Interlobular Septal Thickening

Jonathan H. Chung, MD

DIFFERENTIAL DIAGNOSIS

Common

Cardiogenic Pulmonary Edema
Lymphangitic Carcinomatosis
Sarcoidosis
Usual Interstitial Pneumonitis

Less Common

Pulmonary Vein Stenosis
Pulmonary Alveolar Proteinosis
Venoocclusive Disease
Alveolar Septal Amyloidosis

Rare but Important

Erdheim Chester Disease
Leukemic Infiltration
Diffuse Pulmonary Lymphangiomatosis
Acute Eosinophilic Pneumonia

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Most often due to pulmonary edema or lymphangitic carcinomatosis
Smooth thickening
- Cardiogenic pulmonary edema
- Lymphangitic carcinomatosis
Nodular or irregular thickening
- Lymphangitic carcinomatosis or sarcoidosis

Helpful Clues for Common Diagnoses

Cardiogenic Pulmonary Edema
- Due to imbalances in Starling forces: Usually due to increased pulmonary venous pressure
  - Left-sided heart failure (myocardial infarct or ischemic cardiomyopathy)
  - Fluid overload or renal failure
  - Mitral valvular disease
- Interlobular septal thickening; Kerley B and Kerley A lines on chest radiograph
- Diffuse hazy, air-space opacities
  - Characteristically central predominant due to higher concentration of lymphatics in peripheral aspect of lungs
- Cardiomegaly
- Signs of coronary artery disease (coronary artery calcification, CABG, coronary artery stents, subendocardial fatty metaplasia)
Lymphangitic Carcinomatosis
- Most common with primary lung adenocarcinoma
  - Also breast, stomach, pancreas adenocarcinoma
- Asymmetric nodular (beaded) or smooth interlobular septal thickening
- Peribronchial and peribronchovascular thickening
- Pleural effusion and hilar/mediastinal lymphadenopathy common
Sarcoidosis
- Upper and mid lung, small perilymphatic nodules (along interlobular septa, subpleural, peribronchovascular)
- Subcentimeter centrilobular nodules
- Air-trapping
- Nodular interlobular septal thickening
- Symmetric hilar and mediastinal lymphadenopathy; ± calcification
- Perilymphatic nodules may coalesce into focal nodular consolidation or foci of ground-glass opacity
- Low-density lesions in spleen and liver; hepatosplenomegaly, upper abdominal lymphadenopathy
Usual Interstitial Pneumonitis
- Interlobular and intralobular septal thickening predominate in peripheral and basilar aspects of lungs
- Costophrenic angles most severely affected
- Traction bronchiectasis, honeycombing, and architectural distortion
- Mild mediastinal lymphadenopathy not uncommon

Helpful Clues for Less Common Diagnoses

Pulmonary Vein Stenosis
- Multiple etiologies
  - Extrinsic compression or invasion of pulmonary vein, thrombosis of pulmonary vein, post ablation stenosis
- Asymmetric interlobular septal thickening, peribronchial thickening, and peribronchovascular thickening
- In distribution of affected pulmonary vein
- Ipsilateral pleural effusion
Pulmonary Alveolar Proteinosis
- Diffuse or patchy airspace opacities often with geographic distribution
- Interlobular and intralobular septal thickening common
- Most often idiopathic
- Much less often secondary to hematological malignancy, massive silica inhalation, drugs, infection, or congenital causes
Venoocclusive Disease
- Rare cause of pulmonary arterial hypertension
- Pulmonary arterial dilation
- Smooth or nodular interlobular septal thickening
- Centrilobular ground-glass nodules
- Pericardial and pleural effusions
Alveolar Septal Amyloidosis
- Respiratory involvement in amyloidosis common though respiratory symptoms uncommon
- Alveolar septal subtype of amyloidosis least common
- Interlobular and intralobular septal thickening with micronodules (often in subpleural distribution)
- Affected areas may calcify; ossification less common

Helpful Clues for Rare Diagnoses

Erdheim Chester Disease
- Non-Langerhans cell histiocytosis primarily involving long bones; up to 1/3 have pulmonary involvement
- Smooth interlobular septal thickening
- Smooth pleural thickening or pleural effusions
- Soft tissue encasement of aorta, great vessels, and kidneys
- Bilateral symmetric osteosclerosis of metaphyses and diaphyses of long bone
Leukemic Infiltration
- History of leukemia
- Asymmetric or symmetric interlobular septal thickening, may be nodular
- Peribronchial and peribronchovascular thickening
- Patchy, multifocal airspace opacities
- Intrathoracic lymphadenopathy common
Diffuse Pulmonary Lymphangiomatosis
- Congenital proliferation and dilatation of lymphatics
- Diffuse interlobular septal and peribronchial thickening
- Extensive infiltration of mediastinal fat
- Pleural or pericardial effusions
- Mild mediastinal lymphadenopathy
Acute Eosinophilic Pneumonia
- Probable hypersensitivity reaction to inhaled agents; possible association with smoking
- Imaging mimics pulmonary edema
  - Ground-glass opacities > consolidation
  - Interlobular septal thickening
  - Pleural effusions
- Acute high fever, profound dyspnea, myalgia, pleuritic chest pain
- Responds rapidly to corticosteroids