Most Appropriate Initial Investigation for Rectal Cancer Patient with Dyspnea
A chest radiograph (CXR) is the most appropriate initial investigation for a patient with rectal cancer presenting with dyspnea of 15 days duration.
Rationale for Chest Radiography as First-Line Investigation
The American College of Radiology (ACR) Appropriateness Criteria (2025) explicitly recommends chest radiography as the first-line imaging modality for patients with chronic dyspnea of noncardiovascular origin 1. This represents the most current evidence-based guideline for this clinical scenario.
Why Chest Radiography is Optimal
Chest radiography should generally be the initial imaging study in chronic dyspnea, as it provides sufficient diagnostic information to justify its routine use and can reveal a wide variety of abnormalities that guide further imaging decisions 1.
In patients with rectal cancer, chest radiography serves dual purposes: evaluating the cause of dyspnea AND screening for pulmonary metastases, which are common in colorectal malignancies 2, 3.
Using an algorithmic approach, the combination of chest radiograph and laboratory evaluation results in a specific diagnosis in one-third of cases 1.
Critical Context: Rectal Cancer and Pulmonary Metastases
Pulmonary metastasis is frequent in rectal cancer, and chest imaging is recommended for preoperative staging in these patients 3, 4.
In a study of 103 rectal cancer patients, 8.7% had pulmonary metastases detected on imaging, and chest X-ray failed to detect metastases in 44% of these cases 3. However, CXR remains the appropriate initial test, with CT reserved for abnormal findings or high clinical suspicion.
Chest CT detected metastatic disease in 17% of patients with normal chest X-rays in one series, particularly in tumors within 5 cm of the anal verge 2.
Why Other Options Are Less Appropriate
ECG (Option B)
- ECG evaluates cardiac causes of dyspnea, but the ACR guidelines prioritize chest radiography for initial evaluation of dyspnea when the etiology is unclear 1.
- ECG would be appropriate if cardiac ischemia or arrhythmia were suspected, but this is not the primary concern in a cancer patient with subacute dyspnea.
V/Q Scan (Option C)
- V/Q scanning is specific for pulmonary embolism evaluation, not a first-line test for undifferentiated dyspnea 1.
- While cancer patients have increased thrombotic risk, V/Q scanning would only be appropriate after initial chest radiography suggests pulmonary embolism or if there are specific clinical features of PE.
Pulmonary Function Tests (Option D)
- PFTs are not imaging studies and do not evaluate for structural lung disease or metastases 1.
- PFTs may be useful later if obstructive or restrictive lung disease is suspected, but cannot detect the life-threatening causes of dyspnea in a cancer patient (metastases, pleural effusion, lymphangitic carcinomatosis).
Clinical Algorithm
Step 1: Obtain chest radiograph (CXR) as initial investigation 1.
Step 2: If CXR is abnormal or shows indeterminate findings, proceed to chest CT without contrast for further characterization 1.
Step 3: If CXR is normal but clinical suspicion remains high (particularly for metastatic disease in rectal cancer), chest CT is indicated as it detects lesions missed by plain radiography 2, 3.
Important Caveats
Chest radiography has significant limitations: it may miss up to 50% of pulmonary nodules and metastases compared to CT 5.
In rectal cancer patients with locally advanced disease (T3/T4), particularly tumors in the mid or lower rectum, chest CT should be strongly considered even with normal CXR due to the high rate of occult pulmonary metastases that alter treatment strategy 3.
Pulmonary tumor microembolism can present with severe dyspnea and completely normal imaging, including both CXR and CT, though this is rare 6. If dyspnea is severe and progressive with negative imaging, consider tissue diagnosis.
The 15-day duration qualifies as subacute to chronic dyspnea (>2 weeks), making the systematic approach outlined in the ACR guidelines appropriate rather than an acute emergency workup 1.
Answer: A) CXR