Idiopathic pneumonia syndrome (IPS) refers to diffuse lung injury which can occur following haematopeotic stem cell transplantation where neither an infectious nor non-infectious aetiology can be found.
The incidence of IPS is thought to be around 12% following haematopoetic stem ...
Idiopathic pulmonary fibrosis (IPF) is a clinical syndrome and considered the most common and the most lethal form of pulmonary fibrosis corresponding to the histologic and imaging pattern of UIP. It is more common in middle age or elderly men and diagnosed by:
histological or imaging pattern ...
Idiopathic pulmonary haemosiderosis (IPH) is an uncommon form of pulmonary haemosiderosis. It is characterised by the triad of
iron deficiency anemia
diffuse pulmonary infiltrates, usually represented by diffuse pulmonary haemorrhage
The diagnosis is usually made by exclusion 1.
Idiopathic pulmonary ossification (also known as bony metaplasia of lung) is a rare disorder with unknown cause characterised by bony tissue within the lung.
The condition is asymptomatic but mild symptoms, restrictive pulmonary physiology, and impaired transfer factor hav...
IgG4-related disease (IgG4-RD) is a systemic disease that is characterised by extensive IgG4-positive plasma cells and T-lymphocyte infiltration of various organs.
This condition has been known by many other names in the past, such as IgG4-related sclerosing disease, IgG4-related s...
IgG4-related lung disease is a recently described condition. It may occur with or without systemic involvement. It is considered part of the spectrum of IgG-4 related disease.
On HRCT of the chest, it may be categorised into four major subtypes 5:
solid nodular type
Immune reconstitution inflammatory syndrome (IRIS) is paradoxical deterioration of a pre-existing illness following abrupt improvement in an individual's immune function. It is classically seen in HIV/AIDS patients following initiation of highly active anti-retroviral therapy (HAART). Increasing...
Implantable loop recorders, also known as insertable cardiac monitors, are small insertable devices that continuously monitor and record cardiac rhythms. They are placed subcutaneously and used for the evaluation of patients with recurrent unexplained episodes of palpitations or syncope. They sh...
Incidental lung nodules are encountered commonly in routine cross-sectional imaging. The risk of developing cancer in very small nodules (<5 mm) is very low. However, clear-cut recommendations are still not in place with high variation in practice amongst reporting radiologists 1. As a result, i...
The incomplete border sign is useful to depict an extrapulmonary mass on chest radiograph.
An extrapulmonary mass will often have a inner well-defined border and an ill-defined outer margin 1-3. This can be attributed to the inner margin being tangential to the x-ray beam and has good inherent ...
Incomplete double aortic arch is a rare vascular ring anomaly wherein a segment of the minor aortic arch, usually the left, is atretic.
As in the case of other vascular rings, this anomaly can cause 1:
Some patients may reach adulthood with...
Increased cardiothoracic ratio describes widening of the cardiac silhouette on a chest radiograph. This is only of use when making an assessment of a PA chest x-ray since the AP chest x-ray causes the artefactual magnification of the heart and the cardiothoracic ratio is altered.
Increased retrosternal airspace is an indicator of hyperinflation of the lungs and is usually due to emphysema.
The thickness of the space between the ascending aorta and the posterior margin of the sternum (3 cm inferior to the sternomanubrial joint) and is normally no more than 2.5 cm 1 altho...
Infectious bronchiolitis refers to subtype of bronchiolitis where there is an definite infective precipitant. It falls under the sub group in inflammatory bronchiolitides and by some authors is considered a type of cellular bronchiolitis 3. It tends to be more clinically severe in children than ...
The inferior accessory fissure of the lung, also known as Twining's line, divides the medial basal bronchopulmonary segment from the rest of the lower lobe.
This accessory fissure is present in around 12% of people when examined with CT and is visible on 5-8% of frontal chest x-rays. It is appr...
The inferior mediastinum is the box-shaped space in the mediastinum below the transthoracic plane of Ludwig between the wedge-shaped superior mediastinum above and the diaphragm and inferior thoracic aperture below. There are no physical structures that divide the superior and inferior mediastin...
The inferior pulmonary ligament (or just the pulmonary ligament) is a normal anatomical structure that is often seen on chest x-ray and CT chest.
The inferior pulmonary ligament is a fused triangular-shaped sheet of parietal and visceral pleura that extends from the hilum to the...
The inferior thoracic aperture connects the thorax with the abdomen.
