Right Retroperitoneum, Left Retroperitineum, Mesenteric Vessels

Trauma/EM:  Retroperitoneal Hemorrhage: Retroperitoneal hemorrhage may occur secondary to trauma (blunt or penetrating injury) or non-traumatic causes (spontaneous or iatrogenic). Patients with retroperitoneal hemorrhage may present insidiously before entering hypovolemic shock due to severe blood loss. In some cases, physical exam will be significant for bruising/edema in the periumbilical and flank regions; respectively known as Cullen’s sign (tracking of hemorrhage from retroperitoneum to umbilicus along gastrohepatic and falciform ligaments) and Gray Turner’s sign (extravasation of hemorrhage across the transversalis fascia and tracking along quadratus lumborum muscle). Contrast-enhanced CT is generally diagnostic. The life-threatening bleeding associated with retroperitoneal hemorrhage must be rapidly accessed for identification of bleed origin and management. Anterior access to the retroperitoneum is relatively complex and time-consuming due to the intervening intraperitoneal organs and mesentery. Instead, quick access to the retroperitoneum is generally achieved through left or right medial visceral rotation. Recall that the ascending and descending colon are anchored to the lateral body wall: the point where the visceral peritoneum of the colon meets the parietal peritoneum of the body wall is the white line of Toldt (make sure to see this in lab!). Incision of this creates the dissection plane into the retroperitoneum that is continued just superficial to the posterior abdominal muscles. As the dissection plane is developed, various organs (i.e., the viscera) including the kidneys, ureters, ascending or descending colon are medially rotated. This can be done on the left (the Mattox maneuver) for access to the aorta or the right (the Cattel-Braasch maneuver) for access to the IVC. The Mattox maneuver generally involves rotation of the stomach, spleen, and pancreas as well. See image below for visualization of procedure.

Procedure: Celiac Plexus Block: The celiac plexus are the bundles of nerves located around the celiac trunk, SMA, renal arteries branching off the aorta. This plexus is formed by the greater and lesser splanchnic nerves (sympathetic) and the branches of the vagal trunk (parasympathetic). Functionally, these nerves regulate physiological function of and blood flow to many abdominal organs. Additionally, the celiac plexus transmits pain signals from the abdominal viscera to the central nervous system. As a result, the celiac plexus is a key target in pain management strategies for patient’s suffering from intractable abdominal pain caused by malignancy (e.g., pancreatic) and pancreatitis. Block is classically achieved through injection of an anesthetic or neurolytic agent (choice depends upon etiology of pain) into the celiac plexus. Access to the celiac plexus is achieved through an anterior or posterior para-aortic approach under image guidance. Anterior approach generally involves transversing bowel and liver. The posterior approach entails insertion of the needle through paraspinous musculature.

Embryology: Horseshoe Kidney: The embryological development of the kidneys is multi-staged and complex. Horseshoe kidney occurs when the primitive kidneys fuse at their lower poles; this point of fusion is the isthmus. In addition to this abnormal isthmus, horseshoe kidneys generally differ from normal kidneys in their location and vasculature. Primitive kidneys begin development low in the abdomen before ascending. In the case of horseshoe kidney, the isthmus can be “caught” by the origin of vasculature (e.g., IMA) coming off the aorta thus impeding normal ascent. Vasculature of the horseshoe kidney can be highly variable with multiple renal arteries from the aorta/iliac vessels and aberrant veins. Horseshoe kidney is generally asymptomatic and incidentally discovered. If symptomatic, presenting signs are generally non-specific and imaging is diagnostic. We have a horseshoe kidney in lab; ask to see it!

Surgery/Autopsy: Kidney Transplant: In patients who are functionally anephric, dialysis is used to perform many of the kidney’s filter functions. However, dialysis cannot completely substitute for physiologic kidney function thus outcomes for dialysis patients tend to be poor. For this reason, dialysis is best viewed as a bridge to renal transplant (when possible). Think: are the patient’s native kidneys removed? No! Recall that the kidneys are retroperitoneal and receive ~25% of the cardiac output: access and removal of these would be time-consuming and operatively complex in patients who are severely ill to begin with. Removal of native kidneys is considered in cases of severe infection (pyelonephritis) or severe renal enlargement (e.g., polycystic kidney disease). Now, what about the donor kidney- where is it placed and how is it vascularized? Again, to avoid complicated access to the retroperitoneum, the new kidney is generally implanted in the right iliac fossa (lower right abdomen) and connected to the iliac vessels. If you see a kidney recipient, palpation of the kidney graft in this region is typical during physical exam. On a separate note, ask about innervation of the donated kidney in lab!

Anatomical Variations: IVC Variations: During development, there is a complex system of left- and right-sided embryological veins that ultimately fuse and regress to give rise to the mature caval system. If this process goes awry, IVC variations develop. Persistence of an embryological cardinal vein can give rise to a duplicated IVC. If the right-sided embryological veins inappropriately regress and left-sided ones persist, a left-sided IVC develops. In some cases, the infrarenal IVC (i.e., below the kidney) can be entirely missing. Though rare, these variants are important to identify prior to operations such as abdominal aortic aneurysm repair, nephrectomy, and IVC filter placement.

Imaging:

Imaging Correlate: