Understanding Superior Mesenteric Artery Syndrome
Introduction
Superior Mesenteric Artery Syndrome (SMAS) is a rare, yet impactful condition with a history spanning over a century. First identified in 1861, SMAS is characterized by a compression of the third part of the duodenum due to narrowing of the space between the superior mesenteric artery and the aorta. This article aims to shed light on SMAS, providing comprehensive information about its description, risk factors, and understanding for those afflicted by the condition or interested in learning more.
Definition
Superior Mesenteric Artery Syndrome is a gastrointestinal disorder where the duodenum is compressed between two arteries, leading to partial or complete blockage of the duodenum.
Description of Superior Mesenteric Artery Syndrome
SMAS occurs when the distance between the superior mesenteric artery (SMA) and the aorta is reduced, typically due to loss of the mesenteric fat pad, leading to a compression of the duodenum – the part of the digestive tract that connects the stomach to the small intestine. This compression results in symptoms such as nausea, vomiting, abdominal pain, and weight loss.
The progression of SMAS can vary greatly among individuals. Some may experience intermittent symptoms, while others may face more persistent, debilitating issues affecting their quality of life. If left untreated, severe cases may lead to malnutrition and other serious complications.
SMAS is not a common condition. While precise prevalence is unknown, it’s estimated that SMAS affects around 0.013%-0.3% of the population. Both men and women can develop this condition, although it’s slightly more common in young women.
Risk Factors for developing Superior Mesenteric Artery Syndrome
Lifestyle Risk Factors
Certain lifestyle factors can potentially contribute to the development of SMAS. Rapid weight loss, often due to conditions like anorexia nervosa or other causes, is the most common risk factor. This is because weight loss can lead to a reduction in the mesenteric fat pad that normally keeps the SMA and the aorta separated. Other potential factors include prolonged bed rest or immobilization, which can lead to muscle wasting and loss of the mesenteric fat pad.
Medical Risk Factors
Medical conditions that affect the abdomen can also put individuals at risk of developing SMAS. These include abdominal or spine surgery, which might alter the normal anatomy of the abdomen. Conditions such as burns, trauma, or infections that require long-term treatment or bed rest could also increase the risk. Lastly, conditions leading to rapid weight loss, such as cancer or chronic illnesses, are associated with a higher risk of SMAS.
Genetic and Age-Related Risk Factors
While there’s no direct genetic predisposition to SMAS, individuals with certain anatomical variations, like a lower positioned SMA or a shorter ligament of Treitz, are at a higher risk. It’s also more common in people between the ages of 10 and 30, particularly in those with a thin or slender body build. While age itself is not a risk factor, younger people might be at higher risk due to factors associated with growth spurts, body changes, and lifestyle habits typical of this age range.
Clinical Manifestations
Abdominal pain
Abdominal pain is a common symptom of Superior Mesenteric Artery Syndrome, experienced by approximately 90% of patients. It occurs due to the compression of the duodenum causing partial or complete obstruction of the gut. This obstruction leads to a buildup of gas and fluid, resulting in a stretched abdomen, which subsequently causes pain. It can be more prevalent during the advanced stages of the disease.
Nausea
Nausea is reported in about 80% of SMAS patients. As the passage of food is obstructed, the body reacts by creating a sensation of queasiness or the urge to vomit. This can occur at any stage of the disease and is not specific to any particular patient group.
Vomiting
Vomiting, experienced by 75% of SMAS patients, is a direct result of the duodenal obstruction. As the passage is blocked, the body attempts to expel the contents of the stomach, resulting in vomiting. It is more common in the later stages of the disease when the obstruction becomes more severe.
Weight loss
Approximately 70% of SMAS patients suffer from weight loss. This occurs due to a combination of decreased food intake because of early satiety, nausea, vomiting, and a lack of nutrient absorption due to the duodenal obstruction. Weight loss can be particularly severe in the advanced stages of the disease.
Early satiety
About 60% of patients with SMAS experience early satiety. This is when the stomach feels full after eating only a small amount of food. The duodenal obstruction causes food to stay in the stomach longer than usual, creating a sense of fullness and reducing the patient’s appetite.
Bloating
Bloating is reported in about 50% of patients with SMAS. As the compressed duodenum prevents gas from passing through the digestive system, it can cause the abdomen to feel full and tight, leading to bloating.
Acid reflux
Approximately 45% of SMAS patients experience acid reflux. This condition is characterized by a burning sensation in the chest (heartburn), caused by stomach acid backing up into the esophagus due to the obstruction in the duodenum. It can occur in any stage of the disease.
