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 (singular: interlobular 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 intra...
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 ...
An interstitial lung abnormality (ILA) is an imaging descriptor often encapsulating several imaging patterns of increased lung density / attenuation detected on chest CT scans in patients with no prior or established history of interstitial lung disease.
It is considered a relative...
Interstitial lung disease (ILD) is an umbrella term that encompasses a large number of disorders that are characterized 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...
Interstitial lung disease associated with systemic sclerosis (SSc-ILD) is one of the important pulmonary manifestations of systemic sclerosis. It usually gives a NSIP type pattern with an UIP pattern occurring less commonly 7. It can sometimes produce a rapidly progressive interstitial lung dis...
A useful mnemonic to remember the causes of interstitial lung diseases which do not cause volume loss is:
E: eosinophilic granuloma (pulmonary Langerhans cell histiocytosis)
N: neurofibromatosis type 1
T: tuberous sclerosis
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 pneumonia with autoimmune features (IPAF) is a term given for patients with interstitial lung disease (ILD) who show some features related to autoimmunity but without meeting full criteria for a defined connective tissue disease.
Interstitial thickening is pathological thickening of the pulmonary interstitium and can be divided into:
interlobular septal thickening
intralobular septal thickening
secondary pulmonary lobules
Interventricular septal bulge (also known as a sigmoid septum) is a common finding in imaging studies in the elderly population and refers to an isolated thickened basal septum resulting in a sigmoid configuration.
Although it is currently unclear whether this entity is part of the normal agin...
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 several conditions of variable etiology 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.
Rarely there may be anomalous communication of the pleural spaces anteriorly.
Intrapulmonary lipomas are rare fat containing benign lung lesions.
They mostly occur in the adult population, with occurence in the pediatric population extremely rare.
As with all lipomas they are composed of adipose tissue. The origin of the peripheral intrapulmonar...
Intrapulmonary lymph nodes, or pulmonary lymph nodes, are normal lymph nodes found within the lung parenchyma itself. They are commonly found during the assessment of CTs of the chest and are, sometimes, difficult to distinguish from pulmonary nodules.
The pulmonary lymph nodes are divided into...
Sarcomatoid neoplasms involving the chest comprise of a broad group of tumors that occur in the lung, mediastinum, pleura, and chest wall. These tumors have mesenchymal component.
primary sarcomatoid tumors of the chest
usually arising from the chest wall
Ewing sarcoma of the c...
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 necrotizing aspergillosis (CNA) or semi-invasive asperg...
Invasive mucinous adenocarcinoma of the lung is a subtype of invasive adenocarcinoma of the lung formerly known as mucinous bronchoalveolar carcinoma (BAC). They are more likely to be multicentric and tend to have a worse prognosis than non-mucinous types.
In 2011, the Internation...
This is a basic article for medical students and other non-radiologists.
Hemoptysis 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 dyspnea which may be secondary to suppression of respirat...
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' and refers to finding normally-asymmetric bilateral structures to be similar. It is used in the context of heterotaxy and is of two types:
Mirror image of the structures on the left side o...
The jellyfish sign refers to the sonographic appearance of atelectatic lung "swimming" within a large pleural effusion. The mobility of the lung within pleural fluid implies an absence of lung consolidation and the absence of pleural adhesions 1. It is also suggestive of a transudative pleural e...
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 tumor that involves the lymphovascular system. The tumor can involve the pulmonary, gastrointestinal, cutaneous and musculoskeletal systems.
There are four recognized variants 1:
classic (chronic): multiple distal lower extre...
Kartagener syndrome (also known as Kartagener-Afzelius syndrome) is a subset of primary ciliary dyskinesia, an autosomal recessive condition characterized by abnormal ciliary structure or function, leading to impaired mucociliary clearance.
The prevalence of primary ciliary dyski...
Getting a film with Kerley lines in the exam is one of the many exam set-pieces that can be prepared for.
There are bilateral basal interstitial lines that extend to the pleural surface - these are septal (Kerley B) lines. There is slight asymmetry of th...
Keutel syndrome is an extremely rare inherited condition characterized by
cartilage calcification which include
trachea - with resultant tracheobronchial stenosis
pulmonary arterial stenoses
brachytelephalangism (short fingers and nails that resemble drumsticks)
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 Kirklin sign is different from the Kirklin complex, a gastric finding on upper GI fluoroscopy.
History and etymology
Byrl Raymond Kirkli...
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 hospitalized patients 3.
The knuckle sign refers to the abrupt tapering or cutoff of a pulmonary artery secondary to an embolus. It is better visualized on CT pulmonary angiography (CTPA) than chest x-ray. This is an important ancillary finding in pulmonary embolism (PE), and often associated with the Fleischner sign of...
KRAS (shortened name for the gene Kirsten RAt Sarcoma viral oncogene homolog) mutations are associated in a number of malignancies including:
certain adenocarcinomas of the lung
colorectal carcinoma 1
pancreatic ductal adenocarcinoma
Several germline KRAS mutations have also been found to b...
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...
This article lists a series of labeled imaging anatomy cases by system and modality.
CT head: non-contrast axial
CT head: non-contrast coronal
CT head: non-contrast sagittal
CT head: angiogram axial
CT head: angiogram coronal
CT head: angiogram sagittal
CT head: venogram axial
Lactate dehydrogenase (LDH or LD) is a key enzyme in most cells, catalyzing the reversible conversion of pyruvate to L-lactate. Its contemporaneous main clinical uses are limited primarily to the investigation of hemolysis, serous collections and as a tumor marker.
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 two described lambda signs:
lambda sign (twin pregnancy)
lambda sign (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 hemosiderosis and celiac 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 D ...
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 multisystem 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 is more descriptive of its...
