The M sign refers to the characteristic "M" configuration of the inferior frontal gyrus, as it forms (from front to back) the pars orbitalis, pars triangularis, and, pars opercularis.
M-line of Cremin is an imaginary line that can be used to determine the level at which the blind pouch ends in anal atresia, determining whether the anal atresia is a high or a low type.
The line is drawn perpendicular to the long axis of the ischium on the lateral view and passes through the j...
Macaroni sign is a sign seen in Takayasu arteritis on ultrasound. It represents smooth, homogeneous and moderately echogenic circumferential thickening of the arterial wall that occurs in Takayasu arteritis. The sign is highly specific for Takayasu arteritis, more commonly noted in the common ca...
Macdonald criteria, published in 1990 3, are used to assess response to first-line treatment of glioblastoma, but have been largely superseded by the RANO criteria which have become the mainstay of assessment.
For a general discussion see glioma treatment response assessment in clinical trials...
The MacEwen triangle (also called the suprameatal triangle or mastoid fossa) is a small triangular depression affecting the inner table of the temporal bone.
The lines forming the triangle are:
anterior: posterior border of the external acoustic meatus
superior: posterior root of the zygomati...
The Mach bands effect refers to an optical phenomenon from edge enhancement due to lateral inhibition of the retina 2. This is inbuilt edge enhancement mechanism of the of the retina, where the edges of darker objects next to lighter objects will appear lighter and vice versa; creating a false s...
Machine learning is an avenue of computer science that can extrapolate information based on observed patterns. More specifically, machine learning is becoming an increasingly important tool in the medical profession as a primary computer-aided diagnosis algorithm or a decision support system. It...
Macrocephaly is a clinical and radiological term that refers to a generalised increase in size of the cranial vault.
This slightly differs from the term megalencephaly which means an increase in size of the brain parenchyma.
Macrocerebellum, also known as cerebellar hyperplasia, refers to a rare condition characterised by an abnormally enlarged cerebellum with preserved architecture and shape. It is usually demonstrated on imaging with a thickening of the cortical gray matter of the cerebellar hemispheres.
Macrocystic honeycombing refers to a morphological sub type of honeycombing. Many publications consider the individual lung cysts to be greater than 4mm to be classified into this category. This form is considered to be more associated with UIP 3.
Macrodactyly in its broadest sense is a descriptive term which refers to enlargement of all the elements of a digit 1. This can mean either the hand or foot. Often it is equated with its most common cause, macrodystrophia lipomatosa 4. Rarely it can be seen as a form of Proteus syndrome 2
Macrodystrophia lipomatosa is a rare form of localised gigantism, and many terms have been used interchangeably, with resulting confusion. They include macrodactyly, megalodactyly, digital gigantism, macromelia, partial acromegaly, macrosomy, and limited gigantism 3.
It is worth noting that ma...
Macroglossia means an enlarged tongue. It may be absolute (greater than the 95th centile) or relative (enlarged compared with oral cavity).
Recognised associations include:
tends to be a relative macroglossia
may also have intermi...
Macronodular adrenal hyperplasia refers to a morphological type of adrenal hyperplasia in which there is adrenal enlargement in the form of large distinct nodules. It can be congenital or acquired.
A specific subtype under this entity is adrenocorticotropin independent macronodular adrenocortic...
The increased globe size or macrophthalmia may have many differentials:
buphthalmos (congenital glaucoma)
macrophthalmus in neurofibromatosis type 1 (NF1)
connective tissue disorders: Marfan syndrome, Ehlers-Danlos syndrome
Madelung deformity is due to premature closure or defective development of the ulnar third of the distal epiphysis of the radius. This deformity results in a radial shaft that is bowed with increased interosseous space and dorsal subluxation of the distal radioulnar joint.
It can be bilateral ...
Mnemonics for remembering the associations of Madelung deformity include:
H: Hurler syndrome
O: osteochondroma (multiple hereditary exostoses)
C: congenital, e.g. Turner syndrome
Madelung disease, also known as Madelung-Launois-Bensaude syndrome or neck lipomatosis, is a rare benign entity clinically characterised by the presence of multiple and symmetric, non-encapsulated masses of fatty tissue, usually involving the neck and the upper region of the trunk.
Madelung dyschondrosteosis refers to a dysplasia associated with a Madelung deformity 1,2.
