European Journal of Cardiovascular Medicine

Interstitial lung disease (ILD) represents a heterogeneous group of diffuse parenchymal lung disorders characterized by varying degrees of inflammation and fibrosis, which impair gas exchange and lung mechanics [1]. Globally, ILD prevalence is approximately 1.9 million, with over 120,000 deaths reported in 2015, emphasizing its significant health burden [2]. The clinical and prognostic implications are highly dependent on the specific ILD subtype, underlining the need for precise diagnostic strategies [3].

High-resolution computed tomography (HRCT) has emerged as the cornerstone in the diagnostic workup of ILD. Unlike conventional chest radiography, HRCT offers superior spatial resolution, enabling visualization of fine pulmonary structures such as interlobular septa, intralobular lines, and small cysts [4]. Diagnostic accuracy for patterns such as usual interstitial pneumonia (UIP), nonspecific interstitial pneumonia (NSIP), organizing pneumonia (COP), lymphangioleiomyomatosis (LAM), and pulmonary Langerhans cell histiocytosis (LCH) relies heavily on HRCT’s ability to delineate distinctive imaging features [5,6].

In idiopathic pulmonary fibrosis (IPF), identification of a definite or probable UIP pattern on HRCT can establish the diagnosis in approximately 94% of cases, with high specificity, potentially obviating the need for surgical lung biopsy [7]. Consequently, international guidelines advocate for HRCT-centric diagnostic pathways: when HRCT reveals definite or probable UIP in the appropriate clinical setting, a diagnosis of IPF can be rendered without histological confirmation [8]. This paradigm facilitates expedited management and mitigates biopsy-associated morbidity.

Moreover, HRCT supports multidisciplinary discussion (MDD) by providing prognostically relevant information. For example, NSIP pattern carries a better prognosis than UIP, guiding therapeutic decisions [9]. CT features such as extent of fibrosis, honeycombing, traction bronchiectasis, and ground-glass opacities are integrated with clinical data to differentiate ILD subtypes and stratify patients for treatment.

Standardized acquisition protocols enhance HRCT’s diagnostic yield. Thin-section imaging (≤1‑1.5 mm), high spatial-frequency reconstruction, appropriate kVp/mAs settings, and inspiratory/expiratory series afford detailed lung parenchymal assessment while maintaining acceptable radiation exposure [4,10]. Consistency in technique enables reliable pattern comparison across patients and centers.

The objective of this study was to evaluate HRCT findings in 100 patients with suspected ILD, correlating radiological patterns with demographic variables, smoking status, and clinical history. This analysis aims to describe the distribution of HRCT features across ILD subtypes, thereby reinforcing HRCT’s diagnostic and prognostic utility.

A total of 100 patients who met the specified inclusion criteria underwent HRCT evaluation for suspected ILD. HRCT findings were correlated with conventional chest radiographs. In addition, relevant clinical history and laboratory investigations were reviewed from patient records to aid in diagnosis.

Inclusion Criteria: Patients who were referred for HRCT by clinicians for evaluation of suspected ILD, either due to normal or equivocal findings on chest radiographs, or to facilitate differential diagnosis in cases with nonspecific radiological abnormalities, were included in the study.

Exclusion Criteria: There were no specific exclusion criteria except for patients in whom CT examination was contraindicated.

Imaging Equipment: The HRCT scans were performed using a 128-slice Siemens SOMATOM Definition AS scanner and a GE BrightSpeed 16-slice CT scanner.

Scanning Parameters:

• Patient Position: Supine
• Scanner Settings:
• Tube voltage (kV): 120
• Tube current (mAs): 100–200 (effective) or dynamic adjustment
• Collimation: 1 mm
• Scan Time: 1–2 seconds
• Matrix Size: 512 × 512
• Scan Range: From the apices of the lungs to the domes of the diaphragm
• Reconstruction Algorithm: High-frequency spatial bone algorithm
• Windows: 100/900 HU or 50/1000 HU

Technique: Written consent was taken and procedure was properly explained to patient. Patient was placed on gantry table in the supine position with both arms raised above the heads. He/she was taught prior to procedure to hold breaths in deep inspiration and expiration wherever required. A digital AP scannogram was obtained in suspended full inspiration. Axial scans were obtained at 10 mm intervals from lung apices to domes of diaphragm. Modification in the above technique were done if indicated. Prone scans were taken to determine whether opacities in the dependent lung are abnormal or not. Scans were also taken at the end of deep expiration to detect air trapping.

HRCT was instrumental in diagnosing a wide spectrum of ILDs in the study population. A total of 100 ILD cases were analyzed, revealing diverse demographic and radiological patterns.

The majority of ILD cases were observed in individuals aged 50–59 and 60–69 years, each accounting for 24% of cases, followed by the 40–49-year age group (18%) (Table 1). Idiopathic interstitial pneumonias (IIPs) were the most prevalent diagnosis across all age groups, with the highest concentration noted in the sixth and seventh decades. Rare entities such as pulmonary Langerhans cell histiocytosis (LCH), lymphangioleiomyomatosis (LAM), and eosinophilic lung disease were confined to younger age groups, particularly those below 50 years. Cases of pneumoconiosis were primarily found in individuals aged 40–69 years.

