Left paraduodenal hernia: Embryological and radiological findings

Left paraduodenal hernia (PDH), may present as a surgical emergency with an increased risk of strangulation and incarceration. The diagnosis is challenging because of the non-specific presentation. In the absence of common epigastric or upper abdominal pathology and non-resolving symptoms, a high index of suspicion is required to diagnose left PDH. This report describes a case of radiologically diagnosed left paraduodenal hernia and subsequent successful surgery. It also includes a review of midgut embryology, and the anatomy and radiology of left PDH.


Introduction
Abdominal hernias are categorised into external and internal hernias. External hernia represents herniation of intestinal loops through a defect in the wall of the abdomen or pelvis. An internal hernia is defined by herniation of a viscus through a normal or abnormal peritoneal or mesenteric aperture within the peritoneal cavity. Internal hernias are rarely encountered in general practice, however, on the background of increased liver transplantations and gastric bypass surgery for bariatric treatment, the incidence of internal hernia is becoming more prevalent. 1 Internal hernia can be asymptomatic or cause significant discomfort, dependent on the duration and reducibility of the hernia. Hence, this entity may present a clinical challenge and imaging, especially if symptomatic, is imperative. Paraduodenal hernias (PDH) are the commonest of the internal hernias and are classified into left and right, with the former being more prevalent. 1

Case report
The index patient was a 57-year-old male who presented with vague, intermittent, recurrent abdominal pain. The pain evolved into a worsening epigastric pain radiating to the back with associated vomiting. The supine plain radiograph of the abdomen ( Figure 1) demonstrated a well-circumscribed mass projected in the left upper quadrant of the abdomen. Free intraperitoneal air was excluded on the erect radiograph (not shown). Additionally, ultrasound excluded cholelithiasis, peripancreatic fluid, a left renal lesion and obstructive uropathy. Markers of infection were minimally increased. Amylase levels were normal.
Given the presence of a left upper quadrant mass on plain radiography that was suboptimally appreciated on ultrasound, computed tomography (CT) was requested. Multiphase contrasted CT imaging was performed with prior administration of oral contrast ( Figure 2). A cluster of jejunal bowel loops was noted within a sac in the left upper quadrant of the abdomen. Dilatation of the proximal duodenum and jejunal loops within the sac was evident with loss of the normal duodenal and jejunal configuration. Failure of transit of oral contrast into the terminal ileum was noted. Engorgement of the mesenteric vessels entering the hernial sac was visualised with surrounding fat stranding. There were no features of pneumatosis intestinalis. The inferior mesenteric vein and the ascending branch of the left colic artery were seen along the anterior margin of the hernial sac ( Figure 3). These collective findings were in keeping with a left PDH and bowel obstruction.
Intraoperative findings (Figure 4) confirmed the congenital defect (white arrow), presence of fossa of Landzert, and jejunal bowel loops within the left PDH. The patient recovered without further complications or recurrence of symptoms.
Left paraduodenal hernia (PDH), may present as a surgical emergency with an increased risk of strangulation and incarceration. The diagnosis is challenging because of the non-specific presentation. In the absence of common epigastric or upper abdominal pathology and non-resolving symptoms, a high index of suspicion is required to diagnose left PDH. This report describes a case of radiologically diagnosed left paraduodenal hernia and subsequent successful surgery. It also includes a review of midgut embryology, and the anatomy and radiology of left PDH.

Ethical consideration
This article followed all ethical standards for research. Consent was acquired from the patient to include the data and images in the manuscript. Data and images in the manuscript were anonymised.

