Lung fissures are a double-fold of visceral pleura that either completely or incompletely invaginate lung parenchyma to form the lung lobes.
Each lung has an oblique fissure separating the upper lobes from the lower lobes and the right lung has a horizontal fissure that separates the right upp...
Lung hyperinflation is a common feature of patients with chronic obstructive pulmonary disease (COPD). It is also linked to ageing and other chronic diseases that cause airflow obstruction.
The airflow limitation during expiration is produced by two factors:
destruction of the lung ...
Lung parenchyma is the portion of the lung involved in gas transfer - the alveoli, alveolar ducts and respiratory bronchioles. However, some authors include other structures and tissues within the definition.
parenchymal lung disease
The lung point sign is a highly specific ultrasound sign of pneumothorax. It involves visualising the point where the visceral pleura (lung) begins to separate from the parietal pleural (chest wall) at the margin of a pneumothorax.
In the absence of pneumothorax, the two pleural layers slide a...
Lung-RADSTM (or lung imaging reporting and data system) is a classification proposed to aid with findings in low-dose CT screening exams for lung cancer. The goal of the classification system is to standardize follow-up and management decisions. The system is similar to the Fleischner criteria b...
Lung torsion is the rotation of a lung or lung lobe about its bronchovascular pedicle and resulting in ischaemia. It is very rare, and typically occurs in the setting of lobectomy or pneumonectomy. It has also been reported as a rare complication of less invasive procedures such as video-assiste...
Lung transplant complications can occur at variable time intervals following transplantation. It is essential for radiologists to be aware of specific complications as chest imaging is routinely used in the post-transplant assessment.
When reporting a postoperative chest radiograph or CT, it is...
Lung volume reduction surgery (LVRS) is an emerging promising palliative treatment option for select patients with severe, debilitating pulmonary emphysema. It usually involves bilateral wedge resection of 20-30% of the most diseased lung through a median sternotomy. It has been proposed that L...
Lymphangioleiomyomatosis (LAM) is a rare multi-system disorder that can occur either sporadically or in association with the tuberous sclerosis complex (TSC) and is often considered a forme fruste of TSC.
It almost exclusively affects women of childbearing age 7. The estimated in...
Lymphangitic carcinomatosis, or lymphangitis carcinomatosa, is the term given to tumour spread through the lymphatics of the lung and is most commonly seen secondary to adenocarcinoma.
The demographics will reflect that of the underlying malignancy (see below).
A mnemonic for the causes of lymphangitic carcinomatosis is:
Certain Cancers Spread By Plugging The Lymphatics
L: larynx and lung
Lymphocele of the thoracic duct (thoracic duct cyst) is usually asymptomatic or less commonly may present as left supraclavicular fossa mass 1.
The clinical significance of a thoracic duct cyst lies in its misidentification as a pathological lesion at radiological assessment, whi...
Lymphocytic interstitial pneumonitis (LIP) is a benign lymphoproliferative disorder characterised by lymphocyte predominant infiltration of the lungs. It is classified as a subtype of interstitial lung disease. It also falls under the umbrella of non-lymphomatous pulmonary lymphoid disorders.
Lymphomatoid granulomatosis (LG), also known as angiocentric lymphoma or angiocentric immunoproliferative lesion, is a rare type of non-Hodgkin's lymphoma.
There is a recognised association with antecedent infection with the Epstein Barr virus (EBV).
It can affect a variety of org...
Pulmonary manifestations of lymphomatoid granulomatosis are important since the lung is one of the most frequent sites of involvement in lymphomatoid granulomatosis. It falls under the group of pulmonary angiitis and granulomatosis.
Some consider the condition to be midway between ov...
The Macklin effect describes one of the pathophysiological processes of pneumomediastinum in blunt chest trauma. The Macklin effect accounts for ~40% of severe blunt traumatic pneumomediastinum. Exclusion of tracheobronchial and oesophageal causes of pneumomediastinum is mandatory to exclude con...
Macrocystic honeycombing refers to a morphological subtype of honeycombing. Many publications consider the individual lung cysts to be greater than 4 mm in diameter to be classified into this category. This form is considered to be more commonly associated with UIP 3.
Major aortopulmonary collateral arteries (MAPCAs) are persistent tortuous fetal arteries that arise from the descending aorta and supply blood to pulmonary arteries in the lungs usually at the posterior aspect of hilum.
