Acute airspace opacification with lymphadenopathy is a subset of the differential diagnosis for generalised airspace opacification and includes:
post-obstructive causes (usually chronic, but 'new' changes can occur)
primary lung cancer
Acute bilateral airspace opacification is a subset of the larger differential diagnosis for airspace opacification. An exhaustive list of all possible causes of acute bilateral airspace opacities is long, but a useful way to consider the huge list is via the material within the airways:
Acute unilateral airspace opacification is a subset of the differential diagnosis for airspace opacification.
The exhaustive list of all possible causes would be huge, but a useful framework includes:
pus, i.e. infection
Air space opacification is a descriptive term that refers to filling of the pulmonary tree with material that attenuates x-rays more than the surrounding lung parenchyma. It is one of the many patterns of lung opacification and is equivalent to the pathological diagnosis of pulmonary consolidati...
The differential for air space opacities is extensive, and needs to be interpreted in context of chronicity (previous imaging) and clinical context. It is therefore useful to divide airspace opacities as follows:
acute airspace opacities with lymph node enlargement
acute airspace opacities: un...
Apical pleural cap refers to a curved density at the lung apex seen on chest radiograph.
The frequency of apical pleural thickening increases with age 3.
It arises from a number of causes:
idiopathic: chronic ischaemic aetiology is favoure...
Dilatation of the ascending aorta is a common finding in the elderly but unusual in younger patients.
In adults, an ascending aortic diameter greater than 4 cm is considered to indicate dilatation 4. Aneurysmal dilatation is considered when the ascending aortic diameter reaches or ex...
Bat wing or butterfly pulmonary opacities refer to a pattern of bilateral perihilar shadowing. It is classically described on a frontal chest radiograph but can also refer to appearances on chest CT 3,4.
Bat wing pulmonary opacities can be caused by:
pulmonary oedema (e...
Bilateral axillary lymphadenopathy can result from a number of causes and generally implies a systemic process. They include:
autoimmune diseases, e.g.:
systemic lupus erythematosus (SLE)
Bronchial wall thickening is an imaging descriptor used to describe abnormal thickening of bronchial walls and can arise from a vast number of pathological entities. It is one of the causes of peribronchial cuffing.
The presence of bronchial wall thickening usually (but not always) implies infl...
There are numerous causes of calcified mediastinal lymph nodes.
Common causes include:
infectious granulomatous diseases
Uncommon causes include:
Pneumocystis jiroveci (PCP) pneumonia
thyroid carcinoma: papi...
Calcified pulmonary (lung parenchymal) densities can occur in a number of conditions.
healed varicella pneumonia 1
pulmonary alveolar microlithiasis
occupational lung diseases
coal workers pneumoconiosis
See the main article on calcified pulmon...
Calcification associated with pulmonary emboli is usually associated with chronic pulmonary embolism. Calcification is occasionally related to prior congenital cardiac repairs 1.
If it is purely high attenuating, consider
polymethylmethacrylate (PMMA) embolism into the ...
Calcified pulmonary nodules are a subset of hyperdense pulmonary nodules and a group of nodules with a relatively narrow differential.
The most common cause of nodule calcification is granuloma formation, usually in the response to healed infection.
Calcifying pulmonary metastases are rare. These should not be confused with metastatic pulmonary calcification.
Calcification in metastases can arise through a variety of mechanisms: bone formation in tumours osteoid origin, calcification and ossification of tumour cartilage, dystrop...
The cardiophrenic space is usually filled with fat. However, lesions originating above or lower to the diaphragm can present as cardiophrenic angle lesions.
The more common lesions encountered include:
pericardial fat pad
pericardial fat necrosis
There are relatively few causes of calcification of the ascending aorta 1-3:
atherosclerosis (this usually spares the ascending aorta)
Cavitating pneumonia is a complication that can occur with severe necrotising pneumonia and in some publications, it is used synonymously with the latter term 2. It is a rare complication in both children and adults.
Cavitation associated with Mycobacterium tuberculosis is separately discussed...
