Lacrimal gland masses can be classified into two broad groups - inflammatory (~50%) and neoplastic, either lymphoma (25%) or salivary gland type tumors (~25%).
affects ~25% of patients with systemic disease
orbital inflammatory pseudotumour
A large for date uterus is a clinical observation based on uterine fundal height, which may result in referral for ultrasound assessment, usually in mid to late pregnancy.
constitutionally large fetus
Large joint dislocation is a not uncommon presentation to emergency rooms. Described in order of comonality:
posterior dislocation of the hip
When a pleural effusion is large and unilateral, concern for an underlying abnormality should be raised. Causes include:
primary effusion lymphoma
Laryngeal cysts can occur in any part of the larynx, but are more frequent in supraglottic locations, such as the epiglottis and vallecula. The prevalence of each location varies on different studies.
The laryngeal cysts represent a rare group, about 5%, of benign laryngeal lesio...
Lateral epicondyle fractures are rare epicondylar fractures. They are much rarer than medial epicondyle fractures and represent avulsion of the lateral epicondyle. They are usually seen in the setting of other injuries 1-3.
Incidence typically peaks in the pediatric age group (6-...
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...
Lead poisoning or plumbism is a multisystem condition due to the way in which lead interferes with the function of virtually every organ system. Plumbism most severely manifests due to its devastating effects on the CNS, but it also has important deleterious consequences on the skeletal, renal, ...
The left atrial (LA) line monitors LA pressure and is indicative of left ventricular function, preload and afterload. The LA line enters from the left superior vein and exits the far side of the chest.
The LA line is a single lumen catheter unlike the right atrial line, which is double lumen. N...
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...
When a central venous catheter that is supposed to project over the superior vena cava is abnormally located to the left of the mediastinum a limited differential of left paramediastinal catheter position should be considered 1:
located within a vein
left sided superior vena cava
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.
Left upper lobe consolidation refers to consolidation in part (incomplete) or all (complete) of the left upper lobe.
Consolidation refers to the alveolar airspaces being filled with fluid (exudate/transudate/blood), cells (inflammatory), tissue, or other material.
The list of causes...
Leg bowing in children is common and often developmental.
The differential includes:
exaggeration of normal age-related angulation changes at the knee
neonates and infants normally have varus angulation that gradually corrects within 6 months of w...
Leiomyoma is a benign smooth muscle (myometrial) tumor, most commonly found in the uterus.
Leiomyoma is classified by location:
leiomyoma of the urinary bladder
solitary cutaneous leiomyoma
vascular leiomyoma (angiol...
Leptomeningeal enhancement refers to a diffuse or focal gyriform or serpentine enhancement that can be seen in the following conditions:
tuberculous meningitis (can also be focal)
CNS cryptococcal infection
coccidioidal meningitis (c...
Lesions of the corpus callosum are uncommon and arise from multiple different etiologies. The lesions can be classified according to underlying pathophysiology 4-6.
agenesis of the corpus callosum
enlarged perivascular spaces
tubonodular pericallosal lipoma: associated with dysgen...
Leukemia is a hematological neoplasm characterized by the overproduction of immature (blasts) or abnormally differentiated cells of the hematopoietic system in the bone marrow that often, but not always, extends into the peripheral blood.
This article aims to provide an overview of leukemia as...
Leukocoria (also spelled as leucocoria or leukokoria) refers to an abnormal white reflection from the retina of the eye. Despite its color, 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 leukoc...
The leukodystrophies are a heterogeneous group of disorders that primarily affect the white matter of the central nervous system. They are particularly encountered in childhood as many are genetically determined and represent abnormalities in white matter metabolism. A number of leukodystrophies...
Linear atelectasis refers to a focal area of subsegmental atelectasis that has a linear shape. Depending on its shape, it is also known as plate, discoid or band atelectasis. Linear atelectasis may appear to be horizontal, oblique or perpendicular and is very common. It usually occurs as a conse...
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 diverticulum. Also known as a persistent omphalomesenteric duct hernia. It is most frequently encountered in the inguinal region.
blind-ending tubular structure arising from antimesenteric border of small bowel and extendi...
Liver lesions represent a heterogeneous group of pathology ranging from solitary benign lesions to multiple metastases from a variety of primary tumors.
Liver lesions may be infiltrative or have mass effect, be solitary or multiple, benign or malignant.
Assessment of liver lesions takes into c...
