¹Consultant fetal medicine specialist, Davangere scan centre, Davangere, Karnataka, India.
²Department of Radiology, SSIMS & RC, Davangere, Karnataka, India.

*Corresponding author:Suhasini Vittal Rao, Consultant fetal medicine specialist, Davangere Scan Centre, Davangere, Karnataka, India, E-mail: drsuhasini2010@gmail.com

Copyright: © 2025 Akhil. M. Kulkarni, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Article Information:Submission: 16/06/2025; Accepted: 05/08/2025; Published: 06/08/2025

Abdominal vascular compression syndromes constitute a collection of infrequent but clinically important conditions caused by external compression of abdominal vessels or by vascular structures exerting pressure on hollow organs. Key syndromes include Median Arcuate Ligament Syndrome (MALS), Nutcracker Syndrome (NCS), Superior Mesenteric Artery (SMA) syndrome, SMA-like syndrome, Retrocaval Ureter & Portal Biliopathy. These conditions are often underrecognized, as they can present with vague abdominal or urinary symptoms, while many affected individuals remain symptom-free. This review focuses on essential CT imaging findings and clinical correlations that assist in diagnosing symptomatic patients.

Keywords:Vascular Compression Syndromes; MALS; Nutcracker Syndrome; SMA Syndrome; SMA Like Syndrome; Retrocaval Ureter; Portal Biliopathy

Abdominal vascular structures may be subjected to compression by surrounding anatomical elements, or conversely, may compress adjacent hollow organs. The resulting symptoms tend to be nonspecific, leading frequently to diagnostic delays or misdiagnoses. Although these syndromes have been recognized for several decades, they remain insufficiently understood. Untreated cases risk significant complications. Because these conditions span multiple specialties, they present substantial diagnostic challenges, underscoring the need for heightened clinical awareness and recognition[1].

Anatomical variants or morphological changes predisposing to vascular compression are sometimes incidentally detected in asymptomatic patients undergoing imaging for unrelated reasons. Therefore, clinical correlation is critical to avoid overdiagnosis, and imaging findings alone should not be the basis for diagnosis[1].

Non-invasive imaging techniques like ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) are useful in identifying vascular compression syndromes affecting the abdomen and pelvis. Of these, contrast-enhanced CT is typically the modality of choice when clinical suspicion arises, owing to its ability to clearly depict vascular structures and their anatomical relationships with surrounding tissues[1,2].

This review outlines the underlying pathophysiology and clinical manifestations of various abdominal vascular compression syndromes, emphasizing key CT imaging findings that assist in establishing a precise diagnosis.

Median Arcuate Ligament Syndrome (MALS), also referred to as Dunbar syndrome or celiac artery compression syndrome, was first described by Harjola in 1963 [1,3]. This condition arises from a fibrous arch known as the median arcuate ligament, which connects the diaphragmatic crura at the T12–L1 vertebral level and usually courses above the origin of the celiac artery [4]

In 10–24% of asymptomatic individuals, this ligament crosses anteriorly over the proximal celiac artery [5]. While many such compressions are clinically silent, a subset results in sufficient arterial stenosis to impede blood flow and provoke symptoms [4].

This syndrome most often affects individuals between 20 and 40 years of age, typically women with a lean body build [6]. The main symptoms are chronic epigastric discomfort after meals, nausea, and weight loss-signs of intermittent compression of the celiac artery [1]. Nonetheless, nearly 85% of those with this anatomical pattern do not exhibit symptoms, and findings are often discovered incidentally during CT imaging for unrelated issues [1,7,8] [Figure 2].

Multidetector CT (MDCT), due to its high spatial resolution, enables clear visualization of the median arcuate ligament—thickness beyond 4 mm is considered abnormal [8] [Figure 1B]. Since axial images may not reveal the full extent of compression, sagittal reconstructions are essential to assess both the ligament and celiac artery origin. A distinctive hooked or “J-shaped” narrowing at the origin of the celiac artery (Figure1A) serves as a key imaging sign distinguishing MALS from atherosclerotic changes. The compression is often persistent, even during inspiration. Additional findings may include post-stenotic dilatation and development of collateral vessels such as the pancreaticoduodenal arcade from the superior mesenteric artery [9].

Symptomatic cases of MALS are usually treated by surgically releasing the median arcuate ligament, sometimes accompanied by celiac ganglion removal or vascular bypass procedures. These interventions generally lead to long-term relief from symptoms [10].

