B value measures the degree of diffusion weighting applied, thereby indicating the amplitude (G), time of applied gradients (δ) and duration between the paired gradients (Δ) and is calculated as:
b = γ² G² δ² (Δ−δ/3)
Therefore, a larger b value is achieved by increasing the gradient amplitude ...
The Bo in MRI refers to the main magnetic field and is measured in Tesla. The majority of MRI systems in clinical use are between 1.5T and 3T.
Altering the field strength will affect the Larmour frequency at which the protons precess.
1.5T vs 3T
Baastrup syndrome (also referred to as kissing spines) results from adjacent spinous processes in the lumbar spine rubbing against each other and resulting in hypertrophy and sclerosis with focal midline pain and tenderness relieved by flexion and aggravated by extension.
Bacillary angiomatosis is an infective complication in those with the acquired immunodeficiency syndrome (AIDS) 3. Amongst other widespread multi-organ manifestations, the infection causes skin lesions which can be similar to those of Kaposi sarcoma.
Characterised by a non-neoplastic...
Backwash ileitis is seen in patients with ulcerative colitis (UC), where the entire colon is involved. In such cases the terminal ileum is oedematous.
Backwash ileitis extends contiguously backward from the cecum without skip regions. One source estimates it to occur in 6% of patients with UC, ...
The Bado classification is one of the more widely used classifications for Monteggia fracture-dislocations, and mainly focuses on the radial component. Four types are recognised and are generally based on the principle that the direction in which the apex of the ulnar fracture points is the same...
This classification was initially proposed by Bailey in 1929 2 and remains the most widely used classification system at time of writing (July 2016).
Bailey classification of second branchial cleft cysts provides a structure for classing second branchial cleft cysts into four types. It is no lo...
Baker cysts (or popliteal cysts) are fluid-filled distended synovial-lined bursa arising in the popliteal fossa between the medial head of the gastrocnemius and the semimembranosus tendons via a communication with the knee joint. They are usually located at or below the joint line.
The Balint syndrome is characterised by:
simultanagnosia (inability to perceive more than one object at a time)
It typically results from damage to the parieto-occipital regions, and has been associated with 1-3:
posterior cortical ...
Balkan nephropathy refers to a degenerative interstitial nephropathy endemic to the Balkan states, which is associated with a very high rate of transitional cell carcinomas of the renal pelvis and upper ureter.
The condition is largely restricted to the villages along the Danube ...
A ball and socket ankle joint is a variant affecting the ankle where there is a rounded or spherical configuration to talar dome with the corresponding concavity of the tibial plafond. The distal fibula may or may not be involved.
The aetiology has been debated with two theories prop...
Ball and socket joints are a type of synovial joint where the spheroid articular surface of one bone sits within a cup-like depression of another bone.
The ball and socket configuration allows for movement with 3 degrees of freedom, which is more than any other type of synovial joint...
The ball of wool sign, also referred to as the yarn sign or congealed water lily sign, is an ultrasound appearance, representing degeneration of hydatid cysts (WHO class CE 4). The inner side of cyst detaches from the cyst wall and folds on itself, causing a change from anechoic (fluid) to a sol...
The Ballet sign refers paralysis of voluntary movements of the eyeball with preservation of the automatic movements. Sometimes this sign is present with exophthalmic goitre and hysteria.
Balloon breast brachytherapy (BBB) is a technique for delivering radiation treatment in women with early stage breast cancer. It is given after lumpectomy, or surgical removal of a small breast cancer and is a short alternative to the more traditional method of using seven weeks of external beam...
The balloon on a string sign refers to the appearance of the ureter on intravenous urography in ureteropelvic junction obstruction. It is seen due to the high and eccentric point of exit of ureter from a dilated renal pelvis.
Balo concentric sclerosis (BCS) is a rare and severe monophasic demyelinating disease, considered a subtype of multiple sclerosis, appearing as a rounded lesion with alternating layers of hyper and hypoattenuation giving it a characteristic 'bullseye' or 'onion bulb' appearance 1,9.
BALT lymphoma is an abbreviated term for bronchus-associated lymphoid tissue lymphoma. These neoplasms fall under the broader umbrella of mucosa associated lymphoid tissue (MALT) lymphomas. It is sometimes considered a type of primary pulmonary lymphoma.
Up to half of pat...
The Balthazar score is a subscore within the CT severity index (CTSI) for grading of acute pancreatitis.
The CTSI sums two scores:
Balthazar score: grading of pancreatitis (A-E)
grading the extent of pancreatic necrosis
The Balthazar score was originally used alone, but the addition of a sc...
