Normal lung CT in elderly differs from the young

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Thin-section CT findings usually associated with interstitial lung disease are frequently seen in asymptomatic elderly individuals and are absent in younger subjects; therefore, these findings may not necessarily represent clinically relevant disease, according to research published in this month’s edition of Radiology.

“To the best of our knowledge, there has been no prospective thin-section CT study that has examined the morphology of the lung parenchyma in asymptomatic older individuals,” the authors wrote. “In an increasingly aged population, establishing the “normal” CT appearance of the older lung is important in order to avoid misdiagnosis of clinically important disease and the potentially harmful investigations and treatment that might ensue.”

Axial prone thin-section CT image of an asymptomatic 78-year-old woman who was a non-smoker and had been a city dweller for 39 years. Image shows a subpleural bilateral fine reticular pattern of limited extent (grade 2). Image and caption courtesy of the Radiological Society of North America.

Two study groups (older group, over 75 years of age; younger group, less than 55 years of age) were prospectively identified from outpatient requests for CT of the abdomen or brain. Radiologists from London-based Hammersmith Hospital, Royal Brompton Hospital and Guy and St. Thomas’ NHS Trust conducted CT chest exams of 56 consecutive volunteers (40 patients from the older group and 16 patients from the younger group) with no known respiratory disease.

Prone inspiratory thin-section CT imaging of the thorax from the lung apices to the bases (without intravenous contrast agent) was performed in all subjects with an 8-slice CT scanner (Lightspeed Ultra, GE Healthcare) with 1-mm section thickness, 20-mm section interspacing, 120 kVp, and 400 mAs, the researchers reported.

The images were anonymized and reviewed for lung nodules or other potentially important unsuspected disease (none was detected in either group) and reviewed on a soft-copy workstation. Two thoracic radiologists with 10 and 20 years experience, respectively, assessed the images.

A limited predominantly subpleural basal reticular pattern was identified in the majority (24 of 40, 60 percent) of individuals in the older group and was absent (0 of 16) in the younger group, according to the researchers. In addition, cysts were seen in 10 (25 percent) of the 40 subjects in the older group but were seen in none of the subjects in the younger group.

The team also reported that bronchial dilation and wall thickening were seen significantly more frequently in the older group than in the younger group. They noted that all findings were independent of pack-year smoking history with multiple logistic regression analysis.

“Our findings are important because there is the potential for confusion with the CT appearance of clinically relevant interstitial lung disease, which could result in unnecessary follow-up and potentially harmful treatment,” the authors noted. “However, the CT patterns described in our study may not be of clinical importance because the majority of individuals had normal pulmonary function, and thus, these findings likely reflect the normal spectrum of morphology of aging lung.”

The team observed that a possible limitation to their study may be their decision to include ex-smokers.

“An advantage of including ex-smokers, apart from the group being more representative of the general population, was that we were able to demonstrate that there was no correlation between the presence of the observed CT features and smoking history,” they wrote.

They also noted that many of the individuals in the study were lifelong city dwellers; as such, there may be an environmental cause for the CT findings they identified, which might not be reproduced in a rural population.

The main findings of our study were a limited extent of predominantly bilateral basal subpleural reticular pattern and occasional scattered cystic air spaces,” the authors wrote. “The clinical relevance of recognizing these findings is that they may be part of the normal spectrum of senescent lung and should not be over-interpreted to represent clinically important disease. In an increasingly elderly population, definition of normality in such individuals will become important.”