Thickening of the bile duct wall can stem from a variety of etiologies.
bile duct wall thickening
bile duct walls are typically not visible when normal
possible narrowing of the ducts with obstruction
possible secondary signs of cholangitis, including debri...
The bimastoid line has been described and used to evaluate basilar invagination on frontal skull plain film and coronal reconstructed CT image.
The bimastoid line is drawn between the inferior tips of the of mastoid processes bilaterally. The tip of the odontoid process of C2 normally projects ...
Bird fancier lung refers to a type of hypersensitivity pneumonitis occurring as a response to avian antigens (usually inhaled proteins in the dust of bird feathers and droppings). It can have acute, subacute and chronic clinical presentations.
For a broad discussion on this entity, please refer...
Birth trauma relates to those conditions caused by both physical/mechanical and hypoxic injuries.
Birth trauma occurs in ~5 per 1000 births 2.
Bladder outlet obstruction can arise from a number of conditions affecting the urethra and/or bladder outlet.
Patients often present with difficulty in urination, retention and urinary discomfort 2.
Obstruction can be caused by multiple etiologies but is most...
Differential diagnosis for bladder wall thickening depends on whether the bladder is adequately distended. The bladder wall may be thickened if:
>3 mm when distended
>5 mm when nondistended
If the bladder is not distended, then it is difficult to exclude artifactual thickening from a collapse...
Blalock-Taussig shunt, also known as Blalock-Thomas-Taussig shunt, is a palliative procedure designed to increase pulmonary arterial blood flow in patients with right ventricular outflow tract obstruction (e.g. tetralogy of Fallot) or during initial staged repair of hypoplastic left heart syndro...
Bleomycin lung toxicity is an uncommon but recognized complication that can occur with the chemotherapeutic drug bleomycin.
Bleomycin is an antitumour antibiotic which was initially isolated from a strain of Streptomyces verticillus in 1966. It is commonly used (either alo...
Blow out bone metastases or expansile bone metastases are typically only encountered in a relatively small number of primary malignancies, including 1:
renal cell carcinoma
Occasionally the sclerotic metastases of prostate cancer may also be expansile ...
Blumensaat line, also known as the intercondylar line, is the line drawn along the roof of the intercondylar notch of the femur on sagittal view of the knee.
It can been used for:
indicating relative position of patella - normally intersects the lower pole of the patella
evaluating for ACL in...
Blunt traumatic neck injury is uncommon because it is usually protected by the head, shoulders, and chest. This term is generally used to refer to injuries of the neck besides to cervical spine injuries, which are common.
Blunt injury to the neck is most commonly from motor vehicle ...
Body packing refers to the internal concealment of drugs within the gastrointestinal tract or other orifices. People who do this may be called body packers, (drug) mules, stuffers, couriers or swallowers. Drugs may be concealed within condoms, foil, latex or cellophane.
There is ...
Bone age assessment is used to radiologically assess the biological and structural maturity of immature patients from the hand and wrist x-ray appearances. It forms an important part of the diagnostic and management pathway in children with growth and endocrine disorders. It is helpful in the di...
Conditions associated with bone deformity from softening includes:
bowing of long bones
biconcave vertebral bodies / codfish vertebra
There are several bony lesions that can involve or depict a sequestrum.
brodie abscess: osteomyelitis
certain soft tissue tumors (with bony extension)
malignant fibrous histiocytoma
metastasis (especially from breast car...
Bone mineral density (BMD) is defined as the amount of mineral (calcium hydroxyapatite) per unit of bone.
BMD can be measured by various methods with DEXA the most prevalent
gamma rays: replaced by radiographic methods
single-energy photon absorptiometry (SPA) was super...
Bone within a bone is a descriptive term applied to bones that appear to have another bone within them. There are numerous causes including:
thoracic and lumbar vertebrae (neonates and infants)
growth recovery lines (after infancy)
cortical splitting and new periostitis
sickle cell d...
Boogard's angle is measured by drawing a line from basion to opisthion and another line along the plane of the clivus to the basion intersecting the first line - the angle between these two lines is measured .
The normal angle is 126° +/- 6°. If the angle measures more than 136° it is indicativ...
Borderline breast disease (BBD) refers to a group of conditions while being not completely malignant are still concerning. Usually an excision biopsy is recommended if entities falling into borderline breast disease is detected on core biopsy.