Bamboo spine is a radiographic feature seen in ankylosing spondylitis that occurs as a result of vertebral body fusion by marginal syndesmophytes. It is often accompanied by fusion of the posterior vertebral elements as well.
A bamboo spine typically involves the thoracolumbar and or lumbosacr...
A banana fracture refers to a complete, horizontally oriented pathological fracture seen in deformed bones affected by Paget disease. This term is often used to describe incremental fractures that occur in Paget disease as well, which represent a type of insufficiency fracture.
The former of th...
The banana sign is one of the many notable fruit inspired signs.
It is seen on axial imaging through the posterior fossa of fetus and is associated with the Chiari II malformation. It describes the way the cerebellum is wrapped tightly around the brain stem as a result of spinal cord tethering ...
Band heterotopia, also known as double cortex syndrome, is a form of diffuse grey matter heterotopia affecting almost only women. Refractory epilepsy is present in nearly all affected patients, with partial complex and atypical absence epilepsy being the most common syndromes.
On imaging, this ...
The band of Giacomini, also known as the tail of the dentate gyrus is the anteromedial continuation of the dentate gyrus, which in turn is part of the hippocampal formation, along with the hippocampus, subicular complex and entorhinal cortex. It is an important anatomical landmark of the inferio...
A Bandl ring may be seen during imaging of a patient in labour.
It is considered to be an uncommon finding in modern obstetrics (0.01-1.26%).
It is a pathologic retraction ring at "Barnes boundary line", which separates the upper contractile portion of the uterus from ...
Bankart lesions are a common complication of anterior shoulder dislocation and are frequently seen in association with a Hill-Sachs lesion.
They result from detachment of the anterior inferior labrum from the underlying glenoid as a direct result of the anteriorly dislocated humeral ...
Bannayan-Zonana syndrome is a rare hamartomatous disorder.
Inheritance is by autosomal dominant transmission with few reported sporadic cases. Male predominance is also reported.1
Bannayan-Zonana syndrome characterized by :
Bannayan–Riley–Ruvalcaba syndrome (BRRS or BRR syndrome) is a very rare autosomal dominant hamartomatous disorder caused by a mutation in the PTEN gene. It is considered in the family of hamartomatous polyposis syndrome.
There are no formal diagnostic criteria for this disease, but characterist...
Bardet-Biedl syndrome (BBS), previously known as the Laurence-Moon-Bardet-Biedl syndrome (LMBBS), is a rare autosomal recessive hereditary condition.
The clinical spectrum includes:
retinal anomalies: similar to that of retinitis pigmentosa
Bare orbit sign, is described as a characteristic appearance of orbit, where the innominate line is absent. The innominate line is a projection of the greater wing of the sphenoid, and its absence or destruction is responsible for this appearance.
It is the classical frontal radiograph sign of ...
Bariatric intragastric balloon therapy is a relatively new form of bariatric surgery, which involves balloons being inflated inside the lumen of the stomach. The balloons reside in the stomach and the mechanism of action is presumably due to stretching the stomach, inducing postprandial fullness...
Barium peritonitis is a rare complication of gastrointestinal fluoroscopy, and occurs when there is gastrointestinal tract perforation and spillage of barium into the peritoneal cavity.
Barium in the peritoneal cavity is treated as a foreign body with resultant immune response that ...
Barium studies of the small intestine are still considered an effective modality to show the bowel loops in a cost-effective way.
Small bowel follow through (SBFT) or transit study
routine investigation for delineation of all parts the small bowel
done with barium meal after havin...
Barium swallow is a dedicated test of the pharynx, oesophagus, and proximal stomach, and may be performed as a single or double contrast study. The study is often "modified" to suit the history and symptoms of the individual patient, but it is often useful to evaluate the entire pathway from the...
Barkovich classifies focal cortical dysplasias among the his extensive classification system for malformations of cortical development, distributing them as follows:
Type I and type IIb (transcortical dysplasia - Taylor type with balloon cells) as non-neoplastic malformations due to abnormal ne...
Barrett oesophagus is a term for intestinal metaplasia of the oesophagus. It is considered the precursor lesion for oesophageal adenocarcinoma.
Barrett oesophagus is thought to have a prevalence of 3-15% in patients with reflux oesophagitis. Mean age at diagnosis is 55 years old 5...
Barrow caroticocavernous fistula classification divides caroticocavernous fistulas into direct (type A) or indirect (types B-D). This classification was proposed by Barrow et al. in 1985 1 and at the time of writing (mid 2016) remains the most widely used system for describing caroticocavernous ...
