Differential Diagnosis
- Single most likely diagnosis
- Colorectal Cancer: The presence of a focal mass-like structure in the sigmoid colon concerning for malignancy, along with the patient's symptoms of bright red blood per rectum and abdominal pain, makes colorectal cancer a highly likely diagnosis. The recent normal colonoscopy with biopsies may seem contradictory, but it's possible that the cancer developed rapidly or was missed during the procedure.
- Other Likely diagnoses
- Diverticulitis: The patient's symptoms of abdominal pain and bright red blood per rectum, combined with the CT findings of wall thickening and possible colitis, could also suggest diverticulitis. However, the presence of a mass-like structure makes this diagnosis less likely.
- Inflammatory Bowel Disease (IBD) exacerbation: The patient has a history of follow-up with a doctor for Crohn's/UC, and the CT findings of wall thickening and possible colitis could indicate an IBD exacerbation. However, the presence of a mass-like structure and the patient's recent normal colonoscopy make this diagnosis less likely.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Ischemic Colitis: Although the patient's lactic acid levels decreased on repeat testing, ischemic colitis is a potentially life-threatening condition that should not be missed. The patient's symptoms of abdominal pain and bright red blood per rectum, combined with the CT findings of poor colonic wall delineation and fluid in the rectum, could suggest ischemic colitis.
- Infectious Colitis: The patient's symptoms of abdominal pain and bright red blood per rectum, combined with the CT findings of wall thickening and possible colitis, could also suggest infectious colitis. Although the patient denies recent antibiotic use, travel, or sick contacts, infectious colitis is a potentially life-threatening condition that should not be missed.
- Rare diagnoses
- Intussusception: Although rare in adults, intussusception could cause the patient's symptoms of abdominal pain and bright red blood per rectum. The CT findings of a focal mass-like structure could potentially represent an intussusception.
- Vascular Malformation: A vascular malformation, such as an arteriovenous malformation (AVM), could cause the patient's symptoms of bright red blood per rectum. However, this diagnosis is rare and would require further imaging or endoscopic evaluation to confirm.