Swallowing difficulties
Swallowing difficulties or dysphagia is a less common symptom, affecting around 25% of patients. It results from a disruption in the normal flow of food, causing discomfort or difficulty while swallowing.
Abdominal distension
About 20% of SMAS patients experience abdominal distension, where the stomach appears enlarged. This occurs due to the buildup of gas or fluids behind the area of the duodenum that is obstructed.
Diagnostic Evaluation
To diagnose Superior Mesenteric Artery Syndrome, doctors employ a series of tests that focus on imaging the abdomen and assessing gastrointestinal function. These evaluations aim to visualize the narrowing between the superior mesenteric artery and the aorta, which causes the duodenal compression, as well as the secondary effects of this compression.
Upper gastrointestinal (GI) series
An Upper GI series, experienced by 70% of patients, is a series of X-rays of the esophagus, stomach
, and duodenum. The patient drinks a contrast solution, often barium, which coats the digestive tract and makes it visible on X-rays. This test helps visualize any obstruction in the duodenum. Positive results indicating SMAS include a delay in contrast passage, distention of the stomach, and a narrowed angle between the aorta and SMA. If results are negative but symptoms persist, further evaluations may be necessary.
Computed tomography (CT) scan
A CT scan is an imaging test that provides a detailed view of all types of tissue. Around 60% of patients undergo this test. It is performed by taking a series of X-rays from different angles, which are then combined by a computer to create cross-sectional images. It can help identify a narrowed aortomesenteric angle, which is a hallmark of SMAS. If the scan does not reveal this feature, but symptoms persist, additional diagnostic procedures should be considered.
Magnetic resonance imaging (MRI)
An MRI is another imaging test that uses strong magnets and radio waves to generate detailed images of the body’s structures. Approximately 50% of patients get an MRI. It’s particularly effective for soft tissue visualization and can show a reduced distance between the SMA and aorta, characteristic of SMAS. If an MRI comes back negative for SMAS, but the patient continues to experience symptoms, further testing may be required.
Esophagogastroduodenoscopy (EGD)
EGD, also known as upper endoscopy, is a procedure where a thin tube with a camera is inserted through the mouth to visualize the esophagus, stomach, and duodenum. About 40% of patients go through this test. In SMAS, EGD may show a distended stomach and a compressed duodenum. If EGD doesn’t confirm SMAS, but symptoms persist, other diagnostic tests should be performed.
Barium swallow test
In a barium swallow test, the patient drinks a barium-containing liquid that coats the digestive tract, making it visible on X-rays. It’s performed in approximately 35% of patients. In SMAS, the test could reveal an obstruction in the duodenum or a delay in contrast passage. If the test comes back negative, further evaluations should be conducted if symptoms continue.
Blood tests
Blood tests are done to assess overall health and rule out other conditions. Approximately 30% of patients have these tests. While blood tests do not diagnose SMAS directly, abnormal results, like low blood counts or malnutrition markers, could suggest SMAS in the context of consistent symptoms. If results are normal but symptoms persist, more specific diagnostic evaluations are required.
Stool tests
Stool tests are done to check for abnormalities that could suggest a digestive tract problem. Around 25% of patients get this test. Although stool tests cannot diagnose SMAS directly, certain abnormalities, like the presence of undigested food, could point towards SMAS. If stool tests are normal but symptoms continue, further evaluations are warranted.
Gastric emptying study
A gastric emptying study measures how quickly food leaves the stomach. It’s conducted in about 20% of patients. Delayed gastric emptying can suggest SMAS. If the study doesn’t confirm SMAS but symptoms persist, other diagnostic tests should be performed.
Abdominal X-ray
An abdominal X-ray is a quick and painless test used to visualize structures in the abdomen.
It’s done in about 15% of patients. In SMAS, an X-ray might show a distended stomach or a gas-filled duodenum. If the X-ray is normal but symptoms persist, further evaluations should be done.
If all diagnostic evaluations come back negative but symptoms continue, it is important to communicate this with your healthcare provider. Further investigation may be necessary, possibly including referral to a specialist or additional testing. Remember, you know your body best and persistent symptoms warrant further evaluation.
