Teaching Case

The splanchnic collateral circulation can be highly complex and variable, and it's understanding can provide critical information prior to surgical intervention. We present a case of multiple visceral arterial stenoses and splanchnic collaterals revealed by CT angiography. However, detailed anatomical description and therapy required elucidation by conventional angiographic techniques.

A 22 year old male presented with uncontrolled hypertension, bilateral renal bruits and left ventricular hypertrophy. A CT renal angiogram showed bilateral severe renal artery stenosis with a proximal right renal artery aneurysm (figure 1). Fibromuscular dysplasia was considered and conventional angiography confirmed a tight right renal ostial stenosis with a post stenotic aneurysm (figure 2). There was no beading in the renal arteries, but there was a tight stenosis at the coeliac axis origin and a critical stenosis of the SMA (figure 3), plus an extensive collateral circulation (figure 4). Doppler ultrasound revealed coeliac artery compression by the arcuate ligament. Right renal artery stenting was attempted, but the acute ostial angle made this impossible. Therefore, the aneurysm was ligated with insertion of an aorto-renal bypass graft. The coeliac artery was decompressed by dissection of the median arcuate ligament. Post-operative DTPA scintigraphy showed 93% right renal function and 7% left renal function. The aortic root and arch were normal on angiography, and histology of the aneurysm showed no evidence of arteritis nor fibromuscular hyperplasia. Laboratory screening showed no suggestion of thrombophilia nor vasculitis. Lastly, a left renal artery stent was inserted which strictured initially, therefore it was expanded using balloon dilatation (figure 5). Despite previous decompression, the coeliac axis was found to be stenotic, and was also stented successfully (figure 6). Subsequently a brain MR angiogram showed no evidence of arterial stenosis nor aneurysm. Seven months after presentation, the patient remained well.

The aetiology of arterial occlusion or stenosis includes: thromboembolic disease, atherosclerosis, aneurysm, congenital vasculopathy (e.g. coarctation), or vasculitis (1). The second most common cause of renal artery stenosis, following atherosclerosis, is fibromuscular dysplasia (FMD) (2). This is a hyperplastic disorder of medium to small sized arteries with a “string of beads” appearance on conventional angiography. FMD usually occurs in young adults, particularly females. It was thought to be the initial diagnosis, but none of the typical appearances were present, and histology showed no evidence of FMD. However, there are rarer types of FMD, presenting as smooth segmental stenoses, which do not respond as well to balloon dilatation (2). Vasculitis and atherosclerosis were ruled out, and the aortic arch was normal. Therefore congenital vasculopathy was the most likely aetiology, or possibly one of the FMD variants. This is supported by a well established collateral circulation, which would be present in a primary disorder. The collaterals found in this case included the gastroduodenal and pancreaticoduodenal arteries, two collaterals from the splenic artery to the SMA and IMA, and a large marginal artery of Drummond (figure 4). The marginal artery of Drummond is a well known collateral, paralleling the wall of the large intestine (3, 4). It is not always continuous, and is absent at Griffith’s point (figure 7) in 43% of people (5). If this link is absent, and the IMA is removed at surgery, then infarction of the descending colon can occur. There is also another anastomosis between the SMA and IMA, called the Arc of Riolan (3). It is centrally located, joining the middle and left colic arteries in the distal third of the transverse mesocolon (6). There are also variants called the central anastomotic artery and the meandering mesenteric artery (7). The primary anastomotic links between the coeliac artery and SMA are the gastroduodenal and pancreaticoduodenal arteries, and the dorsal pancreatic artery (8, 9). There are also many uncommon variants (8), such as the Arc of Bühler, which represents a persistence of the embryonic ventral segmental arteries (9). Collaterals from the splenic artery to the SMA and IMA have not previously been described in the literature. In this case, conventional angiography proved the most informative modality due to demonstration of blood flow, and due to improved views using multiple projections. The direction of flow was shown by contrast passing from the IMA down the marginal artery of Drummond to the SMA, and subsequent filling of the coeliac axis via the pancreaticoduodenal and gastroduodenal arteries (figure 4). Multi-detector CT has also demonstrated a clear view of the collaterals described. It requires less contrast material, is less invasive, and is quicker. However, it does not give information on flow direction (10), it is not suitable for intervention, and volume averaging leads to underestimation of stenosis severity (11). MR angiography is already being used in the peripheral circulation (12) , providing similar dynamic images to conventional angiography. It’s application to the visceral circulation is yet to be well proven (13).