Embryologically, the intersegmental arteries regress with the no...
Malignant pleural disease usually heralds a poor prognosis, whether it represents a primary pleural malignancy or metastatic involvement.
Clinical presentation is variable. Patients may be asymptomatic or have pleuritic pain. If associated with a sizeable pleural effusio...
A number of staging systems have been described for staging of malignant pleural mesothelioma. Below is the International Mesothelioma Interest Group TNM staging system.
T - Tumour
Tx: primary tumour cannot be assessed
T0: no evidence of primary tumour
Manubriosternal and sternoxiphoidal joint fusion can be partial or complete, and may be a normal anatomic variant.
Complete fusion can be seen at a young age. Pathological fusion can be seen in old age secondary to fusion caused by bridging osteophytes 2. It may also be seen in inflammatory art...
The manubriosternal joint, sometimes referred to as the sternomanubrial joint, is the articulation between the upper two parts of the sternum, the manubrium and sternal body. It is at the level of the sternal angle or angle of Louis, which is at the 2nd costal cartilage and the intervertebral d...
Marijuana (cannabis or bong) lung refers to the presence of large apical bullae in patients who regularly smoke marijuana. A definite causative link between smoking marijuana and bullous lung disease has not been established, and the association may just be coincidental.
The Masaoka staging system is commonly adopted for thymomas 1-3, and is the most important determinant of survival following surgical resection 4:
stage I: intact thymic capsule
stage II: capsular invasion into adjacent mediastinal fat or pleura
stage III: macroscopic invasion into adjacent o...
A massive pulmonary embolism is a situation there is are acute pulmonary emboli with very large embolic burden. It is usually characterised by1
systemic hypotension (defined as a systolic arterial pressure < 90 mm Hg or
a drop in systolic arterial pressure of at least 40 mm Hg for at least 15...
Mastocytosis is a disorder of excessive mast cell proliferation, which is now classified as a myeloproliferative neoplasm. Two clinical entities fall under the mastocytosis umbrella: cutaneous (urticaria pigmentosa) and systemic mastocytosis (with or without cutaneous manifestations). The articl...
Maximum Intensity Projection (MIP) consists of projecting the voxel with the highest attenuation value on every view throughout the volume onto a 2D image 1.
Such an algorithm is rather simple: for each XY coordinate, only the pixel with the highest Hounsfield number along the Z-axis is represe...
Mean pulmonary arterial pressure (MPAP) can be estimated by echocardiogram ultrasound study. It is calculated by the formula:
(PASystolic pressure +2 PADiastolic pressure) / 3
Normal MPAP is less than 20 mmHg and considered elevated when it exceeds 25 mmHg at rest or 30 mmHg with exertion.
Meconium aspiration occurs secondary to intrapartum or intrauterine aspiration of meconium, usually in the setting of fetal distress, often in term or post-term infants.
Up to 10-15% of live births after 34 weeks can present with meconium stained fluid but only 1-5% of neonates de...
Medial pneumothorax refers to the abnormal collection of air on medial aspect of the pleural cavity. This occurs when the quantity of air is small.
Chest radiograph (supine)
Seen as a linear lucent area along the medial aspect of lung at the interface of the pleural surf...
Medial stripe sign refers to an area of increased lucency at the interface of the medial lung and the mediastinum in case of medial pneumothorax. A small volume of pneumothorax generally accumulates anteriorly or medially which can be difficult to detect hence this sign holds a certain significa...
Mediastinal haemangioma is a location specific subtype of a haemangioma.
There incidence account for less than 0.5% among all mediastinal masses 1.
Up to half of patients may be asymptomatic 1. Others may present with non-specific symptoms, such as cough, c...
Mediastinal lipomatosis refers to a condition where there is a deposition of a large amount of mature adipose tissue in the mediastinum. It is a relatively common benign cause of mediastinal widening.
It is the result of increased deposition of normal unencapsulated fat 1.
Mediastinal lymphadenopathy associated with interstitial lung disease can be a frequent feature although its presence has limited value in the differential diagnosis. In certain forms of interstitial lung disease, the extent of lymph node enlargement may correlate to disease activity or progress...
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 lymphoma is common, either as part of disseminated disease or less commonly as the site of primary involvement.