These entities include:
atypical ductal hyperplasi...
Bowel wall thickening is a useful finding on imaging studies and has a number of different causes.
The reason for bowel wall thickening depends on the underlying etiology but includes submucosal edema, hemorrhage, and neoplastic infiltration.
In describing bow...
Brachial plexitis refers to inflammatory change involving the brachial plexus. This is in contrast to a brachial plexopathy meaning any form of pathology involving the brachial plexus.
Brachial plexitis is more commonly seen in men between 30 and 70 years of age and is bilateral i...
Brachytherapy, also known as sealed source radiotherapy or endocurietherapy, is a form of radiotherapy where a radioactive source is placed, under the guidance of imaging, within or next to the area requiring treatment.
Brachytherapy has been used to treat:
breast cancer (ofte...
Brain stones, also known as cerebral calculi, refers to large intracranial calcifications that may be solitary or multiple.
If symptomatic, patients most commonly present with seizures.
Localization of brain stones can help narrow the underlying etiology but...
Breast calcifications can arise from a vast number of etiologies.
They are extremely common and can be present in ~85% of mammograms 8. Their frequency increases with age. Up to 50% of breast cancers can be associated with calcification while 15-30% of calcifications biopsied for...
Metastases from breast cancer can be a frequent finding in routine onco-radiological practice.
With the universal use and acceptance of screening mammography, the isolated clinical presentation from metastases from breast carcinoma has become rare in clinical practice. Hi...
Breast cysts are a common mammographic and sonographic finding, and can be of different types:
simple breast cyst: typically is a well-defined, anechoic lesion with imperceptible wall and posterior acoustic enhancement 1
complicated breast cyst: contains intracystic echoes or debris with other...
Breast density refers to the amount of fibroglandular tissue in a breast relative to fat. It can significantly vary between individuals and within individuals over a lifetime.
There are four descriptors for breast density on mammography in the 5th edition of BI-RADS 1-2:
Breast implants are increasingly common in general breast radiology practice.
Breast implants may be placed behind the glandular tissue but in front of the pectoral muscle:
The second position of breast implants ...
Breast lumps have different characteristics that allow simplification of differential diagnosis by breaking down the vast list into sections. Consider whether the lump fits into one of these categories.
Spiculation is a feature of neoplasms and all masses that display spicula...
Bridging (or fusion) of the pubic symphysis can be associated with various systemic and local causes, including 1-3:
Bronchial atresia is a developmental anomaly characterized by focal obliteration of the proximal segment of a bronchus associated with hyperinflation of the distal lung.
On imaging, it commonly presents as a proximal focal tubular shaped opacity radiating from the hilum associated with a dista...
Bronchiolectasis is a descriptive term which is given to dilatation of bronchioles, which are of smaller caliber than bronchi. It can arise of a number of pathologies.
bronchiectasis: dilatation of larger aiways
Bronchiolitis is a broad term that refers to any form of inflammation of the bronchioles. It is often used in situations where there inflammation primarily occurs in airways smaller than 2 mm 6. It can carry variable clinical, functional and morphological expression. Bronchiolar disease may be ...
Broncho-esophageal fistula (BOF) refers to abnormal communication between a bronchus and the esophagus.
For congenital fistulas, please refer to the article on congenital tracheo-esophageal fistula.
A small proportion of patient with congenital forms may present in adult...
Following are the main differentiating features of bronchopleural fistula and lung abscess on plain radiographs and CT 1:
bronchopleural fistulas have mostly lenticular shape of space
length of air fluid level in bronchopleural fistula in different projections is unequ...
Buckle rib fractures are typical of an anterior compressive force to the chest, most commonly external cardiac massage, but can be seen following any such traumatic injury.
Buckle rib fractures occur in all ages, even very elderly patients. Thus ribs are not the same as most adult lo...
Major duodenal papilla is a conic or cylindric protuberance at the medial aspect of the descending or horizontal duodenum at the site of the sphincter of Oddi. It is finding on small bowel follow-though (and endoscopy) and has a relatively long differential.
On cross sectional imaging, the unde...