The inferior thoracic aperture is irregular in shape and is more oblique and much larger than the superior thoracic aperture. The diaphragm occupies and closes the inferior thoracic aperture, thereby separating ...
Thoracic manifestations of both ulcerative colitis and Crohn's disease can be variable and can't be used to differentiate between these entities.
They can develop at any time with respect to the clinical onset of the underlying disease. Actually, they can also predate the colonic disease or dev...
While the term bronchiolitis in itself implies "inflammation" of the bronchioles by definition, some authors group the term inflammatory bronchiolitis as a specific group in terms of imaging as distinct from the more fibrotic - constrictive type 1.
Conditions that are described under this inclu...
Inflammatory myofibroblastic tumours (IMT), also known as plasma cell granulomas, are rare neoplasms that have a diverse spectrum of biological behaviour.
It can occur at any age and there is currently no recognised gender predilection.
Composed of spindle cells (key ...
Inflammatory myofibroblastic tumours of the lungs are a location specific type of inflammatory myofibroblastic tumours.
They are very rare with their incidence reported at approximately 0.04-1% of all the pulmonary neoplasms 1. While it can affect any age group, around 25% of case...
Infusothorax is a complication of central venous catheter malposition where the catheter tip is located in the pleural space and the infusion of the fluid collects inadvertantly in the pleural space in the form of a pleural effusion. Longer term complications depend on the fluid being infused.
The innermost intercostal muscles are muscles of respiration. They are the deepest intercostal muscles located in the intercostal spaces, and contract along with the internal intercostal muscles to reduce the transverse dimension of the thoracic cavity during expiration.
Innominate artery compression syndrome, also known as brachiocephalic artery compression syndrome, is a rare cause of tracheal stenosis that occurs in the paediatric population.
It can only occur in the presence of an aberrantly positioned thymus that forces the aortic arch or innomi...
Inorganic dust types are derived from mineral rather than biological elements (organic compounds). Inhalation of these dusts may result in lung disease (pneumoconiosis), often after years of cumulative exposure.
The commonest inhaled dusts that cause disease are asbestos, silica and coal dust. ...
Intercostal lung hernia is defined as protrusion of the lung beyond the confines of the thoracic cage. It is an uncommon entity.
Hernias which are symptomatic may cause dyspnoea, chest wall pain or a visible or palpable chest bulge (most common in intercostal lung hernias...
The intercostal muscles are an important group of muscles in the intercostal spaces (between the ribs) that contract during respiration. Three muscles are classically described, from superficial to deep:
external intercostal muscles
internal intercostal muscles
innermost intercostal muscles
The intercostal nerves are the somatic nerves that arise from the anterior divisions of the thoracic spinal nerves from T1 to T11. These nerves in addition to supplying the thoracic wall also supply the pleura and peritoneum.
Intercostal nerves can be divided into atypical and ty...
Intercostal nerve neurilemmomas, also known as intercostal nerve schwannoma or neurinoma, are nerve sheaths encapsulated tumours affecting intercostal nerves.
Please refer to the article on schwannomas for a broad discussion about these tumours.
They account for less than 10% ...
The intercostal spaces are the space between the ribs. There are 11 spaces on each side and they are numbered according to the rib which is the superior border of the space.
The intercostal spaces contain three layers of muscle: the external, internal and innermost layers with t...
The interface sign is a feature seen on HRCT chest imaging and refers to the presence of irregular interfaces at the margins of pulmonary parenchymal structures or the pleural surface of the lung. It suggests interstitial thickening.
The interlobular septa (sing: septum) are located between the secondary pulmonary lobules and are continuous with both the subpleural interstitium (peripheral connective tissue) and the peribronchovascular interstitium (axial connective tissue) as well as the more delicate intralobular septa.
There are many causes of interlobular septal thickening, and this should be distinguished from intralobular septal thickening. Thickening of the interlobular septa can be smooth, nodular or irregular, with many entities able to cause more than one pattern.
Causes of septal thickening...
The internal intercostal muscles are important muscles of respiration. They number eleven on each side and are located in the intercostal spaces, reducing the transverse dimension of the thoracic cavity during expiration.
The internal intercostal muscles are the middle muscle of ...
The internal thoracic artery (previously called the internal mammary artery) supplies the anterior body wall and its associated structures from the clavicles to the umbilicus.
The internal thoracic artery arises from the first part of the subclavian artery in the base of...
Diffuse interstitial lung disease encompasses a large number of disorders that are characterised by cellular infiltrates in a periacinar location. While some disease processes may cause significant injury to the underlying lung parenchyma (e.g. usual interstitial pneumonia), some do not (e.g. pu...
