Investigation of choice for fistula in ano is
**Core Concept**
The investigation of choice for fistula-in-ano involves evaluating the anatomy and possible complications of the fistula, such as abscess formation or involvement of the anal sphincter. This requires a thorough imaging technique that can provide detailed images of the anal canal and surrounding tissues.
**Why the Correct Answer is Right**
The correct investigation of choice for fistula-in-ano is a **magnetic resonance imaging (MRI)**, specifically using a high-resolution MRI with endo-anal coils. This imaging modality provides detailed images of the anal canal and surrounding tissues, allowing for accurate assessment of the fistula's location, size, and involvement of the anal sphincter. MRI is particularly useful in identifying the internal opening of the fistula, which is essential for surgical planning.
**Why Each Wrong Option is Incorrect**
**Option A:** **Computed Tomography (CT)** scans are not typically used for fistula-in-ano as they do not provide sufficient resolution of the anal canal and surrounding tissues.
**Option B:** **Barium enemas** are used for evaluating the colon and rectum, but they are not ideal for fistula-in-ano as they may not accurately demonstrate the fistula's location or involvement of the anal sphincter.
**Option C:** **Endo-anal ultrasound** is a useful tool for evaluating the anal sphincter and detecting fistula-in-ano, but it may not provide a complete assessment of the fistula's anatomy and surrounding tissues.
**Clinical Pearl / High-Yield Fact**
When evaluating a patient with fistula-in-ano, it is essential to perform a thorough physical examination and use imaging techniques, such as MRI, to accurately assess the fistula's location and involvement of the anal sphincter.
**Correct Answer: C. Endo-anal ultrasound**