Etiology and morphology of anal ulcer
Anal ulcer (also known as anorectal ulcer or anal erosion) is a mucosal defect arising from a broad spectrum of factors.
Infectious agents play a significant role in the development of ulceration. Among sexually transmitted infections (STIs), the most frequent causes are chlamydial infection and lymphogranuloma venereum, with syphilis and gonorrhea being less common. Specific lesions are caused by Mycobacterium tuberculosis: anal canal tuberculosis can progress and lead to the formation of an anal fistula. Viral lesions, particularly herpesvirus infection, typically cause ulcers in immunocompromised individuals.
Non-infectious causes include:
- Inflammatory bowel disease (IBD): Crohn's disease provokes ulcers in 50% of cases, and ulcerative colitis in 18%. On histological examination, tissue changes are non-specific in nature.
- Traumatic and mechanical factors: a classic example is solitary ulcer syndrome, which is closely associated with trauma and mucosal prolapse.
- Iatrogenic (drug-induced) factors: mucosal defects can occur due to prolonged local use of rectal suppositories (e.g., containing indomethacin).
- Systemic diseases: ulcers accompany mucocutaneous syndromes (Stevens-Johnson syndrome, Behçet's disease) and various atrophic skin diseases.
Anal fissure: characteristics and causes
Anal fissure (acute or chronic) is morphologically a non-specific elongated ulcer. Its typical localization is the distal part of the anal canal, with the defect crossing the dentate line.
In cases of undetermined etiology, a traumatic origin is considered most likely. The mechanism of development is associated with severe stretching of the distal portion of the anal canal during the passage of feces. The main triggering factor is the presence of coarse plant fibers in the stool.
The second most frequent group of causes is iatrogenic postoperative complications. Fissures very frequently form during the recovery period following surgical removal of hemorrhoids (hemorrhoidectomy). In addition, chronic inflammatory bowel diseases characteristically lead to the appearance of anal fissures.
Viral infections: CMV and HPV
Viral pathogens cause specific changes in the tissues of the anogenital region that require careful microscopic analysis.
Cytomegalovirus infection (CMV) Develops predominantly against the background of severe immunodeficiency, including in AIDS. Macroscopically, the infection manifests as proctitis and the formation of perianal ulcers. These ulcers are frequently covered with pseudomembranes and carry a high risk of intestinal wall perforation. Microscopic examination reveals viral metamorphosis: specific inclusions—the "owl's eye" phenomenon—form within epithelial and endothelial cells.
Condyloma acuminatum (anogenital warts) Caused by human papillomavirus (HPV serotypes 6, 11, 16, and 18; type 6 dominates in the perianal region). The disease affects the urogenital tract and anal canal (statistically more common in homosexual men). Macroscopically, the process starts with the formation of papules that transform into vegetations.
The histological picture of HPV infection includes:
- Pronounced acanthosis and papillomatosis.
- Hyperkeratosis in the epithelium of the anal canal.
- Basal cell hyperplasia.
- Koilocytic atypia of Malpighian layer cells (perinuclear vacuolization).
- Multinucleated cells, eosinophilic inclusions, and dyskeratosis phenomena.
- Subepithelial inflammatory infiltration.
Important: upon detection of nuclear hyperchromasia, marked cellular pleomorphism, and high mitotic activity, malignancy is diagnosed—the development of intraepithelial neoplasia or carcinoma in situ.
Specific bacterial infections
This group of lesions includes gonococcal infection, chlamydial infection, and syphilitic proctitis. The main route of transmission for these pathogens is sexual (infections are predominantly registered in homosexual men). The morphological picture in the anal canal tissues in these diseases fully corresponds to the characteristic systemic and tissue features of these specific infections.
For quick memorization of the classical histological triad in HPV infection (condyloma acuminatum), use the acronym APK: Acanthosis, Papillomatosis, Koilocytosis.
Class and exam questions
Which microscopic feature is pathognomonic for CMV involvement of the anal canal?
Cytomegalovirus infection is characterized by the "owl's eye" phenomenon—the formation of specific viral inclusions inside epithelial and endothelial cells.
What is the most frequent cause of anal fissure formation?
Fissures most commonly have a traumatic etiology. They occur during severe stretching of the distal part of the canal by fecal masses, especially if coarse plant fibers are present in them.
Which histological changes indicate malignancy of a condyloma acuminatum?
Transformation into intraepithelial neoplasia or carcinoma in situ is indicated by the appearance of nuclear hyperchromasia, cellular pleomorphism, and high mitotic activity.
What else to study on this topic
- Pathogenesis of solitary ulcer syndrome and mucosal prolapse.
- Histological picture of non-specific changes in Crohn's disease and ulcerative colitis.
- Mechanisms of anal fistula formation against the background of a tuberculosis process.
- Differential diagnosis of carcinoma in situ and intraepithelial neoplasia.
- Morphological features of syphilitic proctitis.
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