An interstitial lung pattern is a regular descriptive term used when reporting a plain chest radiograph. It is the result of the age-old attempt to make the distinction between an interstitial and airspace (alveolar) process to narrow the differential diagnosis.
A re-read of the timeless work o...
Interstitial thickening is pathological thickening of the pulmonary interstitium and can be divided into:
interlobular septal thickening
intralobular septal thickening
secondary pulmonary lobules
The intralobular septa (sing: septum) are delicate strands of connective tissue separating adjacent pulmonary acini and primary pulmonary lobules. They are continuous with the interlobular septa which surround and define the secondary pulmonary lobules.
Intralobular septal thickening is a form of interstitial thickening and should be distinguished from interlobular septal thickening. It is often seen as fine linear or reticular thickening.
It has been described with any conditions of variable aetiology which include
The intrapleural or pleural space is the fluid-filled space in between the parietal and visceral layers of the pleura. In normal conditions it contains only a small amount of serous pleural fluid.
A pleural effusion is the pathological accumulation of pleural fluid, and when ...
Intrapulmonary lipomas are rare fat containing benign lung lesions.
They mostly occur in the adult population, with occurence in the paediatric population is extremely rare.
As with all lipomas they are composed of adipose tissue. The origin of the peripheral intrapulm...
Intrapulmonary lymph nodes are a type of intrathoracic lymph nodes. They can be quite common on routine CT examinations of healthy patients.
perifissural lung nodules 2
CT: HRCT chest
around 6 mm in size (usually reported range around 3-8.5 mm) 1
most tend to...
Sarcomatoid neoplasms involving the chest comprise of a broad group of tumours that occur in the lung, mediastinum, pleura, and chest wall. These tumours have mesenchymal component.
primary sarcomatoid tumours of the chest
usually arising from the chest wall
Ewing sarcoma of the...
Invasive aspergillosis is a form of pulmonary aspergillosis seen in patients with decreased immunity. It comprises a number of entities that are discussed individually:
subacute invasive pulmonary aspergillosis (previously known as chronic necrotising aspergillosis (CNA) or semi-invasive asperg...
Invasive mucinous adenocarcinoma of lung is a subtype of invasive adenocarcinoma of the lung. It was formerly known as mucinous bronchoalveolar carcinoma.
Mucinous carcinomas originate from columnar mucus-containing cells (c.f. non-mucinous tumours which arise from Clara cells or typ...
Isolated unilateral absence of the pulmonary artery (IUAPA) is the congenital absence of the left or right pulmonary artery. When found in combination with other congenital vascular abnormalities it is known as unilateral absence of the pulmonary artery (UAPA).
Isomerism is a term which in general means 'mirror-image'. It is used in the context of heterotaxy and is of two types:
Mirror image of the structures on the left side of the chest along the left-right axis of the body, i.e. patients with isomeri...
The juxtaphrenic peak sign or diaphragmatic tenting refers to the peaked or tented appearance of a hemidiaphragm which can occur in the setting of lobar collapse. It is caused by retraction of the lower end of diaphragm at an inferior accessory fissure (most common 1), major fissure or inferior ...
Kaposi sarcoma is a low-to-intermediate grade mesenchymal tumour that involves the lymphovascular system. The tumour can involve the pulmonary, gastrointestinal, cutaneous and musculoskeletal systems.
There are four recognised variants 1:
classic (chronic): multiple distal lower ext...
Kartagener syndrome is a subset of primary ciliary dyskinesia, an autosomal recessive condition characterised by an abnormal ciliary structure or function, leading to impaired mucociliary clearance.
The prevalence of primary ciliary dyskinesia is approximately 1 in 12,000-60,000 ...
Getting a film with Kerley lines in the exam is one of the many exam set-pieces that can be prepared for.
The film goes up and after a couple of seconds pause, you need to start talking:
There are bilateral basal interstitial lines that extend to the pleural surface - these are Kerley B l...
The Kirklin sign refers to a deformity of the normal gastric air bubble on an upright chest radiograph due to a mass lesion of the gastric cardia or fundus.
The differential for a Kirklin sign includes
gastrointestinal stromal tumour (G...
Klebsiella pneumonia refers to pneumonia resulting from an infection from the organism Klebsiella pneumoniae.
There tends to be a higher prevalence in older patients with alcoholism and debilitated hospitalised patients 3.
Klebsiella pneumoniae is amongst the most com...
