Superior mesenteric artery compression disorders

Superior mesenteric artery
compression disorders
RAD Magazine, 40, 474, 23-24
Dr Bilal Amin Sethi
Speciality registrar in radiology
Aberdeen Royal Infirmary
email: [email protected]
and bloating, epigastric pain, nausea and vomiting.2,5 The
pain is characteristically relieved on lying prone in a left
decubitus position. This is explained by the fact that the
mesentery and small bowel move from the right side of the
abdomen to the left, widening up the aortomesenteric angle.
Patients may present acutely with signs and symptoms of
duodenal obstruction or they may complain of chronic
abdominal pain which may last for months or even years.4
Radiographic findings2,4
The superior mesenteric artery (SMA) originates
from the anterior aspect of the abdominal aorta,
just below the celiac trunk at the level of the L1
vertebra. Normally, the SMA is surrounded by
fat and lymphatic tissues which provide a cushion
between it and its surrounding structures. The
mesenteric fat pad between the SMA and aorta
forms a natural angle between them, called the
aortomesenteric angle. The normal aortomesenteric angle is 25-60º. The aortomesenteric distance, the distance between aorta and SMA, is
usually 10-28mm.1 Loss of this cushion of fat can
lead to acute angulation of the SMA and reduction in the aortomesenteric distance. This in turn
can cause extrinsic vascular compression of other
structures by the SMA, giving rise to two distinct
vascular compression disorders:
1) SMA syndrome (Wilkie’s syndrome) – compression of the third part of the duodenum by
the SMA.
2) Renal vein entrapment (Nutcracker
syndrome) – compression of the left renal vein
by the SMA.
SMA vascular compression disorders are thus triggered
by any condition that diminishes the normal fat cushions,
causing angulation and reduction in distance between the
aorta and SMA. Fat cushion loss is commonly seen under
conditions of severe weight loss – anorexia nervosa, hypercatabolic states (burns, trauma, malignancy, major surgery)
and malabsorption.2 Various surgical procedures, eg bariatric
surgery, scoliosis surgery, ileoanal pouch anastomosis and
aortic aneurysm repair, can also directly or indirectly reduce
the aortomesenteric angle.3
Since the SMA causes extrinsic compression of two different anatomical structures, the clinical presentation and
course of the disease, radiographic findings and treatment
are different in each case, dependent on the structure that
is affected.
Superior mesenteric artery syndrome
SMA syndrome (also known as Wilkie’s syndrome, aortomesenteric compression, arteriomesenteric duodenal compression or duodenal vascular compression) was originally
described by Von Rokitansky in 1842, but reported in
the literature by Wilke in 1927.1,4 It is characterised by
acute angulation of the SMA causing compression of the
third part of the duodenum, duodenal ‘clamping’, leading to
obstruction.
Clinical presentation
Symptoms associated with SMA syndrome are vague and
non-specific. They commonly include abdominal distension
Plain radiograph: Demonstrates dilated, fluid and gas filled
stomach.
Barium studies: Shows dilated first and second parts of
the duodenum with an abrupt transition point in the third
part (figure 1). Other signs include extrinsic compression
of the third part of the duodenum and collapsed small bowel
distal to the compression.
Computed tomography (CT): Contrast enhanced CT is the
imaging modality of choice today. It can be used to reach
the correct diagnosis immediately. An abdominal CT does
not only allow direct visualisation of the obstructed bowel
in relation to the SMA, but can also demonstrate narrowing
of the aortomesenteric angle and reduction of the aortomesenteric distance. In addition, other causes of obstruction
can be excluded (figure 2).
Treatment
Treatment is initially conservative with a high success rate.5
Conservative measures commonly include gastric decompression via a nasogastric tube, fluid-electrolyte balance and
nutritional support, which is provided either with total parenteral nutrition or feeding via a nasojejunal tube placed in
the proximal jejunum. Manoeuvring patients to prone leftsided decubitus position during meals may also be helpful.4,5
Oral feeding is encouraged after the initial weeks and once
the patient gains weight.
