Chronic active ileitis

By Jason Wasserman MD PhD FRCPC
August 3, 2024

This article was written by pathologists. It aims to help patients understand their pathology report for chronic active ileitis. It includes sections on what chronic active ileitis is, its causes, symptoms, diagnosis, and the microscopic features observed in pathology.

What is chronic active ileitis?

Chronic active ileitis is a term for tissue injury caused by long-term inflammation of the ileum, the final part of the small intestine. The term “chronic” indicates that the inflammation has been present for an extended period, while “active” means that there are ongoing signs of inflammation and tissue injury. This condition can affect the absorption of nutrients and cause various gastrointestinal symptoms.

What causes chronic active ileitis?

Chronic active ileitis is a pattern of inflammation and injury that can be caused by a variety of medical conditions, including:

• Crohn’s disease: Crohn’s disease is the most common cause of chronic active ileitis. It is a type of inflammatory bowel disease (IBD) that can affect any part of the gastrointestinal tract but often involves the ileum.
• Infections: Certain bacterial, viral, or parasitic infections can cause inflammation of the ileum.
• Autoimmune disorders: Conditions where the immune system attacks the body’s own tissues, leading to chronic inflammation.
• Medications: Long-term use of certain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), can contribute to chronic inflammation and tissue injury.
• Ischemia: Reduced blood flow to the ileum can cause inflammation and damage over time.

What are the symptoms of chronic active ileitis?

The symptoms of chronic active ileitis can vary but often include:

• Abdominal pain: Cramping or discomfort, typically in the lower right side of the abdomen.
• Diarrhea: Frequent, loose, or watery stools.
• Weight loss: Unintentional weight loss due to malabsorption of nutrients.
• Fatigue: Persistent tiredness and lack of energy.
• Fever: Low-grade fever may be present due to ongoing inflammation.
• Anemia: Low red blood cell count due to chronic blood loss or poor nutrient absorption.

How is the diagnosis of chronic active ileitis made?

The diagnosis of chronic active ileitis is made through a combination of clinical evaluation, imaging studies, and a biopsy of the ileum. First, your doctor will assess your symptoms and medical history and perform a physical examination. Then, imaging studies such as CT scans, MRI, and endoscopy are typically performed to visualize inflammation and narrowing of the ileum. During the endoscopy, a biopsy is performed, and the tissue from the ileum is examined under a microscope by a pathologist.

What does normal healthy tissue from the ileum look like under the microscope?

The normal ileum has tall, finger-like projections called villi, with deep crypts (glands) at the base. The lamina propria, the tissue between the villi, contains a mixed population of immune cells, including lymphocytes and plasma cells.

What are the microscopic features of chronic active ileitis?

When a pathologist examines a biopsy from the ileum, they look for specific features under the microscope. These include:

• Chronic inflammation: A larger than normal number of lymphocytes and plasma cells in the lamina propria, indicating long-term inflammation.
• Active inflammation: Neutrophils infiltrating the mucosa, often seen in the crypts (cryptitis) or forming crypt abscesses.
• Mucosal ulceration: Erosion or ulceration of the mucosal lining.
• Architectural distortion: Changes in the normal structure of the mucosa, including branching and shortening of the crypts.
• Fibrosis: Scarring of the tissue, which can lead to narrowing of the ileum.
• Granulomas: In Crohn’s disease, clusters of immune cells called granulomas may be present, indicating a specific type of inflammation.

What does “chronic active” mean?

In pathology, “chronic” refers to architectural changes in the tissue, such as branching and shortening of the crypts, indicating long-term tissue damage. “Active” refers to ongoing inflammation and tissue injury involving neutrophils, a type of immune cell. Taken together, these terms mean that the condition has been present for a long time and that new tissue injury is still taking place.

Levels of activity in chronic active ileitis

Chronic active ileitis can be divided into different activity levels based on the severity of inflammation and tissue injury. These levels include mild, moderate, and severe, each with distinct microscopic features and clinical implications.

Mild activity

Microscopic features: A slight increase in intraepithelial lymphocytes, rare neutrophils in the lamina propria, minimal cryptitis, and mild architectural changes, such as slight crypt branching.

Moderate activity

Microscopic features: Moderate increase in intraepithelial lymphocytes and neutrophils, more pronounced cryptitis with c, and noticeable architectural distortion.

Severe activity

Microscopic features: Dense infiltration of neutrophils and lymphocytes, extensive crypt abscesses, significant mucosal ulceration, and marked architectural distortion with fibrosis.

Learn more pathology

Atlas of Pathology