Lung mass overview
Synonyms and keywords:Pulmonary mass

# Overview
Lung mass (also known as "Pulmonary mass") is defined as any area of pulmonary opacification that measures more than 30 mm (3 cms) in the lung. Lung mass are abnormal growths found in the lung which can be either be benign or malignant. The most common cause of a pulmonary mass is lung cancer (in 95% of cases). Other less common causes of lung mass include granuloma, lipoma, tuberculosis, and aspergillosis.  Lung mass may be classified according to the location, imaging features, size, and distribution. The incidence rate of lung mass is approximately 58 per 100,000 individuals in the United States. The incidence of lung mass increases with age. Lung mass has a wide age distribution. However, the majority of these lesions are more often diagnosed in adults with the median age at diagnosis between 35 to 75 years. Males are more commonly affected than females with male to female ratio of 2:1. There is no racial predilection for lung mass. The most common symptom of a lung mass is cough, which will gradually persist over time. Other symptoms may include dyspnea, hemoptysis, chronic coughing, wheezing, and chest pain. In some cases, lung mass may be asymptomatic. A vital feature in the evaluation of lung mass includes malignancy assessment. The evaluation approach of lung mass starts with initial morphological evaluation of the mass (size, margins, contours, and growth). Other characteristics, such as location, clinical features, and distribution may be helpful for the therapeutic management, surveillance, and follow-up of the lung mass. As lung mass can be divided into two categories such as benign pulmonary mass and malignant pulmonary mass. Based upon these categories, complementary diagnostic studies and management include PET/CT scan, CT scan, non-surgical biopsy, and surgical resection.

# Historical Perspective
The first reported case of lung mass dates back to early 1400s when around 50% of miners in Germany and Czech Republic died of a pulmonary disease called Bergkrankheit. In 1929, German physician, Fritz Lickint published a paper suggesting that lung mass patients were likely to be smokers and launched an anti tobacco campaign in Germany. In 1950's, United States physician Cuyler Hammond and Ernest Wynder provided additional corroboration for a causal association between smoking and lung cancer.

# Classification
Lung mass may be classified on the basis of histopathology into benign lung mass and malignant lung mass. In addition, lung mass can be sub-classified according to the location, imaging features, size, and distribution.

# Pathophysiology
It is thought that lung mass is the result of genetic and environmental factors. Genetic mutation leads to uncontrolled cell proliferation which predispose to tumorigenesis. Genes involved in the pathogenesis of lung mass include mutations in K-ras oncogene and TP53 tumor-suppressor gene. Other genes include mutation in  EML4-ALK, PIK3CA, c-MET, NKX2-1, LKB1 and BRAF kinase. Environmental factors include smoking (most important carcinogen), radon, asbestos, viral infections, and states of chronic lung inflammation, all of which may predispose to cellular damage and DNA mutations that may further lead to development of lung mass.

# Causes
The most common cause of a pulmonary mass is lung cancer (in 95% of cases). Other less common causes include hamartomas, Hodgkin's lymphoma, pleural malignant mesothelioma, metastasis, granuloma, lipoma, tuberculosis, and aspergillosis.

# Differential Diagnosis
Lung mass must be differentiated from other causes that cause cough, chest pain, or wheezing such as primary lung cancer,  pulmonary abscess, granulomas, tuberculosis, and metastases.

# Epidemiology and Demographics
The incidence of lung mass is approximately 58 per 100,000 individuals in the United States. The incidence of lung masses increases with age; the median age at diagnosis is between 35 to 75 years. Males are more commonly affected with lung masses than females with a male to female ratio of 2:1. There is no racial predilection for lung mass.

# Risk Factors
The most potent risk factor in the development of lung mass is smoking. Other important risk factors include family history of lung cancer and high levels of air pollution.

# Screening
According to the U.S. Preventive Services Task Force (USPSTF) there is sufficient evidence to recommend routine screening for lung mass. 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 history of smoke 30 pack-years or more and either continue to smoke or have quit within the past 15 years (grade B recommendation).