It is a form of mesomelic dwarfism, especially if the condition is bilateral or there is a family history of short stature.
Maduromycosis, also known as Maduramycosis or eumycetoma is caused by various fungi (e.g. madurella mycetomi) or actinomycetes (e.g. nocardia brasiliensis) which usually affects the feet.
Initially a nodule, or abscess over months to years progresses to a chronic infection with the f...
Maffucci syndrome is a congenital nonhereditary mesodermal dysplasia characterised by multiple enchondromas with soft-tissue venous malformations (haemangiomas).
On imaging, it is usually portrayed by a short limb with metaphyseal distortions due to multiple enchondromas, which may appear grote...
The Magerl classification of thoracolumbar spinal fractures is based on the three column concept by Denis, and the McAfee classification. It relies exclusively on CT findings.
A: compression injuries
A1: impaction fractures
A1.1: endplate impaction
A1.2: wedge impaction
The magic angle is an MRI artifact which occurs on sequences with a short TE (less than 32ms; T1W sequences, PD sequences and gradient echo sequences).
It is confined to regions of tightly bound collagen at 54.74° from the main magnetic field (B0), and appears hyperintense, thus potentially be...
Magnetic resonance cholangiopancreatography (MRCP) is a non-invasive imaging technique to visualize intra and extrahepatic biliary tree and pancreatic ductal system.
It can provide the diagnostic range equivalent to the ERCP and so it can replace the ERCP in high risk patient to avoid significa...
Magnetic resonance parkinsonism index (MRPI) can be used in MRI studies to predict the presence of progressive supranuclear palsy (PSP) in patients with clinically unclassifiable parkinsonism.
MRPI is calculated by measuring the width of the superior cerebellar peduncle in the coronal plane, th...
Magnetic susceptibility artifacts (or just susceptibility artifact) refer to a variety of MRI artifacts that share distortions or local signal change due to local magnetic field inhomogeneities from a variety of compounds.
They are especially encountered while imaging near metallic orthopedic ...
Magnetisation transfer (MT) imaging is an MRI technique that can be used to exploit contrast between tissues where 1H protons are present in three states1:
bound to macromolecules
in free water
as water in the hydration layer between the macromolecules and the free water
To assess MT, an off...
Magnetism is a property of matter that is a result of the orbiting electrons in atoms. The orbiting electrons cause the atoms to have a magnetic moment associated with an intrinsic angular momentum called spin.
Magnetic field strengths are measured in tesla (T), a derived SI unit. The equivale...
Magnets used for MRI are of three types: permanent, resistive and superconductive.
Permanent MRI magnets use permanently magnetized iron like a large bar magnet that has been twisted into a C-shape where the two poles are close together and parallel. In the space between the poles the magnetic ...
A magnification view in mammography is performed to evaluate and count microcalcifications and its extension (as well the assessment of the borders and the tissue structures of a suspicious area or a mass) by using a magnification device which brings the breast away from the film plate and close...
The magnetic resonance imaging in multiple sclerosis (MAGNIMS), which is a European collaborative research network, published in 2016 new recommendations to upgrade the imaging diagnosis criteria for multiple sclerosis (MS). These came as a consensus, based on evidence-based and expert opinions ...
Maiden waist deformity is the appearance of the deviation of bilateral ureters. This typically occurs in retroperitoneal fibrosis. In this condition, there is medial drawing of the ureter due to deposition of fibrous tissue in the lumbosacral junction. Due to involvement of both ureters, the cou...
Maisonneuve fracture is the combination of a spiral fracture of the proximal fibula and unstable ankle injury which could manifest radiographically by widening of the ankle joint due to distal tibiofibular syndesmosis and/or deltoid ligament disruption, or fracture of the medial malleolus. It is...
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...
The major salivary glands are the largest and most important of the salivary glands and comprise of:
paired parotid glands
paired submandibular glands
paired sublingual glands
salivary gland tumours
Malacoplakia of the urinary tract is an uncommon chronic granulomatous inflammatory disease of the bladder wall. Malakoplakia (meaning "soft plaque") can affect any organ, but the urinary bladder is the commonest location.
Malacoplakia has a peak incidence in middle age and has a ...
Male breast cancer is exceptionally rare and only accounts for less than 0.25% of male malignancies and ~0.5-1% of all breast cancer (both genders).
