The heart is a hollow, muscular organ of the middle mediastinum, designed to pump oxygenated blood around the systemic circulation and de-oxygenated blood around the pulmonary circulation
The heart has a somewhat conical form and is enclosed by pericardium. It is positioned poste...
There are four heart chambers, the right atrium, left atrium, right ventricle and left ventricle. These receive blood from the body and lungs and contract to transmit blood to the lungs for oxygenation and to the body for use in metabolism.
It is best to list the four chambers in order of the s...
This is a basic article for medical students and other non-radiologists
Heart failure is a syndrome of cardiac ventricular dysfunction, where the heart is unable to pump sufficiently to meet the body's blood flow requirements.
Although it is useful to divide the signs an...
The Heimlich valve, also known as the flutter valve, is a unidirectional valve to ensure that gas/fluid drained from the pleural space cannot flow back in.
The Heimlich valve is cheap, easy to use, and does not require clamping unlike 'traditional' thoracostomy drainage tubes. Suction can stil...
The Heiner syndrome is a rare form of primary pulmonary hemosiderosis associated with an allergy to cow's milk. The syndrome includes:
rectal blood loss with hypochromic microcytic anemia
pulmonary infiltrates (often recurrent)
There are many thoracic complications that can occur following hematopoietic stem cell transplantation. These can precipitate during various stages following transplantation and can be either infectious or noninfectious.
The hemiazygos vein is the asymmetric counterpart to the azygos vein and forms part of the azygos venous system.
The hemiazygos vein is formed by the confluence of the left ascending lumbar and left subcostal veins.
The hemiazygos vein enters the thorax either ...
Complete white-out of a hemithorax on the chest x-ray has a limited number of causes. The differential diagnosis can be shortened further with one simple observation: the position of the trachea. Is it central, pulled or pushed from the side of opacification? Is there pulmonary volume loss or vo...
Hepatic hydrothorax (HH) is an uncommon manifestation of cirrhosis with ascites. It is one of the pulmonary complications of cirrhosis with portal hypertension.
It is characterized by formation of pleural effusions usually greater than 500 mL, in patients with portal hypertension without any o...
Pulmonary hepatisation refers to the alteration of lung tissue such that it resembles liver tissue. It is a stage of lobar pneumonic consolidation.
In the early stage, hemorrhagic fluid accumulates within the alveoli and gets organized resulting in a pathological appearance called "r...
Hepatopulmonary syndrome (HPS) refers to the combination of
hepatic dysfunction (cirrhosis)
hypoxemia (alveolar-arterial O2 gradient of >15 mmHg; >20 mmHg in >64 years old patients)
peripheral pulmonary arterial dilatation (due to right to left micro-shunts)
It is estimated to ...
Hereditary connective tissue diseases are a group of connective tissue disease that have a degree of inheritance risk. They include:
Marfan syndrome: genetic disease causing abnormal fibrillin
Ehlers-Danlos syndrome: progressive deterioration of collagen and affects joints, heart valves, orga...
Hereditary hemorrhagic telangiectasia (HHT), also known as Osler-Weber-Rendu syndrome, is a rare inherited disorder characterized by abnormal blood vessel formation in the skin, mucous membranes, and organs including the lungs, liver, and central nervous system.
Hermansky-Pudlak syndrome (HPS) is a rare syndrome which consists of:
oculocutaneous hypopigmentation (albinism)
abnormal storage of autofluorescent pigment (ceroid or lipofuscin)
typically occurs within lysosomal organelles of the cells of multiple organs and the reti...
Heroin-induced pulmonary edema is an aetiological subtype of non-cardiogenic pulmonary edema. It may be prevalent in up to 40% of patients admitted with a heroin overdose 2.
It is defined by some authors as a syndrome in which a patient develops significant hypoxia (room air saturation< 90% wit...
Hiatus hernias occur when there is herniation of abdominal contents through the esophageal hiatus of the diaphragm into the thoracic cavity.
The prevalence of hiatus hernia increases with age, with a slight female predilection.
Many patients with hiatus her...
High altitude pulmonary edema is a subtype of pulmonary edema and is caused by prolonged exposure to an environment with a lower partial oxygen atmospheric pressure.
It occurs most frequently in young males and ~24-48 hours after they have made a rapid ascent to heights greater th...
High attenuation lymphadenopathy has been described with:
Kaposi sarcoma 1,6
angioimmunoblastic lymphadenopathy (AILD)
Kimura disease (due to nodal hemorrhage) 6
metastatic hypernephroma (presumed due to nodal hemorrhage) 6
If there is calcification associated...
The hilar point on chest radiographs is formed by the outer margins of the superior pulmonary vein and the descending pulmonary artery as they cross past each other.
The hilum convergence sign is a useful chest radiograph sign to help distinguish a bulky hilum due to pulmonary artery dilatation from a juxtahilar mass/nodal enlargement.
If pulmonary artery branches are visible through the opacity and converge towards the waist of the heart (positive hilum c...
The hilum overlay sign is useful in differentiating cardiac enlargement from a mediastinal mass. It refers to an abnormally dense hilum on frontal chest radiograph with preserved visualization of the hilar vessels.
If a mass arises from the hilum, the normal pulmonary vessels (interlobar arte...
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 characterized 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 o...
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 (often abbreviated as 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 c...
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 pediatric 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 increas...
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
water lily sign: endocyst flo...
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) esophagus is a motility disorder of the esophagus. This condition is primarily diagnosed with manometry with high intra-esophageal pressure and normal peristalsis. Most patients will have a normal barium swallow.
Hypercontracting esophagus ("nutcracker esophagus")...
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 ade...
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 characterized 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 characterized 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 characterized 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 hemorrhage.
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 etiology can be found.
The incidence of IPS is thought to be around 12% following haematopoetic stem c...
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 hemosiderosis (IPH) is an uncommon form of pulmonary hemosiderosis. It is characterized by the triad of
iron deficiency anemia
diffuse pulmonary infiltrates, usually represented by diffuse pulmonary hemorrhage
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 characterized 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 characterized 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 categorized 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...
Infantile fibrosarcoma of the lung, also known as primary bronchopulmonary fibrosarcoma, is a very rare spindle-cell tumor.
More than 80% of cases are reported to occur within the 1st year of life. There is a slight predominance in male infants 1,2.
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 tumors (IMT), also known as plasma cell granulomas, are rare neoplasms that have a diverse spectrum of biological behavior.
These tumors were previously referred as inflammatory pseudotumour.
They can occur at any age and there is curr...
Inflammatory myofibroblastic tumors of the lungs are a location-specific type of inflammatory myofibroblastic tumors.
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 cases ...
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 pediatric population.
The brachiocephalic or innominate artery usually takes its origin to the left of the trachea. T...
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 hernias are defined as a protrusion of the lung beyond the confines of the thoracic cage. They are uncommon, mostly seen post trauma or thoracotomies.
Hernias which are symptomatic may cause dyspnea, chest wall pain or a visible or palpable chest bulge (...
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 tumors affecting intercostal nerves.
Please refer to the article on schwannomas for a broad discussion about these tumors.
They account for <10% of primary n...
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 characterized 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...