Pulmonary nodule overview

# Overview
Pulmonary nodule (also known as " Solitary pulmonary nodule" or "SPN") is defined as a relatively well defined round or oval pulmonary parenchymal lesion equal or smaller than 30 mm in diameter. Pulmonary nodule is usually surrounded by pulmonary parenchyma and/or visceral pleura and is not associated with lymphadenopathy, atelectasis, or pneumonia. Pulmonary nodule may be classified according to size (> 8 mm vs.  8 mm), attenuation (pure solid vs. part-solid), and distribution (solitary vs. multiple). It can also be classified into benign and malignant based on the radiological findings.Causes of pulmonary nodules can be classified into etiologies presenting with solitary or multiple lesions. Common causes of solitary pulmonary nodule include tuberculosis, primary lung cancer, granuloma, and rheumatic disease. Common causes of multiple pulmonary nodules include pulmonary neoplasms and tumor metastasis from other parts of the body. Pulmonary nodule may be differentiated according to imaging (size, border characteristics, and attenuation), histological, and clinical features, from other diseases that demonstrate similar imaging findings. Common differential diagnoses of pulmonary nodule include hamartoma, granulomas, rheumatoid nodule, and metastatic lesions. Pulmonary nodules are common. The estimated prevalence of incidental pulmonary nodule ranges between 0.09% to 7% in the general population. The incidence rate of  pulmonary nodule increases with age, tobacco use, and prior cancer; the median age at diagnosis is between 35 to 70 years. The prevalence of malignancy among pulmonary nodules ranges between 0.2% to 50%. Males are more commonly affected with pulmonary nodule than females. The male to female ratio is approximately 2 to 1. There is no racial predilection to pulmonary nodule. According to the U.S. Preventive Services Task Force (USPSTF), screening for suspected lung cancer by low-dose computed tomography is recommended every year among smokers who are between 55 to 80 years old and who have smoking history of 30 pack years or more and either continue to smoke or have quit within the past 15 years (grade B recommendation). A hallmark feature in the evaluation of pulmonary nodule is the malignancy risk assessment. The evaluation approach for pulmonary nodule will mainly depend in the initial morphological evaluation of the nodule (size, margins, contours, and growth). Other characteristics, such as location, clinical features, and distribution may be helpful in the risk assessment, management, surveillance, and follow-up of pulmonary nodule. Pulmonary nodule can be divided into 3 risk categories: low risk, intermediate/moderate, and high risk. Based upon these risk categories, complementary diagnostic studies and management include: PET/CT scan, CT scan, non-surgical biopsy, and surgical resection. Lung biopsy is the study of choice to diagnose pulmonary nodule. Biopsy for pulmonary nodule may be classified into 2 categories: non-surgical biopsy and surgical biopsy. Biopsy findings associated with pulmonary nodule will depend on tumor histology. Common types of lung tissue biopsy for solitary pulmonary nodule include conventional bronchoscopic-guided transbronchial biopsy, bronchoscopic-transbronchial needle aspiration, endobronchial ultrasound-guided sheath transbronchial biopsy, and endobronchial ultrasound-guided transbronchial needle aspiration. Common indications for biopsy in pulmonary nodule include: high risk nodule (> 65%), intermediate risk nodule with a high risk patient profile, intermediate risk nodule with a positive positron emission tomography scan. Pulmonary nodules are generally asymptomatic. In some cases, patients may develop non-specific symptoms, such as difficulty breathing, hemoptysis, chronic cough, wheezing, and chest pain. Obtaining a detailed history is an important aspect of making a diagnosis of solitary pulmonary nodule. Specific areas of focus when obtaining history include previous infection of tuberculosis, previous or current smoking history, history of immunological conditions, high occupational risk profession, or recent traveling. Patients with pulmonary nodule usually are well-appearing. Physical examination of patients with pulmonary nodule usually has no remarkable findings. In some cases, solitary pulmonary nodule may show findings associated with the underlying condition. There are no diagnostic laboratory findings associated with pulmonary nodule. There are no ECG findings associated with pulmonary nodule. On conventional radiography, characteristic findings of solitary pulmonary nodule include well-defined, small, and rounded opacities within the pulmonary interstitium, usually 8 mm in diameter and normally surrounded by normal aerated lung. There are no echocardiography/ultrasound findings associated with pulmonary nodule. CT scan is the method of choice for the diagnosis of solitary pulmonary nodule. On CT, characteristic findings of solitary pulmonary nodules include ground-glass opacity, rounded mass, and less than 30 mm in size. The evaluation of solitary pulmonary nodule will depend on the following characteristics: calcification pattern, size, location, growth, shape, margins, attenuation, and contrast enhancement. On MRI, characteristic features of pulmonary nodule include higher soft tissue contrast, lack of radiation exposure, lesion characterization by evaluation of signal intensities, and characterization of the dynamics of contrast uptake. Other imaging studies include PET/CT scanning, which may be useful as a staging modality, detection of occult disease, and malignancy assessment. Other diagnostic studies for solitary pulmonary nodule include transthoracic percutaneous fine needle aspiration, bronchoscopy, and mediastinoscopy. The optimal management approach of solitary pulmonary nodule mainly depends on the nodule size and growth. Other parameters, such as location and distribution may also be helpful. Surgical resection is often recommended among patients with a malignant likelihood of solitary pulmonary nodule. On the other hand, solitary pulmonary nodules with benign features are eligible for periodic CT surveillance. Surgical excision is the mainstay therapy for malignant or high risk pulmonary nodules. In pulmonary nodule, surgical procedure selection will depend on the size, margins, and size of the tumor. The preferred surgical procedure is wedge resection by video-assisted thoracic surgery and subsequent pathological evaluation. Primary prevention of solitary pulmonary nodule includes avoidance of active and passive smoking, exposure to asbestos, and high risk occupational jobs. The American College of Chest Physicians (ACCP) and Fleischner Society guidelines offer a strategy to manage and follow up on pulmonary nodule.

