A patient presents with a deep tear at the posterior aspect of the anal canal causing severe pain with defecation and bright red blood; which is the most likely diagnosis?

• A. External hemorrhoid
• B. Anal fissure
• C. Internal hemorrhoid
• D. Perianal abscess

Answer: (B)

A tear in the anoderm at the posterior midline with severe pain during defecation and bright red blood is the classic presentation of an anal fissure. These tears are typically located in the posterior aspect because that area has less robust blood supply and is subjected to high sphincter tone, which can cause ischemia and painful spasm. The key clues are the intense pain with bowel movements and fresh blood on the toilet paper, reflecting a shallow, linear mucosal tear rather than a lump or abscess.

External hemorrhoids can bleed and be painful if thrombosed, but they are usually described as palpable lumps at the anal verge rather than a discrete mucosal tear with focal severe pain on defecation. Internal hemorrhoids tend to bleed but are often painless unless they prolapse and strangulate. A perianal abscess causes fever, swelling, and tender fluctuance, not a solitary deep tear with pure, sharp pain at defecation. Thus, the presentation fits an anal fissure best.