DOI: 10.1148/rg.255055001
RadioGraphics 2005;25:1177-1182
© RSNA, 2005
Median Arcuate Ligament Syndrome: Evaluation with CT Angiography1
Karen M. Horton, MD,
Mark A. Talamini, MD and
Elliot K. Fishman, MD
1 From the Russell H. Morgan Department of Radiology and Radiological Sciences (K.M.H., E.K.F.) and Department of Surgery (M.A.T.), Johns Hopkins Medical Institutions, 601 N Caroline St, JHOC 3253, Baltimore, MD 21287. Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received January 7, 2005; revision requested January 26 and received February 22; accepted February 25. All authors have no financial relationships to disclose.
Address correspondence to K.M.H. (e-mail: kmhorton{at}jhmi.edu).
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Abstract
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The median arcuate ligament is a fibrous arch that unites the diaphragmatic crura on either side of the aortic hiatus. The ligament usually passes superior to the origin of the celiac axis. However, in some people, the ligament inserts low and thus crosses the proximal portion of the celiac axis, causing compression and sometimes resulting in abdominal pain. The diagnosis of clinically significant celiac axis compression, referred to as median arcuate ligament syndrome, is traditionally made with conventional angiography; however, the condition can now be diagnosed with three-dimensional computed tomographic (CT) angiography. In patients with median arcuate ligament syndrome, CT angiograms demonstrate a characteristic focal narrowing in the proximal celiac axis. The focal narrowing has a characteristic hooked appearance, which can help distinguish this condition from other causes of celiac artery narrowing, such as atherosclerotic disease. Once the disorder has been diagnosed, surgery can be performed to relieve the compression. In some patients, the ligamentous constriction of the celiac axis causes vascular damage, which may require vascular reconstruction. CT angiography can play a role in the diagnosis of median arcuate ligament syndrome by demonstrating the characteristic focal narrowing of the celiac artery in patients presenting with the appropriate clinical symptoms.
© RSNA, 2005
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Introduction
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The median arcuate ligament is a fibrous arch that unites the diaphragmatic crura on either side of the aortic hiatus. The ligament usually passes superior to the origin of the celiac axis. In 10%–24% of people, however, the ligament may cross anterior to the artery; in some of these individuals, the ligament may actually compress the celiac axis, compromising blood flow and causing symptoms (1). Although the diagnosis of celiac artery compression is traditionally made by using conventional angiography, the use of thin-section multidetector computed tomography (CT) and of three-dimensional (3D) imaging techniques has greatly improved the ability to obtain detailed images of the mesenteric vessels noninvasively. Compression of the celiac axis by the median arcuate ligament produces characteristic findings visible at CT angiography. This article reviews the clinical and radiologic findings in median arcuate ligament syndrome (also referred to as celiac artery compression syndrome). The potential pitfalls in the diagnosis are also discussed.
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Anatomy
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The diaphragmatic crura arise from the anterior surface of the L1–L4 vertebral bodies on the right and the first two or three lumbar vertebral bodies on the left. In addition, the crura arise from the intervertebral disks and anterior longitudinal ligament (2). The crura pass superior and anterior to surround the aortic opening and to join the central tendon of the diaphragm.
The median arcuate ligament is a fibrous arch that unites the diaphragmatic crura on either side of the aortic hiatus. The ligament usually passes over the aorta at the level of the first lumbar vertebral body, superior to the origin of the celiac axis (Fig 1). However, in 10%–24% of people, the ligament may be low and therefore cross over the proximal portion of the celiac axis, causing a characteristic indentation (Fig 2). In a small subset of these patients, the median arcuate ligament can compress the proximal celiac axis enough to be hemodynamically significant and cause symptoms.
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Figure 1. Drawing from the sagittal perspective demonstrates the typical anatomy of the median arcuate ligament as it crosses anterior to the aorta and superior to the origin of the celiac axis.
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Median Arcuate Ligament Syndrome
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The median arcuate ligament syndrome (or celiac artery compression syndrome) was first described in 1963 by Harjola (3). The definition of the syndrome relies on a combination of both clinical and radiographic features. It typically occurs in young patients (20–40 years of age) and is more common in thin women, who may present with epigastric pain and weight loss (4). The abdominal pain may be associated with eating, but not always (5). At physical examination, an abdominal bruit that varies with respiration may be audible in the midepigastric region. Symptoms are thought to arise from the compression of the celiac axis, resulting in a compromise in blood flow.
