Page 2 – Geometric Distortion (Lung)

Table 1 – Definition and Overview

Concept Explanation
Definition Geometric distortion refers to disruption of the normal pulmonary or bronchovascular architecture, such that the usual geometric relationships between anatomical structures—vessels, airways, fissures, and pleural surfaces—are visibly altered on imaging.
Fleischner Society Glossary (adapted) “Distortion” is the abnormal displacement, angulation, or curving of bronchi, vessels, fissures, or septa—typically due to fibrosis, mass effect, or collapse.”
Visual Characteristics Displacement or bowing of fissures, stretching or crowding of vessels or bronchi, architectural bending or kinking
Common Causes Chronic fibrosis, collapse, traction from masses, or prior infection/surgery
Clinical Significance Suggests chronic structural remodeling and often indicates underlying irreversible disease, especially in interstitial lung diseases (ILDs)

Table 2 – Other Findings to Look For on CT

Associated Finding Explanation / Context
Traction bronchiectasis Dilated airways pulled abnormally by fibrotic tissue
Fissural displacement Fissures pulled toward fibrotic or collapsed lung regions
Volume loss Associated with architectural distortion due to collapse or fibrosis
Parenchymal bands Linear fibrotic scars extending to the pleura or fissures
Subpleural reticulation Often seen adjacent to areas of distortion, particularly in UIP pattern

Table 3 – Classification of Geometric Distortion

Category Type / Description Common Causes
By Etiology Fibrotic distortion Seen in ILDs (e.g., UIP, NSIP, asbestosis)
Mass effect distortion From tumors or large nodules
Collapse-related distortion From lobar collapse or chronic atelectasis
Post-surgical or post-infectious Scarring or fibrosis following intervention or infection
By Direction Centripetal (pulling in) Traction from fibrosis or volume loss
Centrifugal (pushing out) Mass effect displacing normal structures
By Severity Mild (localized) Subtle bending or deviation of vessels/fissures
Moderate to severe Obvious displacement, collapse, or traction bronchiectasis

Table 4 – Differential Diagnosis: Most Likely

Category Diagnosis Imaging Features
Inflammatory / Fibrotic Usual Interstitial Pneumonia (UIP) Basal and subpleural reticulation, honeycombing, traction bronchiectasis, fissural distortion
Post-infectious / Sequelae Post-TB fibrosis Volume loss, bronchiectasis, fibrotic bands, distortion of bronchi and vasculature
Neoplastic Post-treatment scarring from lung cancer Fibrotic distortion surrounding a resected area or prior radiated field

Table 5 – Differential Diagnosis: Other Possibilities

Category Diagnosis Imaging Features
Inhalational / Occupational Asbestosis Subpleural lines, honeycombing, fibrosis, pleural plaques with distortion
Iatrogenic / Surgical Post-lobectomy changes Volume loss, shifted mediastinum, and architectural disruption
Congenital / Structural Congenital lobar emphysema (rare) Local overinflation may cause distortion of adjacent structures

Table 6 – Radiologic Strategy and Guidelines

Structure Under Concern Radiologic Strategy Guideline / Source
Lung parenchyma Use high-resolution CT (HRCT) to evaluate extent, cause, and severity of distortion ACR Appropriateness Criteria: Chronic dyspnea, suspected ILD
Airways and vasculature Correlate with signs of traction or compression; consider 3D reconstructions if needed Fleischner Society Guidelines on ILD patterns

Table 7 – Pearls

Insight Explanation
Geometric distortion is a sign, not a diagnosis Always evaluate for underlying cause—fibrosis, mass, or prior infection
Most commonly reflects fibrosis Especially in ILD, the presence of distortion supports irreversible lung injury
Look for traction bronchiectasis as a companion finding Traction-related airway dilatation confirms chronicity
Fissural distortion is a subtle clue Flattening, bowing, or angulation of fissures can point to early fibrosis
Not always diffuse Distortion may be focal, especially after surgery or localized infection

136228cL.lungs-reticulation-ILD-mild.jpg

Reticulation ILD Geometric Distortion of the Secondary Lobules 72 year old female showing reticular changes at the lung bases characterised by irregular thickening of the interlobular septa geometric distortion of the secondary lobules (b,c ringed) Ashley DAvidof TheCommonVein.net 136228cL

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