Median arcuate ligament syndrome
Median arcuate ligament syndrome (MALS), also known as celiac artery compression syndrome or Dunbar syndrome, was first described in 1963 by Harjola [1]. The median arcuate ligament is an arch-like fibrous band that unites the diaphragmatic crura on either side of the aortic hiatus at the level of the first lumbar vertebral body. The ligament usually passes superior to the origin of the celiac artery; however, in 10–24% of the subjects, the ligament may cross anterior to the proximal portion of the celiac artery and compress the celiac axis resulting in compromised blood flow [2]. It is commonly seen in young patients aged between 20 and 40 years with a slight female predilection. The affected individual presents with chronic postprandial abdominal pain, weight loss, and epigastric bruit.
Imaging findings
The typical findings of MALS on CT angiography include focal narrowing of the proximal celiac artery with a characteristic hooked appearance, more pronounced in end-expiration/inspiration. This appearance is better appreciated in the sagittal view which helps to distinguish MALS from atherosclerotic narrowing (Fig. 1). The other findings appreciated are post-stenotic dilatation in severe stenosis and collaterals vessels such as pancreaticoduodenal arcade from the superior mesenteric artery.
Management
There is no definitive consensus in the management of MALS. The definitive treatment for a clinical and radiologically proven case of MALS is a surgical or laparoscopic division of median arcuate ligament to restore normal blood flow in the celiac artery (Fig. 2) [3]. However, complex surgical procedures such as the vascular reconstruction of the celiac axis, aortoceliac bypass, and reimplantation of the celiac artery may be required in some patients [4].
Superior mesenteric artery syndrome
SMA syndrome also known as Wilkie’s syndrome was first described in 1927 as a rare cause of obstruction of the third part of the duodenum due to compression between the SMA and the aorta. The prevalence of SMA syndrome is around 0.13–0.3% with a female predilection and nearly two-thirds of affected individuals are between 10 and 39 years of age [5].
The SMA arises at the L1–2 level and courses anteriorly and inferiorly, forming an angle with the aorta known as the aorto-mesenteric angle (AMA). The third portion of the duodenum crosses between the aorta and the proximal SMA at approximately the L3 level. Normally, the third portion of the duodenum is surrounded by retroperitoneal fat, which provides a “cushion” for the duodenum between the anterior SMA and posterior aorta and helps maintain a wide aorto-mesenteric distance (AMD) and aorto-mesenteric angle (AMA). Various studies have reported the normal range of the AMD and AMA and to be 25° to 60° and 10–28 mm, respectively [6].
Symptoms include postprandial epigastric pain and fullness, nausea, vomiting, weight loss, and anorexia. The pain may classically be relieved by lying on prone or left lateral decubitus position [7].
Imaging findings
CT is best performed in the late angiographic phase for the simultaneous optimal depiction of the vascular anatomy and the bowel wall. In SMA syndrome, both the AMA and AMD are reduced with a value of 6° to 15° and 2 to 8 mm, respectively (Figs. 3 and 4) [6]. The proximal duodenum and stomach are dilated due to obstruction.
Management
The treatment is usually conservative and consists of fluid and electrolyte balance, small liquid meals, nasojejunal feeding to bypass the level of obstruction, and mobilization of the patient into left lateral decubitus or prone position [8]. Surgical options include duodenojejunostomy, gastrojejunostomy, or lysis of the ligament of Treitz with derotation of the bowel—Strong’s procedure [9].
Portal biliopathy
Portal biliopathy or portal ductopathy refers to the biliary obstruction that is associated with cavernous transformation of the portal vein due to portal vein thrombosis [10]. The patients are usually asymptomatic. Rare clinical presentations with jaundice, cholangitis, or choledocholithiasis could also be seen. Stricture formation is a well-known complication [11].
Imaging findings
CT clearly depicts the cavernous transformation of the portal vein, marked dilatation of the intra- and extrahepatic portions of the parabiliary and peribiliary plexuses, and gallbladder varices (Fig. 5) [12]. MDCT can show secondary biliary ductal dilatation caused by the portal collaterals thus excluding a cholangiocarcinoma or extrinsic compression by metastatic adenopathies as the cause of obstruction [13].
Management
Asymptomatic portal biliopathy does not require treatment. In a symptomatic case, the treatment ranges from endoscopic treatment which includes balloon catheter dilation, endoscopic papillotomy, and stent insertion. When endoscopic decompression fails, transjugular intrahepatic portosystemic shunt (TIPS) could be considered. Biliary intestinal bypass is the next treatment of choice, when TIPS fails to significantly reduce symptoms [14].
Nutcracker syndrome
The term “nutcracker phenomenon” refers to the entrapment of the left renal vein between the superior mesenteric artery and the abdominal aorta, leading to impaired venous outflow from the left kidney as well as the gonadal vein. When associated with clinical symptoms, this entity is termed as “nutcracker syndrome” [15]. The condition was first described as ‘left renal vein entrapment syndrome’ by Grant in 1937 and can occur in any age group with a slight female predominance [16]. Gender prevalence is, however, controversial [17].
The pubertal growth spurt can be attributed as a causative factor, as the increase in height can lead to narrowing of the angle between the superior mesenteric artery and aorta [18]. When this angle becomes lesser than 35°, as evident on a CT, it supports the diagnosis of anterior nutcracker syndrome. The much less common posterior nutcracker syndrome occurs due to compression of an abnormal retro-aortic left renal vein between the abdominal aorta and the vertebral body.