The average age of diagnosis of male breast cancer is 60-70 years, which is later than female breast cancer.
Male breast disease includes a wide spectrum of conditions. Many conditions and entities that affect the female breast may also affect the male breast.
male breast cancer
pseudogynaecomastia - fat deposition within th...
Male pseudohermaphroditism (MPH) is a variation of gender development.
Patients with male pseudohermaphroditism have 46 XY karyotype and may manifest as a female phenotype with various degrees of undervirilization secondary to partial androgen insensitivity.
The male reproductive system (or tract) includes:
It can be imaged using almost the entire range of imaging modalities but ultrasound and MRI are most often used (in part because these modalities are n...
The male urethra is a fibromuscular tube that drains urine from the bladder. It has a longer, more complicated, course than the female urethra and is also more prone to pathology.
The male urethra measures, on average, 18-20 cm in length. It commences at the internal urethral ori...
A helpful mnemonic to remember the 4 segments of the male urethra from proximal to distal.
Pet My Big Penis
Posterior urethra equates to the prostatic and membranous urethras. Anterior urethra equates to the bulbous and penile urethras.
Malgaigne fracture is an unstable type of pelvic fracture, which involves one hemipelvis, and results from vertical shear energy vectors.
One of the clinical features is shortening of the leg on the affected side.
It comprises of two ipsilateral pelvic ring fr...
Malignant biliary tract obstruction (MBTO) represents a group of conditions that cause obstructive jaundice. While most examples are the result of pancreatic head cancers, other malignancies may be causative.
This is a summary article; we do not have a more in-depth reference...
Malignant fibrous histiocytomas (MFH), which has more recently been classified as pleomorphic undifferentiated sarcoma (PUS) and formerly known as fibrosarcoma, is considered the most common type of soft tissue sarcoma. It has an aggressive biological behaviour and a poor prognosis.
Paediatric malignant liver tumours are rare, some of which occur only in children but that are similar to those that occur in adults.
Malignant liver tumours account for ~1% of paediatric malignancies 2.
Broadly, any malignant liver mass can be defined as a metastasis ...
Malignant melanoma is a malignant neoplasm that arises from melanocytes (or cells that derive from melanocytes). Melanocytes predominantly occur in the basal layer of the epidermis and most melanomas, therefore, arise in the skin. However, melanocytes do occur in other locations and can give r...
A malignant mixed germ cell tumour of the ovary is a subtype of ovarian germ cell tumour. These are not to be confused with malignant mixed Müllerian tumours of the ovary.
These tumours are rare. They most commonly affect adolescent women of reproductive age 1.
Malignant mixed Mullerian tumours (MMMT), sometimes referred to as a carcinosarcoma, are uncommon malignancies that can occur anywhere along the female genital tract.
It is comprised of both epithelial (carcinomatous) and stromal (sarcomatous) components.
Implicated risk factors inc...
Malignant mixed Mullerian tumours (MMMT) of the ovary, also known as carcinosarcoma of the ovary, are a rare type of mixed ovarian tumour with both epithelial and stromal components.
They are very rare and account for less than 1% of all ovarian cancers. Most women are post-menopa...
Malignant mixed Mullerian tumour (MMMT) of the uterus, also known a uterine carcinosarcoma, is the commonest (up to 50%) uterine sarcoma. They are thought to account for 2-8% of all malignant uterine cancers 1-2. The uterus is the commonest site for malignant mixed Mullerian tumours 1.
Malignant mixed tumours of salivary glands, according to the WHO classification, comprise three tumours:
carcinoma ex pleomorphic adenoma
arises from pre-existing pleomorphic adenoma
carcinosarcoma (true mixed tumour of the salivary glands)
true malignant mixed tumour
99% also ...
Malignant neoplasms involving the uterus account for a significant proportion of all female cancers.
They can be classified as:
endometrial carcinoma : commonest: >90% of all uterine malignancies
endometrioid carcinoma of the uterus: commonest histological type, ~80%
papillary serous carcino...
Malignant oesophageal neoplasms are much more common than benign oesophageal neoplasms, especially if the patient is symptomatic.
oesophageal carcinoma (90%)
oesophageal squamous cell carcinoma (SCC)
oesophageal spindle cell carcinoma
Malignant ovarian lesions can have typical sonographic features, and thus ultrasound is the imaging of choice for initial evaluation of suspected ovarian neoplasm.
