Key points
- Paraseptal (distal acinar) emphysema – alveolar destruction at the periphery of the acinus, abutting the pleura and interlobular septa.
- Single subpleural row of thin-walled lucencies along the pleura, fissures and septa, with upper lobe predominance.
- Lucencies are typically <1 cm; spaces ≥1 cm are bullae, which may coalesce into giant bullae.
- Smoking is the usual cause; predisposes to spontaneous pneumothorax.
- Chief mimic is honeycombing – one layer, upper lobes and no fibrosis versus stacked layers, lung bases and reticulation.
Imaging findings
- CT: round or oval lucencies in a single row along the subpleural lung, interlobar fissures and interlobular septa; walls are thin and well defined, corresponding to the septa.
- CT: upper lobe, often posterior, predominance; may be isolated or combined with centrilobular emphysema; subpleural bullae are frequent.
- Radiograph: typically normal unless bullae are large enough to appear as peripheral avascular lucencies.
Differential diagnosis
- Honeycombing (UIP) – stacked rows of cysts, basal and subpleural, with reticulation and traction bronchiectasis.
- Centrilobular emphysema – lucencies centred within the secondary lobule, sparing a subpleural rim, without perceptible walls.
- Lymphangioleiomyomatosis – diffuse round thin-walled cysts in all zones without a zonal gradient.
- Pulmonary Langerhans cell histiocytosis – bizarre-shaped cysts with nodules, sparing the costophrenic angles.
Classification
- Fleischner Society emphysema subtypes: centrilobular, panlobular, paraseptal and irregular (cicatricial); paraseptal corresponds to distal acinar emphysema.
What to do next
- Smoking cessation; spirometry and DLCO may be normal in isolated disease.
- Counsel on pneumothorax risk from bulla rupture; bullectomy with pleurodesis for recurrent pneumothorax or a giant bulla compressing lung.
- Review the lower lobes for fibrosis – emphysema with basal honeycombing suggests combined pulmonary fibrosis and emphysema (CPFE), in which DLCO is markedly reduced.
References
- Yuan Q, Yang X, Gu Y, Nie K, Liu J, Yue S, et al. Ultra-Low-Dose Photon-counting Detector CT for Emphysema Assessment: A Head-to-Head Comparative Study with Low-Dose CT. Radiology. 2026;318(1):e251609. PMID: 41557898.
- Cabanne E, Revel MP. Post-COVID-19 Vanishing Paraseptal Emphysema. Radiology. 2021;299(2):E249. PMID: 33620292.
- Sharma N, Justaniah AM, Kanne JP, Gurney JW, Mohammed TL. Vanishing lung syndrome (giant bullous emphysema): CT findings in 7 patients and a literature review. J Thorac Imaging. 2009;24(3):227-30. PMID: 19704328.
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