Superior mesenteric artery syndrome
Superior mesenteric artery (SMA) syndrome is a very rare,
life-threatening gastro-vascular 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 an 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 and visceral
fat. In addition, the aortomesenteric distance is 2-8 millimeters, as opposed to the typical 10-20.
SMA syndrome was first described in 1861 by Carl Freiherr von Rokitansky
in victims at autopsy, but remained pathologically undefined until 1927 when Wilkie published the first comprehensive series of 75 patients.
Only 0.013 - 0.3% of upper-gastrointestinal-tract barium studies support
rarest gastrointestinal disorders known a diagnosis, making it one of the to medical science. With only about 500 cases reported in the history of English-language medical literature, recognition of SMA syndrome as a distinct clinical entity is controversial, though it is widely recognized as a clinical entity. SMA syndrome is estimated to have a mortality rate of 1 in 3.
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 include early satiety, nausea, vomiting, extreme "stabbing"
postprandial abdominal pain (due to both the duodenal compression and the compensatory reversed peristalsis), abdominal distention/distortion,
eructation, external hypersensitivity or tenderness of the abdominal area, and severe malnutrition accompanying spontaneous wasting. This, in turn, increases the duodenal compression, spurring a vicious cycle. "Food
fear" is a common development among patients with the chronic form of SMA syndrome. 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 slightly easing the constriction. Symptoms are often
aggravated when leaning to the right or taking a supine (face up) position.
Retroperitoneal fat and lymphatic tissue normally serve as a cushion for
the duodenum, protecting it from compression by the SMA. SMA syndrome is thus triggered by any condition involving an insubstantial cushion and narrow mesenteric angle. SMA Syndrome can present in two forms:
chronic/congenital or acute/induced.
Patients with the chronic, congenital form of SMA syndrome predominantly have a lengthy or even lifelong history of abdominal complaints with intermittent exacerbations depending on the degree of duodenal compression. Risk factors include anatomic characteristics such as: aesthenic (very thin or "lanky") body build, an unusually high insertion of the duodenum at the ligament of Treitz, a particularly low origin of intestinal malrotation around an axis formed by the SMA. the SMA, or
Predisposition is easily aggravated by any of the following: poor motility  retroperitional tumors, loss of appetite, of the digestive tract,
malabsorption, cachexia, exaggerated lumbar lordosis, visceroptosis, abdominal wall laxity, peritoneal adhesions, abdominal trauma, rapid
linear adolescent growth spurt, weight loss, starvation, and catabolic
states (as with cancer and burns).
The acute form of SMA Syndrome develops rapidly after traumatic incidents that forcibly hyper-extend the SMA across the duodenum, inducing the obstruction. Causes include prolonged supine bed rest (as with the application of body casts), spinal cord injury, scoliosis, scoliosis surgery, or left nephrectomy.
SMA syndrome is extremely rare, evident in only 0.013 - 0.3% of upper-gastrointestinal-tract barium studies. However, unfamiliarity
with this condition in the medical community coupled with its intermittent and nonspecific symptomatology probably results in its underdiagnosis.
As the syndrome involves a lack of essential fat, four of every five afflicted are underweight, often to the point of sickliness and emaciation.
Females are impacted twice as often as males, with 75% of cases occurring between the ages of 10 and 30. Common co-morbid conditions include
hyperchlorhydria (noted in 50% of cases), peptic ulcer disease (25-45%), pancreatitis and scoliosis.
Renowned American actor, director, producer, and writer Christopher Reeve suffered from the acute form of SMA syndrome as a result of spinal cord injury.
SMA syndrome is estimated to have a mortality rate of 1 in 3. Delay in the diagnosis of SMA syndrome can result in fatal catabolysis (advanced malnutrition), dehydration, oliguria, electrolyte abnormalities, hypokalemia, acute gastric rupture or intestinal perforation (from prolonged mesenteric ischemia), gastrectasia, spontaneous upper gastrointestinal bleeding, hypovolemic shock, aspiration pneumonia, or sudden cardiovascular collapse (from increased velocity of bloodflow in the SMA due to the reduced mesenteric angle).
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) abruptly preceding constriction by the SMA.
A diagram of a healthy mesenteric angle.
A diagram of a compressed duodenum due to a reduced mesenteric
Diagnosis is very difficult, and usually one of exclusion. SMA syndrome is thus considered only after patients have undergone an extensive evaluation of their gastrointestinal tract including upper endoscopy,
colonoscopy, and evaluation for various malabsorptive, ulcerative and inflammatory instestinal conditions with a higher diagnostic frequency. Diagnosis may follow x-ray examination revealing duodenal dilation
followed by abrupt constriction proximal to the overlying SMA, as well as a delay in transit of four to six hours through the gastroduodenal region. Standard diagnostic exams include abdominal and pelvic computed
tomography (CT) scan with oral and IV contrast, upper gastrointestinal
series (UGI), and, for equivocal cases, hypotonic duodenography. Once the diagnosis is made, vascular imaging studies such as ultrasound and
contrast angiography may be used to indicate increased bloodflow velocity through the SMA, signifying risk of sudden, fatal circulatory collapse.
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. However, the reason for the persistance
of gastrointestinal symptoms even after surgical correction has been
peristalsis in recently traced to the remaining prominence of reversed contrast to direct peristalsis.
Since females between the ages of 10 and 30 are most frequently afflicted, it is not uncommon for physicians to initially and incorrectly assume that emaciation is a choice of the patient instead of a consequence of SMA syndrome in its chronic form. Patients in the earlier stages of chronic SMA syndrome often remain unaware that they are ill until substantial damage to their health is done, since they may attempt to adapt to the condition by gradually decreasing their food intake or naturally gravitating toward a lighter and more digestible diet. Eating disorder
treatment protocols involving forced refeeding and behavioral therapy are noted to have poor outcomes with individuals suffering from SMA syndrome, contributing to the high mortality rate of the condition.
Upper gastrointestinal series showing duodenojejuonostomy (white arrow).
SMA syndrome can present in acute, acquired form (i.e. abruptly emerging
within an inpatient stay following scoliosis surgery) as well as chronic
form (i.e. developing throughout the course of a lifetime and advancing due to environmental triggers, life changes, or other illnesses). Acute cases usually respond to medical management, while chronic cases require surgical intervention.
In acute or mild 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). Pro-motility agents such as metoclopramide may also be beneficial. Symptoms typically improve after restoration of weight,
except when reversed peristalsis persists, or if regained fat refuses to accumulate within the mesenteric angle.
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.
Performed as either an open surgery or laparoscopically,
duodenojejunostomy involves the creation of an anastomosis between the duodenum and the jejunum, bypassing the compression caused by the AA and the SMA. Less common surgical treatments for SMA syndrome include Roux-en-Y duodenojejunostomy, gastrojejunostomy, 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. The world's first robotically assisted intestinal bypass for SMA syndrome was performed on July 30, 2008 at the London Health Sciences Centre in Ontario, Canada.
The possible persistence of symptoms after surgical bypass can be traced
peristalsis in contrast to direct to the remaining prominence of reversed
peristalsis, although the precipitating factor (the duodenal compression) has been bypassed or relieved. Reversed peristalsis has been shown to
a complex and invasive open respond to duodenal circular drainage—surgical procedure originally implemented and performed in China.