Compression of the left renal vein by the duodenum
I describe here for the first time in medical research a functionally relevant compression of the left renal vein by the food filled duodenum which causes substantial post-prandial pain in this patient which has been so far undiagnosed.
Not rarely patients complain about increasing abdominal pain shortly after the ingestion of food. Usually, the stomach is suspected to be the cause of the pain.
I present here for the first time an unusual explanation for such a symptomatology: The compression of the left renal vein by the filling duodenum due to an oblique passage of the duodenum in front of the left renal vein.
In most individuals the duodenum crosses cranially (above) or caudally (below) the left renal vein within the angle consisting of the superior mesenteric artery (SMA) and the aorta. Thus, usually the filling duodenum does not interfere with the left renal vein.
The case I describe here for the first time was different. The patient complained about increasing upper abdominal pain about 5 minutes after the beginning of a meal. The pain became so severe that the patient could not eat sufficiently and lost 13 kg within a few months. The pain was located in the upper midabdomen and the left flank as well as in the left hypochondrial area (below the left lower margin of the rib cage) and was most severe while walking around standing after a meal.
With functional ultrasound it could be demonstrated that the enlarging horizontal portion of the duodenum was lying obliquely in front (ventrally) of the left renal vein thus squeezing the left renal vein due to the limited space for both tubular structures inbetween the aorta and the superior mesenteric artery. The enlarging stomach during a meal squeezes the left renal vein from left and above thus pushing the venous blood into the pre-caval segment which is blocked by the filling duodenum.


That this observation is not just a funny coincidence but explains the post-prandial pain as an increasing pressure inside the left renal vein and the left kidney was demonstrated by a sharply decreasing left renal parenchymal perfusion with the PixelFlux technique after a meal while standing – which was the constellation of maximal suffering of the patient.
PixelFlux is able to measure very precisely the amount of blood passing through the kidneys in different layers of the parenchyma. It gives us the opportunity to pinpoint specific and so far undescribed effects of everyday conditions for instance the uptake of food or certain movements of the trunk onto the kidney.
The effect of the left renal vein compression by the filling duodenum was most pronounced while standing or sitting after a meal: The perfusion of the left kidney drops by 69%!
PixelFlux does not only tell is that the perfusion is impaired by the filling duodenum but also explains the pain since it can measure the intraparenchymal pressure (the pressure inside the kidney and thus inside the left renal vein) by comparing different layers of the renal parenchyma (tissue). The most peripheral tissue layer below the renal capsule contains the smallest vessels of the renal vascular tree. These tiny vessels can be compressed more easily than the more central vessels which contain mor blood and therefore require more counterpressure to suppress their perfusion. The counterpressure comes from the increasing pressure inside the left renal vein which is the blocked outflow from the kidney while the arterial influx from the heart is not affected by the duodenum.
Thus, the ratio of the peripheral to the central perfusion of the renal parenchyma describes the pressure changes due to increasing counterpressure from an increasingly compressed left renal vein. This is just what is demonstrated in the diagram below: Standing post-prandially causes a reduction of the peripheral perfusion of the left kidney by 47% whereas the perfusion of the right kidney drops only by 16%! This is the proof that the increasing filling of the duodenum causes a continuously increasing pressure onto the left renal vein thus reducing its peripheral perfusion especially when the patient is standing upright after a meal.

The following video immediately demonstrates the dynamic nature of the compression: The duodenum fills up and then suddenly releases the pressure when the filling of the horizontal portions crosses the threshold for overcoming the counterpressure by the surrounding structures while the left renal vein is seen in the beginning as a tapering wide structure before it is overshadowed by the area in the filling horizontal portion of the duodenum.
In this illustrative case not only the dynamic compression of the left renal vein could be demonstrated, which was strictly dependent on the uptake of food and subsequent filling of the duodenum, but also its impact onto the renal perfusion further underscored the hemodynamic effect of this compression. Thus, the filling duodenum was not only a innocent bystander but increased the pressure onto the left renal vein while the stomach pushed the blood against the duodenal barrier to such an amount that the left renal perfusion decreased. This furthermore gives rise to pain in the left renal vein and the left kidney (mid abdomen and left upper abdomen and left lower thorax) due to the increasing tension which is developing with the steadily increasing congestion of the left renal vein since the venous outflow is becoming more and more obstructed by the enlarging amounts of food in the duodenum.