Cavitating pulmonary metastases refer to pulmonary metastases which then tend to cavitate. The term is similar but may not be identical to cystic pulmonary metastases in which the wall of the former may be thicker.
Cavitation is thought to occur in around 4% of lung metastases 2.
Distribution of bronchiectasis can help in narrowing the differential diagnosis. Central bronchiectasis is typically seen in:
allergic bronchopulmonary aspergillosis (ABPA)
congenital tracheobronchomegaly (a.k.a. Mounier Kuhn syndrome)
Williams Campbell syndrome (rare)
Centrilobular lung nodules refer to an HRCT chest imaging descriptor for small 5-10 mm lung nodules which are anatomically located centrally within secondary pulmonary lobules. The term is applied on the basis of location of the nodule and not its morphology that is they may be well defined or p...
Chronic bilateral airspace opacification is a subset of the differential diagnosis for airspace opacification. An exhaustive list of all possible causes of chronic bilateral airspace opacities is long, but a useful framework is as follows:
granulomatosis with polyangi...
Chronic interstitial pneumonitis is a broad descriptive term where an interstitial pneumonia has a prolonged course. It can arise of a range of aetiologies. The term does not usually imply a specific radiographic pattern and includes UIP, NSIP or other pattern. As a general rule there is little ...
Chronic suppurative lung disease (CSLD) refers to a group of conditions which includes:
primary ciliary dyskinesia
This term is usually used in the context of paediatric patients.
Chronic unilateral airspace opacification is a subset of the differential diagnoses for airspace opacification. An exhaustive list of all possible causes of chronic unilateral airspace opacities is long, but a useful framework is as follows:
Cicatrisation atelectasis is a form of lung atelectasis which occurs as a result of scarring or fibrosis that reduces lung expansion. Cicatrisation atelectasis is classic in tuberculosis. The term is closely related to cicatrisation collapse when an entire lobe is collapsed from the same process...
A coin lesion refers to a round or oval, well-circumscribed solitary pulmonary lesion. It is usually 1-5 cm in diameter and calcification may or may not be present 1,3. Typically but not always the patient is asymptomatic 1.
The differential diagnosis for such lesions i...
Compressive atelectasis refers to a form of lung atelectasis due to compression by a space-occupying process.
Some authors describe it as a subtype of compressive (relaxation) atelectasis where the reduction in lung volume is greater than its normal relaxed state 1. Whereas others describe it a...
Crazy paving refers to the appearance of ground-glass opacity with superimposed interlobular septal thickening and intralobular septal thickening, seen on chest HRCT. It is a non-specific finding that can be seen in a number of conditions.
A number of entities can present as cyanotic congenital heart disease. These can be divided into those with increased (pulmonary plethora) or decreased pulmonary vascularity :
increased pulmonary vascularity
total anomalous pulmonary venous return (TAPVR) (types I and II)
transposition of the...
Cystic lung disease is an umbrella term used to group the conditions coursing with multiple lung cysts.
The clinical presentation is an important clue to the differential diagnosis of cystic lung diseases 12.
Diseases that present with insidious dyspnoea or spontaneous ...
Cystic lesions in paediatric patients are usually congenital lesions and, as such, can be seen antenatally and following delivery.
These congenital lesions are predominantly covered by the overarching diagnosis of bronchopulmonary foregut malformation. This is ...
The differential diagnosis for cystic masses of the mediastinum include:
oesophageal duplication cyst
cystic teratoma of mediastinum
cystic degeneration of an intrathoracic tumour
Cystic or necrotic appearing lymph nodes can be caused by a number of infectious, inflammatory or malignant conditions:
squamous cell carcinoma metastases
plasmacytoid T-cell leukaemia
acute myeloid leukaemia
herpes simplex lymphade...
Cystic pulmonary metastases are atypical morphological form on pulmonary metastases where lesions manifest as distinct cystic lesions. It is slightly different from the term cavitating pulmonary metastases in that the lesions are extremely thin walled.
It has been reported with many ...
Cystic retroperitoneal lesions can carry a relatively broad differential, which includes:
retroperitoneal mucinous cystadenoma
retroperitoneal cystic teratoma
retroperitoenal cystic mesothelioma
pseudomyxoma retroperitonei with cystic change
perianal mucinous c...
