Intrasinus calcification is a phenomenon whereby calcification is formed within the paranasal sinuses. It can occur to varying extents, therefore leading to varying degrees of attenuation on CT. Such calcification may occur either concurrently within an opacified sinus or in an aerated sinus, de...
Intraventricular metastases are a very rare finding. A few intracranial tumors and some extracranial tumors metastasize to the ventricles. The most common site of intraventricular metastasis is the trigone of the lateral ventricles due to high vascularity of the choroid plexuses. The next most c...
Intraventricular neoplasms are rare and arise from periventricular structures such as the walls of the ventricular system, the septum pellucidum and the choroid plexus. Many tumor types arise from or can bulge into the ventricular system, although there are certain lesions that are relatively re...
Joint ankylosis has a relatively broad differential including 1-5:
chronic reactive arthritis
juvenile idiopathic arthritis
surgical ankylosis (arthrodesis)
coalition, e.g. tarsal, c...
A J-shaped sella is a variant morphology of the sella turcica, whereby the tuberculum sellae is flattened, thus forming the straight edge of the "J". The dorsum sellae remains rounded and forms the loop of the "J".
Differential diagnosis for a J-shaped sella includes 1,2...
Jugular fossa masses comprise a range of pathological lesions that arise from or extend into the jugular fossa in the skull base. Although not a common location for tumors it is not unusual for jugular fossa lesions to be discovered incidentally on cross-sectional imaging.
Juvenile osteoporosis refers to osteoporosis occurring in children.
It can arise from a number of causes 1-4:
osteoporosis pseudoglioma syndrome
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 pseudotumor
Lacrimal sac masses are very uncommon and more commonly have a malignant (~80%) rather than benign (~20%) etiology.
granulomatosis with polyangiitis
When a pleural effusion is large and unilateral, concern for an underlying abnormality should be raised. Causes include:
primary effusion lymphoma
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, ...
When a central venous catheter that is supposed to terminate in the superior vena cava or right atrium is abnormally located to the left of the mediastinum and below the level of the brachiocephalic vein, a limited differential of left paramediastinal catheter position should be considered 1:
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...
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...
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...
Lobar consolidation is the term used to describe consolidation in one of the lobes of the lung. It infers an alveolar spread of disease and is most commonly due to pneumonia.
Consolidation refers to the alveolar airspaces being filled with fluid (exudate/transudate/blood), cells (inf...
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:
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...
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
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)
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 years old
diffuse bony sclerosis
permeative process in bone
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...
Mass-forming intrahepatic cholangiocarcinomas (MF-ICC), also referred as peripheral cholangiocarcinomas, compromise one of the three recognized growth patterns of intrahepatic cholangiocarcinomas.
On imaging, these tumors usually present as large and relatively well-defined hepatic masses with...
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.
Maurice "Mo" M Reeder (1933-2013) was an American radiologist who is remembered for his contributions to radiology education in the United States, in particular, the development of the radiology-pathology teaching program at the Armed Forces Institute of Pathology.
Maurice Merrick R...
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...
Meary's angle or talus-first metatarsal angle has been used to identify the apex of deformity in patients with pes cavus and pes planus on lateral weight-bearing foot radiographs. It is the angle between a line drawn from the centers of longitudinal axes of the talus and the first metatarsal.
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 or ascend to/into the head.
Vascular access devices
peripherally inserted central catheters (PICC)
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...
Megaesophagus 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, ca...
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 pseudotumor, 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 pseudotumors are large focal solid or semiliquid masses around t...
The metaphyseal blanch sign (or 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 the ...
The differential diagnosis for metaphyseal lesions includes:
aneurysmal bone cyst
simple bone cyst
giant cell tumor
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 duplication 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 ...
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...
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 mixed cystic and solid pituitary region mass has a limited differential.
both papillary (more solid) and adamantinomatous (more cystic)
cystic change / necrosis / previous hemorrhage
Most other solid and enhancing pituitary region mas...
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:
septic arthritis (8-27%)
rheumatoid arthritis (RA) (11-16%)
Less common 2:
HADD (hydroxyapatite deposition disease)
reactive arthritis 2
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 short differential.
Rathke cleft cyst
craniopharyngioma (adamantinomatous 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 gallbladder are extremely rare epithelial cystic tumors formed by mucin-producing cells. They are histologically similar to the other mucinous cystic tumors found elsewhere in the body.
For the lesions involving the bile ducts, please refer to:
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
Mucoid impaction, also referred to as mucus plugging, mucous plugging, bronchial mucocele or bronchocele formation, refers to airway filling by mucoid secretions and can be obstructive or non-obstructive. It is a common pathological finding in chest imaging.
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
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 leukemia
chronic inflammatory demyelinating polyneuropathy
cranial nerve enhancement: for comple...
The differential diagnosis for multiple cystic neck lesions is different to that for a solitary cystic neck mass.
Cystic neck lesions are seen in:
metastatic squamous cell carcinoma: older patient, M>F
metastatic papillary thyroid carcinoma: usually a younger patient, ...
Multiple endocrine neoplasia (MEN) syndromes are a collection of syndromes characterized by the presence of, as the name would suggest, multiple endocrine tumors. They are autosomal dominant in inheritance.
MEN1 (Wermer syndrome)
MEN2 (multiple endocrine adenomatosis)
MEN2a (Sipple syndrome)
Multiple filling defects within a ureter, as seen on conventional IVU or CT IVU, have a relatively small differential including:
spreading or multifocal transitional cell carcinoma (TCC)
multiple ureteral stones (steinstrasse)
Intracranial calcifications are common in certain locations and often are of no clinical concern.
The two most commonly encountered types of calcification include:
normal age-related intracranial calcifications
intracranial arterial atherosclerosis
Concerning calcifications are much less co...
Myonecrosis is a myopathy involving infarction of skeletal muscle and can have the appearances of an intramuscular mass.
Myonecrosis has a variety of causes 1,2:
sickle cell crisis
post-traumatic (see: calcific myonecrosis)
A narrow fetal thorax on antenatal ultrasound can be present with a number of anomalies which include:
Jeune syndrome - asphyxiating thoracic dysplasia
short rib polydactyly syndro...
The interpedicular distance is the measurement between the pedicles on frontal/coronal imaging, which can be narrowed in a number of situations.
thanatophoric dysplasia 2
widening of interpedicular distance
See reference 1 for an old but interesti...
Causes of neonatal distress can be broadly split into intrathoracic, extrathoracic and systemic:
respiratory distress syndrome (RDS)
transient tachypnea of the newborn (TTN)
meconium aspiration syndrome
bronchopulmonary dysplasia (BPD)
patent ductus arteriosus (PDA)
The differential diagnosis for masses of the cauda equina region is often considered separately to the remainder of the spinal cord. It is often difficult to determine whether masses in this region are intramedullary or intradural-extramedullary.
Most common tumors
Nephrocalcinosis, previous known as Anderson-Carr kidney or Albright calcinosis, refers to the deposition of calcium salts in the parenchyma of the kidney. It is divided into several types, with differing etiologies, based on the distribution:
medullary nephrocalcinosis: 95%
Nerve root enhancement is phenomenon described on post contrast MRI scans that can be observed in a number of situations.
post-operative nerve root enhancement
disseminated spinal leptomeningeal metastases