Introduction

Cross-sectional imaging plays a major role in the teaching of anatomy, especially in relation to the gastrointestinal (GI) tract. It demonstrates the relations of the GI tract with other abdominal structures and hence allows us to understand local disease processes and the pathways of local and distant spread.

In particular CT and MRI scanning are used to image the small and large bowel in their entirety, whilst ultrasound has taken its place as a more focused tool in the GI tract. It is used transabdominally at high frequencies (10 and 13.5 MHz) to image the pylorus for pyloric stenosis, the appendix, terminal ileum for Crohn’s disease and the small/large bowel for intussusception in children. Endoscopic and endocavity ultrasound is used to visualize the proximal GI tract for tumour staging and the anal canal for sphincter tears and fistulae.

Barium studies are still widely used either as a diagnostic tool or, in conjunction with CT or MRI, as a problem-solving tool. Therefore, knowledge of luminal anatomy and its variants remains crucial.

Embryology and development

The GI tract extends from the mouth to the anus, and originates from the primitive foregut, midgut and hindgut (Fig. 11.1).

Foregut

The forgut consists of the pharynx, oesophagus, stomach and the first and second parts of the duodenum. The blood supply of these structures is predominantly derived from the coeliac artery, apart from the mid oesophagus, which derives its arterial supply from the thoracic aorta directly and the proximal third of the oesophagus from the inferior thyroid vessels.

During development, the pancreas and liver arise from buds of the foregut, in the region of the second part of the duodenum, hence the intimate relationship with the bile ducts, portal and hepatic vessels.