Surgery is considered for symptomatic patients if conservative treatment fails or if weight gain does not improve
symptoms. There is no consensus regarding the duration of
conservative management and this is left to the discretion
of the treating clinicians. Surgical options include Treitz ligament lysis with mobilisation of the duodenum, gastrojejunostomy, duodenal derotation, duodenojejunostomy and
SMA transposition surgery.3-5 Duodenojejunostomy is the
most common procedure and with advancements in laparoscopic techniques, laparoscopic duodenojejunostomy offers a
minimally invasive therapeutic option. It is also effective in
majority of the patients.4
Left renal vein entrapment
Left renal vein entrapment refers to the extrinsic compression of the left renal vein (LRV) between the SMA and
aorta, resulting in obstruction and dilatation of the vein.6,7
In the literature the condition is commonly called the
Nutcracker syndrome (NCS) or Nutcracker phenomenon
(NCP), and these terms are used interchangeably. However,
NCP refers to the anatomic and haemodynamic findings
whereas NCS is reserved for patients manifesting clinical
symptoms of the abnormality.7 LRV compression was first
reported by El-Sadr and Mina in 1950. The term NCS was
coined by the Belgian physician De Schepper (1972).8
Clinical presentation
Several clinical features are associated with NCS. Most common is haematuria which can vary from micro to macrohaematuria. This is caused by rupture of the thin walled
veins into the collecting systems due to renal vein hypertension.6 Haematuria may or may not be associated with
flank pain.
The next common symptom is pain. As a result of the
LRV compression and venous reflux, prominent collateral
veins may develop, causing pelvic congestion9 (figure 3).
This in turn can present as gonadal vein pain syndrome,
characterised by abdominal or flank pain with dyspareuria,
dysmenorrhoea and varicocele. Varicoceles almost always
occur on the left side.7,8
Mild to moderate proteinuria is also commonly seen.9
Radiographic findings
Intravenous urogram: Often normal, but in some cases
notching of the renal pelvis and ureters due to extrinsic compression from collateral vessels may be seen.7,9
Doppler ultrasound (DUS): Real-time DUS is recommended as the first diagnostic test for LRV entrapment,
even though agreed diagnostic criteria are not established.7,8
Measurements of the LRV AP diameter and peak velocities
using DUS aids in the diagnosis of LRV entrapment.
Average normal LRV diameter is 4-5mm with a transition
in calibre at the level of extrinsic compression. In LRV
entrapment, stenosis of the LRV occurs at the aortomesenteric portion with distension of the vein. This increases the
ratio of the renal hilum diameter to the aortomesenteric
diameter.8 DUS is also used to measure the pressure gradient. Normally the pressure gradient between LRV and inferior vena cava is less than 1mmHg. A gradient of 1mmHg
or more indicates LRV hypertension.10
Computed tomogram (CT): CT demonstrates narrowing
of the aortomesenteric angle and LRV compression between
the aorta and SMA (figure 4). Associated collaterals can
also be easily visualised.