# Classification
Pulmonary nodule may be classified according to size (> 8 mm vs.  8 mm), attenuation (pure solid vs. part-solid), and distribution (solitary vs. multiple). It can also be classified into benign and malignant based on the radiological findings.

# Causes
Causes of pulmonary nodules can be classified into etiologies presenting with solitary or multiple lesions. Common causes of solitary pulmonary nodule include tuberculosis, primary lung cancer, granuloma, and rheumatic disease. Common causes of multiple pulmonary nodules include pulmonary neoplasms and tumor metastasis from other parts of the body.

# Differentiating Solitary Pulmonary Nodule from Other Diseases
Pulmonary nodule may be differentiated according to imaging (size, border characteristics, and attenuation), histological, and clinical features, from other diseases that demonstrate similar imaging findings. Common differential diagnoses of pulmonary nodule include hamartoma, granulomas, rheumatoid nodule, and metastatic lesions.

# Epidemiology and Demographics
Pulmonary nodules are common. The estimated prevalence of incidental pulmonary nodule ranges between 0.09% to 7% in the general population. The incidence rate of  pulmonary nodule increases with age, tobacco use, and prior cancer; the median age at diagnosis is between 35 to 70 years. The prevalence of malignancy among pulmonary nodules ranges between 0.2% to 50%. Males are more commonly affected with pulmonary nodule than females. The male to female ratio is approximately 2 to 1. There is no racial predilection to pulmonary nodule.

# Screening
According to the U.S. Preventive Services Task Force (USPSTF), screening for suspected lung cancer by low-dose computed tomography is recommended every year among smokers who are between 55 to 80 years old and who have smoking history of 30 pack years or more and either continue to smoke or have quit within the past 15 years (grade B recommendation).

# Diagnosis

## Evaluation of Pulmonary Nodule
A hallmark feature in the evaluation of pulmonary nodule is the malignancy risk assessment. The evaluation approach for pulmonary nodule will mainly depend in the initial morphological evaluation of the nodule (size, margins, contours, and growth). Other characteristics, such as location, clinical features, and distribution may be helpful in the risk assessment, management, surveillance, and follow-up of pulmonary nodule. Pulmonary nodule can be divided into 3 risk categories: low risk, intermediate/moderate, and high risk. Based upon these risk categories, complementary diagnostic studies and management include: PET/CT scan, CT scan, non-surgical biopsy, and surgical resection.

