Differentials
Anal fissure
SIGNS / SYMPTOMS
Pain occurs primarily during bowel movements and may improve in the next few hours. Anal fissures are frequently associated with rectal bleeding.
Physical examination can distinguish between the 2 conditions although anesthesia will occasionally be needed for an adequate examination. On physical examination, fissures are located in the anterior or posterior midline, are without induration, and are tender to palpation. Secondary finding of an anal fissure may be present (sentinel pile).
INVESTIGATIONS
Diagnosis is usually clinical. However, MRI or CT pelvis may be used in difficult-to-examine cases to exclude anal fissure (both investigations are very sensitive and specific for anorectal abscesses).
Thrombosed hemorrhoid
SIGNS / SYMPTOMS
Usually presents with the sudden onset of perianal pain and swelling.
On physical examination, thrombosed hemorrhoids are swollen, with minimal induration or signs of inflammation, and are frequently bluish in color.
INVESTIGATIONS
Diagnosis is clinical.
Pilonidal abscess
SIGNS / SYMPTOMS
Very difficult to distinguish clinically, but physical examination may do so. While anorectal abscesses are usually immediately adjacent to the anus, pilonidal abscesses are characteristically located in the intergluteal region and frequently have a visible sinus tract in the midline.
INVESTIGATIONS
MRI or CT pelvis may be used in difficult-to-examine cases to exclude pilonidal abscess (both investigations are very sensitive and specific for anorectal abscesses).
Infected epidermoid inclusion cyst
SIGNS / SYMPTOMS
Difficult to distinguish clinically, but physical examination can do so in some cases. While anorectal abscesses are usually immediately adjacent to the anus, infected epidermoid inclusion cysts are more commonly >3 cm from the anal verge.
INVESTIGATIONS
MRI or CT pelvis may be used in difficult-to-examine cases to exclude infected epidermoid inclusion cyst (both investigations are very sensitive and specific for anorectal abscesses).
Perianal hidradenitis suppurativa
SIGNS / SYMPTOMS
The presenting signs and symptoms are the same as those for anorectal abscesses, but physical examination can often distinguish between the conditions. Perianal hidradenitis suppurativa is usually associated with hidradenitis in other areas, most commonly the axilla and inguinal areas. While anorectal abscesses are usually single, abscesses associated with hidradenitis are more commonly multiple and usually associated with purulent drainage from multiple sinus tracts.
INVESTIGATIONS
Diagnosis is clinical.
STIs
SIGNS / SYMPTOMS
History of anal-receptive sex with or without immunosuppression (e.g., HIV), rectal discharge, severe anal pain, and malaise may be present.
Physical examination may reveal systemic fever, lymphadenopathy, or anal discharge. In addition, rectal examination, usually under anesthesia, will reveal rectal mucosal changes consistent with proctitis.
INVESTIGATIONS
Rectal swab for microscopy, Gram stain, and culture usually reveals the causative organism (e.g., Neisseria gonorrhoeae, Chlamydia trachomatis, Herpes simplex, Treponema pallidum).
In addition, stool microscopy and culture, serologic testing, and tissue biopsy may help confirm diagnosis.
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