Important differentials

Question 1

Causes of chronic consolidation

Answer 1

1) Organizing pneumonia
2) Chronic Eosinophilic pneumonia
3) Lipoid pneumonia
4) Neoplastic: mucinous, lymphoma, radiation change

Question 2

Causes of acute gg

Answer 2

1) Pulmonary edema - cardiogenic, non-cardiogenic
2) Infection (atypical, viral, opportunistic) + ASPIRATION
3) Hemorrhage/vasculitis
4) Acute eosinophilic pneumonia
5) Subacute HP - will be more long standing/chronic

Question 3

Causes of chronic gg

Answer 3

Same entities as chronic consolidation, but add:

• Subacute HP (ground glass, centrilobular nodules, mosaic attenuation)
• ILDs - NSIP, DIP, LIP
• Alveolar proteinosis (central predominant gg, with septal thickening and crazy paving); and other causes of crazy paving including hemorrhage

Question 4

Ddx crazy paving

Answer 4

1) Alveolar proteinosis
2) Pulmonary hemorrhage
3) ARDS
4) Mucinous adenoCa
5) PJP
6) OP
7) Lipoid pneumonia - can look to for low attenuation areas on the soft tissue windows

Question 5

Ddx centrilobular nodules

Answer 5

Vascular

• Vasculitis (i.e. Goodpastures)
• Angio-invasive fungal
• Angio-invasive mets

Infectious

• TB, non-TB mycobacterium (MAC), atypicals, mycoplasma
• Aspiration

Inhaled

• RB-ILD
• HP (subacute)
• Pneumoconiosis

Others

• Follicular bronchiolitis - associated with collagen vascular, immunodeficiency
• LCH

Question 6

Ddx perilymphatic nodules

Answer 6

• Sarcoidosis
• Pneumoconiosis (silicosis, coal workers pneumoconiosis)
• Lymphangitic carcinomatosis

Question 7

Ddx random nodules

Answer 7

• Mets
• Septic emboli
• LCH (not angiocentric like mets and emboli)

DDx of miliary pattern (subtype of random) - disseminated TB, mets and fungal infection

Question 8

Ddx tree in bud nodularity

Answer 8

Almost always from endobronchial spread of infection

• TB or atypical mycobacteria (MAI), mycoplasma
• Viral infections - esp RSV, h. flu
• Bacterial pneumonia
• Aspiration pneumonia
• Airway invasive aspergillus (in immunocomp. pt) - rarely

Non-infectious - RA, Srogren - follicular or constrictive bronchiolitis
Rarely mets

Question 9

DDx single cavitary nodule

Answer 9

• Malignancy (usu squamous cell)

- Infection - TB

Question 10

DDx multiple cavitary nodule

Answer 10

Think hematogenous:

• Septic emboli
• Mets
• Vasculitis (GPA) - this should be top of differential in an outpatient

Question 11

DDx multiple lung cysts

Answer 11

• Emphysema
• LCH - irregular cysts, nodules, upper lobe distribution
• LAM - innumerable thin walled cysts + chylous effusion
• LIP - sjrogren’s
• PCP - cysts seen in late stage
• Diffuse bronchiectasis

Question 12

Ddx basal predominant fibrosis

Answer 12

• UIP
• NSIP
• End-stage asbestosis

Question 13

Ddx upper predominant fibrosis

Answer 13

• End stage sarcoid
• End stage silicosis
• Chronic HP
• Ankylosing spondylitis

Question 14

Ddx halo sign

Answer 14

Key differential:

• Angioinvasive aspergillosis* classic + other opportunistic infection including Mucor
• Hemorrhagic mets - thyroid, renal, melanoma, choriocarcinoma
• AdenoCa

Question 15

DDx reverse halo/atoll sign

Answer 15

Key differential:

1) OP* classic (from CTD, drug reaction, previous infection) i.e. dermatomyositis, RA - multi-focal
2) Pulmonary infarct, especially septic - broad pleural contact, bubbly lucency centrally
3) Opportunistic fungal infection: specifically Mucor > invasive aspergillosis

Other less common causes: vasculitis, tumour (things that cause cavitation)