Overview 

Mycobacterium Avium Complex (MAC) is a type of bacteria that lives everywhere. It's in soil, water, air, moisture, and even in your bathrooms. MAC can enter the airways and cause chronic lung disease with symptoms similar to tuberculosis. MAC Lung Disease (MAC-LD), however is an infection that is rare in healthy individuals. 

Patients with HIV/AIDS or other underlying lung conditions are highly susceptible to the disease and are susceptible additionally to risk of the infection spreading to other organs.¹ Due to this, a prompt and accurate diagnosis is crucial. Specifically, radiographic imaging is an essential step in diagnosing the disease. 

Different forms of MAC Lung disease (MAC-LD) exist, which require different treatment approaches and offer different potential outcomes. Accurate diagnosis with the use imaging techniques is crucial.²

Understanding Radiographic Imaging

What Is Radiography?

Radiography is an imaging method that helps to create images of the inside of your body for examination. It creates a radiographic image, also known as a radiograph. 

There are different radiographic techniques that exist that are used in the scope of medicine, including X-ray, Computed Tomography (CT), Magnetic Resonance Imaging (MRI) and Ultrasound. 

The main radiograph focus in this article will be chest radiography.

Chest radiography

Healthcare providers commonly use chest radiographs to examine the structure and function of the lungs and assessment of the thorax. 

X-ray images of your lungs can reveal significant abnormalities such as:⁴  

• Airway obstructions
• Presence of fluids 
• Thickening of lung tissue 
• Cancerous growths 

Producing radiographic such as X-rays are fast and cost effective, in comparison to more expensive modalities such as CT or MRI, making X-ray radiography the first line of imaging action for many lung diseases.⁵

How does MAC-LD Present

Signs and Symptoms

MAC-LD is a relatively uncommon infection affecting 1 to 65 people per 100,000, depending on location.⁶

Common symptoms of the infection include:⁷

• Shortness of breath
• Chronic cough 
• Fever
• Hemoptysis 
• Night sweats 
• Shortness of breath

Sometimes, MAC-LD can remain without symptoms, or may progress slowly over the years.^6,9 In cases of persistent or recurring symptoms, the condition becomes chronic in about 94% of patients.⁸

Risk factors 

Immunocompromised patients face a higher risk of developing MAC-LD. In particular, the infection is often a chronic complication of HIV/AIDS.⁸

Patients with a history of other lung conditions are more susceptible to infection, including:^7,8,9,10,11

• Bronchiectasis
• Chronic Obstructive Pulmonary Disease  (COPD)
• Cystic fibrosis 
• Lung cancer 

Becoming infected with MAC-LD is associated with an age range of 65 and above.⁶ Although some studies indicate a sex prevalence in MAC-LD for people assigned female at birth (AFAB), this appears to depend on the region.^6,8

How is MAC-LD diagnosed?

Symptoms of MAC-LD are nonspecific, meaning many other diseases can present similarly in individuals.⁸ In particular, MAC infections are often confused with a close bacterial relative, Mycobacterium tuberculosis, which causes the same symptoms and gives similar laboratory results.¹²

To rule out tuberculosis or any other bacterial infection completely, your doctor will request a sputum sample from you for a microbiological analysis. 

However, even finding MAC in a patient's sputum can't paint the entire picture for a case of MAC-LD. 

MAC can be recognise into two primary forms of the disease radiographically

• Nodular bronchiectatic form 
• Fibro-cavitary form

These 2 forms are only distinguishable by imaging.⁸ Each form affects your lungs differently and requires a unique treatment plan.² 

Understanding the difference between these two types of MAC-LD opens the door to more effective, targeted treatment that helps improve outcomes. 

Fibro-cavitary form of MAC-LD 

In the case of the fibro-cavitary form of MAC-LD, a chest radiograph will show two main patterns in the lungs

• Cavities 
• Signs of fibrosis

Cavities

Cavities are hollow spaces in the lungs surrounded by a mass.²³ In MAC-LD, these cavities often form in the upper portion (lobes) of the lungs.²⁰

Lung fibrosis 

Fibrosis refers to the formation of scar tissue of soft tissue. When MAC-LD spreads beyond the airways and the bacteria begin to invade the lung tissue, it can trigger an inflammatory reaction in the tissue. While this inflammation sometimes resolves, in other cases, it causes permanent injury, leading to thickening and scarring of the lung walls.  Lung fibrosis can cause respiratory difficulties, posing a significant threat to the health of patients with this form of MAC-LD.²⁴

Through radiographic imaging, medical professionals can accurately identify the location and size of the cavities as well as the extent of the fibrosis.²⁰ Radiographs can also detect early signs of this form of the disease, enabling timely treatment and increasing the likelihood of a better patient outcome.²⁵