Discussion
Left paraduodenal hernia represents an internal abdominal hernia. Internal hernias are defined by the protrusion of a viscus through a normal or abnormal peritoneal or mesenteric aperture within the peritoneal cavity. The orifice may be congenital or acquired, secondary to post-surgical, postinflammatory or a traumatic defect. Congenital defects include normal apertures, such as foramen of Winslow, and abnormal apertures arising from anomalies of internal rotation and peritoneal attachments. 1 In understanding the pathogenesis and clinical manifestations of left PDH, it would be imperative to review the embryology of the normal sequence of events relating to the midgut position. The midgut is suspended in the midline by its dorsal mesentery and undergoes a sequential pattern of rotations that is divided into three stages ( Figure 5).     The mechanism of formation of the left PDH was best described by Callander et al. 4 Abnormalities in the rotation of the pre-arterial segment in the second stage as it rotates posteriorly and then to the left of the superior mesenteric artery results in a left PDH. During this process, the bowel invaginates into an unsupported area of the descending mesocolon resulting in the anterior margin being formed by the ascending branch of the left colic artery and the inferior mesenteric vein. The small bowel comes to lie in a sac, lined by peritoneum, posterior to the mesentery of the descending colon. The terminal ileum enters the peritoneal cavity through the neck of the sac to reach the caecum ( Figure 6).
Treitz has dictated three prereqsuisites for the occurrence of a left PDH: (1) the presence of a fossa (fossa of Landzert), (2) the presence of the inferior mesenteric vein in the neck of the sac and (3) sufficient mobility of the small bowel to allow it into this sac derived from this fossa. 5 The fossa of Landzert is located to the left of the fourth part of the duodenum, extending posteriorly to the descending mesocolon. The opening is immediately inferior to the duodenojejunal junction and bordered anteriorly by the inferior mesenteric vein and ascending branch of the left colic artery.
Paraduodenal hernias are the most common type of internal hernias, accounting for 50% of cases. 7 Left PDH is three times more common than right PDH with a male predilection of 3:1. 7   The associated risk of strangulation and intestinal infarction of more than 50% over the course of a lifetime, makes it necessary to investigate symptomatic patients. The high rate of mortality associated with these complications justifies the role of CT early in the pre-operative diagnosis of PDH. 9 The characteristic CT appearance consists of an abnormal cluster or sac-like mass of dilated small bowel loops lying between the stomach and pancreas, to the left of ligament of Treitz. There is usually mass effect that displaces the posterior wall of the stomach, the duodenal flexure inferiorly and the transverse colon inferiorly. The mesenteric vessels supplying the herniated small bowel, appear crowded, engorged and stretched at the entrance of the hernial sac. 10 The ascending branch of the left colic artery and the inferior mesenteric vein form an important CT landmark along the anterior margin of the hernia.
Our patient presented with vague, intermittent and recurrent abdominal pain that was progressively worsening. The impression of a mass within the left upper quadrant of the abdomen on plain radiography was characterised at CT, which demonstrated pathognomonic features of a left PDH. Urgent surgical intervention confirmed the diagnosis and the patient recovered without complications.
This case report aimed to highlight the importance of plain radiograph interpretation in the background of an internal hernia, which if present, will allude to underlying pathology. Although this may be non-specific, it will support the need for further cross-sectional imaging to delineate the pathology. The case report further describes and diagrammatically illustrates the pertinent aspects of midgut embryology, allowing the radiologist to appreciate the pathogenesis of a left PDH. Identifying the abnormal configuration of the proximal small bowel and associated vascular landmarks assists in the correct interpretation and diagnosis. Internal hernias are rarely seen in clinical practice and it is important for radiologists to familiarise themselves with this concept, as the adverse outcome of an unsuspected or unidentified PDH can result in ischaemia, strangulation and obstruction with mortality between 20% and 50% due to delayed management. 11

Conclusion
Left PDH represents a clinically challenging and elusive diagnosis. An understanding of the mesenteric, peritoneal folds, anatomy of the duodenal fossa and embryology of the midgut is important to make the diagnosis. It is imperative for radiologists and surgeons to familiarise themselves with this uncommon condition, especially in patients presenting with non-resolving vague epigastric pain. Plain radiograph may be suggestive, however, CT remains the gold standard for the diagnosis.