# Diagnosis

## Evaluation of Lung Mass
A vital feature in the evaluation of lung mass includes malignancy assessment. The evaluation approach of lung mass depends upon the initial morphological findings of the mass such as size, margins, contours, and growth. Other characteristics such as location, clinical features, and distribution may be helpful in the therapeutic management, surveillance, and follow-up of the lung mass. Lung mass can be divided into two categories such as benign pulmonary mass and malignant pulmonary mass. Based upon these categories, complementary diagnostic studies and management include PET/CT scan, non-surgical biopsy, and surgical resection. CT scan is the initial method of choice for evaluation of lung mass. The following algorithm outlines the various steps involved in the assessment of a lung mass. 
For complete algorithm on evaluation of lung mass please click here

## Staging
According to the American Joint Committee on Cancer (AJCC) staging system, there are 4 stages of malignant lung mass, based on 3 factors; tumor size, lymph node invasion, and metastasis. Each stage is assigned a letter and a number that designate T for tumor size, N for node invasion, and M for metastasis.

## History and Symptoms
The most common symptom of a lung mass is cough, which will gradually persist over time. Other common symptoms may include dyspnea, hemoptysis, wheezing, and chest pain. Lung mass may also cause loss of appetite, fatigue and cachexia. A positive history of smoking, exposure to asbestos, tuberculosis infection, or a high risk occupation may be present in patients with lung mass. In addition, symptoms related with lung mass will vary depending upon the size and location of tumor. 

## Physical Examination
Physical examination findings of lung mass will depend on the location of the tumor. Lung mass with central location may cause crackling sounds, focal wheezing, voice hoarseness, and tachypnea. Lung mass with peripheral location can present with pleurisy findings such as reduced chest expansion. Common physical examination of patients with lung mass, include crackling or bubbling noises, decreased/absent breath sounds, and whispered pectoriloquy.

## Laboratory Studies
Laboratory findings associated with lung mass varies with underlying presentation. The findings may range from normal to severe elevated. In general, a thorough laboratory evaluation is necessary to accurately assess, diagnose and stage the severity of lung mass. Lab evaluations include complete blood count, electrolytes, serum calcium, alkaline phosphatase, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, serum creatinine, albumin, and lactate dehydrogenase.

## X ray
An x-ray may be helpful in the diagnosis of lung mass. Findings on an x-ray suggestive of lung mass include rounded or spiculated mass, bulky hilum, and lobar collapse.

## CT scan
CT scan is the method of choice for the evaluation of lung mass. On CT scan, characteristic findings of lung mass include single pulmonary nodule or mass with localized area of parenchymal consolidation and bubble-like areas of low attenuation within the lung mass (characteristic finding).

## Biopsy
Biopsy for lung mass may be classified into two categories such as non-surgical biopsy and surgical biopsy. Biopsy findings associated with lung mass will depend on tumor histology. Common types of lung tissue biopsy for pulmonary mass 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 lung mass include suspected lung cancer and to rule out malignant features (lymph node involvement).

# Treatment

## Medical Therapy
Medical therapy of lung mass depends upon the histopathological analysis. In general, the therapy for lung mass consists of surgical excision, radiation therapy, chemotherapy, and targeted therapy.

## Surgery
Surgery is the initial treatment choice for patients of lung mass with resectable tumors. Surgical excision is also the mainstay therapy for malignant lung mass. In lung mass, surgical procedure selection will depend on the size, margins, and invasion of the tumor. Common surgical procedures for the treatment of lung mass include wedge resection, segmentectomy, lobectomy and lung volume reduction surgery.

## Primary Prevention
Effective measures for the primary prevention of lung mass include smoking cessation and avoidance of second hand smoking. Lifestyle changes, such as healthy diet rich in fruits and vegetables and regular exercise may also reduce the risk of lung mass.