CHAPTER 6
Abdominal cavity: anatomy, structural anomalies, and hernias

Stella Joyce¹, Kevin P. Murphy^1,2, Michael M. Maher1, and Owen J. O’Connor¹

¹ Department of Radiology, University College Cork, Cork University Hospital, Cork, Ireland

² Mercy University Hospital, Cork, Ireland

Introduction

This chapter provides a pictorial reference depicting anatomical structural anomalies encountered within the abdominal cavity. These anomalies may be broadly divided into developmental and adult patterns of anatomical variation. Structural anomalies are benign processes that tend to respect intact anatomy; their locations and appearances are therefore determined by the boundaries of the abdominal cavity, intra‐ and retroperitoneal divisions, and the peritoneal cavity subdivisions.

The abdominal cavity may be affected by a wide variety of hernias. Internal hernias are difficult to diagnose clinically, and computed tomography (CT) plays a vital role in assessment. Surgical repair remains the definitive management option for groin hernias. Adult diaphragmatic hernias are most frequently posttraumatic in origin; the left hemidiaphragm is most commonly affected.

Abdominal cavity anatomy

The abdominopelvic cavity is bounded superiorly by the diaphragm, inferiorly by the pelvic floor, and circumferentially by the abdominal wall. The abdominopelvic cavity is divided into intraperitoneal and retroperitoneal components by the peritoneum; the peritoneal cavity is further subdivided into several spaces and recesses via peritoneal reflections. They in turn are subdivided into ligaments, omenta, and mesenteries. Most notably, the peritoneal cavity is partitioned into supra‐ and inframesocolic compartments by the transverse mesocolon.

Developmental and childhood structural anomalies of the abdominal cavity

A disorder of the physiological developmental rotation of the small bowel is termed malrotation. The key concern is the propensity for midgut volvulus with resultant obstruction and bowel ischemia. Imaging confirmation is usually performed using an upper gastrointestinal fluoroscopic contrast study (Figure 6.1).

Congenital intraabdominal cystic lesions include lymphangiomata, mesenteric cysts, enteric cysts, and enteric duplication cysts. Many are detected antenatally and are asymptomatic (Figure 6.2).

Exomphalos (omphalocele) is a persistence of the physiological umbilical small bowel herniation, and has coverings of amnion and peritoneum. Gastroschisis involves an anterior abdominal wall hernia that lies lateral to the umbilicus, and which lacks any coverings. Unlike gastroschisis, an omphalocele is associated with other congenital anomalies in 54% of cases.

Congenital pediatric groin hernias occur in 3–5% of births and up to 30% of premature (usually male) infants. The vast majority are indirect inguinal hernias as a result of incomplete closure of the processus vaginalis (canal of Nuck in females).

A Morgagni‐type congenital diaphragmatic hernia is an anteromedial parasternal defect that is frequently right‐sided (90%). A Bochdalek hernia (Figures 6.3 and 6.4) is a left‐side predominant (80%) congenital defect in the posterolateral diaphragm that is more common than a Morgagni hernia. Pulmonary hypoplasia and pulmonary hypertension are key concerns.

Adult abdominal hernias

A hernia may be defined as the abnormal protrusion of an organ or tissue out of the body cavity in which it normally lies.

The key elements of a hernia are the hernia sac, neck, and contents. Any cause of increased intraabdominal pressure will predispose to abdominal wall herniation, in addition to conditions that result in weakening of the abdominal wall. Clinical evaluation is sufficient to diagnose an abdominal wall hernia in most cases. Irreducible (incarcerated) hernias may be associated with bowel obstruction or bowel ischemia due to strangulation.

Photo depicts upper GI study in a neonate with vomiting due to malrotation. — **Figure 6.1** Upper GI study in a neonate with vomiting due to malrotation. Lateral view demonstrates a “corkscrew” appearance of the duodenum (arrow) which has torted around itself.

Photo depicts axial T2-weighted magnetic resonance image that demonstrates an incidental simple left iliac fossa lymphangioma (arrow). — **Figure 6.2** Axial T2‐weighted magnetic resonance image that demonstrates an incidental simple left iliac fossa lymphangioma (arrow).

Acquired adult diaphragmatic hernias are rare. Although the majority are posttraumatic in origin (Figure 6.5), with the left hemidiaphragm affected most frequently, other causes include a delayed diagnosis of congenital diaphragmatic hernia, in addition to iatrogenic diaphragmatic hernia. Approximately 11% of congenital diaphragmatic hernias present during adulthood.

The inguinal canal is an oblique channel, approximately 4 cm long, through the inferomedial anterior abdominal wall. It is a site of potential weakness. The adjacent femoral canal represents the medial compartment of the femoral sheath. Inguinal hernias account for over 70% of abdominal wall hernias, with femoral hernias responsible for 5–15% of cases. Direct inguinal hernia occurs due to protrusion of contents through the posterior canal wall medial to the epigastric vessels while the indirect type leads to extension of contents through the deep ring (Figures 6.6–6.10).

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