Histoplasmosis is an endemic mycosis caused by Histoplasma capsulatum.
Pulmonary histoplasmosis is the most common manifestation of this infectious disease. Disseminated or extra-pulmonary (pericardial, articular) histoplasmosis is often seen in immunosuppressed patients. As such, these are in...
Acquired immunodeficiency syndrome (AIDS) is an immunosuppressed state, caused by infection with the human immunodeficiency virus (HIV). It is characterised by opportunistic infections, neoplasms and neurological manifestations.
According to the United Nations programme on HIV/AID...
Pulmonary manifestations of HIV/AIDS are a major contributor to morbidity and mortality related to the disease. The differential in an HIV patient with a chest complaint is broad. Infectious causes are the most common, however, neoplasms, lymphoma and interstitial pneumonias also play a signific...
HIV associated follicular bronchiolitis is a form of bronchiolitis that occurs in those with HIV.
It has been described in both HIV-positive children and adults.
It is manifested by bronchial-associated lymphoid tissue hyperplasia thought to be due to repetitive antige...
HIV-associated neoplasms are numerous and can be broadly divided into two groups:
associated but not AIDS defining malignancies
The development of these malignancies in HIV affected individuals generally implies progression to AIDS 4:
Pulmonary manifestations of Hodgkin lymphoma are relatively rare, present in 5-12% of patients at the time of diagnosis. It is relatively more common with the nodular sclerosing subtype. Pulmonary involvement usually indicates stage IV disease.
Bilateral involvement is ...
The Hoffman-Rigler sign is a sign of left ventricular enlargement inferred from the distance between the inferior vena cava (IVC) and left ventricle (LV).
On a lateral chest radiograph, if the distance between the left ventricular border and the posterior border of IVC e...
The holly leaf sign refers to the appearance of pleural plaques on chest x-rays. Their irregular thickened nodular edges are likened to the appearance of a holly leaf.
Holt-Oram syndrome (HOS) is an autosomal dominant syndrome that results in congenital heart defects and upper limb anomalies:
congenital heart defects
atrial septal defect (ASD) (commonest cardiac defect 4)
ventricular septal defect (VSD)
upper limb abnormalities
Honeycombing is a CT imaging descriptor referring to clustered cystic air spaces (between 3-10 mm in diameter but occasionally as large as 2.5 cm) which are usually subpleural and basal in distribution. They can be subdivided into:
The walls ...
The horizontal fissure (also called the minor fissure) is a unilateral structure in the right lung that separates the right middle lobe from the right upper lobe.
The horizontal fissure arises from the right oblique fissure and follows the 4th intercostal space from the sternum u...
Horseshoe lung is one of the rare congenital anomalies of the lung. A band of pulmonary parenchyma is formed extending between the right and left lungs. The pulmonary tissue can be seen either anterior to the aorta or posterior to the pericardium at the caudal end.
Hospital-acquired pneumonia (HAP) or nosocomial pneumonia is defined by the American Thoracic Society (ATS) guidelines as pneumonias that occur more than 48 hours after hospital administration but were not present at the time of admission.
It can be a common cause of pneumonia in ...
Hot tub lung refers to pulmonary disease in otherwise healthy patients that can occur by secondary exposure to aerosolized non-tuberculous mycobacteria in contaminated hot water-steam (classically described in hot tubs, hence the name).
It can present as an acute pulmona...
A hybrid lesion in paediatric chest radiology refers to a combination of a congenital pulmonary airways malformation (CPAM) and a pulmonary sequestration (most commonly extralobar). It falls under a type of bronchopulmonary foregut malformation. Due to more sophisticated imaging, they are increa...
There are several signs of hydatid cysts seen associated with hydatid disease:
cumbo sign: air is seen between the pericyst and the laminated membrane of the cyst
serpent sign: internal rupture of the cyst with collapse of membranes of the parasite into the cyst
spin sign / whirl sign: detac...
Hydatid cysts result from infection by the Echinococcus, and can result in cyst formation anywhere in the body.
There are two main species of the Echinococcus tapeworm 1,2:
pastoral: dog is a main host; most common form
sylvatic: wolf is a main h...
Hydropneumothorax is a term given to the concurrent presence of a pneumothorax as well as a hydrothorax (i.e. air and fluid) in the pleural space.
It may arise in various situations which include
A hyparterial bronchus is any bronchus originating inferior to the level of the pulmonary artery. Conversely, the right superior lobar bronchus can be referred to by its anatomical relationship to the pulmonary arteries as being eparterial.
The term may be encountered in the classification of ...
Hyperattenuating pulmonary abnormalities can result from a variety of processes and have varied radiographic appearances. It is easiest, for the purposes of radiology, to divide them into:
hyperdense linear or reticular opacities
hyperdense pulmonary nodules
hyperdense pulmonary mass
Hypercontracting (nutcracker) oesophagus is a motility disorder of the oesophagus. This condition is primarily diagnosed with manometry with high intra-oesophageal pressure and normal peristalsis. Most patients will have a normal barium swallow.
