What Is A Pulmonary Nodule?

Pulmonary nodules, commonly referred to as ‘spots’ or ‘shadows’ on the lung, are abnormal growths of tissue found in one or both lungs. They are a frequent finding in the adult population with up to 30% of CT chest scans performed on adults showing one or more pulmonary nodules.¹ The vast majority of them are benign (non-cancerous)¹ and they are often found incidentally when scanning a person's chest for signs of other diseases.¹ Further investigation or treatment will depend on the size, appearance, and location of the nodule as well as the background of the patient.

Read on to understand what causes pulmonary nodules to form, how they are assessed, and what follow-up or treatment, if any, they require.

What defines a pulmonary nodule?

Pulmonary nodules are abnormal growths of tissue found in the lungs. Most nodules are incidental findings, found when a scan is performed to detect other diseases in the lung such as infection, trauma, or autoimmune diseases.² Whilst they are predominantly reported on CT chest scans, larger nodules can be seen on chest X-rays.¹

Pulmonary nodules are defined as any unidentified space-occupying opacities in the lung that measure between 3mm and 3cm.² On chest imaging they are usually seen as rounded structures completely surrounded by aerated lung.² They are subdivided into solid and subsolid nodules, depending on their appearance, with subsolid nodules further differentiated into pure ground-glass nodules and mixed-solid nodules.² Solid nodules are the most common kind of nodule found.²

Why are pulmonary nodules significant?

Whilst the vast majority of pulmonary nodules are benign (non-cancerous), a small minority of nodules can be indicative of a more serious underlying pathology such as lung cancer.³ It is therefore essential that clinicians are able to distinguish between those nodules that are benign and don't require any further treatment and those that require further investigation or management.

Common causes of pulmonary nodules

The most common causes of a pulmonary nodule are a granuloma or a benign neoplasm (tumour). Granulomas are areas of ‘scar tissue’ that are formed in the lung as a result of current or previous bacterial or fungal infection, or as a result of chronic inflammation due to inflammatory diseases such as sarcoidosis or rheumatoid arthritis.⁴ Benign (non-cancerous) tumours such as pulmonary hamartomas are also common causes. These have no malignant potential and do not usually cause any corresponding symptoms.⁴

Diagnosis and assessment of a nodule

Once a pulmonary nodule has been detected, either incidentally when looking for signs of other chest diseases or as part of a targeted screening process, then it is important for the overseeing clinician to decide whether or not further investigation is warranted. Striking the balance between identifying potential lung cancer at an early stage and avoiding harm and expense from over-investigating low-risk nodules can be difficult, and clinicians will rely on country-wide guidance which is regularly reviewed and takes into account the latest research.

Why is it important to accurately assess a nodule?

Whilst the vast majority of nodules found in the lung are granulomas, hamartomas, or due to other benign conditions, a small minority, approximately 1.5%, are due to malignancy (cancer).⁵ It is important to weed out those nodules that may represent an underlying malignancy as early detection and consequently early treatment of lung cancer can radically alter one's prognosis. In general, nodules that are classified as ‘sub solid’ have been found to be at higher risk of being a malignancy.⁵

How will your doctor assess your nodule?

When assessing a pulmonary nodule your physician will take into account the following factors before deciding on the best route of care.⁶

• Previous history of, or, ongoing malignancy
• Category and appearance of the nodule on imaging (is it solid or subsolid)
• Size and location of the nodule
• Results from prediction tools such as the Brock model to analyse the risk of malignancy
• Further scan results: where applicable your physician may order other imaging tests such as a PET-CT scan to further investigate your nodule and to provide a more accurate risk percentage for malignancy.

After assessing the pulmonary nodule(s) your clinician will choose to take one of four routes:

• No further action required: If your nodule is very small (<5mm diameter) or has been assessed to be very unlikely to be malignant then your clinician will recommend no further imaging or treatment.⁵ 
• Further investigation required: If your nodule is larger than 5mm or has other characteristics that may be of some concern then your clinician will recommend surveillance. This will likely involve CT imaging at various intervals to monitor any growth or change in your nodule.⁵
• Biopsy: An image-guided or excision biopsy will be recommended if there is a statistically significant (10–70%) chance that your nodule is malignant. This risk will have been calculated using both the Brock risk assessment model and PET-CT scan results.⁵
• Excision of nodule or non-surgical treatment: If the chances of your nodule being malignant are greater than 70%, based on the previous assessments,  your clinician will discuss with you the possibility of either excising (cutting out) the nodule, further surgical management, or non-surgical treatment options.⁵

Risk factors

Although anyone can develop a pulmonary nodule, and the vast majority of them are harmless, there are some risk factors⁷ that your doctor will take into account when evaluating your nodule, as they increase your chances of malignancy.

