Introduction
Superior mesenteric artery syndrome (SMAS) is a clinical condition that
is characterized by compression of the third part of duodenum between
the aorta posteriorly and the superior mesenteric artery (SMA)
anteriorly. Von Rokitansky described the syndrome for the first time in
1861. Later, in 1927, pathophysiology of SMAS was described in detail
by Wilkie, giving this syndrome another name
“Wilkie’s syndrome”.1 This syndrome can present with
very non-specific symptoms and thus making it difficult for prompt
diagnosis and differentiating it from other conditions such as
cholelithiasis, peptic ulcer disease, and abdominal angina. Therefore,
the key to diagnose this condition is a high index of suspicion. In this
report, we present an unusual yet possible case of “recurrent” acute
pancreatitis as a result of superior mesenteric artery syndrome.
Case presentation
A 45-year-old man presented to the hospital with a 24-hour history of
worsening upper abdominal, bilateral flank pain, and nausea without
emesis. His past medical history consists of congestive heart
failure, history of acute myocardial infarction, lower urinary tract
symptoms, benign prostatic hyperplasia, vitiligo, congenital ureteropelvic junction obstruction status post left pyeloplasty. He experienced
similar symptoms months back when it resolved on its own. On
presentation, he was hemodynamically stable with a history significant for
unintentional weight loss of 35Ibs. The patient denied fever, chills, or
loose stools. Physical examination was significant for epigastric
tenderness. Laboratory data demonstrated normal kidney function,
glucose 100 (70-99 mg/dL), lipase 1552 (73-393U/L), unremarkable
urinalysis, albumin 3.1 (3.4-5.4 g/dL) and calcium 8.3
(8.6-10.3 mg/dL). Diagnostic imaging included contrasted-computed
tomography (CT) of the abdomen and pelvis, which showed inflammation in
the tail of the pancreas without necrosis. In addition, dilation of the
second and third portion of the duodenum with an abrupt change in
caliber (Figures 1-2) along with the narrow aortomesenteric angle of
18° (Figure 3) was also observed. The patient was managed
conservatively with intravenous fluids, intravenous morphine, and nothing
per mouth status. Gastric decompression was not performed because of
incomplete obstruction. Diet was advanced gradually. Other potential
causes of acute pancreatitis like gall bladder stones or biliary
obstruction, alcohol or drug-induced pancreatitis were ruled out.
Ultrasound showed no gall stones or biliary obstruction. Based on the
patient’s clinical presentation, laboratory, and radiographic findings,
he was diagnosed with SMAS -associated acute pancreatitis. The patient was readmitted again two months later with a similar presentation. CT
of the abdomen and pelvis showed acute pancreatitis complicated by
splenic vein thrombosis with resolution of duodenal dilation. During the
recurrent episode, he was again conservatively treated as well with
subsequent excellent recovery.
Discussion
SMAS is considered a rare but serious condition with an estimated
incidence of 0.1-0.3%.2 Though SMAS can occur at any
age, it has been mostly reported in adolescent or young adults.
Anatomically, SMA rises from the aorta at L1-2 level forming an angle
with the aorta called aortomesenteric angle, normally 45–60°, while the
third part of duodenum passes between the aorta and SMA at L3
level.3 Normally, a retroperitoneal fat pad sitting at
the angle between the aorta and SMA maintains adequate aortomesenteric
angle, and thus prevents duodenal compression.3,4Hence, factors that result in a loss of retroperitoneal fat and a
decrease of aortomesenteric angle and aortomesenteric distance can
potentially cause compression of the third part of the duodenum, so
called SMAS.
Factors that lead to an acute angulation of SMA can be either congenital
or acquired. Congenital anomalies such as short Treitz ligament,
malrotations and peritoneal adhesions have been described in association
with this clinical condition.5,6 On the other hand,
most common risk factors that cause a decrease in aortomesenteric angle
are acquired and related to a loss of retroperitoneal fat following
severe weight loss. Causes of excessive weight loss include but not
limited to eating disorders, cachexia, malabsorption, polytrauma,
malignancy and acquired immunodeficiency syndrome, large extensive
burns, and major surgeries.7 Additionally, SMAS has
been reported following orthopedic correction of spinal deformities, so
called cast syndrome.8 According to previous studies,
pronounced lumbar lordosis in females makes them more prone to develop
this condition particularly in the age range from 10-39
years.6
Furthermore, acute pancreatitis complicated by SMAS is an extremely rare
presentation, and only very few cases, describing this association, have
been reported in the literature.9,10,11 This is the
first report to describe SMAS in association with “recurrent” acute
pancreatitis, to the best of our knowledge. In our patient, we believe
that the recent excessive and rapid weight loss had resulted in a loss
of retroperitoneal fat and, subsequently, a decrease in aortomesenteric
angle, which lead ultimately to the duodenal compression. This was
evident on the CT scan of the abdomen and pelvis, which was notable for
the narrow aortomesenteric angle in addition to the compressed third
part of duodenum leading to small bowel obstruction and dilation along
with acute pancreatitis. The exact mechanism of pancreatitis in SMAS is
still unknown, but it is proposed that the secondary
occlusive postpapillary syndrome due to duodenal compression could cause
reflux of bile into pancreas causing inflammation. On the other hand,
inflammation of the pancreas could also cause paralytic ileus or
peripancreatic edema thus reducing the aortomesenteric
angle.9
Importantly, before SMAS diagnosis is made, other causes of GI
obstruction should be ruled out, utilizing various imaging modalities.
Traditionally, upper gastrointestinal barium swallow study has been used
to diagnosis SMAS, which shows distended stomach and proximal duodenum
along with abrupt vertical or oblique external compression of the third
part of the duodenum.12 Also, conventional mesenteric
angiography with hypotonic duodenography used to be the most efficient
diagnostic tool for this syndrome in the past.12Nevertheless, other noninvasive imaging modalities are more routinely
utilized nowadays to diagnosis SMAS with high diagnostic accuracy
including, multidetector CT scan, CT angiography and magnetic resonance
angiography. 4,13 These imaging techniques can
accurately demonstrate duodenal obstruction due to SMA compression along
with a narrow aortomesenteric angle and distance seen in this
syndrome.13,14,15 Furthermore, in patients with
proximal duodenum obstruction, an aortomesenteric angle of less than 22°
along with an aortomesenteric distance less than 8mm on imaging
corresponds strongly to SMAS. 7,16
As it was shown in our patient, SMAS complicated by acute pancreatitis
is usually conservatively treated by correcting electrolyte
disturbances, gastroduodenal decompression and nutritional support, with
an ultimate goal of weight gain to allow for retroperitoneal fat pad
reinforcement.5 Surgery is indicated for patients
where conservative management fails.18 Available
surgical options include gastro jejunostomy, duodenojejunostomy and
lysis of the ligament of Treitz with mobilization of the
duodenum.19,20 Duodenojejunostomy is the preferred
surgical approach due to lower rates of surgical complications in
addition to lower failure rate.21