Interpretation of Imaging Chapter 2: Recognizing Key High-Resolution Computed Tomography (HRCT) Patterns

Watch Chapter 3 here.

Hello, and welcome back to the Interstitial Lung Disease Explainer Video Series. I am Dr Joseph Mammarappallil, a cardiothoracic radiologist at The Duke Medical Center. This series focuses on interpreting high-resolution computed tomography, or HRCT, specifically in diagnosing and characterizing progression in interstitial lung diseases, or ILDs. In this video, you will learn how to recognize key imaging patterns, understand their clinical implications, and integrate radiology findings into multidisciplinary care. 

Before we look at individual ILD patterns, it is important to recognize the three hallmark HRCT findings that signal pulmonary fibrosis. Those are reticulation, traction bronchiectasis, and honeycombing. 

• Reticulation appears as a network of fine linear opacities caused by thickening of the interlobular and intralobular septa. This reflects early fibrotic changes and architectural distortion within the lung parenchyma.

• Traction bronchiectasis refers to bronchial dilatation due to fibrotic pulling of the surrounding tissue. Its presence is a key marker of chronic disease and irreversible architectural distortion. 

• Honeycombing represents the end stage of fibrosis and is seen as stacked cystic airspaces with well-defined walls, typically in the subpleural and basal areas of the lung. 

Recognizing these three fibrotic features and noting their distribution and extent is foundational to HRCT interpretation. They not only distinguish fibrotic from nonfibrotic ILD but also provide context for understanding disease behavior and chronicity. 

Let’s now review the individual HRCT patterns that help us recognize different presentations of ILD. 

We’ll begin with usual interstitial pneumonia, or the UIP pattern. The most important and specific HRCT feature of UIP is subpleural, basal honeycombing, which is usually 3 to 10 mm in diameter and sometimes as large as 2.5 cm. Additional fibrotic characteristics include a reticular pattern accompanied by traction bronchiectasis.

Ground-glass opacities can also be seen in UIP, but they are generally less prominent than the fibrotic changes. On HRCT, these appear as hazy areas of increased density that do not completely obscure underlying vessels. They typically reflect areas of active inflammation and may indicate a potentially reversible component of lung injury within an otherwise fibrotic pattern. 

Next is nonspecific interstitial pneumonia, or NSIP, where the most common HRCT findings include ground-glass opacities, traction bronchiectasis, lobar volume loss, and non-septal reticular abnormalities, typically involving the lower and peripheral regions of the lungs. 

Although relatively characteristic of NSIP, subpleural sparing appears in only about 21% to 30% of patients. 

Unlike UIP, the NSIP pattern is not pathognomonic but rather suggestive of the underlying pathology. 

Fibrotic changes such as volume loss and traction bronchiectasis are frequently present, while honeycombing is rarely observed. 

Over time, NSIP can evolve into a fibrotic form. This is clinically significant because the degree of fibrosis helps guide management decisions and may indicate a need for earlier therapeutic intervention. 

Other important patterns to recognize on HRCT include organizing pneumonia and lymphatic interstitial pneumonia (LIP).  

In organizing pneumonia, there is a range of findings on HRCT, with the three most common being consolidation, ground-glass opacification, and perilobular opacity.  

Consolidation appears on HRCT as a dense area of increased opacity that obscures the underlying lung vessels and airways. It represents complete filling of the alveoli, most often with inflammatory cells or in some cases, fibrotic tissue. 

In LIP, HRCT usually reveals diffuse or lower-lobe-predominant ground-glass opacities, thin-walled cysts, centrilobular or perivascular nodules, and interlobular septal thickening. 

The coexistence of ground-glass changes and scattered cysts is considered characteristic of LIP, though mild reticulation may develop in chronic disease. 

LIP is strongly associated with autoimmune diseases, particularly Sjögren syndrome and rheumatoid arthritis, making it an important consideration in connective tissue disease–related ILD. 

The key takeaway is that HRCT brings clarity to the clinical picture of ILD. With the support of multidisciplinary colleagues, even complex scans become manageable. This structured approach not only guides diagnosis and monitoring but also creates a clear clinical story that supports ongoing management decisions. 

ACR – American College of Rheumatology 

ATS – American Thoracic Society 

CHEST – American College of Chest Physicians 

CTD-ILD – Connective Tissue Disease–Related Interstitial Lung Disease 

DLCO – Diffusing Capacity of the Lung for Carbon Monoxide 

ERS – European Respiratory Society 

FVC – Forced Vital Capacity 

GGO – Ground-Glass Opacity 

HRCT – High-Resolution Computed Tomography 

ILD – Interstitial Lung Disease 

IPF – Idiopathic Pulmonary Fibrosis 

JRS – Japanese Respiratory Society 

LIP – Lymphocytic Interstitial Pneumonia 

MDD – Multidisciplinary Discussion 

NSIP – Nonspecific Interstitial Pneumonia 

OP – Organizing Pneumonia 

PFTs – Pulmonary Function Tests 

SARDs – Systemic Autoimmune Rheumatic Diseases 

UIP – Usual Interstitial Pneumonia 

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