• Current or former smoker
•  Older than 65
• Have had or currently have a malignancy
• Family history of malignancy
• History of radiation therapy to the chest
• Exposure to asbestos or radon
• Comorbid chronic lung diseases such as COPD

Surveillance

If your nodule is between 5–8mm in diameter or has been assessed to have <10% risk of malignancy using the Brocks assessment tool then you will likely be placed under surveillance. This means you will have a repeat chest CT scan at either 3 months or 1 year. Your doctor will be looking for any changes that have occurred to your nodule in the intervening time, in particular, any change to size. This is called the volume doubling time and it measures the amount of time that the nodule has taken to double in size. If this is less than 400 days then it will be classified as high risk for malignancy and you will likely be referred for further assessment and management.⁵ 

Biopsy procedures

Depending on the results of the nodule assessment, the patient may need to undergo further investigation in the form of a biopsy. This means that a small sample of the nodule will be extracted under surgical conditions and then evaluated under a microscope. This enables your clinician to accurately diagnose the type of pulmonary nodule you have and whether it is malignant or benign. There are two different types of biopsy that can be performed.

• CT-guided biopsy: This is the most commonly performed biopsy and has a sensitivity of 90% and a specificity of 94%.⁵ This means that it is highly accurate at determining whether or not a nodule is malignant, however, the results must be taken into account with the pre-biopsy probability. A negative biopsy result cannot necessarily rule out a malignancy if the pre-biopsy prediction was very high (over 90%). However, a negative biopsy result and a lower pre-biopsy risk prediction can make a confident assumption that the nodule is non-cancerous.⁵ As with any procedure, there are risks that surround it. The most common complication arising from a CT-guided biopsy is a pneumothorax which may require invasive treatment.
• Bronchoscopy biopsy: This type of biopsy is performed by inserting a tiny camera, under sedation, into the patient's airway and either excising the whole nodule or cutting off a small sample. This form of biopsy is not considered to be as accurate as a CT-guided biopsy but depending on the positioning of the nodule may be the preferred option. A common complication is a pneumothorax or bleeding which in 0.2% requires further treatment.⁵
• Surgical biopsy: This is an excision biopsy where the nodule is removed in its entirety and may be accompanied by a lobectomy (removal of a lung lobe) depending on clinical suspicion and location. This is usually performed when the suspicion of malignancy is very high.⁵

Surgical management 

If the suspicion of malignancy is very high, a biopsy has confirmed malignancy or the suspicion of malignancy remains very high despite the results of the biopsy being negative/indeterminate, then the surgical team may recommend removal of the nodule and/or a lobectomy (removal of the affected lung lobe). The gold standard treatment modality for malignant or ‘highly likely’ malignant pulmonary nodules is surgical removal.⁸ 

Once the benefits and risks have been weighed up and discussed with the patient and it has been decided that surgical removal of the malignancy is the best course of action, then there are three surgical methods by which this can be achieved.⁸

• Video-assisted thoracic surgery (VATS): Minimally invasive surgery using a small camera. The camera, also called a thoracoscope, and surgical instruments are inserted into the lungs through small cuts in the chest wall.
• Open thoracotomy: Opening of the chest to reveal the lungs and removal of nodule and other affected lung tissue.
• Robotic-assisted thoracic surgery (RATS): Minimally invasive surgery using robotic equipment to assist in the surgery.

Non surgical management – radiotherapy 

If a patient is not a candidate for surgical management of their malignant nodule, or they have refused surgery, then they may be offered a course of stereotactic body radiotherapy.⁸ This uses carefully targeted beams of energy to destroy the affected tissue.

Prevention and risk reduction

So far, no preventative measures have been found to reduce the risk of developing lung nodules. However, you can reduce your risk of developing lung cancer. The most impactful way to reduce the risk of lung cancer is to not smoke or to stop smoking if you already do so. Environmental precautions should also be taken especially for those who work in an industry with known environmental hazards such as asbestos.

Prognosis and outlook

The outlook after finding out that you have a pulmonary nodule is very good. Over 95% of nodules are benign and will not cause you any harm.¹ If it is determined that your nodule has a significant risk of malignancy then early diagnosis and early treatment are of paramount importance and can drastically improve your prognosis.

Summary

• Pulmonary nodules are a common entity in the adult population¹
• They are often found incidentally when imaging the chest for other disease pathologies and rarely cause symptoms⁵
• 96% of nodules are benign¹
• A doctor will determine which course of action to take. This can range from no further action required, surveillance, further imaging, biopsies, or surgical management
• Make healthy lifestyle decisions to reduce your overall risk of developing malignancy

Questions to ask your doctor

If you have been diagnosed with a pulmonary nodule then you may be feeling concerned or anxious about what this means and what might happen next. Consider asking your physician these questions to help you make sense of the situation.

• Will I need any further tests?
• Will I need to undergo a biopsy?
• How long will it be before I have a scan, biopsy, or consultation with a specialist?
• Are there any symptoms or complications I should look out for?