Lymphomas are responsible for approximately 15% of all primary mediastinal masses, and 45% of anterior mediastinal masses in children 1. Only 10% of lymphoma...
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...
Mediastinal paragangliomas are rare tumours derived from chromaffin cells (neuroectodermal cells) associated with sympathetic ganglion of the autonomic nervous system. They can arise from two major cluster of sympathetic ganglion cells: paraaortic (aorticopulmonary) and paravetebral (aorticosymp...
A mediastinal pseudocyst is the extension of pancreatic pseudocyst into the posterior mediastinum through oesophageal or aortic hiatus or rarely through the foramen of Morgagni. It is a rare complication of acute or chronic pancreatitis.
It can present with symptoms due t...
Mediastinal teratomas are germ cell tumours located in the anterior mediastinum.
Mediastinal teratomas are the most common extra-gonadal germ cell tumours. They account for approximately 15% of anterior mediastinal masses in adults and approximately 25% of anterior mediastinal mas...
The differential diagnoses for mediastinal widening include:
traumatic aortic injury
aberrant right subclavian artery
azygous continuation of the IVC
pulmonary masses abutting the mediastinum
The mediastinum is a space in the thorax that contains a group of non-delineated organs and their surrounding connective tissue. It lies in the midline of the chest between the pleura of each lung and extends from the sternum to the vertebral column.
The mediastinum contains all...
The International Thymic Malignancy Interest Group (ITMIG) classification of mediastinal compartments was developed to reflect a division of the mediastinum based on cross-sectional imaging. It was in part an effort to consolidate prior discrepant classification systems in use by different medic...
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
Mega oesophagus 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 canc...
Melioidosis is an infectious disease caused by Burkholderia pseudomallei (previously known as Pseudomonas pseudomallei) and is a multisystem disorder which may affect the lungs, brain, visceral organs, or musculoskeletal system.
Melioidosis is a disease of the monsoon season in th...
The melting ice cube sign describes the resolution of pulmonary haemorrhage following pulmonary embolism (PE).
When there is pulmonary haemorrhage without infarction following PE, the typical wedge-shaped, pleural-based opacification (Hampton's hump) resolves within a week while preserving its...
Mendelson syndrome or peptic pneumonia refers to acute chemical pneumonitis caused by the aspiration of stomach contents in patients under general anesthesia.
The etiologic agents is believed to be aspiration of acidic stomach contents, other compounds, e.g. bile, may also play a rol...
A mesenchymal hamartoma of the chest wall is a very rare benign chest wall tumour. It is sometimes classified as a non-neoplastic developmental anomaly rather than a tumour.
They typically present in neonates or infants 1-3.
Many present with a chest wall m...
Mesothelioma, also known as malignant mesothelioma, is an aggressive malignant tumour of the mesothelium. Most tumors arise from the pleura, and so this article will focus on pleural mesothelioma.
Given the presence of the mesothelium in different parts of the body, mesothelioma can arise in va...
This is a basic article for medical students and other non-radiologists.
Pleural mesotheliomas are malignant tumours of the lining of the lungs. There is a strong association with asbestos exposure.
This is a summary article; read more in our article on mesothelioma.
Metastases to the thymus are rare, although they are probably under reported due to lack of symptoms.
Varied primary tumours have been reported to metastasise to the thymus 1,2:
Metastatic axillary lymphadenopathy of unknown primary can be a very chellanging situation.
Usual potential sites include:
occult breast cancer: the incidence of an axillary lymph node manifestation from an occult primary breast cancer is low, ranging from 0.3-0.8% of all patients ...
Metastatic pulmonary calcification (MPC) is a form of pulmonary calcification where there is calcium deposition in normal lung pulmonary parenchyma.
It can occur in a variety of benign and malignant disorders such as:
chronic renal failure: considered commonest cause 5
Methotrexate lung disease is the specific aetiological type of drug-induced lung disease. It can occur due to the administration of methotrexate which is an antimetabolite, which is given for various reasons but commonly to treat rheumatoid arthritis. It is also given alone or in combination wit...
In medical imaging literature, a Mickey Mouse appearance has been given to imaging features that depict that of Mickey Mouse when viewed from the front. It has been described in the following:
progressive supranuclear palsy 1
synonymously with a finger in glove sign
the flared ...