Treatment
Treatment options depend on the severity of symptoms and
age of the patient.10 Conservative approach with observation
and routine urinalysis for at least two years is recommended
in patients with mild haematuria or those under 18 years
of age. It is thought that with formation of collaterals, LRV
hypertension improves and symptoms may resolve.9,10 Use of
ACE inhibitors is also advocated by some in reducing proteinuria associated with LRV entrapment.8
Surgery is only carried out when strongly advocated.6
Surgery may be considered when symptoms are severe or
persistent, and if they fail to resolve after 24 months of conservative treatment.8 Surgical options include LRV transposition, SMA transposition, renal vein-to-IVC shunt, variceal
ligation, gonadal vein bypass and even nephrectomy for persistent haematuria. Recently, endovascular surgery using
endovascular stent graft placement has been applied.7,8,10
Conclusion
SMA compression disorders are uncommon but well documented worldwide. These conditions may be encountered by
clinicians in a variety of specialities and therefore, despite
the low incidence, clinicians should be aware of these compression disorders. With an increasing number of people
with anorexia nervosa and bariatric surgery these disorders
may manifest themselves as atypical complications with
increasing frequency. The symptoms encountered in SMA
compression disorders are non specific and overlap with
other clinical conditions, making recognition and diagnosis
difficult. As a result, patients suffer for a considerable
amount of time before the condition is diagnosed and treatment started. In patients with sudden or severe weight loss
presenting with common symptoms of compression (postprandial epigastric pain, bloating, nausea and vomiting in
SMA syndrome; haematuria, pelvic pain and varicocele in
LRV entrapment) there should be a high suspicion of SMA
compression disorders.
Acknowledgments
Dr Dympna McAteer and Dr Jack Straiton.
References
1. Benjamin C, Bruce A. Superior mesenteric artery syndrome after Roux-enY gastric bypass. JSLS 2010;14(1):143-146.
2. Shetty A, Ranschaert E et al. Radiopaedia. http://radiopaedia.org/articles/superior-mesenteric-artery-syndrome
3. Sante C, Gianfranco G, Gianfranco B. Superior mesenteric artery syndrome – believe in it! Report of a case. Case Rep Surg 2012;2012:282646.
4. Efthimiou M, Kouritas V, Baloyiannis I, Zacharoulis D, Hatzitheofilou K.
Superior mesenteric artery syndrome. Case Rep Gastroenterol 2009;3(2):156161.
5. Truptesh H K, Stephen M, Leon K. Superior mesenteric artery syndrome.
Can J Gastroenterol 2011;25(11):599-600.
6. Jones J, D’Souza D et al. Nutcracker syndrome. http://radiopaedia.org/
articles/nutcracker-syndrome.
7. Andrew K, Thom W R. Nutcracker phenomenon and nutcracker syndrome.
Mayo Clin Proc 2010;85(6):552-559.
8. Yangyan He, Ziheng Wu, Shanwen Chen, Lu Tian, Donglin Li, Ming Li,
Wei Jin, Hongkun Zhang. Nutcracker syndrome – how well do we know
it? Urology 2014;83(1):12-17.
9. Takeyama P, Bhatt S, Dogra V. Nutcracker syndrome. Appl Radiol
2012;41(11):36a-36c.
10. Polgrig M, Topol M, Majos A. An unusual case of left venous renal entrapment syndrome: A new type of Nutcracker phenomemon. Surg Radiol Anat
2013;35:263-267.
stomach
second part
of duodenum
Figure 1A
Water soluble contrast meal shows a normal calibre
stomach, first and second parts of duodenum, however contrast fails to enter the third part.
superior mesenteric artery
stomach
duodenum
Figure 1B
This is the same patient’s CT abdomen examination
carried out two weeks prior to the water soluble
contrast meal. It shows a markedly distended and
fluid filled stomach and proximal duodenum. The
transition point is within the third part of the
duodenum.
Figure 2
Water soluble contrast study in a 69-year-old who
presented with weight loss and persistent vomiting
shows pooling of the contrast within the antrum
and duodenum, at the junction of second and third
parts. This raised a suspicion of SMA syndrome, but
a subsequent abdominal CT showed circumferential
constriction with wall thickening at the second part
of duodenum in keeping with a stenosing tumour
(white arrow).
SMA
abdominal aorta
left renal vein
Figure 4A
Compression of the LRV between the abdominal
aorta and SMA in a 42-year-old who presented with
weight loss. Note the dilated LRV.
Figure 3
Multiple varicosities in the left pelvis (white arrow)
and left flank (black arrow) in a patient with LRV
entrapment.
left renal vein
abdominal aorta
SMA
Figure 4B
Sagittal view showing narrowing of the aortomesenteric angle.

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