Butterfly fragments are large, triangular fracture fragments seen commonly in comminuted long bone fractures. The term is commonly used in orthopedic surgery, and results from two oblique fracture lines meeting to create a large triangular or wedge-shaped fragment located between the proximal an...
CA-125 is a high-molecular-weight glycoprotein found on the surface of Mullerian and coelomic epithelial-derived cell types, and is the best known tumor marker for epithelial ovarian cancer 6. Importantly, it may also be elevated in several other conditions (see differential diagnosis section be...
CA 19-9 (carbohydrate antigen 19-9 or cancer antigen 19-9) is a serum antigen (monosialoganglioside) that has increased diagnostic use in the management of several malignancies, mainly of hepatopancreaticobiliary origin. It is non-specific, however, and can rise in both malignant and non-maligna...
Calcification of the external ear (auricular cartilage) may arise from a number of causes, including:
gout and pseudogout
Calcification of the globe has many causes, varying from the benign to malignant. When calcification is seen of the posterior half of the globe, it could relate to any of the layers (scleral, choroidal or retinal), as it is not possible to separate them out on CT.
drusen: 1% population...
Calcific axillary lymphadenopathy is in general, more concerning than axillary lymphadenopathy alone and is particularly so if it contains microcalcifications. While this is concerning for malignancy, it can also occur from occasional nonmalignant causes
metastatic axillary lymp...
In mammography, the term calcific cluster is usually given to where at least five microcalcifications in one cubic centimeter (that is 1 square cm) on two projections on a non-magnified contact view 1.
Homogeneous, smooth clustered microcalcifications can be due to 2:
There are numerous causes of calcified mediastinal lymph nodes.
Common causes include:
infectious granulomatous diseases
Uncommon causes include:
Pneumocystis jiroveci (PCP) pneumonia
thyroid carcinoma: papi...
Calcified pulmonary (lung parenchymal) densities can occur in a number of conditions.
healed varicella pneumonia 1
pulmonary alveolar microlithiasis
occupational lung diseases
coal workers pneumoconiosis
Large nodules or masses
Calcification associated with pulmonary emboli is usually associated with chronic pulmonary embolism. Calcification is occasionally related to prior congenital cardiac repairs 1.
If it is purely high attenuating, consider
polymethylmethacrylate (PMMA) embolism into the ...
Calcified pulmonary nodules are a subset of hyperdense pulmonary nodules and a group of nodules with a relatively narrow differential.
The most common cause of nodule calcification is granuloma formation, usually in the response to healed infection.
Calcifying pulmonary metastases are rare. These should not be confused with metastatic pulmonary calcification.
Calcification in metastases can arise through a variety of mechanisms: bone formation in tumors osteoid origin, calcification and ossification of tumor cartilage, dystrophi...
Calvarial thickening can occur from a number of causes. These include:
chronic ventricular shunting 1
anemias (largely associated with massive hematopoiesis)
Cancer refers to neoplasms with malignant potential, i.e. for local invasion and metastasis. This article is a list of different cancers or relevant tumor classification systems, although noting that not all tumors are cancerous. For a list of cancer staging systems, see the separate article.
Cantlie's line is a vertical plane that divides the liver into left and right lobes creating the principal plane used for hepatectomy. It extends from the inferior vena cava posteriorly to the middle of the gallbladder fossa anteriorly.
It contains the middle hepatic vein which divides the live...
The capitolunate angle is the angle between the long axis of the capitate and the mid axis of the lunate on the sagittal imaging of the wrist. In a normal situation it should be less than 30o in the resting (neutral) position.
The angle is increased in carpal instability such as with a dorsal i...
Serum carcinoembryonic antigen (CEA) is a cell-adhesive glycoprotein that was discovered in colorectal cancer in 1965, and is hence one of the oldest and most used tumor markers. Its name derives from its normal expression in fetoembryonic liver, gut and pancreas tissue.
Normal range of CEA is ...
Carcinoid tumors of the lung are a subgroup of neuroendocrine tumors of the lung, of lower grade than small cell carcinoma of the lung and large cell neuroendocrine carcinoma of the lung.
For a general discussion, please refer to the article on carcinoid tumors.