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Radiologic Diagnosis
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Conventional Angiography
In the past, median arcuate ligament syndrome was detected during conventional angiography. When the median arcuate ligament passes anterior to the celiac axis, a characteristic superior indentation is noted along the proximal celiac axis, usually about 5 mm from its origin at the abdominal aorta. Any compression caused by this indentation typically is less apparent during inspiration, when the celiac axis assumes a more caudal orientation as the lungs expand. During expiration, compression of the celiac axis typically increases (Figs 3, 4).
Isolated compression of the celiac axis during expiration may not be clinically significant. It is important to realize that up to 13%–50% of healthy patients may exhibit the angiographic feature of compression to a variable degree, especially during expiration (6,7). The vast majority of these patients have no symptoms. Therefore, the radiographic finding of celiac axis compression alone may not be significant, unless it is correlated with clinical symptoms.
Severe compression occurs in approximately 1% of patients and persists during inspiration (7,8). Severe stenosis will result in poststenotic dilatation, and in some cases, the celiac axis will be fed by the superior mesenteric artery via the pancreaticoduodenal arcade.
CT Angiography
Although the diagnosis of median arcuate ligament syndrome is traditionally made by using catheter angiography, the condition has been observed with Doppler ultrasound and CT (4,9). New thin-section multidetector CT scanners, along with 3D software, have greatly improved the ability to obtain high-resolution images of the aorta and its branches. The mesenteric vessels are very well visualized, and in many cases, CT angiographic examination will obviate conventional angiography (Fig 5).
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Figure 5a. (a) Sagittal 3D volume-rendered image of a normal aorta demonstrates the normal appearance of the celiac axis and superior mesenteric artery. (b) Coronal oblique 3D volume-rendered image shows the normal anatomy of the celiac axis and superior mesenteric artery.
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Figure 5b. (a) Sagittal 3D volume-rendered image of a normal aorta demonstrates the normal appearance of the celiac axis and superior mesenteric artery. (b) Coronal oblique 3D volume-rendered image shows the normal anatomy of the celiac axis and superior mesenteric artery.
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For a complete CT angiographic evaluation in patients with suspected median arcuate ligament syndrome, 3D imaging is necessary. The findings characteristic of the syndrome may not be appreciated on axial images alone. Typically, the sagittal plane is optimal for visualizing the proximal portion of the celiac axis, and in many cases, 3D imaging also allows identification of the actual median arcuate ligament. In patients with median arcuate ligament syndrome, CT angiograms demonstrate a characteristic focal narrowing in the proximal celiac axis (Figs 6–8). The focal narrowing has a characteristic hooked appearance, which can help distinguish this condition from other causes of celiac artery narrowing, such as atherosclerotic disease (Figs 9, 10). CT is typically performed during inspiration; therefore, if the focal narrowing is observed during inspiratory CT, it may be clinically significant, since the transient compression seen only during expiration in some patients would not be manifested at inspiratory CT. Also, associated poststenotic dilatation or collateral vessels may suggest actual pathologic conditions and warrant clinical correlation.
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Figure 6a. (a) Sagittal 3D volume-rendered image shows normal anatomy of the celiac axis and superior mesenteric artery. In this case, there is a slight impression (arrow) in the proximal celiac axis, which may be related to a nonobstructing median arcuate ligament. (b) As evident from this axial oblique 3D volume-rendered image of the same patient, the median arcuate ligament and the indentation it causes on the proximal celiac axis can be difficult to detect in the axial plane.
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Figure 6b. (a) Sagittal 3D volume-rendered image shows normal anatomy of the celiac axis and superior mesenteric artery. In this case, there is a slight impression (arrow) in the proximal celiac axis, which may be related to a nonobstructing median arcuate ligament. (b) As evident from this axial oblique 3D volume-rendered image of the same patient, the median arcuate ligament and the indentation it causes on the proximal celiac axis can be difficult to detect in the axial plane.
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Figure 7a. (a) Sagittal 3D image of a patient with epigastric pain demonstrates acute angulation and narrowing of the proximal celiac axis. There is minimal poststenotic dilatation, which creates a "hooked" appearance (arrow) that is characteristic of median arcuate ligament syndrome. (b) Coronal oblique CT angiogram of the same patient reveals a prominent collateral vessel and dilatation of the gastroduodenal artery (arrowhead) that is supplying the common hepatic artery (short arrow) off the superior mesenteric artery (long arrow). This configuration is a common collateral pathway seen in patients with celiac axis stenosis. The patient underwent surgical decompression and experienced relief of symptoms.
