Anal canal diseases

Anal fissure: pathomorphology and clinical course

The disease always manifests as a shallow superficial mucosal defect. However, upon transitioning to a chronic course, the pathological process steadily deepens. Penetration of the defect into the deep layers of the wall occurs, up to the involvement of the muscle fibers of the anal sphincter. If the damage spreads and extends to the perianal skin, pronounced cicatricial changes develop in this area. A characteristic morphological sign of the chronization of the process is the formation of an inflammatory polyp directly in the proximal part of the fissure.

The histological criteria of an anal fissure are considered nonspecific, but they clearly reflect the pattern of inflammation. The biopsy specimen reveals an ulcerated surface densely covered with fibrinous-purulent exudate. Active lymphohistiocytic infiltration is observed along the edges of the ulcer defect, and fibrosis of varying severity is noted in the underlying tissues. The main danger of a fissure lies in its complications: infection of the defect triggers a cascade of purulent processes, leading to the development of a perianal abscess or subcutaneous fistula.

Anorectal abscess

Anorectal abscess (also known as an abscess of the anal region and rectum) is a purulent inflammation of the surrounding tissues. Epidemiologically, this pathology is significantly more common in male patients, and the peak incidence traditionally occurs in the third and fourth decades of life.

Etiology and predisposing factors:

• The primary infectious agent and leading causative agent is Escherichia coli (Escherichia coli).
• Rare causes of suppuration include specific infections: tuberculosis, lymphogranuloma venereum, and actinomycosis.
• Predisposing factors include local pathologies: complicated course of anal fissures, suppuration of hematomas, or the presence of ulcerative hemorrhoids.

Topography of the lesion: Abscesses are predominantly localized in the intersphincteric and perianal spaces. Much less frequently, the inflammatory process extends proximally to the dentate line or directly affects the rectal wall.

Perianal fistula

A perianal fistula (also referred to in clinical practice by synonyms: anal fistula, anorectal fistula) is a formed pathological channel connecting two epithelialized surfaces. On one side, this is the perianal skin, and on the other, the lower portion of the rectum or the anal canal.

The etiopathogenesis of fistulas almost always shares a common nature with anorectal abscesses, as fistulas arise precisely in the locations of abscesses. The most frequent type of pathology is the intersphincteric fistula.

Histological picture of nonspecific types:

• The inner lining of the channel is represented by granulation tissue, covered with fibrin and a robust leukocytic wall.
• Fecal masses are frequently found within the lumen of the fistula.
• Infiltration by lymphocytes and plasma cells of varying degrees of severity is observed within the thickness of the wall.
• The presence of a significant number of eosinophils, as well as the appearance of foreign-body giant cells, is possible.

Differential diagnosis based on histological picture

During microscopic examination of biopsy specimens, it is extremely critical to exclude specific infections and systemic diseases with similar granulomatous morphology. Differential diagnosis is based on the following histological features:

1. Crohn's disease: epithelioid cells are present in the tissues, located together with giant cells.
2. Tuberculosis: similar granulomas are formed, but with the mandatory presence of caseous masses in the center. To confirm the diagnosis, the detection of acid-fast mycobacteria in the biopsy specimen is necessary.
3. Actinomycosis: characterized by the formation of granulomas with pronounced central suppuration, while the presence of histiocytes is an optional sign.
4. Chlamydial infection: may produce a granulomatous reaction, though not always. Histological diagnosis in this case is difficult, and additional serological studies are required for accurate identification of the pathogen.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Morphogenesis and histological structure of the inflammatory polyp in chronic anal fissure
• Features of the cellular composition of granulation tissue in the wall of a perianal fistula
• The role of foreign-body giant cells and eosinophils in the pathogenesis of fistulous tracts
• Rare etiological factors of abscesses: pathomorphology of lymphogranuloma venereum and actinomycosis
• Mechanisms of cicatricial changes in perianal skin with long-standing defects

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