Cardiac chamber enlargement can be recognized by cardiac contour changes, new or different interfaces with adjacent lung, and/or displacement of adjacent mediastinal structures. These are discussed separately:
right atrial enlargement
right ventricular enlargement
left atrial enlargement
Implantable cardiac conduction devices (also known as cardiac implantable electronic devices or CIEDs) are a very common medical device of the thorax, with over one million implanted in the United States of America alone.
There are two major types of cardiac conduction devices: pacemakers and a...
The cardiac curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core cardiac knowledge.
Topics pertaining to the heart and pericardium, but excluding the mediastinum (see: chest curriculum) and great vessels (see: vascular curricul...
Cardiomegaly is a catch-all term to refer to enlargement of the heart, and should not be confused with causes of enlargement of the cardiomediastinal outline, or enlargement of the cardiac silhouette.
There are many etiologies for cardiomegaly:
congestive heart failure
The cardiophrenic space is usually filled with fat. However, lesions originating above or lower to the diaphragm can present as cardiophrenic angle lesions.
The more common lesions encountered include:
pericardial fat pad
pericardial fat necrosis
Cardiovascular (cardiac) shunts are abnormal connections between the pulmonary and systemic circulations. Most commonly they are the result of congenital heart disease.
Blood can either be shunted from the systemic circulation to pulmonary circulation (i.e. 'left-to-right shunt') or ...
Carotid artery stenosis also referred as extracranial carotid artery stenosis, is usually caused by an atherosclerotic process and is one of the major causes of stroke and transient ischemic attack (TIA) 1.
This article refers to stenosis involving carotid bulb and the proximal segment of inte...
Carotid pacemaker, also known as implantable carotid sinus stimulators, is a device that delivers activation energy through the carotid leads and the leads conduct activation energy to the carotid baroreceptors. This is sometimes offered for drug-resistant hypertension. The baroreceptors send si...
Carpal angle is defined by two intersecting lines, one in contact with the proximal surface of the scaphoid and the lunate and the other line through proximal margins of the the triquetrum and the lunate. Its normal value is between 130° and 137°.
It is increased in (> 139°)
The differential for cartilagenous lesions includes:
There are several important causes of an abnormal lunate signal on MRI, the most frequent causes being Kienbock disease (25%), ulnar impaction syndrome (25%) and intraosseous ganglia (20%).1 Appreciation of the pattern of bone signal change can often allow the correct diagnosis to be made.
There are relatively few causes of calcification of the ascending aorta 1-3:
atherosclerosis (this usually spares the ascending aorta)
Causes of a small aorta include:
giant cell arteritis
small aorta syndrome
A cavernous sinus mass has a wide differential including:
orbital apical inflammation with cavernous sinus involvement (Tolosa-Hunt syndrome)
any of the cranial nerves traversing the cavernous sinus: III, IV, V (V1 and V2) and VI
trigeminal schwannoma is ...
Cavitating pneumonia is a complication that can occur with a severe necrotizing pneumonia and in some publications it is used synonymously with the latter term 2. It is a rare complication in both children and adults.
Cavitation associated with Mycobacterium tuberculosis is separately discusse...
Cavitating pulmonary metastases refer to pulmonary metastases which then tend to cavitate. The term is similar but may not be identical to cystic pulmonary metastases in which the wall of the former may be thicker.
Cavitation is thought to occur in around 4% of lung metastases 2.
Distribution of bronchiectasis can help in narrowing the differential diagnosis. Central bronchiectasis is typically seen in:
allergic bronchopulmonary aspergillosis (ABPA)
congenital tracheobronchomegaly (a.k.a. Mounier Kuhn syndrome)
Williams Campbell syndrome (rare)
The central nervous system curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core central nervous system knowledge.
Topics pertaining to the intracranial content (brain, pituitary, dura, intracranial vasculatures). There will be...
Centrilobular lung nodules refer to an HRCT chest imaging descriptor for small 5-10 mm lung nodules which are anatomically located centrally within secondary pulmonary lobules. The term is applied on the basis of location of the nodule and not its morphology that is they may be well defined or p...
Cerebellopontine angle (CPA) masses are relatively common. Although a diverse range of pathologies may be seen in this region, the most common by far is an acoustic schwannoma.
Cerebellopontine angle masses can be divided into four groups, based on imaging characteristics:
Cerebral arteriovenous fistulae (CAVF) are cerebral vascular malformations or acquired conditions in which there is an abnormal direct communication between a venous and an arterial channel without the presence of a true nidus.
dural arteriovenous fistula (DAVF)
caroticocavernous fistula (CCF...