Knuckle sign refers to the abrupt tapering or cutoff of a pulmonary artery secondary to embolus. It is better visualised on CT pulmonary angiography scan than chest x-ray. This is an important ancillary finding in pulmonary embolism (PE), and often associated with the Fleischner sign of dilated ...
The Kveim Stilzbach skin test is a sensitive and specific test for sarcoidosis, requiring the intradermal injection of homogenized spleen or liver material from a patient with known sarcoidosis. In patients with sarcoidosis, a typical sarcoid granuloma will develop at the injection site within 4...
Lady Windermere syndrome refers to a pattern of pulmonary Mycobacterium avium complex (MAC) infection seen typically in elderly white women who chronically suppress the normal cough reflex. A fastidious nature and a reticence to expectorate are believed to predispose such persons to infections w...
There are a number of lambda signs:
lambda sign of twin pregnancy
lambda sign of sarcoidosis
The lambda sign is seen on gallium-67 scans in the setting of thoracic sarcoidosis. Bilateral hilar and right paratracheal lymph nodes are typically involved which can resemble the Greek letter lambda (λ).
lambda sign of twin pregnancy
Lane-Hamilton syndrome (LHS) refers to the rare concurrent association of idiopathic pulmonary haemosiderosis and coeliac disease 1.
It is typically seen in children under the age of 15 but can occasionally be seen in adults.
History and etymology
It was originally described by ...
Langerhans cells are dendritic cells of monocyte-macrophage lineage, containing large granules called Birbeck granules. They are normally found in epithelial surfaces, lymph nodes and other organs, and can also be found elsewhere, particularly in association with Langerhans cell histiocytosis.
Langerhans cell histiocytosis (LCH) is a rare multi-system disease with a wide and heterogeneous clinical spectrum and variable extent of involvement.
Langerhans cell histiocytosis was previously known as histiocytosis X. The newer term is preferred as it's more descriptive of its...
Large cell carcinoma of the lung is one of the histological types of non-small cell carcinomas of the lung.
It is thought to account for approximately 10% of bronchogenic carcinoma 1.
Patient presents with dyspnea, chronic cough and haemoptysis.
Large cell neuroendocrine carcinoma (LCNEC) of the lung is classified as a subtype of large cell carcinoma of the lung. It is also classified as a pulmonary neuroendocrine tumour.
The incidence peaks around the 6th decade 6. There is an increased male predilection 7.
When a pleural effusion is large and unilateral, concern for an underlying abnormality should be raised. Causes include:
extension from sub-diaphragmatic primary infection
Leadless cardiac pacemakers are a recently introduced type of cardiac conduction device. These pacemakers are self-contained right ventricular single-chamber pacemakers that are implanted percutaneously via a femoral approach 1-3.
A leadless cardiac pacemaker can be appre...
Leaky lung syndrome (LLS) refers to a form of non-cardiogenic pulmonary oedema.
Pulmonary oedema due to increased capillary permeability.
LLS is considered as mild form of a part of spectrum of acute lung injury with ARDS at the other end of spectrum ...
Leflunomide induced acute interstitial pneumonia is a form of drug induced interstitial lung disease. The precipitation of radiological evidence of pulmonary infiltrates, clinical acute respiratory illness in the context of a good temporal relationship with commencement of the agent and no clear...
Left atrial appendage (LAA) closure devices refers to a device placed in the LAA in patients with atrial fibrillation who cannot be anticoagulated pharmaceutically to prevent thromboembolic events. It is placed percutaneously via the femoral vein to right atrium to left atrium by forming a punct...
Left atrial enlargement may result from many conditions, either congenital or acquired. It has some characteristic findings on a frontal chest radiograph. CT or MRI may also be used for diagnosis.
An enlarged left atrium can have many clinical implications, such as:
The left atrium is one of the four chambers of the heart. It receives oxygenated blood from the pulmonary circulation that is then delivered to the left ventricle and then into the systemic circulation.
The left atrium is grossly cuboidal, and like the right atrium has an appenda...
The left horizontal (or minor) fissure is an accessory fissure found in around 8% of individuals examined with CT 3. In a prospective study of 2,000 consecutive normal chest X-rays (AP and lateral), a definite left horizontal fissure was identified in 1.6% of the subjects 1.
The left lower lobe (LLL) is one of two lobes in the left lung. It is separated from the left upper lobe by the left oblique fissure and subdivided into four bronchopulmonary segments.
Location and structure
The LLL lies in the posterior and lower aspect of the left hemithorax a...
