, pallor, altered mental status
Absence of palpable pulses distal to the injury (rare).
Signs:
Tenderness and guarding of the abdomen
Rebound tenderness
Decreased bowel sounds or absent bowel sounds
Abdominal distension
Pulsatile abdominal mass (if pseudoaneurysm)
Hemorrhagic shock
Signs of peritonitis
Evidence of external trauma (lacerations, contusions, seatbelt marks).
Diagnostic Criteria:
No specific diagnostic criteria exist
diagnosis is based on high clinical suspicion in the setting of abdominal trauma and confirmed by imaging
The American Association for the Surgery of Trauma (AAST) organ injury scale (OIS) for the small bowel and mesentery can be used for grading severity of associated injuries, which often guides management.
Diagnostic Approach
History Taking:
Mechanism of injury: blunt (high-energy impact, deceleration injuries, seatbelt trauma) versus penetrating (stab wounds, gunshot wounds)
Time since injury
Associated injuries or comorbidities
Previous abdominal surgeries or vascular disease
Vital signs and hemodynamic status of the patient
Any medications affecting coagulation.
Physical Examination:
Thorough abdominal examination: inspection for distension or bruising, auscultation for bowel sounds, palpation for tenderness, guarding, rigidity, and masses
Assessment for pulsatile masses
Examination of the chest, back, and extremities for associated injuries
Monitoring vital signs closely for evidence of ongoing hemorrhage or shock.
Investigations:
FAST (Focused Assessment with Sonography for Trauma) scan: initial screening for intra-abdominal fluid
CT angiography (CTA) of the abdomen and pelvis: gold standard for diagnosing SMA injury, delineating the extent of injury (occlusion, dissection, pseudoaneurysm, active extravasation), and identifying associated injuries
Laboratory tests: complete blood count (CBC) for hemoglobin and hematocrit, coagulation profile (PT/INR, PTT), lactate levels (marker of ischemia), type and crossmatch for blood transfusion
Angiography: can be diagnostic and therapeutic (embolization) for active bleeding or dissection.
Differential Diagnosis:
Other mesenteric artery injuries (e.g., IMA injury)
Blunt aortic injury
Hollow viscus perforation
Solid organ injury (spleen, liver, kidney)
Pancreatic contusion or transection
Bowel obstruction
Mesenteric venous thrombosis
Non-traumatic mesenteric ischemia.
Management
Initial Management:
Immediate resuscitation with intravenous fluids and blood products to stabilize hemodynamic status
Airway, breathing, circulation (ABC) management
Prompt surgical exploration is often indicated in hemodynamically unstable patients with suspected SMA injury
Pain control
Nasogastric tube decompression.
Medical Management:
Not primary for acute SMA injury
Supportive care includes fluid resuscitation, blood product transfusion, and anticoagulation is generally contraindicated in acute active bleeding but may be considered in specific cases of dissection or non-occlusive thrombus without active extravasation, after consultation with vascular surgery.
Surgical Management:
Exploratory laparotomy is typically indicated
Goals are to control hemorrhage, assess bowel viability, and revascularize or excise compromised bowel
Control of proximal and distal SMA (may require mobilizing colon, opening the small bowel mesentery)
If an intact artery with intimal injury or dissection: endovascular repair (stent graft) or open repair (vein patch angioplasty, graft interposition)
If complete occlusion/transection with viable bowel: bypass graft (autogenous vein, synthetic graft) or endovascular stenting
If non-viable bowel: resection of ischemic bowel with primary anastomosis or ostomy
Ligation of distal SMA branches may be necessary
Embolectomy may be attempted if thrombus is present
Damage control surgery may be employed for severe associated injuries or instability.
Supportive Care:
Intensive care unit (ICU) monitoring post-operatively
Continued fluid and electrolyte management
Nutritional support (parenteral or enteral feeding as tolerated)
Antibiotic prophylaxis
Monitoring for signs of post-operative ischemia or complications.
Complications
Early Complications:
Hemorrhagic shock, bowel infarction, sepsis, anastomotic leak, graft occlusion, retained viable bowel after initial assessment, re-bleeding, compartment syndrome, ARDS, renal failure.
Late Complications:
Adhesions and bowel obstruction, incisional hernia, pseudoaneurysm formation at repair site, graft infection, chronic mesenteric ischemia due to compromised collateral flow, short bowel syndrome if extensive resection is required, malabsorption.
Prevention Strategies:
Meticulous surgical technique, careful assessment of bowel viability, adequate revascularization, appropriate graft material selection, aggressive hemodynamic resuscitation, early diagnosis, comprehensive intra-operative imaging, prophylactic antibiotics, judicious use of anticoagulation.
Prognosis
Factors Affecting Prognosis:
Hemodynamic stability at presentation, extent of SMA injury, time to definitive treatment, degree of bowel ischemia, associated injuries, presence of sepsis, patient comorbidities, surgical expertise.
Outcomes:
With prompt diagnosis and management, outcomes can be good
However, delays in treatment significantly worsen prognosis, with high mortality rates associated with bowel infarction and sepsis
Survival rates are significantly lower in patients requiring extensive bowel resection
Successful bypass or repair restores perfusion and allows for recovery of bowel function.
Follow Up:
Regular clinical review to assess for symptoms of ischemia or graft-related complications
Imaging (CTA or angiography) may be required at intervals to assess graft patency and integrity
Dietary modification may be necessary if short bowel syndrome develops
Long-term monitoring for signs of malabsorption.
Key Points
Exam Focus:
SMA injury is a critical surgical emergency
CT angiography is the gold standard for diagnosis
Management hinges on controlling hemorrhage, assessing bowel viability, and revascularization (bypass or endovascular repair) or resection
Non-viable bowel leads to high mortality
Differentiate acute from chronic ischemia management.
Clinical Pearls:
Always suspect SMA injury in high-energy abdominal trauma, especially with unexplained abdominal pain and shock
Early vascular surgery consultation is paramount
Meticulous assessment of bowel viability is key
if in doubt, resect
Consider collateral supply to the bowel when deciding on management
Bypass grafts should ideally be autogenous vein when available and feasible.
Common Mistakes:
Delaying surgical exploration in hemodynamically unstable patients
Inadequate bowel viability assessment
Failure to achieve adequate revascularization
Misinterpreting CTA findings
Undertreating associated injuries
Not considering endovascular options for stable injuries.