Table 1: Age wise distribution of ILD cases

A nearly equal gender distribution was observed, with a slight female predominance (54%) compared to males (46%) (Table 2). IIPs were more common in males, with usual interstitial pneumonia/idiopathic pulmonary fibrosis (UIP/IPF) and desquamative interstitial pneumonia (DIP) showing a higher incidence in men. In contrast, conditions like lymphangitic carcinomatosis, collagen vascular disease-associated ILD, and LAM predominantly affected females.

Table 2: Gender wise distribution of ILD cases

A significant proportion of patients (76%) were nonsmokers, while smokers constituted 24% of the study population (Table 3). Notably, smoking-related ILDs such as DIP and LCH showed a higher occurrence in smokers, although non-smoking-related patterns were predominant in the overall cohort.

Table 3: Proportion of smoking in ILD cases

The radiological profiles demonstrated considerable variability depending on the ILD subtype (Table 4). UIP/IPF cases frequently exhibited interlobular and intralobular septal thickening, architectural distortion, honeycombing, and traction bronchiectasis. Ground glass opacities (GGOs) were prominent in NSIP, LIP, and AIP patterns, with NSIP also showing a high prevalence of fibrosis and septal thickening. Sarcoidosis was distinguished by nodular infiltrates, lymphadenopathy, and a mixed interstitial-alveolar pattern. Cystic lesions were notably seen in LIP and LAM, while centrilobular nodules and emphysema were characteristic of pneumoconioses such as silicosis and coal worker’s pneumoconiosis. Uncommon patterns, including eosinophilic lung disease and pneumocystis pneumonia, were identified by the presence of GGOs, consolidations, and pleural abnormalities.

Table 4: Pattern wise distribution of ILD cases

HRCT has emerged as the cornerstone in ILD assessment, offering non-invasive, high-resolution visualization of lung parenchyma essential for early diagnosis and subtype differentiation. In our study, idiopathic pulmonary fibrosis/usual interstitial pneumonia (UIP/IPF) was the most frequently encountered subtype. It typically manifested with hallmark radiologic findings including basal-predominant subpleural honeycombing, traction bronchiectasis, and interlobular septal thickening—features concordant with international criteria for UIP diagnosis [11,12]. These findings are highly specific for UIP and can often establish a definitive diagnosis without the need for lung biopsy in the appropriate clinical context [13].

Non-specific interstitial pneumonia (NSIP), the second most common subtype in our cohort, showed a predominance of ground-glass opacities, intralobular septal thickening, and relative sparing of honeycombing. These imaging patterns are consistent with previous studies and are known to carry a better prognosis compared to UIP [14]. NSIP predominantly affected younger females and non-smokers, further supporting existing demographic correlations.

Among other ILDs, hypersensitivity pneumonitis, collagen vascular disease-associated ILD, and sarcoidosis were observed with variable imaging findings. Notably, hypersensitivity pneumonitis frequently demonstrated air trapping and centrilobular nodules, whereas sarcoidosis exhibited lymphadenopathy and perilymphatic nodules, consistent with previous literature [14].

Smoking-related ILDs such as desquamative interstitial pneumonia (DIP) and pulmonary Langerhans cell histiocytosis (LCH) were relatively rare but showed expected associations with smoking history and characteristic radiologic features like cystic changes and nodules [15]. Although only 24% of patients in our study were smokers, they were disproportionately represented in smoking-related subtypes, corroborating the pathogenic role of tobacco exposure in these conditions [16].

The diagnostic accuracy of HRCT in ILD is well established. Studies have demonstrated that a definite UIP pattern on HRCT has a positive predictive value exceeding 90% for histopathologic UIP, thereby eliminating the need for invasive procedures in a significant proportion of patients [17]. However, in cases with probable or indeterminate patterns, multidisciplinary evaluation and, if required, lung biopsy remain essential for accurate classification [18].

Importantly, HRCT not only aids diagnosis but also provides prognostic information. Features such as extent of fibrosis, honeycombing, and traction bronchiectasis have been linked to poorer outcomes [19]. Quantitative CT texture analysis is now being explored for predicting disease progression and mortality risk in fibrosing ILDs, offering objective, and reproducible metrics for clinical decision-making [20].

Despite these advantages, HRCT has certain limitations. Interobserver variability in interpreting subtle or overlapping patterns, particularly in early disease, may affect diagnostic consistency. Furthermore, radiologic–pathologic discordance, though uncommon in classic UIP, can pose challenges in atypical or mixed-pattern presentations [21].

In conclusion, HRCT plays an indispensable role in the diagnostic pathway of ILDs. It allows for non-invasive subtype characterization, supports prognostication, and guides the need for biopsy or further testing. Our findings reaffirm the utility of HRCT in differentiating UIP from non-UIP patterns and highlight its value in integrating clinical, radiological, and exposure-related parameters for comprehensive ILD evaluation.

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