Internal hernia is characterized by protrusion of the abdominal viscera through a peritoneal or mesenteric hernia orifice into a compartment in the abdominal cavity. There are various types of internal hernias; however, the type of internal hernia with herniated organs in the retroperitoneal space is called a retroperitoneal hernia.
We encountered two cases of retroperitoneal hernia in which the hernia orifices lacked retropancreatic fascia in the supramesocolic space, and the herniated organs in each case protruded into the mediastinum and extra-pleural space, respectively. To the best of our knowledge, there have been no reports of this type of hernia. In embryology, the ventral and dorsal pancreas occur in the fifth week of the embryo and gradually merge with the posterior peritoneum. The greater omentum and transverse mesocolon completely fuse with each other after physiologic herniation at gestational age 8–9 weeks [2]. Thereafter, Toldt fusion fascia is formed by merging the dorsal peritoneum of the pancreas with the posterior peritoneum [3]. The Toldt fusion fascia behind the pancreas is known as the retropancreatic fascia. The retropancreatic fascia is absent along the pancreas facing the superior mesenteric artery in elder individuals [4]. Considering the location of the hernia orifices in our cases, the absent site of the retropancreatic fascia was assumed to be the orifice of the internal hernia. The mechanism of retropancreatic fascia hernia formation is not known; however, it can be assumed the mechanism is similar to that of paraduodenal hernia formation. Factors involved in the formation of a left duodenal hernia are the presence of a fossa, the presence of the neck of the sac (of the inferior mesenteric vein in left duodenal hernia), and sufficient mobility of the small bowel to allow it to pass into the sac derived from this fossa [5]. In addition, an increased intra-abdominal pressure is required to initiate the hernia. In retropancreatic fascia hernia, the presence of a fossa is the absent site of the retropancreatic fascia and the presence of the neck of the sac is the pancreatic body. The herniated sac prolapses into the posterior mediastinum by intra-abdominal pressure (Fig. 7). In this scenario, there is no need for other defects such as transverse fascia and diaphragm. Since various defect sites rarely occur simultaneously, this mechanism is conceivable.
Retroperitoneal hernia includes paraduodenal, pericecal, intersigmoid, foramen of Winslow, and iatrogenic posterior peritoneal defects. Paraduodenal hernias are the most common type [6] and retroperitoneal hernias caused by posterior peritoneal defects are relatively rare. Initially, we suspected paraduodenal hernia in our cases. However, Case 2 was with malrotation and without Treitz ligament; hence, the paraduodenal site did not anatomically exist. The hernia orifices of Case 1 were apparently above the mesentery roots of the transverse colon, such as in the supramesocolic space, as the operative imaging shows; therefore, the paraduodenal hernia was impossible. Considering the aspect of congenital mechanisms, we believed that a retropancreatic fascial hernia was the cause. Our two cases were considered to have congenital mechanisms. Case 2 was prenatally diagnosed with congenital diaphragmatic hernia; hence, congenital factors were assumed to contribute to the occurrence of retropancreatic fascial hernia. Case 1 was born with a Bochdalek hernia, requiring repair of the diaphragmatic hernia. Retropancreatic fascia hernia occurred approximately 1 month after the repair. Although both congenital and acquired factors were possibly associated with hernia occurrence, congenital factors were assumed to contribute to the occurrence of retropancreatic fascia hernia because the diaphragm was treated only without intraoperative damage to the retroperitoneal space during the primary surgery for Bochdalek hernia. Bochdalek hernia in the prenatal period may conceal the symptoms of a retropancreatic fascial hernia. Repairing the Bochdalek hernia reduced the prolapsed organs, possibly resulting in the protrusion of organs from the absence of the retropancreatic fascia into the peritoneal space and the mediastinum.
We retrospectively reviewed our two patients; however, preoperative diagnosis of a retropancreatic fascial hernia was difficult. Preoperative diagnosis of a retropancreatic fascia hernia is possible with chest and abdominal CT scan; however, we do not routinely perform CT scans in almost all cases with suspected congenital diaphragmatic hernia because moving the patients to a CT room alone poses a risk to these patients. In addition, the range of a CT scan is limited to the chest region. There are three types of congenital diaphragmatic hernia: a posterolateral defect, Bochdalek-type; an anterior defect, Morgagni-type; and a central defect, septum transversum-type [7]. A posteromedial diaphragmatic hernia is very rare; hence, if preoperative imaging shows a medial diaphragmatic hernia, it can suggest the possibility of a retropancreatic fascial hernia. When one cannot detect any defect holes in the preoperative diagnosis of congenital diaphragmatic hernia, hernia orifices in the abdominal cavity need to be searched for, especially in thoracoscopy because this hernia does not extrude into the thoracic cavity but into the extra-pleural space. The treatment of retropancreatic fascial hernia involves reducing the herniated organs and closing the orifices.
