Lesions of the corpus callosum are uncommon and arise from multiple different aetiologies. The lesions can be classified according to underlying pathophysiology 4-6.
agenesis of the corpus callosum
enlarged perivascular spaces
tubonodular pericallosal lipoma: associated with dysge...
Leukocoria (also spelled as leucocoria or leukokoria) refers to an abnormal white reflection from the retina of the eye. Despite its colour, the reflection is related to the familiar red-eye effect. Usually, when a light is shone through the iris, the retina appears red to the observer. In leuko...
The leukodystrophies are dysmyelinating disorders which typically, although not invariably, affect children. They include:
lysosomal storage diseases
globoid cell leukodystrophy (Krabbe disease)
Linitis plastica is a descriptive term usually referring to the appearance of the stomach, although the rectum can also be described this way. The appearance is said to be reminiscent of an old leather water-bottle.
The underlying cause is usually a scirrhous adenocarcinoma with diff...
Littre hernia is a hernia containing a Meckel's diverticulum. Also known as a persistent omphalomesenteric duct hernia. It is most frequently encountered in the inguinal region.
blind ending tubular structure arising from antimesentric border of small bowel and extend...
Liver lesions represent a heterogeneous group of pathology ranging from solitary benign lesions to multiple metastases from a variety of primary tumours.
Liver lesions may be infiltrative or have mass effect, be solitary or multiple, benign or malignant.
Assessment of liver lesions takes into ...
Paediatric liver lesions are a heterogeneous group that include infiltrative lesions and those that demonstrate mass effect. Moreover, they may be solitary or multiple, benign or malignant:
benign liver tumours
malignant liver tumours
There are differing frequencies of both beni...
The liver is one of the most frequently damaged organs in blunt trauma, and liver trauma is associated with a significant mortality rate.
In blunt abdominal trauma, the liver is injured ~5% (range 1-10%) of the time 1,3.
Patients can present with right uppe...
Liver tumours, like tumours of any organ can be classified as primary or secondary.
Liver metastases are by far the most common hepatic malignancy, with many of the most common primaries readily seeding to the liver. This is especially the case with gastrointestinal tract tumours, d...
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:
Locked facet joint is a type of facet joint dislocation that results from jumping of the inferior articular process over the superior articular process of the vertebra below and becomes locked in the position.
It can be unilateral or bilateral.
The tip ...
Long bone metaphyseal cupping is most likely due to the local oligaemia from thrombosis in the terminal epiphyseal arteries to the epiphyseal plate, induced by prolonged regional immobilisation 7.
The differential diagnosis of long bone metaphyseal cupping includes:
Longitudinally extensive spinal cord lesions (LESCL), also known as longitudinally extensive transverse myelitis (LETM), represent extensive involvement of the spinal cord, with abnormal T2 signal traversing at least three vertebral body segments in length.
They are typi...
Longitudinal temporal bone fractures are petrous temporal bone fractures that occur parallel to the long axis of the petrous temporal bone. Although more current classifications of the extent of temporal bone fractures focus on the integrity of the otic capsule rather than the fracture orientati...
Petrous temporal bone fractures are classically divided into longitudinal, transverse or mixed fracture patterns depending on the direction of fracture plane with respect to the long axis of the petrous temporal bone. Some features may aid in distinguishing them.
Loss of intervertebral disc space can be due to a variety of causes:
degenerative disc disease of the spine: most common cause
dialysis related spondyloarthropathy
crystal deposition diseases
Causes of calcifications in the lower abdomen and pelvis include:
seminal vesicle and ductus deferens calcification
dropped stones following chol...
There are a vast range of lower extremity fractures. Below are listed several of such fractures of the lower limb. Many have eponymous names.
Pelvis and femur
anterior inferior iliac spine avulsion injury
proximal femoral fractures
Lower gastrointestinal bleeding usually occurs distal to the ligament of Treitz, and has a wide differential diagnosis:
There are relatively few of causes of low signal intensity renal parenchyma. Causes include:
paroxysmal nocturnal haemoglobinurea.
mechanical: malfunctioning prosthetic cardiac valve
sickle cell disease
hemorrhagic fever with renal syndrome (HFRS)
Lunate dislocations are an uncommon traumatic wrist injury that require prompt management and surgical repair. The lunate is displaced and rotated volarly. The rest of the carpal bones are in a normal anatomic position in relation to the radius.
