Anatomy & Physiology of the Thorax
The thoracic cavity is bordered by the ribs, vertebral column, sternum, and diaphragm. Between each rib is the intercostal space, often used to gain access to the thoracic contents. Within the thoracic cavity lie the lungs, which are lined by the pleural sacs. Between the lungs is an area known as the mediastinum.
The mediastinum contains a compartment referred to as the superior mediastinum. This contains the aortic arch, superior vena cava (SVC), vagus nerve, phrenic nerve, thymus, trachea, oesophagus, thoracic duct, and sternohyoid and sternothyroid muscles.
A further compartment within the mediastinum is known as the middle mediastinum. This contains the heart, pericardium (surrounding the heart), bronchi, tracheal bifurcation, ascending aorta, pulmonary trunk, SVC, cardiac plexus, phrenic nerve, and lymph nodes.
Anatomy & Physiology of the Lungs
In the chest cavity are two lungs, one on the left, one on the right. The left lung lies in close proximity to the arch of aorta and thoracic aorta. The right lung lies in close proximity to the inferior vena cava (IVC), superior vena cava (SVC), and the azygous vein. Both lungs lie closely to the heart and oesophagus.
Each lung is divided into lobes; whilst the right lung is comprised of three lobes, the left lung is comprised of only two lobes. The right lung has a superior lobe, medial lobe, and inferior lobe, separated by a horizontal fissure and oblique fissure. The left lung has a superior lobe and inferior lobe, separated by an oblique fissure. These fissures and lobes are important anatomical locations.
The lungs also have several other anatomical sites which are clinically important:
- Apex – the most superior aspect of each lung, lying above the first rib.
- Base – the most inferior aspect of each lung, sitting on the diaphragm.
- Borders – anterior, inferior, and posterior.
- Surfaces – costal surface, mediastinal surface, diaphragmatic surface.
The hilum is the area which structures enter and leave each lung. Hilar structures include:
- Pulmonary veins
- Pulmonary arteries
The Journey of One Breath
Upon inspiring, oxygen enters the oral cavity through the nose and mouth and then flows through the bronchial tree:
- Oxygen travels down the main, largest, airway known as the trachea.
- The trachea then divides into the left and right main bronchus, entering each lung lobe accordingly.
- The right and left main bronchus then divide into lobar bronchi, which supply each lobe of the lunch.
- The lobar bronchi then further divide into segmental bronchi, supplying the bronchopulmonary segments of the lung.
- The segmental bronchi divide into many, very small, bronchioles, which eventually become terminal bronchioles.
- Each terminal bronchiole has respiratory bronchioles which have outpockets known as alveoli.
In the alveoli, gaseous exchange occurs whereby oxygen enters the blood from the air breathed in, and carbon dioxide is delivered from the blood, into the lungs where it can be expired.
What are the risk factors for lung cancer?
- Smoking – the largest risk factor, with 7 out of 10 lung cancers being caused by smoking, including passive smoking (secondhand).
- Exposure to certain substances:
- Diesel exhaust fumes
- Air pollution
- Chronic lung conditions such as chronic obstructive pulmonary disease (COPD)
- Radon gas exposure
- Family history of lung cancer
What are the symptoms of lung cancer?
- A cough most of the time
- A pre-existing cough which has changed
- Coughing up blood
- Chest/shoulder pain/ache
- Recurrent chest infections or a persistent chest infection
- Loss of appetite
- Unexplained weight loss
- Becoming short of breath undertaking normal activities
- Horner’s syndrome (Pancoast tumour)
- Ptosis (drooping of one eyelid)
- Unilateral anhidrosis in the face (loss of sweating on one side of the face)
- Miosis (one small pupil)
What are the different types of lung cancer?
Small cell lung cancer (SCLC)
Usually as a result of smoking, small cell lung cancer comprises 15-20% of diagnosed lung cancers. These spread rapidly.
Non-small cell lung cancer (NSCL)
Non-small cell lung cancer comprises the majority of lung cancers and can be divided into several types:
- Malignancy that stems from the mucus-producing cells which line the airways. The most common form of lung cancer.
- Squamous cell carcinoma
- Often developing in the centre of the lung, this type of lung cancer originates from squamous cells lining the airways.