The features of malignant ovarian neoplasm on ultrasonography include:
mass >10 cm with locul...
Malignant peripheral nerve sheath tumours (MPNSTs) are forms of peripheral nerve sheath tumours and comprise of malignant forms of neurofibromas and schwannomas. Approximately half of such tumours are seen in individuals with neurofibromatosis type I (NF1), in such cases arising from pre-existin...
Malignant phyllodes tumours of the breast account for up to a quarter of the phyllodes tumours.
Please, refer to the main article on phyllodes tumours for a general discussion.
It is generally thought that it is the stromal component that becomes malignant 4. This may account for t...
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
Malignant salivary gland tumours are staged using the TNM staging system:
Tx: primary tumour cannot be assessed
T0: no evidence of primary tumour
less than or equal to 2 cm in maximal diameter
no extra-parenchymal extension
2-4 cm in maximal diameter
Malignant vascular tumours rare, accounting for <1% of all sarcomas.
Barium meal has been frequently used to differentiate malignant and benign gastric ulcers:
Features suggesting benign gastric ulcer
outpouching of ulcer crater beyond the gastric contour (exoluminal)
smooth rounded and deep ulcer crater
smooth ulcer mound
smooth gastric folds that reach the...
Mallet finger describes a type of injury where there is disruption of the extensor mechanism of the finger at the distal interphalangeal joint (DIP). It is the most prevalent finger tendon injury in sport. The term includes both bony avulsion injury and tendinous injury without avulsion.
The malleus is the most lateral middle ear ossicle, located between the tympanic membrane and the incus.
The malleus has a head, neck, and three distinct processes (manubrium (handle), anterior and lateral processes).
The head is oval in shape, and articulates posteriorly with t...
Mallory bodies are cytoplasmic eosinophylic inclusions in hepatocytes, associated with ballooning and inflammation, found in:
alcoholic fatty liver disease and hepatitis
non-alcoholic fatty liver disease
hepatocellular carcinoma (HCC)
primary biliary cirrhosis (PBC)
Mallory Weiss tears occur due to violent projection of gastric contents against the lower oesophagus, which results in mucosal and submucosal tear with involvement of the venous plexus.
Patients present with massive painless haematemesis.
Tears most commonly ...
Mucosa associated lymphoid tissue (MALT) lymphoma, also called extranodal marginal zone B-cell lymphoma, is a type of low-grade extranodal lymphoma.
MALT lymphoma represents ~7.5% of non-Hodgkin lymphomas. Average age of presentation is 60 years with a slight female predominance ...
MALT lymphomas of the dura (also known as extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue of the dura), are an uncommon form of CNS lymphoma, accounting for an even smaller proportion of dural masses. They are, however, the most common form of primary dural lymphoma.
Mamillopontine distance is defined as the distance between the inferior aspect of the mammillary bodies to superior aspect of the pons. In normal subjects, it should be >5.5 mm.
It is decreased in conditions such as
intracranial hypotension: it is one of the helpful quantitative signs helpful ...
Mammary duct ectasia is characterised by chronic inflammatory and fibrotic changes leading to clogging of debris within the duct. It is of primary importance because of its features mimicking to that of malignancy.
Some publications use this term synonymously with periductal mastit...
The mammary glands
develop in close association with a depot of adipose tissue that is commonly
referred to as the mammary fat pad.
The mammary fat pad is a matrix of adipose
and connective tissue capable of mediating hormone action and synthesizing an
array of growth regulatory molecules.
The mammillary bodies form part of the hypothalamus and have a role in memory, although their exact role is yet to be established.
The mammillary bodies are round, paired structures that are a relay in the Papez circuit and lie in the inferior hypothalamus. They are separated in...
Mammography is a dedicated radiographic technique for imaging the breast.
Types of mammography
In general terms, there are two types of mammography: screening and diagnostic.
Mammography differs significantly in many respects from the rest of diagnostic imaging.
There are numerous mammography views that can broadly be split into two groups
supplementary views - additional information or problem solving
Standard views are those that are performed on routine screening mammograms. The views are usually used for all routine...