Large-cell lung cancer is one of the histological types of non-small-cell carcinomas of the lung diagnosed only on resection, after exclusion of adenocarcinomatous or squamous differentiation.
It is thought to account for approximately 10% of bronchogenic carcinoma 1.
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 tumor.
The incidence peaks around the 6th decade 6. There is an increased male predilection 7. They are rare ...
When a pleural effusion is large and unilateral, concern for an underlying abnormality should be raised. Causes include:
primary effusion lymphoma
Late-onset asthma (LOA) is a form of asthma that precipitates in the adult or the elderly.
The estimated age- and sex-adjusted incidence of newly diagnosed asthma in people older than 65 years at around 0.1% per year 1. There may be a greater female predilection.
Lateral intercostal artery perforator (LICAP) flap is a technique performed in breast reconstruction. It is considered suitable for some patients who have breast cancer in the outer part of the breast. It aims to replace lost breast tissue, fat and occasionally skin that is removed at the time o...
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. There are currently two leadless cardiac pacemakers on the market...
Leaky lung syndrome refers to a form of non-cardiogenic pulmonary edema.
Pulmonary edema due to increased capillary permeability.
Leaky lung syndrome is considered a mild form of a part of the spectrum of acute lung injury with ARDS at the other end of the s...
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 are implantable cardiac devices which are placed in the left atrial appendage for stroke prevention in patients with atrial fibrillation who have contraindications to pharmacological anticoagulation. Depending on the device they may be inserted percuta...
Left atrial enlargement (LAE) 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 (LA) (plural: atria) 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 (LV) and then into the systemic circulation.
The left atrium is grossly cuboidal, and like the r...
Left heart failure (LHF) or left ventricular failure (LVF) is a type of heart failure when the left ventricle is unable to pump blood effectively out of the heart. It is often used synonymously with left ventricular failure. It is one of the commonest causes of cardiogenic pulmonary edema.
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.
Left lower lobe consolidation refers to consolidation in part (incomplete) or all (complete) of the left lower lobe.
Consolidation refers to the alveolar airspaces being filled with fluid (exudate/transudate/blood), cells (inflammatory), tissue, or other material.
The list of causes...
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 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:
The left paraspinal (also known as the paraspinous or paravertebral) line (or stripe) 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.
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 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 subclav...
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. Hence it is a classic chest radiograph case for radiology fellowships exams.
For a general discussion refer to the article on lobar collapse.
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...
Left upper lobe consolidation refers to consolidation in part (incomplete) or all (complete) of the left upper lobe.
Consolidation refers to the alveolar air spaces being filled with fluid (exudate/transudate/blood), cells (inflammatory), tissue, or other material.
The list of cause...
The left upper lobe inferior lingular segment is one of the four bronchopulmonary segments of the left upper lobe. It lies below the superior lingular segment of the left upper lobe.
The left upper lobe superior lingular segment is one of the four bronchopulmonary segments of the left upper lobe. It lies below the apicoposterior and anterior segments of the left upper lobe.
The left ventricle is one of four heart chambers. It receives oxygenated blood from the left atrium and pumps it into the systemic circulation via the aorta.
The left ventricle is conical in shape with an anteroinferiorly projecting apex and is longer with thicker walls than the ...
Legionella pneumonia, also known as Legionnaires' disease, refers to pulmonary infection primarily with the organism Legionella pneumophila. It is sometimes classified as atypical pneumonia.
Legionella pneumonia tends to be more prevalent among immunocompromised patients. Legione...
Lepidic growth is a pathological term referring to a pattern of cell proliferation along the lining of the alveolar structures of the lung as is seen in a subset of lung tumors 1.
History and etymology
‘lepidic’ was coined by the English pathologist John George Adam (1862-1926) whilst at McGil...
Lepidic-predominant adenocarcinoma (LPA) of the lung, formerly known as non-mucinous bronchoalveolar carcinoma, is a subtype of invasive adenocarcinoma of the lung characterized histologically when the lepidic component comprises the majority of the lesion.
The category of 'lepid p...
Leptospirosis results from infection by the zoonotic Leptospira spp. The condition can have multiorgan manifestations. Commonly affected organs include:
lung: pulmonary leptospirosis
liver: hepatic leptospirosis
central nervous system: CNS leptospirosis
skeletal muscle: muscular leptospirosi...
The lesser diaphragmatic apertures allow the passage of smaller structures from the thoracic cavity to abdominal cavity across the diaphragm. They are very much smaller than the other diaphragmatic apertures:
two in the right crus of the diaphragm: transmit greater and lesser right splanchnic n...
Thoracic manifestations of leukemia can be divided into those related to the disease itself and those associated with its treatment. Leukaemias are hematologic malignancies in which occur a proliferation of hematopoietic cells at an undifferentiated or partially differentiated stage of maturatio...
Leukemic cell lysis pneumopathy, also referred to as acute lysis pneumopathy, refers to an acute respiratory failure that can occur in patients with leukemia after the initiation of chemotherapy, particularly in those with hyperleukocytosis. On imaging, it manifests with features of acute respir...
Leukostasis, also known as symptomatic hyperleukocytosis, is a medical emergency in patients with leukemia, particularly acute myeloid leukemia (AML) and in the blast phase of chronic myeloid leukemia (CML), characterized by the over-accumulation of leukemic cells within the small vessels. Altho...
Ligamantum arteriosum calcification can be a common finding on chest CT scans in adults and can increases in prevalence with increasing age and atherosclerosis. It can sometimes even be present in children 3.
Many patterns have been described which include.
punctate: considered commonest
The ligamentum arteriosum (or arteriosus) is the small fibrous remnant of the fetal ductus arteriosum, located between and connecting the proximal left pulmonary artery and the undersurface of the junction of the aortic arch and descending aorta, at the aortic isthmus. The left recurrent larynge...