Nutcracker Syndrome refers to the entrapment of the left renal vein (LRV), most commonly between the superior mesenteric artery and the aorta, known as the “anterior nutcracker” variant. Less frequently, compression occurs between the aorta and the vertebral column when the LRV follows a retro-aortic or circum-aortic course—termed the “posterior nutcracker” [1].

It primarily affects otherwise healthy, thin women in their third and fourth decade of life. The anterior variant is more common, whereas the posterior variant (Figure 5) is rare and its clinical relevance remains unclear [10].

Nutcracker syndrome often presents in young to middle aged adults, with women being more frequently affected. Because diagnostic criteria are not well standardized, diagnosis is frequently missed or delayed. Symptoms result from increased venous pressure in the LRV and may be exacerbated by physical activity. Manifestations range from microscopic haematuria to visible haematuria leading

to anaemia, orthostatic proteinuria, and pain in the left flank due to passage of clots. Reflux into the gonadal vein may lead to left-sided varicocele in males and varicose veins in the pelvis or vulva in females [1].

On axial CT, the “beak sign” is seen as abrupt narrowing of the LRV at the point where it passes between the SMA and aorta, forming an acute angle [Figure 3A] [11,12]. Sagittal reconstructions help assess the aortomesenteric angle (AMA), which normally ranges from 38°– 56°; angles under 35° are suggestive of the syndrome [13,14]. Affected individuals also demonstrate a reduced aortomesenteric distance (AMD), typically narrowed from the normal 10–28 mm to 2–8 mm [1,15] [Figure 3B], [Figure 3C]. A pre- to post-compression LRV diameter ratio exceeding 2.25 has been shown to yield 91% sensitivity and specificity for diagnosis [16]. CT may also reveal dilated gonadal veins and pelvic varicosities, although it cannot assess blood flow velocity or direction [11] [Figure 4A], [Figure 4B].

Management of mild or asymptomatic cases is conservative, focusing on observation. More severe cases require intervention to relieve venous obstruction and hypertension. Surgical options include LRV transposition, external venous stenting, bypass procedures, renal auto-transplantation, or nephrectomy [1].

Superior Mesenteric Artery (SMA) syndrome, first documented by Rokitansky in 1842, results from compression of the third part of the duodenum between the SMA and the aorta, leading to duodenal obstruction [1,13].
A hallmark diagnostic feature of SMA syndrome is the narrowing of the angle between the SMA and the aorta, which normally measures between 38° and 65°. In affected individuals, this angle is significantly reduced. Likewise, the aortomesenteric distance at the level where the duodenum crosses is typically reduced from its normal range of 10–28 mm [13,17,18].

Patients typically show signs of upper gastrointestinal obstruction such as abdominal pain following meals, nausea, vomiting, and unintended weight loss—symptoms linked to delayed gastric emptying. Other potential causes must be excluded, and diagnosis relies on identifying the anatomical abnormality using imaging studies [19].

On CT, the AMA is decreased (6°–22°) and the AMD reduced (2–8 mm) [Figure 7A], [Figure 7B]. Characteristic findings include gastric and proximal duodenal dilation [Figure 6A], [Figure 6B] with abrupt narrowing at the compression site. CT helps localize the obstruction and exclude other causes. Importantly, decreased AMA and AMD without symptoms do not suffice for diagnosis [20,21,22].

The first-line approach involves conservative therapy, including fluid resuscitation, electrolyte correction, and nutritional support often through nasojejunal feeding. Patients are advised to consume small, frequent meals and may benefit from positional adjustments like lying prone or in the left lateral decubitus position. If nonsurgical methods fail, operative options such as duodenojejunostomy, gastrojejunostomy, or division of the ligament of Treitz with bowel derotation (Strong’s procedure) may be considered [1,3,21].

SMA-like syndrome is a newly described condition that mimics the presentation of SMA syndrome but results from compression of the duodenum by vascular structures other than the SMA and aorta. These may include mesenteric or retroperitoneal arteries and veins [23].

This syndrome clinically mimics SMA syndrome and carries similar risks if untreated [23].

On imaging, compression of the third portion of the duodenum may be observed between multiple anterior (mesenteric) and posterior vascular structures. Anatomical variations in the suspensory ligament of the duodenum may contribute to this phenomenon. CT scans may reveal either duodenal compression leading to obstruction [Figure 8A], [Figure 8B] or isolated vascular compression without evidence

of obstruction (Figure 9A) (Figure 9B). CT imaging is particularly helpful in identifying the precise location of the duodenum and ruling out alternative causes of obstruction [21,24].

