Septal Thickening

Summary

This video delves into the diagnostic significance of smooth, nodular, and coarse septal thickening in the lungs, emphasizing the differentiation of common causes like pulmonary edema and lymphatic tumors, as well as rare conditions such as Erdheim-Chester and Niemann-Pick diseases. Key diagnostic tips include analyzing CT and chest X-ray findings, the symmetry of septal thickening, and associated clinical signs. The video provides a structured approach to interpreting septal thickening, guiding healthcare professionals through complex differential diagnoses and ensuring a thorough understanding of these pulmonary conditions.

Takeaways

• 😀 Interlobular septal thickening refers to the thickening of the interlobular septa, which outline secondary pulmonary lobules in the lungs.
• 😀 There are five major lung interstitial compartments: peribronchovascular, subpleural, interlobular septa, intralobular interstitial, and additional minor interstitial components.
• 😀 Septal thickening can appear as smooth, nodular (beaded), or coarse/irregular on CT, with each pattern suggesting different underlying causes.
• 😀 Smooth septal thickening is often seen in hydrostatic pulmonary edema, lymphatic processes, or infiltrative disorders.
• 😀 Nodular septal thickening usually represents a beaded appearance and can be associated with tumor infiltration, such as lymphangitic carcinomatosis.
• 😀 Coarse or irregular septal thickening is typically seen in fibrotic lung diseases and may accompany reticulation, honeycombing, or traction bronchiectasis.
• 😀 Pulmonary edema on imaging may show curly A, B, or C lines on chest X-ray and is often accompanied by cardiomegaly and pleural effusions.
• 😀 Pulmonary veno-occlusive disease (PVOD) presents with a classic triad: septal thickening, pulmonary hypertension (dilated main PA), and lymphadenopathy.
• 😀 Lymphatic distension can result from congenital disorders like lymphangioleiomyomatosis or secondary causes such as thoracic duct injury, often producing chylous pleural effusions.
• 😀 Rare congenital disorders causing septal thickening include Erdheim-Chester disease (multisystem involvement) and Niemann-Pick disease (glycogen storage disease).
• 😀 The primary approach to septal thickening involves assessing symmetry, evaluating associated findings (e.g., cardiomegaly, effusions, systemic disease), and prioritizing differential diagnosis: pulmonary edema and lymphangitic tumor being the most common.

Q & A

What is the interlobular septum and where is it located in the lung?

The interlobular septum is connective tissue that separates secondary pulmonary lobules, which are the major architectural units of the lung. It is located at the periphery of each secondary pulmonary lobule, surrounding it and outlining its boundaries.

What are the three main patterns of septal thickening on CT imaging?

The three main patterns are: 1) Smooth septal thickening – straight, well-defined lines; 2) Nodular septal thickening – beaded or slightly irregular appearance along septa; 3) Coarse/irregular septal thickening – shaggy, corkscrew-like lines, often associated with fibrosis.

How does smooth interlobular septal thickening appear on chest X-ray?

On chest X-ray, smooth septal thickening appears as short, choppy lines at the lung periphery, known as curly B-lines. There may also be lines emanating from the hilum (curly A-lines) and a lace-like network in the lower lung zones (curly C-lines).

What are the most common causes of smooth interlobular septal thickening?

The most common causes are interstitial pulmonary edema, typically hydrostatic or cardiogenic, and lymphangitic tumor (lymphangitic carcinomatosis).

What imaging clues suggest pulmonary edema as the cause of septal thickening?

Imaging clues include symmetric septal thickening, cardiomegaly on chest X-ray, pleural effusions, and ground-glass opacities on CT, usually worse in the lower lung zones. Unilateral edema may occur in venous obstruction or post-ablation settings.

What is the classic triad seen in pulmonary veno-occlusive disease (PVOD)?

The classic triad in PVOD includes 1) smooth septal thickening, 2) pulmonary hypertension (dilated main pulmonary artery), and 3) lymphadenopathy. Patients may worsen when given pulmonary arterial dilators.

How can lymphatic disorders cause smooth septal thickening?

Lymphatic disorders, including congenital conditions like lymphangiomatosis or secondary causes such as thoracic duct injury, can cause smooth septal thickening. Imaging may show dilated lymphatic vessels and chylous pleural effusions.

How does lymphangitic carcinomatosis present on imaging?

Lymphangitic carcinomatosis often presents with smooth or nodular septal thickening, sometimes unilateral, with possible bronchovascular interstitial thickening. It usually occurs in patients with a history of malignancy and may progress from smooth to nodular appearance.

What rare congenital disorders can produce smooth septal thickening?

Rare congenital disorders include Erdheim-Chester disease, a histiocytic disorder with multisystem involvement, and Niemann-Pick disease, a glycogen/lipid storage disorder, both of which can manifest with diffuse smooth septal thickening on CT.

What is the recommended diagnostic approach when encountering septal thickening?

The approach involves assessing symmetry (symmetric favors pulmonary edema, unilateral may indicate lymphangitic tumor or venous obstruction), evaluating associated findings (cardiomegaly, pleural effusions, mediastinal lesions, multisystem involvement), and considering pattern progression (smooth → nodular, coarse/irregular → fibrosis).

What are curly lines and what do they signify on chest X-ray?

Curly lines are short, choppy or lace-like lines seen on chest X-ray that represent smooth interlobular septal thickening. They are classified as curly A, B, or C lines depending on their location and orientation, and can indicate interstitial edema or other causes of septal thickening.

How does venous obstruction after pulmonary vein ablation present on imaging?

Venous obstruction post-ablation can cause unilateral pulmonary edema with smooth septal thickening, pleural effusions, and bronchovascular thickening. CT may show absent or stenotic pulmonary veins on the affected side, indicating impaired venous drainage.