Health Conditions with Similar Symptoms to Superior Mesenteric Artery Syndrome
Gastroesophageal reflux disease (GERD)
GERD is a chronic condition where stomach acid frequently flows back into the esophagus, causing irritation and symptoms like heartburn, chest pain, and difficulty swallowing. This condition can mimic SMAS due to symptoms of acid reflux and discomfort in the stomach area. However, GERD is often distinguished by a burning sensation in the chest that worsens after eating or at night, which is not typical of SMAS. Diagnostic tests such as endoscopy, ambulatory acid (pH) probe tests, and esophageal manometry can help identify GERD.
Peptic ulcer disease
Peptic ulcers are open sores that develop on the inside lining of your stomach and the upper portion of your small intestine. Symptoms can include burning stomach pain, feeling of fullness, bloating, and intolerance to fatty foods, which are also common in SMAS. Unique symptoms, however, include heartburn and mild nausea, which are less common in SMAS. Endoscopy or an upper gastrointestinal series using barium can help diagnose peptic ulcers.
Treatment Options
Medications
Prokinetic agents (e.g., metoclopramide)
Prokinetic agents, such as metoclopramide, work by speeding up the movement of food through the stomach. They are used in SMAS to alleviate symptoms and facilitate gastric emptying. These are usually prescribed as a first-line treatment and can lead to symptom improvement within a few days to weeks.
Acid-suppressing medications (e.g., proton pump inhibitors)
Acid-suppressing medications like proton pump inhibitors reduce the production of stomach acid. They are often used to manage acid reflux symptoms in SMAS. These medications are typically used on a daily basis and can provide symptom relief within a few days.
Procedures
Nasojejunal feeding tube placement
A nasojejunal feeding tube provides nutrition directly to the small intestine through a tube inserted through the nose. This is typically used in severe cases of SMAS when the patient cannot tolerate oral intake. The procedure can lead to improved nutritional status and symptom relief over weeks to months.
Gastrojejunostomy
Gastrojejunostomy is a surgical procedure to create a direct connection between the stomach and the middle part of the small intestine (jejunum). It’s typically reserved for severe cases of SMAS that don’t respond to conservative treatments. The procedure can alleviate symptoms by bypassing the blocked part of the duodenum, leading to significant improvement in symptoms over weeks to months.
Gastric outlet obstruction
Gastric outlet obstruction is a condition where the area between the stomach and the small intestine is blocked, either partially or completely. This condition can present with vomiting, abdominal pain, and weight loss, similar to SMAS. However, the obstruction is typically caused by physical factors such as tumors or ulcers, and the vomiting may contain undigested food. Imaging tests like CT or MRI and a barium swallow study are often used to diagnose gastric outlet obstruction.
Gallbladder disease
Gallbladder disease, such as gallstones, can cause symptoms that resemble SMAS including abdominal pain, nausea, and vomiting. However, pain from gallbladder disease is often concentrated on the right side of the abdomen and may radiate to the right shoulder or back. Diagnosis typically involves ultrasound or a special nuclear medicine scan known as a HIDA scan.
Antiemetics (e.g., ondansetron)
Antiemetics like ondansetron are used to prevent nausea and vomiting, common symptoms in SMAS. They work by blocking the action of chemicals in the body that can trigger nausea and vomiting. These are often used in conjunction with other treatments to manage symptoms and improve quality of life.
Nutritional supplements (e.g., vitamins, minerals)
Nutritional supplements such as vitamins and minerals are often used to correct nutritional deficiencies caused by SMAS. They can be taken orally or administered via a feeding tube. These supplements support overall health and assist in the recovery process.
Duodenojejunostomy
Duodenojejunostomy is a surgical procedure that bypasses the obstructed section of the duodenum by creating a direct connection between the duodenum and the jejunum. It’s often used in severe cases of SMAS when other treatments have failed. Post-surgery, patients can expect gradual relief of symptoms and improved nutritional status over weeks to months.
Jejunostomy tube placement
A jejunostomy tube is a feeding tube that is surgically placed directly into the jejunum, the second part of the small intestine. This allows for direct delivery of nutrition, bypassing the stomach and the duodenum. It’s often used for patients who cannot get adequate nutrition by mouth. The procedure can provide immediate nutritional support and symptom relief.
Pancreatitis
Pancreatitis, or inflammation of the pancreas, can cause upper abdominal pain, nausea, and vomiting, much like SMAS. However, pain associated with pancreatitis often intensifies after eating and may be accompanied by fever and a rapid heart rate. Blood tests for pancreatic enzymes, along with imaging tests such as CT scans and ultrasounds, can help diagnose this condition.
