What is the appropriate next diagnostic step for a 75‑year‑old woman with cough and a right mid‑lung nodular opacity on chest radiograph, given her prior history of pneumonia and findings of bibasilar atelectasis without pneumothorax, pleural effusion, or cardiomegaly?

Appropriate Next Diagnostic Step for a 75-Year-Old Woman with Right Mid-Lung Nodular Opacity

Proceed directly to CT chest with IV contrast to characterize the nodular opacity and exclude malignancy, as recommended by the radiologist's impression and supported by multiple guidelines for evaluating lung nodules in elderly patients with risk factors.

Rationale for CT Chest as the Immediate Next Step

• The chest radiograph impression explicitly states "malignancy must be excluded" and recommends "further evaluation with CT chest," providing direct guidance for the next diagnostic step 1.
• A nodular opacity on chest X-ray in a 75-year-old patient—especially one with prior pneumonia history—requires tissue characterization that plain radiography cannot provide 1.
• CT imaging is far more sensitive than chest radiography for detecting central airway tumors, characterizing nodule morphology (size, margins, calcification pattern), and identifying complications such as post-obstructive pneumonia or mediastinal lymphadenopathy 1.
• The bibasilar atelectasis noted on the current film may represent either age-related changes or early signs of airway obstruction from an endobronchial lesion, which CT can clarify 1.

Why CT Takes Priority Over Other Diagnostic Modalities

• Bronchoscopy is premature at this stage: While bronchoscopy is indicated when there is high suspicion of airway involvement by malignancy (e.g., hemoptysis, persistent symptoms despite antibiotics, or a central lesion on CT), it should follow—not precede—CT imaging to guide the procedure and assess for contraindications such as bleeding risk or vascular invasion 1.
• Empiric antibiotics alone are insufficient: Although infectious or inflammatory etiologies are mentioned in the radiographic differential, treating empirically without tissue diagnosis in a 75-year-old with a new nodular opacity risks delaying cancer diagnosis. If the nodule persists after a trial of antibiotics, malignancy becomes even more likely 1.
• Sputum cytology has low sensitivity: Spontaneously expectorated or induced sputum may provide a diagnosis in some cases of lung cancer, but its yield is poor for peripheral nodules and should not delay definitive imaging 1.

Structured Diagnostic Algorithm

1. Order CT chest with IV contrast immediately to characterize the nodular opacity, assess for lymphadenopathy, evaluate the airways for endobronchial lesions, and identify any pleural or mediastinal involvement 1.
2. If CT reveals a suspicious nodule (irregular margins, spiculation, size >8 mm, or associated lymphadenopathy): proceed to tissue diagnosis via bronchoscopy (for central lesions) or CT-guided biopsy (for peripheral lesions) 1.
3. If CT shows features consistent with infection (e.g., consolidation, tree-in-bud pattern, ground-glass opacities): initiate guideline-concordant antibiotics (e.g., amoxicillin 1 g three times daily or doxycycline 100 mg twice daily for outpatients; ceftriaxone 1–2 g IV daily plus azithromycin 500 mg daily for hospitalized patients) and repeat imaging in 4–6 weeks to confirm resolution 1, 2.
4. If the nodule persists or enlarges on follow-up imaging despite appropriate antibiotic therapy: malignancy is highly likely, and tissue diagnosis becomes mandatory 1.

Key Clinical Pitfalls to Avoid

• Do not assume the nodule is infectious without tissue confirmation or radiographic resolution: In elderly patients, especially smokers or those with prior pneumonia, the positive predictive value of a nodular opacity for malignancy is substantial, and delays in diagnosis worsen outcomes 1.
• Do not delay CT imaging to complete a prolonged antibiotic trial: While a short course of antibiotics (5–7 days) may be reasonable if infection is strongly suspected, CT should be obtained within 1–2 weeks to avoid missing a rapidly progressive cancer 1, 2.
• Do not rely solely on clinical improvement to exclude malignancy: Some lung cancers (e.g., bronchioloalveolar carcinoma) can present with cough and radiographic infiltrates that transiently improve with steroids or antibiotics, mimicking infection 1.
• Do not skip follow-up imaging: Even if the patient's cough resolves, a persistent nodule on chest X-ray mandates CT evaluation and, if necessary, repeat imaging at 6 weeks to document resolution or progression 1, 2.

Special Considerations in This Case

• Age and prior pneumonia history increase malignancy risk: A 75-year-old with recurrent or persistent respiratory symptoms has a higher pretest probability of lung cancer, particularly if there is any smoking history (not specified here but should be elicited) 1.
• Cough as a presenting symptom of lung cancer: Cough is present in >65% of patients at the time lung cancer is diagnosed, and while it is nonspecific, its persistence despite treatment should raise suspicion 1.
• Normal chest radiograph does not exclude malignancy: Studies show that 13–16% of patients with bronchogenic carcinoma have normal chest X-rays, and CT imaging or bronchoscopy may reveal occult central airway tumors 1.

Summary of Evidence Strength

• CT chest for nodule evaluation: Strong recommendation based on multiple guidelines (ACCP, BTS, Fleischner Society) and high-quality observational data showing superior sensitivity and specificity compared with plain radiography 1.
• Bronchoscopy after CT: Conditional recommendation; indicated when CT suggests central airway involvement or when tissue diagnosis is required after CT characterization 1.
• Empiric antibiotics without imaging follow-up: Not recommended; associated with delayed cancer diagnosis and worse outcomes in elderly patients with persistent nodular opacities 1.