Dextrocardia is a congenital cardiac malrotation in which the heart is situated on the right side of the body (dextroversion) with the apex pointing to the right.
Dextrocardia merely refers to the laterality of the heart, it says nothing about the orientation of the patient's other...
Diaphragmatic paralysis (also considered very similar to the term diaphragmatic palsy) can be unilateral or bilateral.
Clinical features are highly variable according to underlying aetiological factor:
unilateral paralysis: asymptomatic in most of the patients as the oth...
Diaphragmatic rupture often results from blunt abdominal trauma. The mechanism of injury is typically a motor-vehicle collision.
Given that the most common mechanism is motor vehicle collisions, it is perhaps unsurprising that young men are most frequently affected. The estimated ...
A small cardiothoracic ratio (CTR) is defined as <42%/0.42 when assessed on a PA chest radiograph, and is often called small heart syndrome. A pathologically-small heart is also known as microcardia.It can be due to/associated with a number of entities:
adrenal insufficiency, e.g. Addison disea...
An anterosuperior mediastinal mass can be caused by neoplastic and non-neoplastic pathology. As their name suggests, they are confined to the anterior mediastinum, that portion of the mediastinum anterior to the pericardium and below the level of the clavicles.
The differential diagnosis for a...
Diffuse airway narrowing can occur from a number of pathologies. These include
granulomatosis with polyangiitis
various infections including
Diffuse alveolar haemorrhage (DAH) is a subset of diffuse pulmonary haemorrhage when bleeding is diffuse and directly into the alveolar spaces. It can occur in a vast number of clinical situations and can be life-threatening.
Blood tends to fill alveolar spaces at multiple sites.
Diffuse pleural thickening refers to a morphological type of pleural thickening. It can occur from malignant as well as nonmalignant causes, which include:
diffuse pleural fibrosis / fibrothorax 6
asbestos related pleural disease: typically seen a continuous sheet of pleural thickening often i...
Diffuse pulmonary haemorrhage (DPH) is a subtype of pulmonary haemorrhage where bleeding into the lung is diffuse. If the bleeding is into the alveolar spaces this can be further subclassified as diffuse alveolar haemorrhage (DAH).
While the exact presentation can vary is...
Diffuse pulmonary nodules are usually seen as multiple pulmonary nodular opacifications on a HRCT chest scan. They can signify disease processes affecting either the interstitium or the airspace. They can range from a few millimetres to up to 1 cm and when very small and numerous there can be so...
Conditions associated with diffuse tracheal narrowing or collapse include (in alphabetical order):
chronic obstructive pulmonary disease (COPD): sabre sheath trachea
granulomatosis with polyangiitis
tracheobronchial tuberculosis 3
tracheomalacia/tracheobronchomalacia (due to col...
Drug and toxin induced pulmonary hypertension is one of the causes of pulmonary arterial hypertension. It falls under group 1.3 under the Dana point classification system of pulmonary hypertension.
A wide range of difference drugs have been associated with developing pulmonary hyper...
Drug-induced lung disease can result from a number of agents and may have a myriad of presentations, ranging from an adult respiratory distress syndrome type picture to established pulmonary fibrosis.
Due to this, it can be extremely difficult to pinpoint the offending agent on imaging appearan...
Dynamic tracheal collapse refers to collapse of the trachea during expiration. It is perhaps best assessed on CT in the end expiratory phase. An inspiratory series is also useful for comparative purposes. The term excessive dynamic airway collapse (EDAC) refers to abnormal and exaggerated bulgin...
Dysphagia refers to subjective awareness of difficulty or obstruction during swallowing. It is a relatively common and increasingly prevalent clinical problem. Odynophagia is the term for painful swallowing.
Fluoroscopy is the mainstay of imaging assessment but manometry can help evaluate the o...
Echogenic fetal lung lesions on antenatal ultrasound can be detected in a number of situations. They include:
Airway obstructions: lung are often enlarged and echogenic bilaterally
congenital high airways obstruction syndrome (CHAOS)
congenital tracheal stenosis
Elevated diaphragm refers to the symmetrical elevation of both domes of the diaphragm.
