Discussion
Diagnosis With Brief Discussion
- Diagnosis
- Squamous cell carcinoma arising from smoking-related interstitial fibrosis
- Radiologic Findings
- Fig 1. Chest radiograph shows reticular opacity predominantly in bilateral lower lobes
Fig 2-3. HRCT shows multiple thin-walled cysts with interrupted septa, reticulation and traction bronchiectasis in both lungs, especially in LUL superior lingular segment, with centrilobular and paraseptal emphysema of the background lung.
Fig 4-5. HRCT shows a 4.1cm-sized solid mass growing along the cyst wall in the RLL posterior basal segment.

- Brief Review
- This patient had a pathologically confirmed squamous cell carcinoma growing along the cyst wall of smoking-related interstitial fibrosis (SRIF).
SRIF is a distinct form of chronic interstitial fibrosis observed in heavy smokers, which is clinically often asymptomatic or mild and frequently discovered as an incidental finding in lung cancer resection specimens. Pathologically, SRIF is characterized by the deposition of deep eosinophilic, thick, hyalinized, "ropey" collagen within alveolar septal walls, resulting in septal thickening; unlike other fibrotic lung diseases, it is distinguished by minimal or absent surrounding inflammation. This fibrosis primarily involves the subpleural and centrilobular parenchyma and, when accompanied by emphysema, manifests in the form of "Airspace Enlargement with Fibrosis (AEF)."
Radiologically, SRIF presents a unique pattern of coexisting emphysema and fibrosis. The most characteristic finding is large, thin-walled cysts formed by fibrosis surrounding emphysematous spaces, which closely mimic the honeycombing of Usual Interstitial Pneumonia (UIP), posing a risk of misdiagnosis. However, SRIF cysts may show interrupted septa, thinner wall, and often spare the subpleural area. Furthermore, on dynamic CT, SRIF cysts may demonstrate collapse on the expiratory phase due to airway communication, whereas honeycombing cysts typically show air-trapping. In conclusion, although SRIF can mimic the radiological pattern of UIP, it carries a much better prognosis, requiring careful differentiation based on smoking history and a detailed analysis of cyst morphology and distribution.
- References
- 1. Kumar A, Cherian SV, Vassallo R, Yi ES, Ryu JH. Current Concepts in Pathogenesis, Diagnosis, and Management of Smoking-Related Interstitial Lung Diseases. Chest. 2018;154(2):394-408.
2. Ryerson CJ, Collard HR. Update on the diagnosis and classification of ILD. Curr Opin Pulm Med. 2013;19:453-459.
3. Katzenstein A-LA. Smoking-related interstitial fibrosis (SRIF): pathologic findings and distinction from other chronic fibrosing lung diseases. J Clin Pathol. 2013;66:882-887.
4. Moore AE, Fels Elliott DR, Kanne JP, Lee GM, Walker CM. Smoking Related Interstitial Lung Disease: Pattern Really Does Matter. Semin Roentgenol. 2025;00:1-16.
5. Watanabe Y, Kawabata Y, Kanauchi T et al. Multiple, Thin-Walled Cysts Are One of the HRCT Features of Airspace Enlargement with Fibrosis. Eur J Radiol. 2015;84(5):986-992.
6. Pathologic imagy: Courtisey of 한정호, www.pathol.net
- Keywords