Microcystic honeycombing is an imaging descriptor on thoracic HRCT/CT which is typically given to denote extremely small cysts typically occurring in a subpleural location on a background of interstitial lung disease. It is typically described in association with non-specific interstitial pneum...
Microlithiasis merely means very small stones and may refer to:
Microscopic polyangiitis (MPA) is small vessel non-granulomatous necrotising vasculitis. It most often affects venules, capillaries, arterioles, and small arteries, although it occasionally involves medium-sized arteries 9.
It typically affects middle aged individuals.
Middle East Respiratory Syndrome coronavirus (MERS-CoV) infection is an uncommon viral infection (<1000 cases) with the first case reported in Saudi Arabia in 2012. It most commonly causes pneumonia and acute renal failure with a mortality rate of ~40%. MERS-CoV raises concern because of its sim...
Distribution of bronchiectasis can help in narrowing the differential diagnosis.
Middle lobe bronchiectasis is typically seen in:
non tuberculous mycobacterial infections
middle lobe syndrome in children
upper lobe bronchiectasis
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 middle mediastinum is an artificial space of the mediastinum divided from the remainder of the extra-pleural intrathoracic cavity by arbitrary lines. It forms the largest component of the inferior mediastinum.
superiorly: superior mediastinum, divided by the thora...
The mid (or middle) zone is one of the four chest radiograph zones.
on frontal chest radiographs, extends between the superior and inferior aspects of the hilum
Migrating pericardial cysts or wandering pericardial cysts are an unusual form of pericardial cysts. They are usually pedunculated and change in position on serial imaging but have all other imaging characteristics supportive of a pericardial or pleuro-pericardial cyst.
Getting a film with miliary nodules 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 multiple tiny soft-tissue density nodules present throughout both lungs with...
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...
Miliary sarcoidosis is a rare thoracic manifesation of sarcoidosis where there are numerous miliary-like nodules scattered throughout the lungs. It is thought to represent less than 1% of cases.
From the limited case reports available, there is some suggestion that this form may ...
Miliary tuberculosis is an uncommon pulmonary manifestation of tuberculosis. It represents haematogeneous dissemination of uncontrolled tuberculous infection and carries a relatively poor prognosis.
It is seen both in primary and post-primary tuberculosis and may be associated with tuberculous ...
Minimal aortic injuries are traumatic aortic lesions that usually involve the intima and are recognised more frequently due to the use of high-resolution imaging.
Minimal aortic injuries account for 10-28% of all blunt traumatic aortic injuries 1,6,7. The proportion of this type o...
Minimally invasive adenocarcinoma of the lung is a relatively new category in the classification for adenocarcinoma of the lung. Lesions that fall into this category refer to small solitary adenocarcinomas <3 cm with either pure lepidic growth or predominant lepidic growth with ≤5 mm of stromal ...
Minimum intensity projection (MinIP) is a data visualization method that enables detection of low-density structures in a given volume. The algorithm uses all the data in a volume of interest to generate a single bidimensional image, in other words, its consists of projecting the voxel with the ...
A misplaced or malpositioned endotracheal tube is a relatively common complication that is detected on post-intubation radiographs.
if the ETT is too high it can rub against the vocal cords and cause cord trauma
if the ETT is too low it can selectively intubate the right or left...
Mitral annular calcification (MAC) refers to deposition of calcium (along with lipid) in the annular fibrosa of the mitral valve.
Annular calcification is seen in up to 35% of elderly patients. It is common in females over 65 years, in those with myxtomatous degeneration of the mi...
Mixed connective tissue disease (MCTD) is a type of connective tissue disease. With regards to clinical and imaging features, it can have significant overlap with other connective tissue disease such as systemic lupus erythematosus and scleroderma 1. It therefore classified as a type of overlap ...
Pulmonary manifestations of mixed connective tissue disease can be seen in a wide range (20-85%) of those of mixed connective tissue disease. It can have multiple manifestations.
More commonly described features include:
an interstitial pneumonitis: 20-65%
pulmonary fibrosis: 20-65%
Mixed dust pneumoconiosis (MDP) is classified as a type of pneumoconiosis. It is sometimes classified pathologically as a pneumoconiosis showing dust macules or mixed-dust fibrotic nodules, with or without silicotic nodules, in an individual with a history of exposure to mixed dust 2.