These should not be confused with perilunate disl...
The lying down adrenal sign is a feature seen usually associated with renal agenesis or renal ectopia. It is an important antenatal sonographic sign.
On an antenatal ultrasound scan, the adrenal of the affected side appears flattened, elongated, and lying along the spine due to absence of the ...
A mnemonic for the causes of lymphangitic carcinomatosis is:
Certain Cancers Spread By Plugging The Lymphatics
L: larynx and lung
Lymph node imaging has become an important task for the radiologist in present days, aiding the clinician in determining whether they are benign or malignant. Multiple modalities are being used for the assessment and characterization of lymph nodes, each with its advantages and drawbacks.
Lytic bone metastases are due to a variety of primary tumours, and are more common than sclerotic metastases (although many may occasionally have mixed lytic and sclerotic components). They include 1:
renal cell cancer
adrenal gland carcinoma and phaeochromocytoma
Lytic skull lesions have a relatively wide differential that can be narrowed, by considering if there are more than one lesion and whether the mandible is involved.
lytic skeletal metastases
epidermoid - scalloped border with a sclerotic rim
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
Here is a list of some of the most useful differential diagnoses in musculoskeletal imaging.
lucent/lytic bone lesions (FEGNOMASHIC)
multiple lucent/lytic bone lesions
benign lytic bone lesions in patients under 30
diffuse bony sclerosis
permeative process in bone
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 the...
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...
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
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...
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...
There are many causes for mandibular periostitis:
Langerhans cell histiocytosis
malignancy (both primary and metastatic)
necrosis, e.g. radiation osteonecrosis
Garre's sclerosing osteomyelitis
March fractures are a name subtype of fatigue/stress fracture. They occur due to repeated concentrated trauma to a normal bone, classically the 2nd metatarsal of the foot but can occur in other weight-bearing bones of the lower limb and pelvis.
Please see the article on s...
The differential diagnosis of masses arising from the foramen of Monro can be approached depending on the age of the patient.
choroid plexus papilloma
Langerhans cell histiocytosis
subependymal giant c...
Mastitis refers to inflammation of the breast parenchyma, of which there are a number of subtypes:
puerperal mastitis: occurs usually from infection with Staphylococcus during lactation
non-puerperal mastitis: not related to lactation, and occurs usually in older women
Maydl hernias are defined as the presence of two small bowel loops within a single hernial sac, that is, there are two efferent and two afferent loops of bowel, forming a "W" shape.
This type of hernia is more prone to strangulation and necrosis. The intervening intra-abdominal loop is also at ...
McBurney point is defined as a point that lies one-third of distance laterally on a line drawn from the umbilicus to the right anterior superior iliac spine. Classically, it corresponds to the location of the base of the appendix 1.
Clinically, McBurney point is relevant for the elicitation of ...
McRae line is a radiographic line drawn on a lateral skull radiograph or midsagittal section of CT or MRI, joining the basion and opisthion.
Normal position of the tip of dens is 5mm below this line. If the tip of the dens migrates above this line it indicates the presence of basilar invaginati...
Meary's angle or lateral talo-first metatarsal angle has been used to identify the apex of deformity in patients with pes cavus and pes planus on lateral weightbearing foot radiographs. It is the angle between a line drawn from the centres of longitudinal axes of the talus and the first metatars...
Meckel cave lesions are numerous. The aim of this article is to list them in an easy way for revision and assessment of differential diagnosis.
Meckel cave tumours account for only 0.5% of all intracranial tumours. The most common histologies include:
trigeminal schwannoma: most c...
Medial epicondyle fractures represent almost all epicondyle fractures and occur when there is avulsion of the medial epicondyle. They are typically seen in children, and can be challenging to identify. Failure to diagnose these injuries can lead to significant long term disability.
Medial epicondylitis (also known as golfer elbow) is an inflammatory condition around the common flexor tendon of the elbow.
It is less common than lateral epicondylitis. As with lateral epicondylitis, it typically occurs in the 4th to 5th decades of life. There is no recognised g...
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...
Medical devices in the abdomen and pelvis are important to be recognised, just like medical devices of the chest. Often we ignore these devices, considering them to be incidental and non-pathological, however it is essential to be aware of potential complications.
