Diagnostic Imaging for Left-Sided Abdominal Pain Radiating to the Lower Back
CT of the abdomen and pelvis with intravenous contrast is the most appropriate initial imaging study for a patient with left-sided abdominal pain radiating to the lower back. 1
Rationale for CT as First-Line Imaging
- CT is the most useful examination for left lower quadrant pain, providing accurate diagnosis and guiding appropriate management regardless of patient sex or body habitus 1
- CT is highly sensitive for detecting small quantities of extraluminal air, which can indicate perforation with potential surgical implications 1
- CT can effectively evaluate the most common causes of left-sided abdominal pain, including diverticulitis, which is frequently associated with pain radiating to the back 1
- CT has superior sensitivity (>95%) for detecting diverticulitis and can provide critical information about disease extent and complications such as abscess formation 1
- CT can identify alternative diagnoses that may mimic diverticulitis or other causes of left-sided abdominal pain 1
Contrast Considerations
- Intravenous (IV) contrast improves characterization and detection of:
- Bowel wall pathology
- Pericolic abnormalities
- Vascular pathology
- Intra-abdominal fluid collections 1
- While unenhanced CT can be accurate in some cases, IV contrast provides optimal assessment of inflammatory processes and potential complications 1
- Low-dose CT techniques can achieve 75-90% radiation dose reduction compared to standard-dose protocols while maintaining similar sensitivity and specificity 1
Special Population Considerations
- For premenopausal women, if gynecologic pathology is suspected as the cause of left lower quadrant pain, transvaginal pelvic ultrasound may be the preferred initial imaging study 1
- For patients with suspected urolithiasis as the cause of flank pain, unenhanced CT is recommended with sensitivity and specificity approaching 100% 1
Alternative Imaging Options (Not First-Line)
Ultrasound
- Transabdominal ultrasound has variable performance for diagnosing causes of left-sided abdominal pain 1
- Graded-compression sonography has reported sensitivity of 77-98% and specificity of 80-99% for diverticulitis, but is highly operator-dependent 1
- Ultrasound is less common in the United States for initial imaging of non-gynecologic left lower quadrant pain 1
- Technical limitations include difficulty in patients who are obese and potential discomfort during compression in patients with acute pain 1
MRI
- MRI is not recommended as the initial imaging test for acute left-sided abdominal pain 1
- Limitations include:
- Less sensitivity for extraluminal air and urinary tract calculi
- Longer acquisition time
- Need for screening for metal/devices
- Greater susceptibility to motion artifacts in symptomatic patients 1
- May be considered in specific scenarios such as pregnant patients when ultrasound is inconclusive 2
Plain Radiography
- Plain radiography has limited diagnostic value in evaluating left-sided abdominal pain 1
- CT is more sensitive and specific for detecting important findings such as extraluminal air, bowel obstruction, or urolithiasis 1
- Plain radiography may only play a role in the triage of severely ill patients with a surgical abdomen 1, 3
Contrast Enema
- Contrast enema is not useful as an initial imaging test for left-sided abdominal pain 1
- It has been largely supplanted by CT for the evaluation of diverticulitis and other causes of left lower quadrant pain 1
- It cannot show extraluminal abnormalities such as abscesses and pericolonic inflammation 1
Common Pitfalls to Avoid
- Relying solely on clinical assessment for diagnosis of conditions like diverticulitis can lead to misdiagnosis in 34-68% of cases 1
- Failure to use IV contrast may limit detection of inflammatory processes and potential complications 1
- Overlooking the possibility of perforated colon cancer, which can mimic diverticulitis both clinically and radiographically 1
- Neglecting to consider extra-abdominal causes of pain such as renal pathology (e.g., Page kidney) that may present with flank pain radiating to the back 4
- Performing unnecessary plain radiographs, which have been shown to have low sensitivity and accuracy in the evaluation of acute abdominal pain 3