Management begins conservatively, focusing on nutritional support and hyperalimentation to restore retroperitoneal fat.

Surgery (gastrojejunostomy or duodenojejunostomy) is considered if symptoms persist [23,25].

The ureter may rarely follow a retrovascular path, such as retroiliac or retrocaval routes, which can lead to compression [26]. Retrocaval ureter is a congenital anomaly caused by abnormal embryological development of the inferior vena cava (IVC) [27]. Under typical development, the intrarenal segment of the IVC originates from the right supracardinal vein, which lies dorsal to the ureter, maintaining the ureter’s lateral position. However, in retrocaval ureter, the ventral subcardinal vein fails to regress, causing the ureter to pass posterior to and encircle the IVC during embryogenesis. This aberrant course results in its compression between the IVC and vertebral column, eventually leading to progressive hydronephrosis [28].

Clinically, patients often report right flank pain, although many remain asymptomatic [28].

Imaging distinguishes two types:
Type 1: The ureter crosses behind the IVC near L3 with a characteristic “S” or “fish-hook” deformity and hydronephrosis in over 50% of casesalso known as the low loop retrocaval ureter [Figure 10] [Figure 11]
Type 2: The retrocaval segment crosses at the renal pelvis with a sickle-shaped curve and mild hydronephrosis, which is less common [29].

Management is tailored based on symptom intensity and renal function status. For mild, asymptomatic cases, watchful waiting may be appropriate. In symptomatic individuals, surgical correction through ureteroureteral reanastomosis anterior to the IVC—along with removal of the retrocaval segment—is commonly performed and typically produces favorable results [30].

Portal biliopathy refers to a collection of abnormalities affecting the bile ducts and gallbladder, typically seen in individuals with extrahepatic portal vein obstruction or portal hypertension [31].
The condition arises primarily through two mechanisms: first, by direct mechanical pressure on the biliary tract from a portal cavernoma [Figure 12] and second, through peribiliary fibrosis triggered by inflammation or ischemia following thrombosis in the

small venous channels within the bile duct wall [4,9,32]. A portal cavernoma is a network of dilated collateral veins surrounding the common bile duct, resulting from cavernous transformation. It is composed of paracholedochal veins (also known as the plexus of Petren) and epicholedochal veins (plexus of Saint), both of which run along the bile duct wall [33].

There are three main types of portal biliopathy: varicoid, fibrotic, and mixed. The varicoid form is due to compression and distortion of the bile duct by large external collaterals (paracholedochal veins), while the fibrotic form is associated with thickening and narrowing of the bile duct caused by intramural compression from smaller collateral veins (epicholedochal veins) [4].

Around 70–100% of individuals who exhibit radiologic features of portal biliopathy do not initially experience symptoms [32]. Only a small subset presents with clinical signs such as prolonged cholestasis or jaundice [4,9,31].

Contrast-enhanced CT is typically performed to rule out alternative causes of biliary dilation, especially since portal biliopathy can resemble malignant distal bile duct strictures, such as those from pancreatic cancer or cholangiocarcinoma [34]. The most characteristic radiologic sign, apart from detecting a portal cavernoma, is the abrupt bending or “kinking” of the common bile duct, usually due to external pressure from enlarged paracholedochal veins [35].

While the majority of cases are asymptomatic and do not need active intervention, patients who develop symptoms—especially from biliary strictures—can be treated effectively using endoscopic approaches such as balloon dilatation, stenting, or performing a sphincterotomy [36].

Although often underrecognized, abdominal vascular syndromes constitute an important and frequently overlooked clinical entity. Their presentations can vary widely—from subtle, nonspecific symptoms to severe and obvious clinical signs—necessitating

increased awareness and a collaborative, multidisciplinary approach to diagnosis and management. Advances in imaging modalities, particularly high-resolution CT and magnetic resonance angiography (MRA), have improved early detection, thereby facilitating timely intervention and enhancing patient outcomes. Despite these technological improvements, abdominal vascular syndromes are still commonly misdiagnosed or diagnosed late, due to their complex clinical manifestations and overlap with more prevalent abdominal diseases. Clinicians and radiologists alike should consider these entities in the differential diagnosis when assessing patients with unexplained abdominal pain, weight loss, or similar symptoms. A thorough grasp of the underlying vascular anatomy, associated pathophysiological mechanisms, and key imaging findings is essential for ensuring effective patient care.

Disclosure: The authors have no conflicts of interest to disclose. None of the authors received outside funding for the production of this original manuscript and no part of this article has been previously published elsewhere.