Pathology of tumours of the small and large intestine

In surgical practice, patients present with intestinal symptoms which may be due to a benign or malignant tumour within the bowel. The symptoms, histological type of tumour, and frequency of occurrence vary according to the region of the bowel affected; some tumour types are more common in specific locations in the bowel. By far the most common tumours (benign and malignant) seen in surgical practice are those of epithelial origin occurring in the large bowel. Small bowel tumours and non-epithelial (e.g. mesenchymal, lymphoid) tumours occur, but with a lower frequency. Benign tumours do not invade or metastasize. They produce their symptoms due to a mass effect which can cause luminal narrowing, compression of surrounding structures, mechanical obstruction and/or a focus for torsion or intussusception. They can also release factors into the systemic circulation such as gastrin, causing Zollinger–Ellison Syndrome, characterized by intractable gastric acid secretion, severe peptic ulceration of the duodenum and jejunum and hypergastrinaemia, or serotonin, causing carcinoid syndrome, respectively. Malignant tumours can invade locally, but can also spread to sites outside the bowel. Signs and symptoms can be due to the mass effect similar to that seen with benign tumours, but also can be due to invasion of surrounding structures and other organs (e.g. liver). This review aims to give a general overview of the pathology of tumours occurring throughout the bowel, mainly focusing on those commonly seen in surgical practice.