Anal Fissure: Pathomorphology and Course
The condition always manifests as a shallow superficial mucosal defect. However, upon transitioning to a chronic course, the pathological process steadily deepens. The defect penetrates into deeper layers of the wall, eventually involving the muscle fibers of the anal sphincter. If the injury extends to involve the perianal skin, pronounced cicatricial (scar) changes develop in this area. A characteristic morphological sign of chronic progression is the formation of an inflammatory polyp directly in the proximal part of the fissure.
Histological criteria for 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 ulcerated defect, and varying degrees of fibrosis are noted in the underlying tissues. The main danger of an anal fissure lies in its complications: infection of the defect triggers a cascade of suppurative processes, leading to the development of a perianal abscess or subcutaneous fistula.
Anorectal Abscess
An anorectal abscess (also known as a perianal or perirectal abscess) represents suppurative 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 pathogen is Escherichia coli.
- Rare causes of suppuration include specific infections such as tuberculosis, lymphogranuloma venereum, and actinomycosis.
- Predisposing factors include local pathologies: complicated anal fissures, suppurating hematomas, or the presence of thrombosed hemorrhoids.
Topography of the Lesion: Abscesses predominantly localize in the intersphincteric and perianal spaces. Considerably less often, the inflammatory process extends proximally to the dentate line or directly affects the rectal wall.
Perianal Fistula
A perianal fistula (synonyms used in clinical practice include anal fistula, anorectal fistula, and rectoperianal fistula) is a formed pathological tract 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 is almost universally shared with anorectal abscesses, as fistulas arise precisely at the sites of previous abscess localization. The most frequent type of pathology is the intersphincteric fistula.
Histological Picture of Nonspecific Types:
- The internal lining of the tract consists of granulation tissue, covered with fibrin and a robust leukocyte wall.
- Fecal masses are frequently found within the lumen of the fistula.
- Infiltration by lymphocytes and plasma cells of varying severity is observed within the wall thickness.
- A significant number of eosinophils may be present, along with the appearance of foreign body giant cells.
Differential Diagnosis by Histological Findings
During microscopic examination of biopsy specimens, it is critical to exclude specific infections and systemic diseases that share a similar granulomatous morphology. Differential diagnosis relies on the following histological features:
- Crohn's Disease: Epithelioid cells are present in the tissues, arranged together with giant cells.
- Tuberculosis: Similar granulomas are formed, but with the mandatory presence of central caseous necrosis. Confirmation of the diagnosis requires the identification of acid-fast bacilli in the biopsy.
- Actinomycosis: Characterized by the formation of granulomas with prominent central suppuration, whereas histiocytes are not an obligatory finding.
- Chlamydial Infection: May produce a granulomatous reaction, though not consistently. Histological diagnosis in this case is challenging, and additional serological tests are required to accurately identify the pathogen.