Medical devices in the neck are regularly observed by radiologists on plain film and CT reporting. They include devices which pass through the neck onto the chest and stomach.
Vascular access devices
peripherally inserted central catheters (PICC)
central venous catheters
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
Renal medullary nephrocalcinosis is the commonest form of nephrocalcinosis and refers to the deposition of calcium salts in the medulla of the kidney. Due to the concentrating effects of the loops of Henle, and the biochemical milieu of the medulla, compared to the cortex, it is 20 times more co...
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...
Meningeal enhancement is a generic term related to the enhancement of the membranes that envelop the brain and spinal cord. Due the anatomical features, this enhancement can be divided in two subtypes:
leptomeningeal enhancement (pial or pial-arachnoid enhancement)
pachymeningeal enhancement (...
Meningoceles are protrusions of the meninges through a defect or weak point in the skull or spine, usually involving the soft tissues beneath the surface of the skin. They are typically categorized into congenital, iatrogenic (e.g. following a craniotomy, sinus surgery, or as a laminectomy compl...
Metachronous breast cancers are two breast cancers that occur in either breast in two different time periods.
Treatment and prognosis
The survival rate of women with metachronous breast cancers diagnosed within 2 years of the original primary is worse than those with unilateral disease 4.
Patients with malignant ureteric obstruction and poor life expectancy usually require placement of ureteral stents to relieve the urinary obstruction and as a palliative measure to reduce pain and avoid major operation.
Metallic ureteric stents have recently been developed to try and offer bett...
A metal-on-metal pseudotumour, also known as aseptic lymphocyte-dominant vasculitis-associated lesion (ALVAL), is a mass-forming tissue reaction around a metal-on-metal hip or knee replacement.
Metal-on-metal pseudotumours are large focal solid or semiliquid masses around...
The metaphyseal blanch sign (a.k.a. metaphyseal blanch sign of Steel) is one of the signs seen on AP views of the adolescent hip indicating posterior displacement of the capital epiphysis.
It is a crescent-shaped area of increased density, that overlies the metaphysis adjacent to the physis on ...
Metaphyseal fractures are fractures that involve the metaphysis of tubular bones. They may occur in paediatric or adult patients.
Examples of metaphyseal fractures:
surgical neck of humerus fracture
distal radial fracture
distal radial buckle fra...
The differential diagnosis for metaphyseal lesions includes:
aneurysmal bone cyst
simple bone cyst
giant cell tumor
Metastases to testis are a rare cause of a testicular mass and may be bilateral in up to 15% of patients.
Metastases to the testes are apparent in ~0.04% of autopsy studies in patients with known malignancy. The average age is 57 years, much older than the primary age for primary...
Metastases to the ovary are relatively common with a documented incidence of 5-30% of all malignant ovarian masses.
These may be incorrectly grouped under Krukenberg tumors, which are signet cell containing tumours that form only 30-40% of all ovarian metastases.
A metastatic intramammary lymph node refers to an intramammary lymph node involved with metastatic or malignant disease.
Sonographic features that suggest metastatic involvement include 4:
disappearance or loss of central echogenic hilar region
The term metatarsalgia refers to pain in the region of the metatarsophalangeal joints. It is a frequent presenting complaint in the foot.
Common causes include 1,2:
interdigital (Morton) neuroma
stress fractures involving the foot
Metatarsus adductus is a type of foot deformity where there is medial deviation of the first metatarsal +/- medial displacement of the metatarsals on the cuneiform. It can be congenital or acquired. It is considered the most common congenital foot abnormality.
Midcarpal (central carpal) dislocation describes an injury where there is dislocation of the capitate from the lunate, and subluxation of the lunate from the radius. This term is somewhat confusing because some authors use "midcarpal dislocation" to refer generally to perilunate and lunate dislo...
There are a range of middle ear tumours, which are more likely to be benign than malignant.
The three most common middle ear tumours are (not in any particular order as there are differences in the literature) 1-3:
glomus tympanicum paraganglioma
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
Midline neck masses have a relatively narrow differential, as few structures are present in the midline. Dividing the causes according to structure of origin is a useful schema.
lymph node(s): Delphian node(s)
thyroglossal duct cyst
One of the most important indicators of increased intracranial pressure due to mass effect is midline shift.
