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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. ^[1]

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,^[1] 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,^[2] with some in the medical community doubting its existence entirely.^[1] Wilkie published the first comprehensive series of 75 patients in 1927.^[3]

SMA syndrome is also known as Wilkie's syndrome, cast syndrome, mesenteric root syndrome, chronic duodenal ileus and intermittent arterio-mesenteric occlusion.^[4] It is distinct from Nutcracker syndrome, which is the entrapment of the left renal vein between the AA and the SMA.

[edit] 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.^[5] Weight loss, in turn, increases the duodenal compression, spurring a vicious cycle.^[6] 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.^[5]

[edit] 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.^[7] Genetic predisposition is easily aggravated by any of the following: poor motility of the digestive tract^[4], 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.^[1]

[edit] 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.^[1] Renown American actor, director, producer, and writer Christopher Reeve suffered from SMA syndrome as a result of spinal cord injury.

[edit] Mortality

Delay in the diagnosis of SMA syndrome can result in death by progressive malnutrition, dehydration, oliguria, electrolyte abnormalities, hypokalemia or intestinal perforation.^[1]