**Core Concept**
Fistula-in-ano is a condition characterized by an abnormal communication between the anal canal and the perianal skin, often resulting from an infection or an abscess. The treatment of fistula-in-ano aims to close the fistulous tract and prevent recurrence.

**Why the Correct Answer is Right**
Fistulotomy is the preferred treatment for fistula-in-ano, as it involves making an incision in the fistulous tract to allow it to heal from the inside out. This approach is effective in resolving the condition in most cases. The procedure is usually performed under local anesthesia, and the fistulous tract is opened to its external opening. The interior of the tract is then cleaned, and the wound is left to heal by secondary intention. This method is preferred over other options because it allows for the complete excision of the fistulous tract and reduces the risk of recurrence.

**Why Each Wrong Option is Incorrect**
**Option A:** Anal dilatation is a procedure used to treat anal fissures, not fistula-in-ano. It involves the use of a dilator to stretch the anal sphincter muscles, which can help to relieve pain and promote healing in cases of anal fissures.

**Option B:** Fissurotomy is a surgical procedure used to treat anal fissures, not fistula-in-ano. It involves making an incision in the anal sphincter muscle to relieve tension and promote healing in cases of anal fissures.

**Option C:** Fistulectomy involves the complete excision of the fistulous tract, but it is not the preferred treatment for fistula-in-ano. This approach can be associated with higher risks of complications, such as incontinence and infection, and is generally reserved for complex cases.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the treatment of choice for fistula-in-ano depends on the location, size, and complexity of the fistulous tract. A thorough examination and evaluation by a surgeon are necessary to determine the best course of treatment.

**✓ Correct Answer: D. Fistulotomy**