Superior mesenteric artery syndrome

Superior mesenteric artery (SMA) syndrome is a rare, life-threatening gastrointestinal disorder characterized by a compression of the third portion of the duodenum by the abdominal aorta (AA) and the overlying superior mesenteric artery. The syndrome is typically caused by a decreased angle of 6°-25° between the AA and the SMA, in comparison to the normal range of 38°-56°, due to a lack of retroperitoneal fat. In addition, the aortomesenteric distance is decreased to 2-8 milimeters, as opposed to the typical 10-20.

SMA Syndrome
SMA syndrome was first described in 1842 by Carl Freiherr von Rokitansky.

SMA syndrome was first described in 1842 by Carl Freiherr von Rokitansky. Only 0.013 - 0.3% of upper-gastrointestinal-tract barium studies support a diagnosis, making it one of the rarest gastrointestinal disorders known to medical science. With only about 400 cases reported in English-language medical literature since the 1800s, recognition of SMA syndrome as a distinct clinical entity is controversial, with some in the medical community doubting its existence entirely. Wilkie published the first comprehensive series of 75 patients in 1927.

SMA syndrome is also known as Wilkie's syndrome, cast syndrome, mesenteric root syndrome, chronic duodenal ileus and intermittent arterio-mesenteric occlusion. It is distinct from Nutcracker syndrome, which is the entrapment of the left renal vein between the AA and the SMA.

Symptoms

Symptoms include early satiety, nausea, bilious vomiting of large quantities of partially undigested food, extreme postprandial abdominal pain, abdominal distention/distortion, eructation, external hypersensitivity of the abdominal area, and spontaneous weight loss. Weight loss, in turn, increases the duodenal compression, spurring a vicious cycle. Symptoms are partially relieved when in the left lateral decubitus or knee-to-chest position. A Hayes maneuver (pressure applied below the umbilicus in cephalad and dorsal direction) elevates the root of the SMA, also easing the constriction. Symptoms are often aggravated when the patient leans to the right or takes a supine (face up) position.

Causes

SMA syndrome can be triggered by any condition involving a narrow mesenteric angle. Patients predominantly have a lengthy or even lifelong history of chronic abdominal complaints, with intermittent exacerbations depending on the degree of duodenal compression. Possibilities usually include constitutional genetic factors, such as aesthenic body build, an abnormally high insertion of the duodenum at the ligament of Treitz, an unusually low origin of the SMA, or intestinal malrotation around an axis formed by the SMA. Genetic predisposition is easily aggravated by any of the following: poor motility of the digestive tract, retroperitional tumors, dietary disorders such as anorexia (loss of appetite) or malabsorption, exaggerated lumbar lordosis, visceroptosis, abdominal wall laxity, rapid linear growth without compensatory weight gain (particularly in teenagers), rapid and/or severe weight loss, starvation, catabolic states (such as cancer and burns), prolonged bed rest, application of body casts, left nephrectomy, spinal cord injury, or scoliosis surgery.

Demographics

Four of every five afflicted are thin and sickly. Females are impacted twice as often as males, with 75% of cases occurring between the ages of 10 and 30. Renown American actor, director, producer, and writer Christopher Reeve suffered from SMA syndrome as a result of spinal cord injury.

Mortality

Delay in the diagnosis of SMA syndrome can result in death by progressive malnutrition, dehydration, oliguria, electrolyte abnormalities, hypokalemia or intestinal perforation.

Diagnosis

Abdominal and pelvic computed tomography scan showing duodenal compression (black arrow) by the superior mesenteric artery (red arrow) and the abdominal aorta (blue arrow).

Upper gastrointestinal series showing extreme duodenal dilation (white arrow).

A diagram of a healthy mesenteric angle.

A diagram of a compressed duodenum due to a reduced mesenteric angle.

Diagnosis of SMA Syndrome is very difficult, and usually one of exclusion. Diagnosis may follow X-ray examination revealing duodenal dilation followed by abrupt constriction proximal to the overlying superior mesenteric artery, as well as a delay in transit of four to six hours through the gastroduodenal region. Suggested exams include abdominal and pelvic Computed Tomography (CT) scan and upper gastrointestinal series (UGI). Endoscopy should be used to rule out other causes of obstruction. Despite the name, SMA syndrome is not a vascular condition. Vascular imaging studies of the abdomen, including computed tomography and contrast angiography, are often normal. In the case of spinal cord injury, impaired abdominal sensation due to nerve damage makes the clinical picture even more obscure. Despite multiple case reports, there has been controversy surrounding the diagnosis and even the existence of SMA syndrome since symptoms do not always correlate well with radiologic findings, and may not always improve following surgical correction.

Treatment

Upper gastrointestinal series showing duodenojejuonostomy (white arrow).

In mild or acute cases, conservative treatment should be attempted first, involving the reversal or removal of the precipitating factor with proper nutrition and replacement of fluid and electrolytes, either by surgically-inserted jejunal feeding tube, nasogastric intubation, or peripherally inserted central catheter (PICC line) administering total parenteral nutrition (TPN). Symptoms typically improve after restoration of weight. If conservative treatment fails, or if the case is severe or chronic, surgical intervention is required. The most common operation for SMA syndrome, duodenojejunostomy, was first proposed in 1907 by Bloodgood. This open surgery involves the creation of an alternate route between the duodenum and the jejunum, bypassing the compression caused by the AA and the SMA. Although highly invasive, open duodenojejunostomy has a 90% success rate. Less common surgical treatments for SMA syndrome include gastrojejunostomy, laparoscopic or Roux-en-Y duodenojejunostomy, anterior transposition of the third portion of the duodenum, intestinal derotation, and division of the ligament of Treitz. Lysis of the duodenal suspensory muscle has the advantage that it does not involve the creation of an intestinal anastomosis.