Who It Affects Most

Fibro-cavitary disease is more common in people assigned male at birth (AMAB) over the age of 50 years. Having a history of other lung diseases, such as chronic obstructive pulmonary dieseas (COPD), is also associated with a higher risk of fibro-cavitary disease.²⁰

Clinical features and course

Fibro-cavitary MAC-LD is the more severe case of the disease, progressing rapidly and significantly over a few years.² This disease is highly associated with higher risks of mortality than nodular MAC-LD, and for this reason, prompt diagnosis and immediate intervention are crucial.^2,26

Nodular bronchiectatic form of MAC-LD

Nodular MAC-LD has distinctive radiographic features that distinguish it from its fibro-cavitary counterpart. 

The two main radiographic signs of this form of MAC-LD are:² 

• Lung nodules 
• Signs of bronchiectasis

Nodules 

Lung nodules are common and usually benign growths that form in the airways particularly the bronchi.¹⁴ They often appear during a lung infection, such as tuberculosis or MAC-LD, and can persist even once the infection has passed.¹⁵ 

Nodules in Nodular MAC-LD appear close together in the bronchi in a pattern known as tree-in-bud.¹⁶ Radiographs clearly show the nodular growths, which appear small white spots along the bronchi.¹⁷

Bronchiectasis 

Bronchiectasis is a chronic lung disease caused by mucus buildup and pooling in the bronchi.¹⁸ The mucus obstructs and dilates the bronchi permanently, limiting airflow and resulting in a recurring cough.¹⁹  

Bronchial dilation is a crucial radiographic feature in nodular bronchiectatic MAC-LD. The severity of MAC-LD can be measured by the extent of dilation and the number of affected points in the bronchi.¹⁶ 

Who does it affect the most 

Nodular MAC-LD tends to affect people AFAB who are elderly and thin.²⁰ It also affects non-smokers more often than expected.²

Clinical features and course

Nodular MAC-LD is the milder form of the MAC-LD, progressing more slowly, typically over several years.^2,21 Furthermore, 40-50% of untreated patients overcome the infection naturally.²² 

For this reason, specialists suggest avoiding immediate intervention and focusing more on monitoring the natural course of the disease. The level of treatment required will also depend on the severity of the disease as determined by your healthcare provider.² 

Regardless of the extent of the treatment, it remains crucial to observe radiographic changes throughout the progression of the disease to ensure that severe cases are identified and treated promptly. Radiographs can be used to track changes in nodule sizes and lung tissue thickness, simplifying the monitoring of the disease for both the patient and the clinician. 

The limitations of Radiographs in MAC-LD

Radiography is a handy tool in chest imaging and can highlight important features of MAC-LD.⁶ However, it's one of the least sophisticated imaging tools available and has several limitations which often require the intervention of other imaging techniques: 

• Difficulty in detecting bronchiectasis: Radiographs are not the best tool for imaging bronchi and, therefore, can't be used in isolation to diagnose bronchiectasis. For suspected cases of nodular MAC-LD, studies recommend using a more advanced form of X-ray imaging known as High-Resolution Computed Tomography (HRCT)²⁷
• 2D imaging: Radiographs project a superimposed image of all of your internal organs from a single perspective. This modality gives limited information on the location of nodules or cavities in the lungs, especially when compared to the 3D images made by HRCT

While X-ray radiographs tend to be used as a first line of imaging investigation in lung diseases, they shouldn't be the only ones. Radiographs should be followed up with a CT scan for a more accurate assessment of lung anatomy. Especially in cases of abnormalities related to MAC-LD, chest X-rays and CT scans are used as complementary methods to best treat and monitor the disease.²⁸

Summary

Mycobacterium avium complex lung disease (MAC-LD) is a complex condition requiring timely diagnosis and personalised care. Imaging, especially radiographic imaging, helps identify disease patterns and guide treatment. X-rays are a fast first step, but work best alongside high-resolution CT scans for detailed lung views.

The two main forms (nodular bronchiectatic and fibro-cavitary) have distinctive features. Nodular MAC-LD progresses slowly, showing small nodules and bronchial dilation, often in older, non-smoking individuals AFAB. The fibro-cavitary form is more aggressive, marked by cavities and lung fibrosis, mainly affecting older individuals AMAB, often with prior lung disease. Recognising these radiographic patterns not only informs prognosis but also helps clinicians respond with the appropriate level of urgency and care.

If you're managing MAC-LD as a patient, caregiver, or clinician, staying informed and engaged in the diagnostic process can make a meaningful difference. 

Ask questions, comprehend the imaging findings, and work closely with your healthcare team to ensure a timely, personalised treatment plan. Being proactive is one of the most important steps you can take toward better lung health.