There is some overlap with causes of an elevated hemidiaphragm.
poor inspiratory effort
An elevated hemidiaphragm may result from direct and indirect causes which include:
above the diaphragm 1
decreased lung volume
prior lobectomy or pneumonectomy
phrenic nerve palsy
contralateral stroke: ...
Empyemas are purulent inflammatory collections within a body cavity. Contrast this with abscesses, which arise within parenchymal tissue, rather than occupying a pre-existing anatomical space.
Colloquially, the standalone term empyema is used to refer to thoracic empyemas but there...
Endobronchial metastases are an uncommon form of intrathoracic metastases. They are much less common than intrapulmonary metastases.
The clinical presentation varies and includes:
post-obstructive pneumonitis from distal obstruction
Enlargement of the cardiac silhouette on a frontal (or PA) chest x-ray can be due to a number of causes 1:
cardiomegaly (most common cause by far)
anterior mediastinal mass
prominent epicardial fat pad
AP projection (from supine radiographs taken ...
The differential of a fat containing solitary pulmonary nodule is very narrow.
In a well circumscribed smooth or lobulated mass (especially if it has been largely stable in size over time) presence of fat is essentially pathognomonic of a pulmonary hamartoma, and usually not further assessment ...
There is a long list of fat containing thoracic lesions. They may involve the mediastinum, lung, pleura or chest wall.
Differential diagnosis includes:
intrapulmonary: fat containing pulmonary lesions
Fatty mediastinal masses are relatively uncommon, and the differential diagnosis is brief, including 1-4:
benign mature teratoma
extravasation of lipid-rich hyperalimentation fluid 3
fibrofatty replacement of the central portion of mediastinal l...
Foregut duplication cysts are a type of congenital duplication cyst. They are sometimes classified under bronchopulmonary foregut malformations.
Entities classified as foregut duplication cysts include:
other enteric cysts
oesophageal duplication cysts
Granulomatous lung disease refers to a broad group of infectious and non-infections conditions characterised by the formation of granulomas.
The spectrum includes
pulmonary non-tuberculous mycobacterial infection
Ground-glass opacification/opacity (GGO) is a descriptive term referring to an area of increased attenuation in the lung on computed tomography (CT) with preserved bronchial and vascular markings. It is a non-specific sign with a wide aetiology including infection, chronic interstitial disease a...
A haemopneumothorax (plural: haemopneumothoraces) (or, less commonly, haematopneumothorax or pneumohaemothorax) is a term given when there is concurrent presence of a haemothorax and pneumothorax. It is a variant of a hydropneumothorax.
Approximately 5% of patients with pneumotho...
Haemoptysis (plural: haemoptyses) refers to coughing up of blood. Generally, it appears bright red in colour as opposed to blood from the gastrointestinal tract which appears dark red. It is considered an alarming sign of a serious underlying aetiology.
Massive haemoptysis is refer...
A haemothorax (plural: haemothoraces), or rarely haematothorax, literally means blood within the chest, is a term usually used to describe a pleural effusion due to accumulation of blood. If a haemothorax occurs concurrently with a pneumothorax it is then termed a haemopneumothorax.
A tension ...
There are many thoracic complications that can occur following haematopoietic stem cell transplantation. These can precipitate during various stages following transplantation and can be either infectious or noninfectious.
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...
High attenuation lymphadenopathy (or adenopathy) variably refers to abnormal lymph nodes with attenuation on CT usually higher compared to muscle, either on a noncontrast exam or following contrast administration (i.e., hyperenhancement) 5.
High attenuation nodes may be due to calcifications or...
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:
Hyperattenuating pulmonary abnormalities refer to lung parenchymal opacities/lesions that are generally higher attenuation on CT than most soft tissues. An exact definition is usually not provided 1-3, while some authors focus on abnormalities that are as subjectively opaque as bony structures 4...
Hyperattenuating pulmonary consolidation refers to a region of lung parenchyma with air space opacification that has higher attenuation on CT than muscle or than expected with typical causes of consolidation such as pneumonia (fluid attenuation) or cancer (soft tissue attenuation).
