Most Likely Diagnosis: Acute Diverticulitis
The most likely diagnosis is acute sigmoid diverticulitis, given the classic presentation of left lower quadrant pain, bright red rectal bleeding, and CT findings of segmental thickening of the descending and sigmoid colon in a 70-year-old woman.
Clinical Reasoning
This patient presents with the hallmark features of acute diverticulitis:
- Left lower quadrant pain with mild tenderness is the most common presenting symptom in adults with diverticulitis 1
- Segmental bowel wall thickening on CT scan of the descending and sigmoid colon represents one of the most common CT findings in acute diverticulitis, along with pericolonic fat stranding 1
- Bright red rectal bleeding can occur with diverticular disease, though it is more commonly associated with diverticulosis; however, it does not exclude diverticulitis 2
- Age 70 years places her in the high-risk demographic, as diverticulitis affects over half the population over 65 years 3
- Elevated white blood cell count (12,000) supports an inflammatory process consistent with diverticulitis 1
CT Imaging Interpretation
The CT findings are diagnostic for diverticulitis with sensitivity and specificity as high as 100% 1. The key finding of segmental thickening of the descending and sigmoid colon is one of the three most common CT findings in acute diverticulitis (the others being pericolonic fat stranding and visible diverticula) 1. CT is the preferred imaging modality for suspected diverticulitis and has a critical role in determining disease extent and severity 1.
Differential Diagnosis Considerations
While the presentation strongly suggests diverticulitis, other conditions to briefly consider include:
- Epiploic appendagitis: Can mimic diverticulitis with left lower quadrant pain but typically shows a fat-density ovoid lesion with hyperattenuating ring sign on CT, not segmental bowel wall thickening 4, 5
- Segmental colitis associated with diverticulosis (SCAD): A rare inflammatory condition that can present similarly but is a distinct entity requiring colonoscopy for definitive diagnosis 6
- Colorectal malignancy: Must be excluded, particularly given that 5-7% of patients undergoing surgery for presumed diverticulitis have unsuspected carcinoma 2
Important Clinical Caveats
Colonoscopy should be performed 6-8 weeks after resolution of acute symptoms to exclude underlying malignancy, as this is a critical follow-up step that cannot be overlooked 7. The presence of rectal bleeding, while consistent with diverticular disease, makes this follow-up even more imperative.
The absence of pericolonic fat stranding mentioned in the CT report (only segmental thickening noted) suggests this may be early or uncomplicated diverticulitis 1. The stable vital signs and absence of peritoneal signs (no rebound or guarding) support uncomplicated disease that can typically be managed medically 1, 2.
Red flags that would suggest complicated diverticulitis requiring more aggressive intervention include: fever, inability to pass gas/stool, severe tenderness with guarding, vomiting, or signs of shock 8. This patient does not exhibit these concerning features.