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Figure 7b. (a) Sagittal 3D image of a patient with epigastric pain demonstrates acute angulation and narrowing of the proximal celiac axis. There is minimal poststenotic dilatation, which creates a "hooked" appearance (arrow) that is characteristic of median arcuate ligament syndrome. (b) Coronal oblique CT angiogram of the same patient reveals a prominent collateral vessel and dilatation of the gastroduodenal artery (arrowhead) that is supplying the common hepatic artery (short arrow) off the superior mesenteric artery (long arrow). This configuration is a common collateral pathway seen in patients with celiac axis stenosis. The patient underwent surgical decompression and experienced relief of symptoms.
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Figure 8a. (a) Sagittal volume-rendered CT angiogram of a patient with abdominal pain demonstrates characteristic kinking of the proximal celiac axis, creating a hooked appearance (arrow). (b) Coronal maximum intensity projection CT angiogram shows the prominent gastroduodenal artery that feeds the common hepatic artery off the superior mesenteric artery.
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Figure 8b. (a) Sagittal volume-rendered CT angiogram of a patient with abdominal pain demonstrates characteristic kinking of the proximal celiac axis, creating a hooked appearance (arrow). (b) Coronal maximum intensity projection CT angiogram shows the prominent gastroduodenal artery that feeds the common hepatic artery off the superior mesenteric artery.
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Figure 9. Sagittal 3D volume-rendered image of a patient with abdominal pain demonstrates a focal narrowing of the proximal celiac axis caused by atherosclerotic disease. This appearance is distinct from the hooked appearance seen in median arcuate ligament syndrome.
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Figure 10. Sagittal maximum intensity projection image of a patient with recurrent abdominal pain reveals focal calcified plaque that causes narrowing of the proximal celiac axis. There is minimal poststenotic dilatation.
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The multiplanar capabilities of 3D imaging are also valuable in identifying the collateral vessels, which develop as a result of celiac axis compression. This information can help determine the hemodynamic significance of the narrowing and is important for surgical planning.
In the imaging protocol for CT angiography, intravenously administered contrast material is necessary to image the mesenteric vessels. We use 120 mL of nonionic contrast agent injected at a rate of 3 mL/sec. Scans are obtained during both the arterial (25 seconds after injection) and venous (50 seconds after injection) phases to ensure opacification of the mesenteric arteries and veins. On our multidetector CT scanner (Siemens Sensation 16; Siemens Medical Solutions, Malvern, PA), we use the 16 x 0.75-mm collimator setting to obtain 0.75-mm-thick sections reconstructed every 0.5 mm for 3D imaging. For hard-copy review, 3-mm-thick sections are adequate.
All the data are then transferred to our 3D workstation (Leonardo workstation; Siemens Medical Solutions, Malvern, Pa) for volume rendering. Use of the 0.75-mm collimators creates isotropic data sets, which allow production of excellent quality 3D images of the aorta and its branches. All images are reviewed by using InSpace software (Siemens Medical Solutions), which enables multiplanar reconstructions as well as interactive 3D volume rendering. The brightness, opacity, window width, and window level can be adjusted in real time to optimize visualization of the mesenteric vessel. We usually use a combination of volume-rendered and maximum intensity projection images. Review and reconstruction of the 3D images can usually be completed in approximately 5 minutes.
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Treatment
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The surgical management of median arcuate ligament syndrome is controversial (10). Many more patients have the anatomic abnormality of low insertion of the median arcuate ligament than actually have symptoms caused by the abnormality. Surgical treatment is more likely to relieve symptoms in patients 40–60 years of age with postprandial pain, greater than 20-lb weight loss, and poststenotic dilatation and collateral vessels (11). In the rare patients who indeed have such symptoms, some will experience relief when the ligament is divided surgically, a task that can now be accomplished laparoscopically (12,13). In others, the ligamentous constriction of the celiac axis causes vascular damage, which may require vascular reconstruction (14). Because surgical ligation of the constricting ligamentous band has been performed with only variable success, many surgeons no longer accept the median arcuate ligament syndrome as a true clinical entity (6,15).
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Conclusions
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Median arcuate ligament syndrome is a controversial entity. It is clear that the abnormally low insertion of the median arcuate ligament can be found in normal asymptomatic people. In a small subset of patients, however, the compression of the celiac axis can cause symptoms that may be relieved after surgical decompression. CT angiography can play a role in the diagnosis of this condition by demonstrating the characteristic focal narrowing of the celiac artery in patients presenting with the appropriate clinical symptoms.
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Footnotes
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Abbreviations: 3D = three dimensional
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References
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Abstract
Introduction