Pediatric 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 tumors
malignant liver tumors
There are differing frequencies of both benign ...
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 tumors, like tumors 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 tumors, due...
Lobar consolidation is the term used to describe consolidation in one of the lobes of the lung. It infers a alveolar spead of disease and is most commonly due to pneumonia.
Consolidation refers to the alveolar airspaces being filled with fluid (exudate/transudate/blood), cells (infla...
Lobar collapse refers to the collapse of an entire lobe of the lung. As such it is a subtype of atelectasis (collapse is not entirely synonymous with atelectasis, which is a more generic term for 'incomplete expansion'). Individual lobes of the lung may collapse due to obstruction of the supply...
Localized pulmonary hemorrhage is a descriptive term for a pulmonary hemorrhage restricted to a particular focal region of the lung. It can range from involving a small focus of hemorrhage to a whole lobe.
Focal pulmonary hemorrhage 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 immobilization 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
There are a vast range of lower extremity fractures. Below are listed several of such fractures of the lower limb. Many have eponyms.
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 causes of low signal intensity renal parenchyma. Causes include:
paroxysmal nocturnal hemoglobinuria
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...
Lung atelectasis refers to collapse or incomplete expansion of pulmonary parenchyma. Note that the term "atelectasis" is typically used when there is partial collapse, whereas the term "collapsed lung" is typically reserved for when the entire lung is totally collapsed.
A mnemonic for the causes of lymphangitic carcinomatosis is:
Certain Cancers Spread By Plugging The Lymphatics
P: prostate and pancreas
L: larynx and lung
Lymph node imaging is a useful technique, aiding the clinician in determining whether nodes are benign or malignant. Multiple modalities are 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 tumors, 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 pheochromocytoma
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
pseudogynecomastia: fat deposition within the b...
Pediatric malignant liver tumors are rare, some of which occur only in children but that are similar to those that occur in adults.
Malignant liver tumors account for ~1% of pediatric malignancies 2.
Broadly, any malignant liver mass can be defined as a metastasis or p...
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 esophageal neoplasms are much more common than benign esophageal neoplasms, especially if the patient is symptomatic.
esophageal carcinoma (90%)
esophageal squamous cell carcinoma (SCC)
esophageal 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 ce...
Masticatory muscle hypertrophy or commonly presenting as temporalis and masseter muscles hypertrophy is a rare disease that affects muscles of mastication and results in "pseudo-masses". Commonly seen in anxious individuals with "bruxism" and in chronic gum chewing 1.
It sometimes gives a "thr...
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
Mastoid air cell opacification can occur in a number of situations and can include a spectrum of inflammatory, neoplastic, vascular, fibro-osseous, and traumatic changes.
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 the 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...
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 centers 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 tumors account for only 0.5% of all intracranial tumors. The most common histologies include:
trigeminal schwannoma: most com...
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's elbow) is an angiofibroblastic tendinosis of the common flexor- pronator tendon group 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. Ther...
Mediastinal lymph node enlargement can occur from a wide range of pathologies. It may occur on its own or in association with other lung pathology.
Although mediastinal lymphadenopathy is used interchangeably - by some - with "mediastinal lymph node enlargement", they are not synon...
Mediastinal mass may be caused by a wide variety of neoplastic and non-neoplastic pathologies. It is helpful to identify the location of the mass since this significantly reduces the breadth of the differential diagnosis.
There are four conceptual compartments of the mediastinum which are larg...
The differential diagnoses for mediastinal widening include:
traumatic aortic injury
aberrant right subclavian artery
azygos continuation of the IVC
pulmonary masses abutting the mediastinum
Medical devices in the abdomen and pelvis are important to be recognized, 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 into 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 esophagus or diffuse esophageal dilatation can be caused by a variety of conditions.
Some of the more common causes are given below 1-3:
malignant stricture, e.g. esophageal cancer, c...
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.
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 pediatric or adult patients.
Examples of metaphyseal fractures:
surgical neck of humerus fracture
distal radial fracture
distal radial buckle frac...
The differential diagnosis for metaphyseal lesions includes:
aneurysmal bone cyst
simple bone cyst
giant cell tumor
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
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 tumors, which are more likely to be benign than malignant.
The three most common middle ear tumors 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. esophageal, bronchial)
primary/secondary cardiac tumor
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 (tumor, hemorrhage, abscess, etc) has the potential to exert mass effect on the brain parenchyma and cause lateral shift of the midline s...
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