These patients can have a highly variable presentation—from being asymptomatic to severe pelvic congestion. The commonest complaint reported by far is microscopic/macroscopic hematuria, which is a result of increased venous pressure in the collecting system. The other symptoms include pelvic pain, flank pain, varicocele, ovarian vein syndrome [19].
Imaging findings
Visualization of the compressed left renal vein along with distended gonadal veins and pelvic congestion guide to the diagnosis (Figs. 6 and 7). The “beak sign” on CT due to the compressed part of the left renal vein and the left renal vein diameter ratio more than or equal to 4.9 (between the hilar and aorto-mesenteric parts) are of high diagnostic value. However, the gold standard investigations include phlebography and intravascular ultrasound [20].
Management
Patients with mild symptoms are managed conservatively—advised weight gain, ACE inhibitors alacepril and aspirin. In non-responsive cases and patients with persisting symptoms, surgical management has been opted, the first line being renal vein transposition along with hybrid repair [21].
Pelvi-ureteric junction obstruction due to crossing of vessels
Obstruction at the junction of the renal pelvis and the proximal ureter, commonly seen as hydronephrosis, can occur due to intrinsic or extrinsic causes. Intrinsic causes being more common in infants and young children, the crossing of vessels is the most common extrinsic cause for PUJ obstruction in elder children and adolescents. As evident from literature, the reported incidence of this condition in early childhood is between 11 and 18.5% and that in late childhood is between 49 and 58% [22]. The common presentations can be flank pain, nausea, vomiting, and flank/abdominal mass due to an enlarged kidney.
Imaging features
The most common vessel attributed to the compression is an aberrant branch of a renal vessel that crosses the pelviureteric junction anteriorly. As a result, there will be moderate to marked hydronephrosis. MDCT in the late-arterial phase allows depiction of both arteries and veins. MDCT with MPR and 3D VR provides an excellent depiction of crossing vessels (Figs. 8 and 9), with a reported positive predictive value of 100% [23]. When available, a functional magnetic resonance urography (fMRU) is of higher value in providing both anatomical—crossing aberrant vessel and functional information [24].
Management
Anderson-Hyne’s dismembered pyeloplasty is the most preferred surgical procedure, which involves excising a small segment of the ureter and transposing the aberrant vessel behind the PUJ. The other options include the Hellstrom technique and Chapman technique [25].
Retrocaval ureter
Retrocaval ureter also referred to as circumcaval ureter or pre-ureteral vena cava is a rare congenital anomaly with the right ureter passing posterior to the inferior vena cava, resulting in hydroureteronephrosis [26]. It is considered as a developmental anomaly of the IVC rather than that of the ureter. The onset of symptoms is usually in the fourth decade and males predominate by a ratio of 3:1. The usual clinical manifestations are right flank pain, hematuria, recurrent urinary infections, and recurrent pyelonephritis [27]. Long-standing HUN can lead to cortical scarring and progressive renal failure.
Imaging features
MDCT and IVU are the two commonest imaging investigations done to evaluate the retrocaval ureter. However, MDCT is preferred, with or without contrast, as it can demonstrate accurately other causes of hydroureteronephrosis. In MDCT, the proximal ureter can be distinctly seen to course posterior to the IVC (Fig. 10) and emerge to the right of the aorta, coming to lie anterior to the right iliac vessels. Evidence of moderate to marked right HUN above the segment abutting the IVC can distinctly be seen using the multiplanar reformats (Fig. 11). Retrocaval ureters are classified into two clinical types: type 1 (commonest, moderate to severe HUN) and type 2 (less severe form) [28].
Management
Treatment options include observation for those who are asymptomatic, reconstructive surgery (Fig. 12) for those with hydronephrosis or nephrectomy if there is cortical atrophy. During surgery, the retrocaval segment is often resected as it remains aperistaltic [27].
May-Thurner syndrome
May-Thurner syndrome (MTS) (also called iliac vein compression syndrome) is a condition that arises as a result of compression of the left common iliac vein by the right common iliac artery. It is also one of the reasons postulated for the increased incidence of deep vein thrombosis in the left lower limb [29]. MTS is particularly prevalent in younger and middle-aged women (mean age = 42 years) [30]. MTS can be suspected in a patient who has unilateral left lower limb swelling and pain without preceding trauma or evidence of infection. Venous ulcerations, varicose veins, and recurrent DVT are the commonest complications of MTS.
Imaging features
Catheter venography was considered the gold standard in diagnosing this condition; however, cross-sectional imaging is currently being preferred as one can obtain additional extra-vascular information. A visualization of greater than 50% stenosis in the luminal diameter of the vein is considered an adequate indicator of LCIV compression related to MTS (Fig. 13) [31]. Complications include thrombosis of the left iliac and proximal femoral veins. Also, CT venography also demonstrates the presence of pelvic collaterals and the presence of intraluminal iliac spurs.
Management
Conservative and invasive/surgical treatments are now being considered outdated. The use of endovascular techniques in the treatment of MTS patients is considered successful and carries lesser risk than invasive surgical treatments. Angioplasty has been found to be associated with low long-term patency rates.
