Bronchioles

2. Findings and Diagnosis

 

Causes of Thickened Interlobular Septa on CT

Cause	Pattern of Septal Thickening	Key Differentiation	Additional CT Findings
Pulmonary Edema (Cardiogenic – Most Common)	Smooth	Associated with cardiomegaly, pleural effusions, and vascular redistribution	Kerley B lines, peribronchial cuffing, ground-glass opacities
Pulmonary Edema (Non-Cardiogenic – ARDS, Renal Failure)	Smooth	No cardiomegaly, often with diffuse lung involvement	Ground-glass opacities, airspace consolidation
Lymphangitic Carcinomatosis	Nodular (“Beaded Septum Sign”)	Irregular, nodular thickening following lymphatic routes, often asymmetric	Pleural effusions, perihilar/mediastinal lymphadenopathy, interstitial nodules
Sarcoidosis	Nodular (“Beaded Septum Sign”)	Perilymphatic distribution, upper lobe predominance	Hilar and mediastinal lymphadenopathy, peribronchovascular nodules
Interstitial Pulmonary Fibrosis (UIP, NSIP, Chronic HP)	Smooth or Nodular	Reticular opacities, honeycombing in UIP, subpleural fibrosis	Traction bronchiectasis, subpleural reticulation
Veno-Occlusive Disease / Pulmonary Hypertension	Smooth	Associated with signs of right heart strain, pulmonary artery enlargement	Centrilobular ground-glass nodules, pleural effusions
Lymphoproliferative Disorders (LIP, NHL, CLL, Multiple Myeloma)	Nodular or Smooth	Diffuse interstitial involvement with lymphadenopathy	Cystic lung changes in LIP, ground-glass opacities
Silicosis / Pneumoconiosis	Nodular (“Beaded Septum Sign”)	Upper lobe fibrosis, nodules along lymphatics	Eggshell calcification of lymph nodes, conglomerate masses

Key Differentiation:

• Smooth Septal Thickening → Common in pulmonary edema, fibrosis, and veno-occlusive disease.
• Nodular (Beaded Septum Sign) → Seen in lymphangitic carcinomatosis, sarcoidosis, and certain lymphoproliferative disorders.

MCQ

1. What is the most likely physiological cause of smooth interlobular septal thickening in CHF?

A) Lymphatic obstruction from tumor spread
B) Inflammatory cell infiltration
C) Elevated pulmonary capillary wedge pressure
D) Fibrosis of the interstitium

Correct Answer: C — Elevated pulmonary capillary wedge pressure

• Increased left atrial pressure leads to pulmonary venous congestion, resulting in fluid leaking into the septa and causing smooth thickening.

Why the others are incorrect:

• A) Tumor spread causes nodular, not smooth, septal thickening.

• B) Inflammatory infiltration is more typical in infection or interstitial pneumonias.

• D) Fibrosis leads to irregular thickening and architectural distortion.

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2. Which part of the secondary pulmonary lobule contains the interlobular septa?

A) Central arteriole
B) Terminal bronchiole
C) Centrilobular parenchyma
D) Periphery of the lobule

Correct Answer: D — Periphery of the lobule

• The interlobular septa outline the lobule and contain pulmonary veins and lymphatics.

Why the others are incorrect:

• A) Central arterioles run through the middle, not the periphery.

• B) Terminal bronchioles also run centrally.

• C) Centrilobular parenchyma refers to the middle tissue zone, not the boundary.

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🩺 Clinical

3. Which of the following symptoms is most suggestive of interstitial edema in CHF?

A) Fever and cough
B) Progressive orthopnea
C) Weight loss
D) Hemoptysis

Correct Answer: B — Progressive orthopnea

• Orthopnea reflects pulmonary venous congestion that worsens when lying flat.

Why the others are incorrect:

• A) Fever and cough suggest infection, not CHF.

• C) Weight loss is nonspecific but more typical in malignancy.

• D) Hemoptysis is more common in infarction, TB, or alveolar hemorrhage.

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4. What is the most likely explanation for small bilateral pleural effusions in CHF?

A) Hemorrhagic effusions due to trauma
B) Hypoalbuminemia
C) Transudative fluid from increased hydrostatic pressure
D) Chylous leakage

Correct Answer: C — Transudative fluid from increased hydrostatic pressure

• CHF increases venous pressure, leading to transudative effusions.

Why the others are incorrect:

• A) Hemorrhagic effusions occur from trauma or malignancy.

• B) Hypoalbuminemia lowers oncotic pressure but is not the primary cause here.

• D) Chylothorax involves lymphatic injury, usually after thoracic surgery or malignancy.

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🩻 Radiology

5. Which CT sign best supports a diagnosis of cardiogenic interstitial pulmonary edema?

A) Beaded interlobular septa
B) Subpleural honeycombing
C) Peribronchial cuffing with ground-glass opacity
D) Peripheral wedge-shaped consolidation

Correct Answer: C — Peribronchial cuffing with ground-glass opacity

• Represents fluid around bronchi and early interstitial involvement in CHF.

Why the others are incorrect:

• A) Beaded septa suggest lymphangitic carcinomatosis.

• B) Honeycombing is a chronic fibrotic finding.

• D) Wedge consolidation may represent infarction or pneumonia.

Memory Images

Secondary Lobule With Thickened Walls
Polygonal Shaped Fort From Above