Hypercontracting oesophagus ("nutcracker oesopha...
There are only a few causes of a pulmonary mass with internal calcification. They include:
granuloma: most common
mucoid calcification of mucinous adenocarcinoma:
gastrointestinal tract ad...
Hyperdense pulmonary nodules are a subset of pulmonary nodules that have relatively increased attenuation, usually caused by calcification within the nodule. Here, we broadly refer to a nodule as a pulmonary opacity <30 mm.
calcified pulmonary nodules are a specific grou...
Hyperimmunoglobulin E (hyper IgE) syndrome (HIES), also known as Job syndrome, consists of a heterogeneous group of complex hereditary combined B- and T-cell immune deficiency diseases characterised by recurrent Staph aureus chest infections, characteristic coarse facial appearance and dental pr...
Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, represents a group of pulmonary disorders mediated by an inflammatory reaction to inhalation of an allergen. These may be organic or inorganic particles (microbes, animal or plant proteins, and certain chemicals) tha...
Hypogammaglobulinaemia is an immune disorder characterised by a reduction in all types of gammaglobulins.
While hypogammaglobulinaemia means some of loss of gammaglobulins, a total loss is termed agammaglobulinaemia which can occur in as an x linked form - X-linked agammaglobuline...
CT scoring systems have been proposed in patients with acute respiratory distress syndrome (ARDS) to predict clinical outcomes. This scoring system was established by Ichikado et al. in 2006 2 and at the time of writing (July 2016), this is the most widely used CT scoring system.
Idiopathic dilatation of the pulmonary trunk is a rare congenital anomaly comprising of pulmonary trunk enlargement with or without dilatation of the right and left pulmonary arteries.
For this diagnosis, exclusion of pulmonary and cardiac diseases (mainly pulmonary valve stenosis) and confirma...
Idiopathic giant bullous emphysema, also known as vanishing lung syndrome (VLS), is characterised by giant emphysematous bullae, which commonly develop in the upper lobes and occupy at least one-third of a hemithorax. It is a progressive condition that is also associated with several forms of em...
Idiopathic interstitial pneumonias (IIPs) are diffuse interstitial lung diseases of unknown cause. A useful mnemonic for the American Thoracic Society-European Respiratory Society (ATS-ERS) classification of IIPs is:
All Idiopathic Chronic Lung Disease aRe Nonspecifically Patterned
Idiopathic interstitial pneumonias (IIPs) are diffuse interstitial lung diseases of unknown cause. They are characterized by cellular infiltration of the interstitial compartment of the lung with varying degrees of inflammation and fibrosis.
For many years many attempts have bee...
The approach to HRCT chest in patients with suspected idiopathic interstitial pneumonia (IIP) is with the aim to:
make sure an appropriate study requested i.e. HRCT chest with optimal individually adjusted protocol and ensure adequacy of the HRCT chest quality (see imaging protocol below)
Idiopathic pauci immune pulmonary capillaritis (IPIPC) is considered a rare type of pulmonary vasculitis. Some authors consider this due be an organ specific subset of microscopic polyangiitis 3. It can result in diffuse alveolar haemorrhage.
It is an isolated small vessel vasculitis...
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 anaemia
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 IgG4-related disease.
On HRCT of the chest, it may be categorised into four major subtypes 5:
solid nodular subtyp...
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 normal clinical practice on CT. 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, it...
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...
This is a basic article for medical students and other non-radiologists
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 magnificat...
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 subgroup 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 a...
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 disease can be variable and cannot 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 deve...
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.
These tumours were previously referred as inflammatory pseudotumour.
They can occur at any age and there is c...
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. ...
The intercostal catheter (ICC or chest tube) is a tube inserted into the pleural space to drain gas or fluid. It is mainly inserted to treat pneumothorax.
The indications are wide and can include 1:
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 sheath 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% o...
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 extremely rare.
As with all lipomas they are composed of adipose tissue. The origin of the peripheral intrapulmona...
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 the lung is a subtype of invasive adenocarcinoma of the lung. It was formerly known as mucinous bronchoalveolar carcinoma.
In 2011, the International Association for the Study of Lung Cancer (IASLC), American Thoracic Society (ATS), and European ...
This is a basic article for medical students and other non-radiologists.
Haemoptysis is the coughing up of frank blood or blood-stained mucus/pus from the lungs and it is an important indicator of pathology. Careful assessment of history, clinical examination and investigations will help elicit...
This is a basic article for medical students and other non-radiologists
Pleuritic chest pain is chest pain that is precipitated by movement or forceful breathing and tends to be sharp in nature. It is often accompanied by a perception of dyspnoea which may be secondary to suppression of respira...
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, also known as diaphragmatic tenting or Kattan sign, 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)...
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 septal (Ke...
The Kirklin sign refers to a deformity of the normal gastric 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 (GIST...
Klebsiella pneumonia, also known as Friedländer 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.
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...