UIP Patterns

UIP

• Basilar and subpleural distribution: The abnormalities are concentrated in the lung bases and along the outer edges of the lungs.
• Reticulations: Fine, linear opacities consistent with interstitial fibrosis.
• Traction bronchiectasis: Dilated airways caused by fibrotic pulling on the surrounding lung tissue.
• Honeycombing: Clusters of cystic airspaces with well-defined walls, typically subpleural in location.

Probable UIP

• Basilar and subpleural distribution: Abnormalities are predominantly located in the lower lung zones and along the lung periphery.
• Reticulations: Linear opacities indicative of interstitial fibrosis.
• Traction bronchiectasis: Mild airway dilation caused by fibrotic pulling on the surrounding tissue.

Indeterminate UIP

• Reticulations
• May be diffuse rather than basilar predominant
• Absence of definite fibrotic features of traction and honeycombing

Alternative Diagnosis

• Mid-lung distribution: The abnormalities are primarily located in the mid zones of the lungs, sparing the bases and subpleural regions typically involved in UIP.
• Central and peribronchovascular involvement: The fibrosis and changes are focused around the central lung and airways, which is atypical for UIP.

UIP Classification Overview

UIP

Probable UIP

Indeterminate UIP

Alternative Diagnosis

• Basilar & Subpleural
• Often heterogeneous
• Occasionally Diffuse

• Upper or mid lung
• Peribronchovascular
• Perilymphatic

• Basilar & Subpleural
• Often heterogeneous
• Occasionally Diffuse

Distribution

• Basilar & Subpleural

• Honeycombing
• Reticulation
• Tractionbrochiectasis

• No honeycombing
• Reticulation
• Traction brochiectasis
• May have mild GGO

• Subtle reticulation
• May have mild GGO ("early UIP pattern")
• CT features and/or distrubition of lung fibrosis that do not suggest any specific etiology ("truly indeterminate UIP")

Features

Findings suggestive of another diagnosis:

• Cysts
• Mosaic attenuation
• Predominant GGO
• Consolidation
• Nodules

Other:

• pleural plaques
• dilated esophagus
• distal clavicle erosions
• extensive lymphadenopahty
• pleural effusions/thickening

Non-UIP Fibrotic Patterns in ILD

Nonspecific interstitial pneumonia (NSIP) & Fibrotic hypersensitivity pneumonitis (HP)

Characteristics

• Share features of fibrosis with UIP
• Have distinct imaging characteristics
• Different clinical implications

Clinical Significance

• Essential for accurate diagnosis
• Guides appropriate patient management
• Informs treatment decisions

Non-Subpleural ILAs

• Located away from the pleural surfaces, typically in central or peribronchovascular regions
• Less likely to progress to ILD and are often incidental findings
• CT: may appear as ground-glass opacities, fine reticulations, or scattered nodular changes without a subpleural or basilar predominance

NSIP

Key Characteristics

• Distinct ILD with more uniform and diffuse pattern than UIP
• Can be primarily fibrotic, inflammatory, or mixed

Imaging Features

• Bilateral ground-glass opacities
• Fine reticulations
• Traction bronchiectasis
• Lacks honeycombing (key differentiator from UIP)
• Lower-lobe predominant
• Subpleural but often spares immediate subpleural lung

NSIP

Clinical Associations

• Connective tissue diseases (CTD)
• Drug-induced lung injury
• Chronic hypersensitivity pneumonitis

Clinical Implications

• Finding NSIP should prompt thorough evaluation for underlying causes, especially CTD
• Often responds to immunosuppressive therapy
• Generally better prognosis than UIP
• Critical for early identification to optimize outcomes
• May progress over time but typically more favorable than UIP
• Targeted therapy for associated systemic disease is important

Fibrotic HP

A chronic, airway-centered fibrotic lung disease caused by prolonged inhalational exposure to organic antigens. Imaging Features

• Mid-to-upper lung predominance (vs. UIP's subpleural/basilar)
• Mosaic attenuation
• Centrilobular nodules
• Peribronchovascular fibrosis
• Air-trapping on expiratory imaging (hallmark of small airway involvement)
• Advanced cases: traction bronchiectasis and reticulation (may resemble UIP)

Fibrotic HP

Clinical Approach

• Exposure history critical for diagnosis
• Management focuses on antigen avoidance Immunosuppressive therapy may benefit some patients Established fibrosis may progress despite treatment

Importance of Differentiation from UIP

• Different prognosis (generally better than UIP)
• Different treatment approach
• Early intervention can significantly impact disease trajectory
• UIP generally not responsive to immunosuppression Enables more precise diagnosis and treatment planning