A 62-year-old former smoker presents with a 3-month history of chronic cough and 5 kg weight loss. High-resolution CT chest reveals a 2.8 cm peripheral mass in the right upper lobe. The structure marked **A** shows a spiculated margin with a linear band of soft tissue tethering the mass to the visceral pleura (pleural tag). Which of the following best describes the pathologic basis of these imaging findings?

Explanation

## Why option 1 is right The spiculated margin and pleural tag seen in structure **A** are hallmark radiologic features of primary lung adenocarcinoma. The spiculation reflects desmoplastic stromal reaction and lymphangitic tumor spread along interlobular septa, while the pleural tag represents fibrous retraction of the visceral pleura toward the tumor mass. These findings have a positive predictive value >90% for malignancy and are classic for adenocarcinoma, the most common histologic subtype of NSCLC and the leading lung cancer in never-smokers and women. Adenocarcinoma characteristically arises in the lung periphery, in contrast to squamous cell carcinoma which is centrally located (Robbins 10e, Lung Tumors). ## Why each distractor is wrong - **Option 2 (cavitary necrosis)**: While cavitation can occur in lung adenocarcinoma (pseudocavitation), it is not the primary pathologic basis of spiculation and pleural tagging. Cavitary lesions are more typical of squamous cell carcinoma and tuberculosis. The spiculated margin is driven by desmoplasia and lymphangitic spread, not necrosis. - **Option 3 (fungal colonization)**: This describes an aspergilloma (structure **C** in the diagram), which presents with an air crescent sign and is seen in cavitary lung disease or immunocompromised states. Fungal lesions do not produce the characteristic spiculation and pleural tag pattern of malignancy. - **Option 4 (vascular malformation)**: This describes a pulmonary arteriovenous malformation (structure **D**), which is a benign vascular lesion without spiculation, pleural tagging, or malignancy-associated imaging features. AVMs are incidental findings often associated with hereditary hemorrhagic telangiectasia. **High-Yield:** Spiculated margin + pleural tag = desmoplasia + lymphangitic spread + pleural retraction = lung adenocarcinoma until proven otherwise; PPV >90% for malignancy. [cite: Robbins 10e — Lung Tumors; Fleischner Society Lung Nodule Guidelines]