## Diagnostic Study of Choice
Lung biopsy is the study of choice to diagnose pulmonary nodule. Biopsy for pulmonary nodule may be classified into 2 categories: non-surgical biopsy and surgical biopsy. Biopsy findings associated with pulmonary nodule will depend on tumor histology. Common types of lung tissue biopsy for solitary pulmonary nodule include conventional bronchoscopic-guided transbronchial biopsy, bronchoscopic-transbronchial needle aspiration, endobronchial ultrasound-guided sheath transbronchial biopsy, and endobronchial ultrasound-guided transbronchial needle aspiration. Common indications for biopsy in pulmonary nodule include: high risk nodule (> 65%), intermediate risk nodule with a high risk patient profile, intermediate risk nodule with a positive positron emission tomography scan.

## History and Symptoms
Pulmonary nodules are generally asymptomatic. In some cases, patients may develop non-specific symptoms, such as difficulty breathing, hemoptysis, chronic cough, wheezing, and chest pain. Obtaining a detailed history is an important aspect of making a diagnosis of solitary pulmonary nodule. Specific areas of focus when obtaining history include previous infection of tuberculosis, previous or current smoking history, history of immunological conditions, high occupational risk profession, or recent traveling.

## Physical Examination
Patients with pulmonary nodule usually are well-appearing. Physical examination of patients with pulmonary nodule usually has no remarkable findings. In some cases, solitary pulmonary nodule may show findings associated with the underlying condition.

## Laboratory Findings
There are no diagnostic laboratory findings associated with pulmonary nodule.

## Electrocardiogram
There are no ECG findings associated with pulmonary nodule.

## X-ray
On conventional radiography, characteristic findings of solitary pulmonary nodule include well-defined, small, and rounded opacities within the pulmonary interstitium, usually 8 mm in diameter and normally surrounded by normal aerated lung.

## Echocardiography and Ultrasound
There are no echocardiography/ultrasound findings associated with pulmonary nodule.

## CT scan
CT scan is the method of choice for the diagnosis of solitary pulmonary nodule. On CT, characteristic findings of solitary pulmonary nodules include ground-glass opacity, rounded mass, and less than 30 mm in size. The evaluation of solitary pulmonary nodule will depend on the following characteristics: calcification pattern, size, location, growth, shape, margins, attenuation, and contrast enhancement.

## MRI
On MRI, characteristic features of pulmonary nodule include higher soft tissue contrast, lack of radiation exposure, lesion characterization by evaluation of signal intensities, and characterization of the dynamics of contrast uptake.

## Other Imaging Findings
Other imaging studies include PET/CT scanning, which may be useful as a staging modality, detection of occult disease, and malignancy assessment.

## Other Diagnostic Studies
Other diagnostic studies for solitary pulmonary nodule include transthoracic percutaneous fine needle aspiration, bronchoscopy, and mediastinoscopy.

# Treatment

## Medical Therapy
The optimal management approach of solitary pulmonary nodule mainly depends on the nodule size and growth. Other parameters, such as location and distribution may also be helpful. Surgical resection is often recommended among patients with a malignant likelihood of solitary pulmonary nodule. On the other hand, solitary pulmonary nodules with benign features are eligible for periodic CT surveillance.

## Surgery
Surgical excision is the mainstay therapy for malignant or high risk pulmonary nodules. In pulmonary nodule, surgical procedure selection will depend on the size, margins, and size of the tumor. The preferred surgical procedure is wedge resection by video-assisted thoracic surgery and subsequent pathological evaluation.

## Primary Prevention
Primary prevention of solitary pulmonary nodule includes avoidance of active and passive smoking, exposure to asbestos, and high risk occupational jobs.

## Secondary Prevention
The American College of Chest Physicians (ACCP) and Fleischner Society guidelines offer a strategy to manage and follow up on pulmonary nodule.