Barth syndrome (BTHS), also referred to as 3-methylglutaconic aciduria type II is an extremely rare X-linked multi-system disorder that is usually diagnosed in infancy.
It is characterised by:
fetal cardiomyopathy: (dilated fetal cardiomyopathy (DCM) +/- endocardial fibroelastosis (EFE) +/- le...
Bartholin gland abscess is a complication that may result from an infected Bartholin gland cyst.
Abscesses are usually in a similar location to Bartholin gland cysts. Features of Bartholin gland abscess are otherwise similar to Bartholin gland cyst described in separate ...
Bartholin gland cysts are located in the postero-lateral inferior third of the vagina and are associated with the labia majora.
Most patients are asymptomatic 4.
Cysts form as a result of an obstruction of the gland's duct by a stone/ stenosis related to prio...
Bartholin gland tumours include:
squamous cell carcinoma of the Bartholin gland: tends to be the most common histological subtype
adenocarcinoma of the Bartholin gland
adenoid cystic carcinoma of the Bartholin gland
Barton fractures are fractures of the distal radius. It is also sometimes termed the dorsal type Barton fracture to distinguish it from the volar type or reverse Barton fracture.
Barton fractures extend through the dorsal aspect to the articular surface but not to the volar aspect. Therefore, i...
Bartter syndrome is a rare inherited renal disorder.
Bartter syndrome is characterised by hyperplasia of the juxtaglomerular cells along with:
hypotension or normotension
elevated plasma renin
The basal ganglia are a group of nuclei in the brain that is interconnected with the cerebral cortex, thalami and brainstem.
In a strict anatomical sense it contains three paired nuclei:
putamen (together with the caudate nucleus and globus pallidus known as corpus striatum)
Basal ganglia calcification is common and is seen in approximately 1% of all CT scans of the brain, depending on the demographics of the scanned population. It is seen more frequently in older patients and is considered a normal incidental and idiopathic finding in an elderly patient but should ...
Basal ganglia haemorrhage is a common form of intracerebral haemorrhage, and usually as a result of poorly controlled long-standing hypertension. The stigmata of chronic hypertensive encephalopathy are often present (see cerebral microhaemorrhages).
Other sites of hypertensive haemorrhages are ...
Basal ganglia signal abnormalities on MRI occur in a wide variety of conditions and are best thought of in terms of the specific signal abnormality. As such they are discussed separately.
increased T2 signal in the basal ganglia
decreased T2 signal in the basal ganglia
increased T1 signal in...
There are many causes of basal ganglia T1 hyperintensity, but the majority relate to deposition of T1-intense elements within the basal ganglia such as:
calcium and phosphate abnormalities
acquired non-wilsonian hepatocerebral degeneration
Hypointensity on T1 weighted images of the basal ganglia, as a general rule is in itself of limited value, and should be correlated with T2 signal, which is usually more informative. Most causes of T2 hyperintensity in the basal ganglia will result in T1 hypointensity (most are afterall due to o...
The causes of basal ganglia T2 hyperintensity can be remembered using the mnemonic LINT:
venous infarction (internal cerebral vein thrombosis)
neurodegenerative / metabolic
Huntington disease: especially caudate heads
Basal ganglia T2 hypointensities can be caused by any of the following and is commonly remembered using the mnemonic ChOMP.
Parkinson disease: more in globus pallidus
Parkinson-plus syndrome: more in putamen
deoxyhemoglobin of hemorrhage
The basal nucleus of Meynert, also known as the nucleus basalis of Meynert, is formed by a group of cells that lies in the substantia innominata. It is rich in acetylcholine and its degeneration has been correlated to Alzheimer disease. It lies anterior to the anterior commissure.
The basal veins, also known as the veins of Rosenthal, are paired, paramedian veins which originate on the medial surface of the temporal lobe and run posteriorly and medially. It passes lateral to the midbrain through the ambient cistern to drain into the vein of Galen with the internal cerebra...
The base of the skull (or skull base) forms the floor of the cranial cavity and separates the brain from the structures of neck and face.
The base of the skull is a bony diaphragm composed of a number of bones including (from anterior to posterior):
Basic factual questions are one of the three types of multiple choice questions on Radiopaedia, the other two being knowledge integration and image interpretation.
Factual questions relate to a single item of factual knowledge, with or without an image. They draw from a single area of knowledg...
The basilar artery is part of the posterior cerebral circulation. It artery arises from the confluence of the left and right vertebral arteries at the base of the pons as they rise towards the base of the brain.
origin: vertebral artery confluence
course: ventral to pons in the pontin...
