Illustration of lungs with glowing embers, symbolizing dormant TB within scar tissue.

Hidden TB? How Scans Can Spot Dormant Dangers

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Nico Varela in Health & Wellness November 2025 • 5 min read.

"Uncover the role of PET/CT scans in detecting active tuberculosis within old, healed lesions, and how it could change treatment strategies."


Tuberculosis (TB) is often thought of as a disease of the past, but it remains a significant global health concern. While active TB—the kind that makes you sick—is what most people think of, there's also such a thing as old, healed TB. This refers to lesions or scars left in the lungs after a previous TB infection. These lesions don't always mean the danger is gone; sometimes, the bacteria can linger in a dormant state, with the potential to reactivate and cause illness later.

Imagine TB as a wildfire that was seemingly put out, leaving behind charred areas. These areas, the old healed TB lesions, might still harbor embers capable of reigniting the fire. Knowing whether those embers are still glowing is crucial for preventing future outbreaks. That’s where a sophisticated tool called 18F-fluorodeoxyglucose positron emission tomography/computed tomography, or 18F-FDG PET/CT, comes into play.

A recent study delved into how PET/CT scans can help identify metabolic activity in these old TB lesions. Metabolic activity, in this case, suggests the TB bacteria might still be active, even if not causing immediate symptoms. This article explores the findings of this research, explaining how PET/CT scans work, who might benefit from them, and what the future implications could be for TB prevention and treatment.

What is Old Healed TB and Why Does It Matter?

Illustration of lungs with glowing embers, symbolizing dormant TB within scar tissue.

Old healed TB refers to the remnants of a previous tuberculosis infection visible on a chest X-ray or CT scan. These remnants often appear as nodules (small lumps) or fibrotic scars, usually in the upper lobes of the lungs or near the hilar area (the central part of the lungs where blood vessels and airways enter). Sometimes, old healed TB can also manifest as bronchiectasis (widening of the airways) or pleural scarring (scarring of the lung lining).

The concern with old healed TB is that the seemingly inactive lesions may still contain dormant Mycobacterium tuberculosis bacteria. These bacteria can persist for years, and under the right conditions (such as a weakened immune system), they can reactivate, leading to active TB disease. Identifying individuals with old healed TB is crucial because they are at a higher risk of developing active TB in the future.

  • Increased risk of active TB: People with old healed TB are more likely to develop active TB compared to those without any signs of previous infection.
  • Potential for reactivation: Dormant bacteria can reactivate, causing new symptoms and making the person contagious.
  • Importance of monitoring: Regular check-ups and monitoring are essential to detect any signs of reactivation early.
Think of it like a garden that once had weeds. Even after pulling the weeds, some roots might remain in the soil. If left unattended, these roots can sprout again, causing new weeds to grow. Similarly, old healed TB lesions can harbor dormant bacteria that can reactivate and cause active TB.

The Future of TB Detection: What's Next?

This research opens exciting possibilities for improving TB detection and prevention. By using PET/CT scans to identify individuals with metabolically active old healed TB lesions, doctors might be able to target preventative treatments more effectively. This could involve closer monitoring, lifestyle interventions to boost the immune system, or even targeted drug therapies to eliminate the dormant bacteria before they reactivate. Further studies are needed to fully understand the implications of these findings and to determine the best course of action for individuals with increased FDG uptake in old healed TB lesions. However, this research represents a significant step forward in our fight against TB, offering a new way to identify and manage those at risk.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

Everything You Need To Know

1

What exactly is Old Healed TB?

Old healed TB refers to the remnants of a previous tuberculosis infection, often visible as nodules or fibrotic scars in the lungs. These lesions result from the body's attempt to contain the Mycobacterium tuberculosis bacteria. Although they might appear inactive on imaging, these areas can still harbor dormant bacteria capable of reactivating and causing active TB.

2

Why are 18F-FDG PET/CT scans useful in detecting potential future active TB?

18F-FDG PET/CT scans are useful because they can identify metabolic activity within old healed TB lesions. This metabolic activity suggests the presence of active TB bacteria, even if the individual is not currently experiencing symptoms. The PET/CT scan uses a radioactive tracer, 18F-fluorodeoxyglucose (18F-FDG), to highlight areas of increased glucose uptake. This indicates areas with higher metabolic activity, which can be associated with the presence of active TB bacteria in the old lesions.

3

What are the implications of finding metabolically active old healed TB lesions?

Finding metabolically active old healed TB lesions using 18F-FDG PET/CT scans suggests an increased risk of future active TB disease. This means the dormant Mycobacterium tuberculosis bacteria within the lesions are potentially poised to reactivate. This information could lead to earlier interventions, such as closer monitoring, lifestyle changes, or even targeted drug therapies to eliminate the bacteria before they cause illness. The key implication is that it shifts the focus from just treating active disease to potentially preventing it.

4

Who might benefit most from PET/CT scans for detecting old healed TB?

Individuals with a history of TB, especially those with old healed lesions on chest X-rays or CT scans, could benefit from 18F-FDG PET/CT scans. High-risk groups, such as those with weakened immune systems or who have been exposed to TB, would also benefit. Those with symptoms suggestive of TB but with negative initial tests might also be considered. The scans can provide a more detailed assessment of the activity within the old healed TB lesions, potentially allowing for earlier intervention.

5

How could this new approach change the way we treat and prevent TB?

This new approach could revolutionize TB management by shifting the focus to prevention. By identifying individuals with metabolically active old healed TB lesions using 18F-FDG PET/CT scans, doctors could target preventative treatments more effectively. This might involve closer monitoring, lifestyle changes to boost the immune system, or even targeted drug therapies to eliminate the dormant Mycobacterium tuberculosis bacteria before they reactivate. The ultimate goal is to reduce the incidence of active TB and improve patient outcomes by addressing the disease at an earlier, potentially asymptomatic stage.

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