Intentional Engagement

1. Findings

Paraseptal Emphysema, Blebs, Bullae, and Simple Lung Cysts: Structural Evaluation

Descriptor	Paraseptal Emphysema	Blebs	Bullae	Simple Lung Cysts
Parts (Components)	Distal alveolar ducts and sacs of the secondary lobule	Focal air collection within the subpleural alveolar spaces	Coalesced emphysematous airspaces, sometimes with fibrous walls	Thin-walled, well-defined air-filled structure within normal lung tissue
Size	Small to moderate, individual airspaces usually ≤10 mm	Small, typically <1 cm	Large, ≥1 cm (can become “giant bullae” >5 cm)	Varies, typically >1 cm but often smaller than bullae
Shape	Linear, rectangular, or elongated, follows interlobular septa	Round or oval, smooth margins	Heterogeneous, lobulated, irregular	Round or oval, uniform, well-circumscribed
Position	Subpleural, along interlobular septa and fissures, predominantly upper lobes	Subpleural, typically in apices	Subpleural or intraparenchymal, predominantly upper lobes but can be anywhere	Can be anywhere in the lung, often randomly distributed
Character (Wall/Contents)	Thin-walled, may contain residual septal remnants or fibrous strands	Extremely thin-walled, almost imperceptible	Thin-walled, but may have fibrous septations or internal strands	Well-defined, thin-walled, smooth, with no solid components
Multiplicity	Multiple and uniform, aligned along pleura	Usually isolated, but can be clustered	Single or multiple, size varies significantly	Single or multiple, may be scattered throughout the lung
Alignment	Linear arrangement, parallel to pleura and fissures	Randomly distributed, often at lung apices	Randomly distributed or clustered, often distorting adjacent lung	Random or scattered, no specific alignment to pleura or fissures
CT Appearance	Well-demarcated, linear subpleural lucencies, preserving interlobular septa	Small, focal, subpleural air spaces, often at lung apices	Large air-filled spaces with irregular contours, may compress adjacent lung	Round, well-defined air-filled spaces with thin, uniform walls
Clinical Significance	Can progress to bullae, may contribute to spontaneous pneumothorax	Most common cause of primary spontaneous pneumothorax, often in young adults	Can cause dyspnea, lung compression, or rupture leading to pneumothorax	Usually incidental, but multiple cysts may suggest cystic lung diseases (e.g., LAM, Birt-Hogg-Dubé, LIP)

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Key Takeaways:

• Paraseptal emphysema has a structured, linear, rectangular appearance, while bullae are heterogeneous in size and shape.
• Blebs are small and localized, while bullae are larger and can distort lung architecture.
• Simple lung cysts are well-defined, uniform, and can appear anywhere in the lung, unrelated to emphysema.
• Cysts differ from bullae in that they are not related to destructive emphysema and may be part of cystic lung diseases (e.g., lymphangioleiomyomatosis [LAM], Birt-Hogg-Dubé, or LIP).

Pathophysiology of Paraseptal Emphysema