Basilar artery fenestration (or more simply, basilar fenestration) is the most common intracranial arterial fenestration. It refers to duplication of a portion of the artery. Its reported is highly variable depending on the technique used:
~0.5% (0.3-0.6%) at angiography (presumably low due to ...
Basilar artery hypoplasia is a rare vascular anomaly of the basilar artery.
Basilar artery hypoplasia is usually accompanied by one or more fo the following:
persistent carotid-vertebrobasilar anastomoses
hypoplastic V4 segments of the vertebral arteries
Basilar invagination, also called basilar impression, is a congenital or acquired craniocervical junction abnormality where the tip of the odontoid process projects above the foramen magnum.
The terms basilar invagination and basilar impression are often used interchangeably becau...
A mnemonic to help recall the cases of basilar invagination is:
P: Paget disease of bone
F: fibrous dysplasia
R: rheumatoid arthritis, rickets
O: osteogenesis imperfecta, osteomalacia
C: Chiari I and Chiari II, cleidocranial dysostosis
The basilar venous plexus lies between the endosteal and visceral layers of the dura on the inner surface of the clivus. It connects the:
inferior petrosal sinuses
superior petrosal sinuses
internal vertebral venous plexus
marginal sinus (around the...
The basion is the median (midline) point of the anterior margin of the foramen magnum.
It is one of the skull landmarks, craniometric points for radiological or anthropological skull measurement.
Various lines and measurements using the basion are made in the diagnosis of ...
The basion-axial interval (BAI), as the name suggests, is the horizontal distance between the basion and the posterior cortex of the axis, used in the diagnosis of atlanto-occipital dissociation injuries.
It is the distance (in mm) between the basion and the superior extension of the posterior ...
The basion-dens interval (BDI), as the name suggests, is the distance between the basion and the tip of the dens, used in the diagnosis of atlanto-occipital dissociation injuries.
It is the distance from the most inferior portion of the basion to the closest point of the superior aspect of the ...
Bat wing 4th ventricle sign refers to the morphology of the fourth ventricle in the Joubert anomaly and related syndromes. The absence of a vermis with apposed cerebellar hemispheres give the fourth ventricle an appearance reminiscent of a bat with its wings outstretched.
It is best demonstrate...
Bat's wing or butterfly pulmonary opacities refer to a pattern of bilateral perihilar shadowing. It is classically described on a frontal chest radiograph but can also refer to appearances on chest CT 3-4.
Bat's wing pulmonary opacities can be caused by:
Batson venous plexus (Batson veins) is a network of veins with no valves that connect deep pelvic veins draining the bladder, prostate and rectum to the internal vertebral venous plexus 1. These veins are important because they are believed to provide a route for spread of pelvic cancer metastas...
Baumann angle, also known as the humeral-capitellar angle, is used for the evaluation of the displacement of paediatric supracondylar humeral fractures. It is measured on a frontal radiograph, with elbow in extension.
This angle is formed by the humeral axis and a straight line through the ep...
Baxter neuropathy is a nerve entrapment syndrome resulting from the compression of the inferior calcaneal nerve (Baxter nerve).
The inferior calcaneal nerve is the first branch of the lateral plantar nerve which courses in a medial to lateral direction between the abductor hallucis muscle and t...
Bayonet deformity is a term used to describe the shape of wrist in certain conditions:
hereditary multiple exostosis with pseudo-Madelung deformity
retarded bone growth of the distal ulna with outward bowing of radius with distal radioulnar joint subluxation
BCGosis is a rare granulomatous disease following intravesical Bacillus Calmette-Guerin immunotherapy used in the treatment of superficial transitional cell carcinoma of the urinary bladder.
It manifests as a miliary pattern best seen in the lungs.
The beak sign of arterial dissection represents a wedge of haematoma at the distal end of the false lumen. It is here that false lumen propagation is occurring. It manifests as an acute angle between the dissection flap and the outer wall. It may be filled with contrast enhanced blood (high atte...
Beak sign in pyloric stenosis is one of the fluoroscopic (barium meal) findings which is useful in the diagnosis of congenital hypertrophic pyloric stenosis.
A beak-like tapering projection of barium is seen entering into the narrowed and compressed pyloric ...
Beals syndrome is a rare connective tissue disorder that has some resemblance to the Marfan syndrome. Affected individuals have arachnodactily, contractures and ear anomalies but without any ocular or cardiac anomalies.