Any intra-axial or extra-axial lesion (tumour, haemorrhage, abscess, etc) has the potential to exert mass effect on the brain parenchyma and cause lateral shift of the midline...
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...
Milking effect phenomenon is a pathognomonic angiographic finding in myocardial bridging of coronary arteries. Systolic compression of coronary vessels with partial or complete decompression during diastole is described as milking effect. Its significance lies in:
increased risk of thrombus fo...
The term milk of calcium (MOC) is given to dependent, sedimented calcification within a cystic structure or hollow organ. This sort of colloidal calcium suspension layering can occur in various regions:
renal: milk of calcium in renal cyst (most common)
breast: milk of calcium in breast cyst
Milk of calcium within a breast cyst is a mammographic feature observed when there is dependent calcium layering within breast cysts. It is typically observed as "tea cup" or "crescent shaped" calcifications on a true lateral (LM or ML) view on occasionally on a MLO view. On a CC view, these cal...
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...
There are numerous mitochondrial disorders that affect the neurological and muscular systems in a variety of ways:
mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS)
myoclonus epilepsy with ragged red fibres (MERRF)
Mitral valve disease (MVD) principally comprise of a two main functional abnormalities, which can occur in isolation or in combination:
In addition other pathologies that affect the mitral valve include:
mitral valve prolapse
mitral annular calcification...
A mixed cystic and solid pituitary region mass has a limited differential.
both papillary (more solid) and adamantimonatous (more cystic)
cystic change / necrosis / previous haemorrhage
Most other solid and enhancing pituitary region ma...
Mixed lytic and sclerotic bone metastases are seen in a number of malignancies:
breast carcinoma: typically sclerotic but 25% are mixed
lung carcinoma: typically lytic but 15% are mixed
carcinoma of the cervix
prostate carcinoma: typically sclerotic but 15% are mixed
Monoarticular arthropathy can result from a number of causes:
HADD (hydroxyapatite deposition disease)
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...
Mostly/purely cystic pituitary region masses have a small differential.
Rathke's cleft cyst
craniopharyngioma (adamantimonatous type): 90% have calcification
Moyamoya syndrome, also termed the moyamoya pattern or phenomenon, is due to numerous conditions that can cause arterial occlusion of the circle of Willis, with resultant collaterals, and appearances reminiscent of moyamoya disease. These conditions include 1-4 :
vessel wall abnormalities
Mucinous cystic neoplasms of the pancreas are the most common cystic neoplasm of the pancreas and include:
mucinous cystadenoma of pancreas
mucinous cystadenocarcinoma of pancreas
intraductal papillary mucinous neoplasms (IPMN) of the pancreas: sometimes classified separately
A mucocele simply refers to accumulation and expansion of a structure by mucus. It occurs in a variety of locations which are discussed separately:
paranasal sinus mucocele
oral cavity e.g. ranula, mucous retention cysts
mucocele of the appendix 1
mucocele of the gallbladder
mucocele of the...
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 ...
Mucopolysaccharidoses (MPS) constitute a group of hereditary disorders, one of a number of lysosomal storage disorders, having in common an excessive accumulation of mucopolysaccharides secondary to deficiencies in specific enzymes (lysosomal hydrolases) responsible for degradation of mucopolysa...
A multicentric breast cancer is a term given to a breast cancer where there are two or more breast cancers separated by normal breast tissue (often taken as 5 cm of separation 4). It is related to but distinct from the term multifocal breast cancer.
At a pathological level It can also mean 2
Multicentric reticulohistiocytosis (MRH) also known as lipoid dermatoarthritis, is a rare systemic disorder.
MRH is considered a form of granulomatous disease 10 characterised by infiltration of multinucleated histiocytes into various tissues, primarily affecting skin and synovium, w...
Multifocal breast cancer refers to two or more individual breast cancers diagnosed at the same time within the same quadrant of the same breast 1.
Multilayered periosteal reaction, also known as a lamellated or onion skin periosteal reaction, demonstrates multiple concentric parallel layers of new bone adjacent to the cortex, reminiscent of the layers on an onion. The layers are thought to be the result of periods of variable growth 2.
The most common causes of multiple cranial nerve thickening and enhancement include:
metastasis (most common)
neurofibromatosis type II
lymphoma and leukaemia
chronic inflammatory demyelinating polyneuropathy
cranial nerve enhancement: for compl...