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...
The idiopathic interstitial pneumonias (IIPs) are diffuse interstitial lung diseases of unknown cause. They are characterised by cellular infiltration of the interstitial compartment of the lung with varying degrees of inflammation and fibrosis.
Over the years many attempts have...
The incomplete border sign is useful to depict an extrapulmonary mass on chest radiograph.
An extrapulmonary mass will often have an 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...
Interstitial lung disease (ILD) is an umbrella term that encompasses a large number of disorders that are characterised by diffuse cellular infiltrates in a periacinar location. The spectrum of conditions included is broad, ranging from occasional self-limited inflammatory processes to severe de...
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...
When a pleural effusion is large and unilateral, concern for an underlying abnormality should be raised. Causes include:
primary effusion lymphoma
When a central venous catheter that is supposed to terminate in the superior vena cava or right atrium is abnormally located to the left of the mediastinum and below the level of the brachiocephalic vein, a limited differential of left paramediastinal catheter position should be considered 1:
Linear atelectasis refers to a focal area of subsegmental atelectasis that has a linear shape. Depending on its shape, it is also known as plate, discoid or band atelectasis. Linear atelectasis may appear to be horizontal, oblique or perpendicular and is very common. It usually occurs as a conse...
Lobar consolidation is the term used to describe consolidation in one of the lobes of the lung. It infers a alveolar spead of disease and is most commonly due to pneumonia.
Consolidation refers to the alveolar airspaces being filled with fluid (exudate/transudate/blood), cells (infla...
Lobar collapse refers to the collapse of an entire lobe of the lung. As such it is a subtype of atelectasis (collapse is not entirely synonymous with atelectasis, which is a more generic term for 'incomplete expansion'). Individual lobes of the lung may collapse due to obstruction of the supply...
Localised pulmonary haemorrhage is a descriptive term for a pulmonary haemorrhage restricted to a particular focal region of the lung. It can range from involving a small focus of haemorrhage to a whole lobe.
Focal pulmonary haemorrhage can occur from a number of causes:
Lung atelectasis (plural: atelectases) refers to collapse or incomplete expansion of pulmonary parenchyma. Note that the term "atelectasis" is typically used when there is partial collapse, whereas the term "collapsed lung" is typically reserved for when the entire lung is totally collapsed.
A mnemonic for the causes of lymphangitic carcinomatosis is:
Certain Cancers Spread By Plugging The Lymphatics
P: prostate and pancreas
L: larynx and lung
Mediastinal lymph node enlargement can occur from a wide range of pathologies. It may occur on its own or in association with other lung pathology.
Although mediastinal lymphadenopathy is used interchangeably - by some - with "mediastinal lymph node enlargement", they are not synon...
Mediastinal mass may be caused by a wide variety of neoplastic and non-neoplastic pathologies. It is helpful to identify the location of the mass since this significantly reduces the breadth of the differential diagnosis.
There are four conceptual compartments of the mediastinum which are larg...
The differential diagnoses for mediastinal widening include:
traumatic aortic injury
aberrant right subclavian artery
azygos continuation of the IVC
pulmonary masses abutting the mediastinum
Medical devices in the thorax are regularly observed by radiologists when reviewing radiographs and CTs.
tubing, clamps, syringes lying on or under the patient
rubber sheets, foam mattresses, clothing, hair braids, nipple piercings etc. may also be visible
Megaoesophagus or diffuse oesophageal dilatation can be caused by a variety of conditions.
Some of the more common causes are given below 1-3:
malignant stricture, e.g. oesophageal cance...
The differential diagnosis for a middle mediastinal mass includes 1-3:
aneurysm, e.g. aortic, pulmonary artery, bronchial artery
foregut duplications cyst (e.g. oesophageal, bronchial)
primary/secondary cardiac tumour
The term miliary opacities refers to innumerable, small 1-4 mm pulmonary nodules scattered throughout the lungs. It is useful to divide these patients into those who are febrile and those who are not.
Additionally, some miliary opacities are very dense, narrowing the differential - see multiple...