**Core Concept**
Ulcerative colitis (UC) is a chronic inflammatory bowel disease (IBD) characterized by diffuse mucosal inflammation, typically starting from the rectum and extending proximally in a continuous manner. The extent and distribution of UC can vary, with different patterns described based on the location and extent of colonic involvement.

**Why the Correct Answer is Right**
The correct answer, **B. Left sided colon distal to splenic flexure is only involved**, refers to pancolitis that spares the right side of the colon, specifically the part distal to the splenic flexure. This pattern is consistent with pancolitis that does not extend beyond the splenic flexure, which is a common variant of left-sided UC. The left-sided involvement in this context refers to the involvement of the descending colon, sigmoid colon, and rectum, while sparing the right-sided colon.

**Why Each Wrong Option is Incorrect**
**Option A:** Proctitis is a more limited form of UC, where only the rectum is involved. While proctitis can be a feature of UC, it does not specifically refer to distal colitis.

**Option C:** Mid transverse colitis is not a recognized pattern of UC. UC typically involves the rectum and extends proximally in a continuous manner, rather than skipping over segments of the colon.

**Option D:** This option is incorrect because the correct answer, B, is indeed a recognized pattern of UC.

**Clinical Pearl / High-Yield Fact**
In UC, the location and extent of colonic involvement can be an important clue to the diagnosis. A patient with pancolitis that spares the right side of the colon, specifically the part distal to the splenic flexure, should be suspected to have left-sided UC.

**✓ Correct Answer: B. Left sided colon distal to splenic flexure is only involved**