. Internal fistulas with colonic diverticulitis are most often
**Core Concept**
Internal fistulas in the context of colonic diverticulitis refer to abnormal connections between the diverticulated colon and adjacent organs, such as the bladder, vagina, or small intestine. This phenomenon is a complication of diverticulitis, often resulting from perforation of a diverticulum.
**Why the Correct Answer is Right**
The most common site for internal fistulas in colonic diverticulitis is between the sigmoid colon and the bladder, known as a colovesical fistula. This occurs due to the proximity of the sigmoid colon to the bladder and the increased pressure within the sigmoid colon during episodes of diverticulitis. The inflammatory process leads to erosion of the mucosa and subsequent formation of a fistulous tract between the two organs.
**Why Each Wrong Option is Incorrect**
**Option A:** While rectovaginal fistulas can occur in women with diverticulitis, they are less common than colovesical fistulas.
**Option B:** Small bowel fistulas can occur, but they are relatively rare compared to colovesical fistulas.
**Option C:** Colorectal fistulas to other organs, such as the skin or the small intestine, are possible but not the most common type associated with diverticulitis.
**Clinical Pearl / High-Yield Fact**
In patients with colonic diverticulitis and suspected internal fistula, a CT urogram or barium enema can help identify the location and extent of the fistula.
**Correct Answer:** C.