An intestinal cyst is a general descriptive term for an abnormal sac-like structure that develops within the wall of the small or large intestine, or in adjacent tissues like the mesentery. These sacs can contain fluid, semi-solid material, or gas, and they are not always true cysts with an epithelial lining. The term “cyst” describes the physical appearance of the lesion, not a specific diagnosis. Understanding the root cause is necessary for proper medical management, as the origins of these formations vary widely, ranging from errors in fetal development to later-life infections or abnormal cell growth.
Congenital and Developmental Anomalies
Cysts resulting from errors during the earliest stages of development are present at birth, even if they only become apparent later in childhood. The most common example is the intestinal duplication cyst, a rare malformation of the embryonic gut tube. These cysts are intimately associated with the gastrointestinal tract, often sharing a common muscular wall with the adjacent healthy bowel segment.
Intestinal duplication cysts have a lining of gastrointestinal mucosa and a layer of smooth muscle. They can be found anywhere from the esophagus to the rectum, but occur most frequently in the small intestine. One theory suggests they arise from a failure of the embryonic gut tube to properly separate or regress during the fourth to eighth weeks of gestation. These remnants can contain ectopic tissue, such as gastric or pancreatic mucosa, which may lead to complications like ulceration and bleeding.
Inflammatory and Obstructive Conditions
Acquired cysts can form later in life as a secondary effect of chronic irritation, mechanical blockage, or inflammation. These causes are distinct from those involving a living pathogen or abnormal cell proliferation.
A pseudocyst is a fluid collection that forms in response to inflammation, often associated with conditions like pancreatitis or Crohn’s disease. Unlike true cysts, pseudocysts lack a true epithelial lining, instead being encapsulated by a wall of fibrous, scar-like tissue. If a pancreatic pseudocyst develops, it can press directly on the adjacent intestinal wall, causing a mass that presents as an extrinsic intestinal cyst.
Pneumatosis Cystoides Intestinalis (PCI) is an acquired condition characterized by multiple, non-malignant, gas-filled cysts within the submucosa or subserosa layers of the intestinal wall. This phenomenon is often linked to underlying conditions that disrupt the intestinal lining, such as inflammatory bowel disease or chronic obstructive pulmonary disease. The gas travels from the intestinal lumen through a damaged mucosal barrier or is produced by gas-forming bacteria trapped within the bowel wall layers.
Cysts filled with lymphatic fluid, known as chylous or chylolymphatic cysts, result from an obstruction within the lymphatic drainage system of the mesentery. The mesentery anchors the intestine to the abdominal wall and contains a network of lymph vessels. When a blockage occurs, lymphatic fluid or chyle, which is rich in fats, accumulates in the vessels, leading to the formation of single or multiloculated fluid-filled sacs.
Infectious and Parasitic Agents
Cysts can form as a direct consequence of the body’s reaction to or as part of the life cycle of a specific pathogenic organism. In these cases, the cyst is essentially a protective or reproductive structure created by the host or the parasite.
Echinococcosis, or hydatid disease, results from infection with the tapeworm Echinococcus granulosus. Humans become accidental hosts by ingesting eggs, which hatch in the intestine and release larvae called oncospheres. These larvae penetrate the intestinal wall and migrate through the bloodstream to various organs, where they develop into large, fluid-filled hydatid cysts. While the liver and lungs are the most common sites, the larvae’s passage through the intestinal wall is the initial step in the disease process.
Another infectious lesion is the ameboma, which can be mistaken for a cystic mass or tumor. This complication arises from invasive amoebiasis caused by the protozoan Entamoeba histolytica. The organism invades the intestinal mucosa, triggering an intense, localized inflammatory reaction that produces a large mass of granulation tissue. This pseudotumor, or ameboma, can present clinically as a cystic lesion, particularly in the wall of the colon or rectum.
Neoplastic and Benign Growths
Some intestinal cysts represent true growths or tumors, arising from the abnormal proliferation of cells within the gastrointestinal tract or its supporting structures. These growths range from entirely benign to those with the potential to develop into cancer.
Mucinous cystic neoplasms (MCNs) are tumors characterized by the production of thick, gelatinous mucus. These lesions are lined by mucus-secreting epithelial cells and can occur in the intestinal mesentery, predominantly in women. MCNs have malignant potential and are classified on a spectrum from benign cystadenoma to a borderline tumor or an invasive mucinous carcinoma, necessitating complete excision.
In the case of cystic adenomas or carcinomas, the cystic appearance is due to the abnormal cellular architecture. Adenomas are benign tumors arising from the glandular tissue of the intestinal lining, and they may develop cystic components as they grow larger. Similarly, certain forms of adenocarcinoma, a malignant tumor, can exhibit cystic degeneration or form mucin-filled spaces, giving the lesion a cystic or semi-solid appearance.
Benign lymphangiomas are growths composed of a proliferation of lymphatic vessels, distinct from obstruction-based chylous cysts. These rare, true tumors of the lymphatic system are considered vascular malformations rather than acquired obstructions. They are typically found in the mesentery of the small bowel, where the dilated lymphatic channels collect fluid, forming a multiloculated cystic mass.