Intestinal obstruction
An intestinal obstruction blocks food or liquid from passing through the small or large intestine. This condition can cause abdominal pain, bloating, and vomiting, which are also symptoms of SMAS. However, the pain of an intestinal obstruction is often severe and sudden. An abdominal X-ray, CT scan, or MRI can detect the blockage.
Pain medications (e.g., opioids)
Pain medications, like opioids, can help manage severe abdominal pain associated with SMAS. However, these must be used cautiously due to the risk of dependency and constipation, another potential SMAS symptom. It’s important that they are used under the strict guidance of a healthcare provider.
Intravenous fluids
As SMAS often causes vomiting and difficulty with nutrient absorption, intravenous (IV) fluids may be administered to prevent dehydration and electrolyte imbalances. IV fluids provide immediate rehydration and are often used in combination with other treatments.
Surgical duodenal mobilization
Surgical duodenal mobilization is a procedure that moves the duodenum (the first part of the small intestine) away from the superior mesenteric artery. This can help alleviate the compression causing SMAS. Following the procedure, patients typically see a reduction in symptoms, with improvement dependent on their overall health and the severity of their condition.
Roux-en-Y duodenojejunostomy
Roux-en-Y duodenojejunostomy is a surgical procedure that reroutes the small intestine to bypass the compressed part of the duodenum, effectively alleviating the symptoms of SMAS. This procedure can bring significant relief and improve the nutritional status of patients, especially those with severe symptoms unresponsive to other treatments.
Inflammatory bowel disease
Inflammatory bowel disease (IBD) includes conditions like Crohn’s disease and ulcerative colitis that involve chronic inflammation of the digestive tract. Abdominal pain, bloating, and weight loss are shared symptoms between IBD and SMAS. However, IBD can also present with symptoms like diarrhea, blood in stool, and fever. Blood tests, stool tests, and colonoscopy can help differentiate IBD from SMAS.
Gastroparesis
Gastroparesis is a condition where the stomach cannot empty in a normal manner, often due to damage to the nerves controlling stomach muscles. Symptoms such as nausea, vomiting, abdominal bloating, and early satiety overlap with SMAS. Gastroparesis is often confirmed by a gastric emptying study, where a patient eats a meal containing a small, harmless amount of radioactive material that can be traced on a scan.
Cancer of the stomach or duodenum
Stomach or duodenal cancers can present with similar symptoms to SMAS, like weight loss, vomiting, and abdominal pain. However, these cancers might also cause dark, tarry stools, anemia, or a palpable mass in the abdomen. Imaging tests like CT or MRI scans, along with biopsy procedures, can help diagnose these cancers.
Antacids
Antacids are over-the-counter medications that neutralize stomach acid to help relieve symptoms like acid reflux and stomach discomfort. These may provide temporary relief for some SMAS symptoms but are not a long-term solution.
Antibiotics
Antibiotics may be used if there’s an infection present due to complications of SMAS, like aspiration pneumonia from chronic vomiting. These medications kill or inhibit the growth of bacteria, helping the body fight off the infection.
Nasojejunal feeding tube placement
In some severe cases of SMAS, where oral intake is inadequate, a nasojejunal feeding tube may be placed. This involves passing a tube through the nose, down into the small intestine (jejunum) to deliver nutrition directly.
Gastrojejunostomy
Gastrojejunostomy is a surgical procedure that connects the stomach directly to the jejunum, bypassing the area of obstruction in the duodenum. This can relieve symptoms and allow better nutrition absorption.
Duodenojejunostomy
Duodenojejunostomy is a surgical intervention often used for severe cases of SMAS. The surgery bypasses the compressed part of the duodenum by connecting it directly to the jejunum, alleviating symptoms of SMAS.
Jejunostomy tube placement
A jejunostomy tube is a feeding tube placed directly into the jejunum through the abdominal wall. It’s used in patients who are unable to take in enough nutrients orally.
Endovascular stenting
Endovascular stenting may be considered in some cases of SMAS. This procedure involves placing a small mesh tube (stent) in the superior mesenteric artery to keep it open and relieve duodenal compression. However, its use is not well established in the treatment of SMAS.
Lysis of adhesions
In cases where SMAS is caused by adhesions (scar tissue) from previous surgeries, lysis of adhesions can help. This
surgical procedure removes the scar tissue causing the obstruction.
Small bowel resection
Small bowel resection involves the surgical removal of a part of the small intestine. It’s typically reserved for severe cases or complications of SMAS, like intestinal perforation or necrosis.