 Introduction/Background Retroperitoneal bleeding is a hemorrhage into the retroperitoneal space, the space located posterior to the parietal peritoneum and anterior to the transversalis fascia. Retroperitoneal bleeding can occur spontaneously (Wunderlich syndrome), including in association with anticoagulation therapies, or be secondary to trauma, aortic rupture, or bleeding from a visceral vessel or mass. Retroperitoneal bleeding can also be iatrogenic, as a complication from surgeries or transfemoral catheterization procedures [1,2]. The retroperitoneum contains a portion of the duodenum, kidneys, adrenal glands, proximal ureters, pancreas, and vascular structures, including the abdominal aorta and proximal renal vasculature. This anatomy provides a variable source of potential bleeding. In the setting of trauma, retroperitoneal bleeding can also be the result of pelvic or spine fractures. Recognition of retroperitoneal bleeding from pelvic fractures is important given that it is associated with an increased need for transfusions and rapid intervention [3]. Vascular bleeding in the retroperitoneum can be from aortic aneurysmal rupture or visceral vessel rupture. The latter can be seen, for example, in the setting of pseudoaneurysms secondary to duodenal or pancreatic inflammation or infection [4]. Retroperitoneal bleeding is also the second most common site of major, or clinically relevant, bleeding seen among cancer patients [5]. Bleeding can be due to the malignancy itself or interventions and treatment, including surgery, upper endoscopy, chemotherapy, or anticoagulation. The many causes for retroperitoneal bleeding can make the diagnosis and management clinically challenging. Assessing for the clinical signs of retroperitoneal bleeding can be difficult given that the location of bleeding is not readily accessible to physical examination and often has an obscured etiology. This can result in the delayed diagnosis of retroperitoneal bleeding [6,7].
Suspected Retroperitoneal Bleed.  Introduction/Background Retroperitoneal bleeding is a hemorrhage into the retroperitoneal space, the space located posterior to the parietal peritoneum and anterior to the transversalis fascia. Retroperitoneal bleeding can occur spontaneously (Wunderlich syndrome), including in association with anticoagulation therapies, or be secondary to trauma, aortic rupture, or bleeding from a visceral vessel or mass. Retroperitoneal bleeding can also be iatrogenic, as a complication from surgeries or transfemoral catheterization procedures [1,2]. The retroperitoneum contains a portion of the duodenum, kidneys, adrenal glands, proximal ureters, pancreas, and vascular structures, including the abdominal aorta and proximal renal vasculature. This anatomy provides a variable source of potential bleeding. In the setting of trauma, retroperitoneal bleeding can also be the result of pelvic or spine fractures. Recognition of retroperitoneal bleeding from pelvic fractures is important given that it is associated with an increased need for transfusions and rapid intervention [3]. Vascular bleeding in the retroperitoneum can be from aortic aneurysmal rupture or visceral vessel rupture. The latter can be seen, for example, in the setting of pseudoaneurysms secondary to duodenal or pancreatic inflammation or infection [4]. Retroperitoneal bleeding is also the second most common site of major, or clinically relevant, bleeding seen among cancer patients [5]. Bleeding can be due to the malignancy itself or interventions and treatment, including surgery, upper endoscopy, chemotherapy, or anticoagulation. The many causes for retroperitoneal bleeding can make the diagnosis and management clinically challenging. Assessing for the clinical signs of retroperitoneal bleeding can be difficult given that the location of bleeding is not readily accessible to physical examination and often has an obscured etiology. This can result in the delayed diagnosis of retroperitoneal bleeding [6,7].