Cerebral atrophy is the morphological presentation of brain parenchymal volume loss that is frequently seen on cross sectional imaging. Rather than being a primary diagnosis, it is the common endpoint for range disease processes that affect the central nervous system. Though often no identifiabl...
Cerebral herniation, also referred to as acquired intracranial herniation, refers to shift of cerebral tissue from its normal location, into an adjacent space as a result of mass effect.
There are a number of different patterns of cerebral herniation which describe the type of herni...
The differential for peripheral or ring enhancing cerebral lesions includes:
demyelination (incomplete ring)
tumefactive demyelinating lesion (incomplete ring)
Vascular malformations of the central nervous system can be divided, as they can elsewhere, into high and low flow malformations.
arteriovenous malformation (AVM)
cerebral AVM (pial/parenchymal AVM)
cerebral proliferative angiopathy
dural arteriovenous fistula (DAVF)
Cervical incompetence refers to a painless spontaneous dilatation of the cervix and is a common cause of second trimester pregnancy failure.
The estimated incidence varies geographically and generally thought to be around 1-1.5% of all pregnancies 1,15.
Cervical spine fractures can occur secondary to exaggerated flexion or extension, or because of direct trauma or axial loading.
The cervical spine is susceptible to injury because it is highly mobile with relatively small vertebral bodies and supports the head which is both heavy and...
Cervical spine injuries can involve the cervical vertebral column, intervertebral discs and cervical spine ligaments, and/or cervical spinal cord. The cervical spine accounts for ~50% of all spinal injuries.
5-10% of patients with blunt trauma have a cervical spine injury 1.
Chamberlain line is a line joining the back of hard palate with the opisthion on a lateral view of the craniocervical junction.
It helps to recognize basilar invagination which is said to be present if the tip of the dens is >3 mm above this line.
McGregor developed a modificatio...
Chance fractures, also referred to as seatbelt fractures, are flexion-distraction type injuries of the spine that extend to involve all three spinal columns. These are unstable injuries and have a high association with intra-abdominal injuries.
They tend to occur from a fl...
Chasing the dragon sign is seen in toxic leukoencephalopathy caused by the inhalation of heroin fumes.
Three stages are recognized:
cerebellar signs and motor restlessness
pyramidal and pseudobulbar signs
spasms, hypotonic paresis, and ultimately death
Only a minorit...
Unfortunately the pediatric population is susceptible to malignancies. The most common entities, in overall order of frequency, are 1-4:
leukemia/lymphoma: ~35% *
acute lymphoblastic leukemia: 23%
Hodgkin disease: 5%
acute myelogenous leukemia: 4%
central nervous system malignancies: ~20%
Cholangitis is a relatively broad descriptive term term referring to inflammation of the bile ducts.
It has many forms and can arise from a number of situations:
primary sclerosing cholangitis
chemotherapy induced cholangitis
eosinophilic cholangitis 5
Chondrocalcinosis is a descriptive term indicating the presence of gross calcium deposition within articular cartilage, i.e. both hyaline and fibrocartilage.
Chondrocalcinosis articularis was an early term for calcium pyrophosphate dihydrate deposition disease (CPPD) 5, which may e...
Chorioretinitis refers to inflammation of the retina and choroid. As a delayed sequelae, it is one of the causes of calcification of the globe. It is often considered a form of posterior uveitis.
various congenital infections such as 2,3
rubella: ocular rubella
There are many signs in radiology that are related to Christmas:
snowcap sign in avascular necrosis
in total anomalous pulmonary venous return
in pituitary macroadenomas
snowstorm appearance in complete hydatidiform and testicular microlithiasis
holly leaf sign in calcified pl...
Chronic bilateral airspace opacification is a subset of the differential diagnosis for airspace opacification. An exhaustive list of all possible causes of chronic bilateral airspace opacities is long, but a useful framework is as follows:
granulomatosis with polyangi...
There are several viral and prion infections which can result in a chronic encephalitis with slow progression into brain atrophy. These have a very poor prognosis with no effective treatment.
Some of these include:
progressive multifocal leukoencephalitis
subacute sclerosing panencephalitis