Superior Mesenteric Artery Syndrome

Superior mesenteric artery syndrome is a deadly but uncommon gastro-vascular condition marked by constriction of the 3^rd section of the duodenum by the overlying SMA or superior mesenteric artery and the AA or abdominal aorta. The condition generally occurs due to an angle of 6 to 25 degrees between the SMA and the AA, as compared to the usual range of 38 to 56 degrees, often because of deficient mesenteric/visceral and retroperitoneal fat. Also, instead of the normal 10 to 20 millimeters, the aorto-mesenteric distance varies between 2 to 8 mm. A narrow angle of the SMA however cannot be sufficient by itself to make a diagnosis. This is because people with reduced body mass index, particularly children, are known to elicit a narrow angle of the SMA without suffering from any of the symptoms of superior mesenteric artery syndrome. The syndrome is more common in females than males, especially in adolescents and older children.

Superior mesenteric artery syndrome is also referred by many other names such as cast syndrome, Wilkie’s syndrome, mesenteric root syndrome, intermittent arterio-mesenteric occlusion, and chronic duodenal ileus. The disorder is different from the Nutcracker syndrome which is characterized by wedging of the left renal vein between the SMA and the AA. However, it is possible for patients to get diagnosed with both SMA syndrome and Nutcracker syndrome.

Symptoms

Some of the common signs and symptoms of superior mesenteric artery syndrome are listed below:

• The most common symptoms include abdominal fullness or early satiety, vomiting of partly digested food, nausea, bloating post meals, abdominal distortion/distention, diarrhea, tenderness or external hypersensitivity in the abdominal region, eructation, heartburn, reflux, and cramp-like or intense stabbing pain in the abdomen which may occur due to compression of the duodenum as well as the compensatory reversed peristalsis.
• The symptoms may worsen when in a face up or supine position, or when leaning towards the right.
• Most individuals with chronic type of superior mesenteric artery syndrome may elicit ‘food fear.’
• Poor weight gain and feeding problems are evident in affected infants.
• Sometimes, patients may experience extreme malnutrition along with spontaneous wasting. This can then elevate the compression and pressure on the duodenum, thereby giving rise to a vicious cycle.
• The root of the superior mesenteric artery can be raised via a Hayes maneuver, i.e., application of pressure under the umbilicus in dorsal and cephalad direction. The maneuver will some partially alleviate the compression.
• Many patients may experience partial alleviation of symptoms when in the knee-to-chest or left lateral decubitus position, or in the face-down/prone position.

Causes

A cushioning effect if provided to the duodenum by the lymphatic tissue and retroperitoneal fat, thereby guarding the duodenum from constriction by the superior mesenteric artery. Hence, any condition that involves narrowing of the mesenteric angle or inadequate cushioning can trigger a case of superior mesenteric artery syndrome. The syndrome are of two broad types, i.e., congenital/chronic or induced/acute.

• Individuals suffering from congenital and chronic type of SMA syndrome usually experience a lifelong or prolonged history of abdominal distress along with episodic aggravations as per the intensity of duodenal constriction.
  • Individuals who are predisposed to developing SMA syndrome may experience easy worsening of the condition due to varied factors such as retroperitional tumors, poor digestive tract motility, starvation, loss of appetite, cachexia, malabsorption, exaggerated lumbar lordosis, laxity of the abdominal wall, visceroptosis, peritoneal scars or adhesions, rapid linear growth spurt during adolescence, abdominal injury or trauma, weight loss, history of neurological trauma or injury, and catabolic states as seen with burns and cancer.
  • Some of the risk factors that can increase the vulnerability to developing SMA syndrome include anatomical features like a body-built that is very lanky or slim; a very low commencement point of the superior mesenteric artery; an abnormally high duodenal insertion point at the ligament of Treitz; or defective rotation of the intestine around an axis created by the superior mesenteric artery.
• Acute type of superior mesenteric artery syndrome forms quickly after trauma causing events that forcefully hyper-stretch and extend the superior mesenteric artery across and over the duodenum.
  • It may be commonly caused due to scoliosis, spinal cord injury, scoliosis surgery, ileo-anal pouch surgery, left nephrectomy, previous abdominal surgery, loss of tone in the musculature of the abdominal wall, lordosis or excessive curvature in the lumbar section of the spine, long-term supine bed rest as is seen with use of body casts, and/or eating disorders.
  • It may however be noted that while superior mesenteric artery syndrome may mimic or occur due to some eating disorder, it is important to differentiate between the two as misdiagnosis in this scenario can prove to be life-threatening.
• It has also been reported that superior mesenteric artery syndrome may occur along with conditions such as peptic ulcers, pancreatitis, and other kinds of intra-abdominal inflammatory ailments.

Treatment Of Superior Mesenteric Artery Syndrome

Treatment of superior mesenteric artery syndrome is aimed at curing the underlying causative conditions and weight gain. Nearly 70 percent of the cases can normally be treated via medical treatment, while surgical intervention may be needed in the rest of the cases.

Doctors will usually opt for medical treatment as the first choice when treating the condition for the first time in a particular patient. Surgery is carried out only when diagnosis reveals the need for emergency surgical intervention. In pediatric cases, doctors generally carry out medical treatment for a trial period of 6 weeks after diagnosis.

A few medical treatment options for superior mesenteric artery syndrome include:

• Mobilizing the patient into the left lateral decubitus or the prone position.
• Placement of a nasogastric tube for gastric and duodenal decompression.
• Doctors may also prescribe the use of pro-motility agents like metoclopramide.
• Removal or reversal of the aggravating factor via better nutrition and replenishment of electrolytes and fluids in the body. This may be done either via a PICC or peripherally inserted central catheter that administers TPN or total parenteral nutrition, or via nasogastric intubation or surgical insertion of a jejunal feeding tube. The symptoms generally alleviate after the weight is restored, expect if the built-up fat does not collect inside the mesenteric angle, or due to persistence of reversed peristalsis.

Duodenojejunostomy is the most common surgical treatment option for superior mesenteric artery syndrome.