The modified PIOPED criteria for the diagnosis of pulmonary embolus (PE) determine the probability of pulmonary emboli following a VQ scan.
two or more large mismatched segmental defects or equivalent moderate/large defects with a normal x-ray
any perfusion de...
The 'moguls of the heart' refer to the bulges of the cardiomediastinal contour on frontal chest radiographs. The cardiomediastinal bulges are likened to skiing moguls (bumps of packed snow on a mountainside sculptured by turning skis). Awareness of their usual locations and aetiologies is helpfu...
Monod sign (often misspelt Monad sign) simply describes gas that surrounds a mycetoma (most commonly an aspergilloma) in a pre-existing pulmonary cavity 1-3.
It should not be confused with the air crescent sign which is seen in recovering angioinvasive aspergillosis 4. The air crescent sign her...
The more black sign is a normal finding in lateral chest x-ray, and refers to the gradual increased apparent radiolucency (blackness) of the vertebral bodies, when proceeding from upper to lower chest. This is due to the increased proportion of the chest comprised of air containing lungs over di...
Mosaic attenuation is a descriptive term used in describing a patchwork of regions of differing pulmonary attenuation on CT imaging. It is a non-specific finding, although is associated with the following:
obstructive small airways disease: low attenuation regions are abnormal and reflect decr...
Mounier-Kuhn syndrome is a somewhat controversial entity and used synonymously with tracheobronchomegaly by most authors 7,8,9.
Mounier-Kuhn syndrome is most frequently seen in middle age men before the age of 50 1,6.
The anatomical and physiological chang...
Mucoepidermoid carcinoma (MEC) of the lung is a type of non small cell lung cancer (NSCLC). It is classified under the group of lung carcinomas of the salivary gland type.
Mucoepidermoid carcinoma (MEC) is the most common of the SGTTLs 9. The tumour is thought to account for ~ 0.2...
Mucoid impaction, also referred to as mucus plugging or bronchocele, airway filling by mucoid secretions and can be obstructive or non-obstructive. It is a common pathological finding in chest imaging.
Mucoid impaction may result from either obstructive or non-obstructive ...
Multifocal micronodular pneumocyte hyperplasia (MMPH) is a rare benign hamartomatous proliferation of type II pneumocytes and is seen in association with tuberous sclerosis (TS). It can occur with or without concurrent lymphangiomyomatosis.
HRCT / Contrast CT Chest
Multilobar pneumonia, as the name suggests, is a lobar pneumonia affecting multiple lobes. Patients with community-acquired multilobar pneumonia have a worse prognosis with longer admissions, more need for ventilatory support and more frequent treatment failure 1.
Multinodular goitre (commonly abbreviated to MNG) is defined as an enlarged thyroid gland (i.e. goitre) due to multiple nodules which may have normal, decreased or increased function.
When increased activity and hyperthyroidism are present then the condition is referred to a toxic...
The musculophrenic artery is one of two terminal branches of the internal thoracic artery.
The musculophrenic artery runs along the costal slips of the diaphragm. It supplies the 7th, 8th and 9th intercostal spaces with paired anterior intercostal arteries, as well as fine branch...
Myasthenia gravis (MG) is the most common neuromuscular junction disease and presents with increasing fatigue brought on by exertion.
Incidence is estimated at 15-20 per 100,000 1,2. Females are more affected (3:1) under the age of 40, but males are more affected by the age of 50...
Mycetoma refers to a chronic and progressively destructive granulomatous disease. The defining clinical triad comprises:
localised mass-like soft tissue injury with
draining sinuses, that
discharge grains of contagious material
It is one of the 17 neglected tropical diseases defined by WHO...
Mycobacterium tuberculosis is a thin, slightly curved bacillus. A member of the Mycobacterium tuberculosis complex, it is an obligate aerobic bacterium that is the aetiologic agent of the majority of tuberculosis cases.
The worldwide incidence of tuberculosis was 8.7 million in 2...
Mycoplasma pneumonia is a type of community-acquired pneumonia caused by the organism Mycoplasma pneumoniae. It is usually grouped under an atypical pneumonia.
It is relatively common in the paediatric population where it is considered the most common community-acquired pneumonia ...