The left lower lobe anteromedial segment (or cardiac segment) is one of the bronchopulmonary segments of the left lower lobe. It is the most anteromedial of the segments within the base of the left upper lobe.
It is the equivalent segment merger of the anterior and medial segments of the right ...
The left main bronchus divides into the left lower lobe bronchus and the left upper lobe bronchus. It is one of the secondary lobar bronchi.
The left lower lobe bronchus is very short and divides immediately into the segmental bronchi. There are usually 10 individual segmental b...
Left lower lobe collapse has distinctive features, and can be readily identified on frontal chest radiographs, provided attention is paid to the normal cardiomediastinal contours. However, the shadow cast by the heart does make it more difficult to see than the right lower lobe collapse.
For a ...
The left lower lobe lateral or lateral basal segment is one of the four bronchopulmonary segments of the left lower lobe. It is the most inferolateral of the segments in the left lower lobe, below the superior segment.
The left lower lobe posterior or posterior basal segment is one of the four bronchopulmonary segments of the left lower lobe. It is the most inferoposterior of the segments in the left lower lobe, below the superior segment.
Due to its low and posterior position, pathology in...
The left lower lobe superior or apical segment is one of the four bronchopulmonary segments of the left lower lobe. It is the most apical of the segments in the left lower lobe, posterior to the upper aspect of the oblique fissure and apicoposterior segment of the left upper lobe.
The left lung is one of two lungs, located in the left hemithorax on the left of the heart and mediastinum.
There are a few differences between the two lungs:
The left lung is smaller in volume than the right lung, with a smaller transverse dimension (due to the heart on the left) but a large...
The trachea bifurcates into the right and left main bronchi at the level of the carina, supplying air to the right and left lungs respectively. Each main or primary bronchus enters the hilum of its lung and gives rise to secondary lobar bronchi, which further divide into tertiary segmental bronc...
When a central venous catheter that is supposed to project over the superior vena cava is abnormally located to the left of the mediastinum a limited differential of left paramediastinal catheter position should be considered 1:
located within the vein
left sided superior vena cava
The left paraspinal (paraspinous or paravertebral) line is a feature of frontal chest x-rays. It is formed by the interface between the left lung and the left posterior mediastinal soft tissues 1. It is more commonly seen than the right paraspinal line.
Lateral displacement of the left paraspin...
The left paratracheal stripe is formed by the interface of the medial pleural surface of the left upper lobe and left lateral border of the trachea and/or or the fat adjacent 1 with air within each structure forming the outline. It may not be visible if the left upper lobe contacts the left subc...
The left pulmonary artery (LPA) is one of the branches of the pulmonary trunk, branching at the level of the transthoracic plane of Ludwig. It is shorter than the right pulmonary artery and represents a direct posterior continuation of the pulmonary trunk. It arches posterosuperiorly over the su...
The left superior intercostal vein drains the left posterosuperior hemithorax and is considered to be part of the azygos venous system even though it does not directly drain into the azygos vein.
Origin and course
The left superior intercostal vein forms by the union of the 2nd...
The left upper lobe (LUL) is one of two lobes in the left lung. It is separated from the left lower lobe by the left oblique fissure and subdivided into four bronchopulmonary segments, two of which represent the lingula.
Location and structure
The left upper lobe lies in the upp...
The left upper lobe anterior segment is one of the four bronchopulmonary segments of the left upper lobe. It is the most anterior of the segments in the left upper lobe lying below and anterior to the apicoposterior segment and above the oblique fissure.
The left upper lobe apicoposterior segment is one of the bronchopulmonary segments of the left upper lobe. As its name suggests, it is the most apical and posterior of the segments within the left upper lobe and is supplied by the left apicoposterior segmental bronchus.
It is the equivalent seg...
The left main bronchus divides into the left upper lobe bronchus and the left lower lobe bronchus. It is one of the secondary lobar bronchi.
The left upper lobe bronchus is very short and divides immediately into the segmental bronchi. There are usually 10 individual segmental b...
Left upper lobe collapse has distinctive features but can be challenging to identify on chest radiographs by the uninitiated.
For a general discussion refer to the article on lobar collapse.
The left upper lobe collapses anteriorly becoming a thin sheet...
Getting a film with left upper lobe collapse in the exam is one of the many exam set-pieces that can be prepared for.
This frontal chest radiograph shows a hazy (or veil-like*) opacification of the left hemithorax that is associated with superior displacement left hilum and horizon...