- Large cell carcinoma
- This form of lung cancer is named as such due to it’s appearance under a microscope of large, round cells.
Mesothelioma is cancer of the pleura that lines the lungs. Very rarely, it may develop in the peritoneum (peritoneal mesothelioma). The majority of diagnoses of mesothelioma are a result of asbestos exposure. Asbestos was a material used in construction, which was thankfully banned in the UK in the late 1990’s. It is thought that inhalation of the asbestos fibres causes irritation and gene mutations leading to cancer.
Unfortunately, very few symptoms are present during the early stages of mesothelioma, with symptoms only becoming apparent usually when a nerve becomes affected or there is pressure placed on another organ. Sadly, due it’s often late presentation, mesothelioma is often very difficult to treat and is rarely cured, with a five-year survival rate of approximately 5%.
International Mesothelioma Interest Group (IMIG) system is used to stage mesothelioma.
A pancoast tumour is lung cancer which develops in the apex of the lung. These area very rare form of lung cancer. Due to the location of the tumour, it is likely that as it grows it will put pressure on and damage a bundle of nerves called the brachial plexus. This leads to impaired sympathetic innervation of the face, producing very classical symptoms, as described above.
How is lung cancer diagnosed?
A chest radiograph is a fast, simple, and non-invasive method of viewing the lungs. Signs of lung cancer on a chest X-ray include:
- White-grey mass
- Hilar lymphadenopathy
- Nodule (pulmonary nodule)
- Signs of pulmonary collapse
- Bronchial obstruction
- Evidence of boney erosions
CT, MRI, and PET CT scans are often performed to gain more detailed imaging and to observe for spread of cancer.
A bronchoscopy is when a long flexible tube is inserted into the airways (bronchi) to observe the inside of the airways. Biopsies may also be taken.
Endobronchial ultrasound scan
Also known as an endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA). This is when a bronchoscopy is performed with an ultrasound probe to create ultrasound images of the lungs and surrounding structures, such as lymph nodes. Biopsies can be taken during this investigation.
Endoscopic ultrasound scan
A flexible tube is inserted down the oesophagus (food tube) and an ultrasound scan is performed to produce images of the structures central to the chest, surrounding the oesophagus.
Biopsies of the lung tissue may be taken through the skin (percutaneous lung biopsy) or surgically. A surgical lung biopsy may be performed laparoscopically (video assisted thoracoscopic surgery (VATS)) or through a thoracotomy. In addition, lymph node biopsies may be taken to assess if there is the presence of cancer in the local lymph nodes.
A mediastinoscopy is an invasive investigation performed to observe the mediastinal structures and take biopsies. This requires a general anaesthetic and involves the surgeon making an incision into the lower part of the neck, and then passing an endoscopy into the mediastinum.
Lung cancer staging
The TNM staging system is most often used to stage lung cancers. This observes:
- Tumour size
- Node (lymph) involvement
- Metastasis presence
The stage of lung cancer will often determine what treatment is appropriate, and also aids with prognosis.
What are the options for treating lung cancer?
Lung cancer treatments depend on the type, stage, and location of the lung cancer . The main treatments include:
- Lobectomy – a single lung lobe is removed.
- Bilobectomy – two lung lobes are removed.
- Pneumonectomy – the whole lung is removed.
- Wedge resection – a section of lung is removed that includes part of one or more lobses.
- Segmentectomy – a segment of lung is removed, including the veins, arteries, and bronchi(oles).
- Sleeve resection – performed when the cancer is centrally located and invading the main bronchi. The affected lung tissue and section of bronchus is removed, with the remaining bronchus ends being reattached.
- Lymph node resection
- Palliative symptom-control
- Inserting a stent to keep the airways open when becoming compressed
- Radiotherapy to shrink the tumour
- Laser treatment
- Light therapy
- Targeted cancer drugs
What is the prognosis for a person with lung cancer?
An individual’s prognosis depends hugely on the type, stage, and location of their lung cancer, in addition to any co-existing conditions they may have. However, on average in England, 40% survive 1 year following diagnosis, 15% survive 5 years following diagnosis, and 10% survive 10 years following diagnosis.