Beam collimators are 'beam direction' devices used in the X-ray tube housing, along with an arrangement of mirrors and lights, in such a way that the light and X-ray fields match each other. They are made of lead shutters which completely absorb the photons, and thus reduce the patient dose as w...
Beam hardening is observed when an X-ray beam comprised of polychromatic energies passes through an object and becomes ‘harder’ where the lower energy photons will be absorbed leaving only the higher energy photons 1.
The resultant artifact has two distinct appearances, streaking or dark bands ...
Ultrasound beam width artifact occurs when a reflective object located beyond the widened ultrasound beam, after the focal zone, creates false detectable echoes that are displayed as overlapping the structure of interest.
To understand this artifact, it is important to remember that the ultraso...
The bear paw sign is seen in xanthogranulomatous pyelonephritis and refers to the cross-sectional appearance of the kidney which is said to resemble the paw of a bear. The renal pelvis is contracted whereas the calyces are dilated, mimicking the toe-pads of the paw.
Beaver tail liver, also known as a sliver of liver, is a variant of hepatic morphology where an elongated left liver lobe extends laterally to contact and often surround the spleen. The parenchyma is normal and thereby has the same risks of hepatic pathology as the rest of the liver except theor...
Beck triad is a collection of three clinical signs associated with pericardial tamponade which is due to excess accumulation of fluid within the pericardial sac. The three signs are:
low blood pressure (weak pulse or narrow pulse pressure)
muffled heart sounds
raised jugular venous pressure ...
Beckwith-Wiedemann syndrome (BWS) is a congenital overgrowth disorder characterised by unique set features that can consist of:
macroglossia: most common clinical finding 4
otic dysplasia ref
localised gigantism / macrosomia
pancreatic islet ...
A mnemonic used to remember the behavioural changes of obstructive sleep apnoea (OSA) is:
P: poor school performance
L: lack of concentration
Behavioural variant frontotemporal lobar degeneration (bvFTLD), also known as behavioural variant frontotemporal dementia, is one of the clinical neurodegenerative diseases associated with frontotemporal lobar degeneration (FTLD).
In the older literature, it is also referred to as Pick disease...
Behçet disease is a multi-systemic and chronic inflammatory vasculitis of unknown aetiology.
The mean age at which Behçet disease occurs is 20-30 years. The disease is most prevalent in the Mediterranean region, Middle East and East Asia. The highest incidence has been reported in...
CNS manifestations of Behçet disease, also known as neuro-Behçet disease, corresponds to the neurological involvement of the systemic vasculitis Behçet disease and has a variety of manifestations.
For a discussion of the disease in general please refer to Behçet disease article.
Thoracic manifestations in Behçet disease have a wide spectrum of appearances.
The reported prevalence of thoracic involvement of Behçet disease is thought to range around 1-8% 2.
CT - HRCT chest
CT can demonstrate the entire spectrum of thoracic manifest...
A bell clapper deformity is a predisposing factor in testicular torsion in which the tunica vaginalis joins high on the spermatic cord, leaving the testis free to rotate. Bell clapper deformity predisposes to intravaginal torsion of the testis.
Bell palsy, also known as idiopathic peripheral facial paralysis, is characterised by rapid onset facial nerve paralysis, often with resolution in 6-8 weeks. As there are numerous causes of facial nerve palsy, many of which can be acute in onset, it is currently a diagnosis of exclusion supporte...
Benedikt syndrome, or paramedian midbrain syndrome, is a midbrain stroke syndrome that involves the fascicles of the oculomotor nerve and the red nucleus resulting in an ipsilateral CN III palsy and crossed hemiataxia and chorea 2.
Using imaging alone, it is difficult to distinguish Benedikt fr...
Benign and malignant characteristics of breast lesions at ultrasound allow the classification as either malignant, intermediate or benign based on work published by Stavros et al in 1995.
Malignant characteristics (with positive predictive values)
Benign enlargement of the subarachnoid spaces in infancy (BESS or BESSI) also known as benign external hydrocephalus (BEH), is as the name implies, a benign enlargement of subarachnoid spaces seen in infancy. It usually involves the frontal lobe subarachnoid spaces, and it is characterised clini...
Benign fibrous histiocytoma is closely related to fibroxanthoma of bone, is a rare lesion usually occurring in the skin where it is known as dermatofibroma.
Typically presents with pain, and most often in the third decade.
Only a few case reports have been pub...
Paediatric benign liver tumours are a relatively rare, but important group of conditions. Importantly, the commonest cause of a benign liver tumour is specific to the paediatric population. The list in descending order of frequency is:
mesenchymal hamartoma of t...