In 2017, the Adrenal Subcommittee of the Incidental Findings Committee of the American College of Radiology published a revised algorithm for the management of incidental adrenal masses in patients who are:
adults (i.e. 18-year-old or over)
asymptomatic for adrenal pathology
referred for imag...
Managing editors at Radiopaedia.org are part of the senior editorial team and have specific roles for development of the site and its content.
As of 2016, there are three managing editors:
Between 2007 (launch) and 2014, Radiopa...
The mandible is the single midline bone of the lower jaw. It consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly at right angles (angle of the jaw). It articulates with both temporal bones at the mandibular fo...
The mandibular canal is located within the internal aspect of the mandible and contains the inferior alveolar nerve, artery and the vein. It starts at the mandibular foramen, on the lingual side of the ramus, continues on buccal surface of body of the mandible and ends at the mental foramen, adj...
The mandibular foramen or inferior alveolar foramen is located on medial surface of ramus of the mandible and is the entrance to the mandibular canal. It transmits inferior alveolar nerve, a branch of the posterior division of the mandibular division of the trigeminal nerve that supplies all the...
The mandibular fossa is the smooth concave articular surface formed by both the squamous and petrous parts of the temporal bone. It is a part of temporomandibular joint and lodges the condyle of mandible.
Mandibular fractures are relatively common especially among young men. Although traditionally the mandible and base of skull are thought to form a complete bony ring, interrupted only by the TMJs. This should mean that the mandible should fracture in two places (akin to the bony pelvis) making s...
Mandibular lesions are myriad and common. The presence of teeth results in lesions that are specific to the mandible (and maxilla) and a useful classification that defines them as odontogenic or non-odontogenic. While it may often not be possible to make a diagnosis on imaging alone, this classi...
Mandibular osteoradionecrosis (ORN) is more common after radiation therapy for head and neck malignancies due to the superficial position of the mandible, which exposes it to high radiation. The maxilla can also be involved, but this is less frequent.
Mandibular ORN may occur in ...
There are many causes for mandibular periostitis:
Langerhans cell histiocytosis
malignancy (both primary and metastatic)
necrosis, e.g. radiation osteonecrosis
Garre's sclerosing osteomyelitis
Mandibular tori are common benign outgrowths of bone from the inner surface of the mandible.
They are composed of compact bone, densely mineralized usually without medullary cavity, and arise from the inner surface of the mandible above the origin of mylohyoid. They are usually bilateral.
Mannose-binding lectin (MBL) deficiency is a condition that affects the immune system.
It may be prevalent in 10-30% of the general population.
Affected individuals have low levels of an immune protein named mannose-binding lectin in their blood. They are prone to recu...
The manta ray sign is a radiographic appearance in bladder exstrophy. It describes wide midline separation of the pubic bones simulating the appearance of a manta ray swimming towards you 1.
On a plain radiograph consider:
open book pelvic injuries: the smooth arc of th...
Mantle cell lymphoma (MCL) is a type of non Hodgkin lymphoma (NHL) and accounts for ~5% of all NHL. It is a malignant neoplasm of virgin B cells that closely resemble normal mantle zone B cells surrounding germinal centres.
They occur in older adults (mean age ~60 years). There is...
The articulation between the upper two parts of the sternum, the manubrium and sternal body, is known as the manubriosternal joint. It is at the level of the sternal angle or angle of Louis, which is at the 2nd costal cartilage and the intervertebral disc of T4 and T5 1. This forms an importa...
The manubrium is the superior part of the sternum. It lies at the level of T3-T4 vertebrae. It forms the superior wall of the anterior mediastinum and its superior border also contributes to the superior thoracic aperture (thoracic inlet). The upper border of the manubrium also serves as the ape...
Maple syrup urine disease (MSUD) is a very rare metabolic disorder. It is an inborn error of amino acid metabolism, which classically affects the brain tissue resulting in impairment or death if untreated.
Manifests itself in the first few days of life (12-24 hours) with ...
A maquet view is a type of radiographic projection of the lower limbs.
They are a well established method of determining the axial alignment of the lower limb in the coronal plane and are of particular use in assessment of total knee replacements.
Construct the weight ...
Marbled pattern of the corpus callosum has been described in the acute phase of neuromyelitis optica (NMO) and represents multiple overlapping lesions with heterogeneous signal 1. This is distinct from the more typical appearance of multiple sclerosis (MS) where smaller separate individual lesio...