Ascending transtentorial herniation is a situation where space occupying lesions in the posterior cranial fossa cause superior displacement of superior parts of the cerebellum through the tentorial notch.
nausea and/or vomiting
rapid progression toward decreased level ...
Ascites is defined as an abnormal amount of intraperitoneal fluid.
Patients with a large volume of ascites can present with abdominal distension (which may be painful), nausea, vomiting, dyspnoea and peripheral oedema 7, 9.
Ascitic fluid is traditionally chara...
Aseptic loosening is considered relatively common complication of hip joint replacements. It is usually considered a long-term complication and is often considered as the most common complication 3.
Aseptic loosening can occur as a result of inadequate initial fixation, mechanical lo...
Asherman syndrome, also known as uterine synechiae, is a condition characterised by the formation of intrauterine adhesions, which are usually sequela from injury to the endometrium, and is often associated with infertility.
There is a tendency for the condition to develop soon af...
The American Spinal Injury Association (ASIA) was developed by the American Spinal Injury Association in 2006, and at the time of writing (July 2016), remains the most widely used scale.
This scale is part of the ASIA spinal cord injury classification. It divides spinal cord injuries into 5 cat...
The original description of the Askin tumour (by Askin and Rosai in 1979 1), and many studies following it have led to a great deal of confusion. Until recently it has been considered a separate entity or as a type of peripheral primitive neuroectodermal tumour, usually of the chest wall.
Aspergillomas are mass-like fungus balls that are typically composed of Aspergillus fumigatus, and are a non-invasive form of pulmonary aspergillosis.
Although the term mycetoma is frequently used to describe these fungal balls, it is an incorrect term to use 5-6.
Aspergillus is a fungal genus consisting of approximately 180 species. It is a ubiquitous fungus found frequently in urban areas especially in decomposing organic matter or water damaged walls and ceilings. Only a few Aspergillus species are associated with human disease.
Aspergillus clavatus is one of the species of Aspergillus that can cause pathology in humans. It is allergenic and causes a hypersensitivity pneumonitis called malt-workers lung.
Aspergillus flavus is a fungus and one of the species of Aspergillus that is common in the environment and responsible for pathology in humans.
It is the second most common cause of pulmonary aspergillosis (after Aspergillus fumigatus) and can additionally cause corneal, otomycotic, and nasoorb...
Aspergillus fumigatus is a fungus of the genus Aspergillus, and is one of the most common Aspergillus species to cause disease in immuno-compromised individuals.
A. fumigatus is a saprotroph (an organism that gets its energy from non-living organic matter) that is widespread in nature, typicall...
Asphyxiating thoracic dysplasia, also known as Jeune syndrome, is a type of rare short limb skeletal dysplasia, which is primarily characterised by a constricted long narrow thoracic cavity, cystic renal dysplasia and characteristic skeletal features. It is also sometimes classified as one of th...
Aspiration bronchiolitis, or diffuse aspiration bronchiolitis, is a condition characterised by a chronic inflammation of bronchioles caused by recurrent aspiration of foreign particles.
The onset of aspiration bronchiolitis can be more insidious than aspiration pneumonia,...
Aspiration pneumonia is caused by a direct chemical insult due to the entry of a foreign substance, solid or liquid, into the respiratory tract.
Aspiration may be clinically silent, or it may present with dyspnoea, cough, or fever. The clinical and radiographic features d...
Asplenia refers to absence of the spleen thereby leading to deficient splenic function.
Seen in 3% of neonates with structural heart disease and in 30% of patients who die from cardiac malposition. The male-to-female ratio is 2:1.
Asplenia can be classified into two t...
Asplenia syndrome (also known as right isomerism or Ivemark syndrome) is a type of heterotaxy syndrome.
There is an increased male predilection. Asplenia syndrome is usually diagnosed in neonates.4
In contrast to polysplenia syndrome, most patients die bef...
Assessment of thyroid lesions is commonly encountered in radiological practice.
hyperplastic / colloid nodule / nodular hyperplasia: 85%
papillary: 60-80% of carcinomas
Ultrasound along with nuclear medicine, is an important modality for assessment of thyroid lesions, and it is also frequently used to guide biopsy. Diagnostic criteria for thyroid nodules continue to evolve with improving ultrasound technology.
The asterion is the junction on the side of the posteroinferior calvarium where three sutures meet:
It is located at the posterior end of the parietotemporal suture, whereas the pterion is located at the anterior end.
It is one of...
Asteroid hyalosis is a degenerative condition of the eye where there is accumulation of calcium soaps in vitreous chamber.
The prevalence increases with age from 0.2% 43-54 year olds to 2.9% in 75-86 year olds. The overall prevalence is 1.2%. It is more commonly unilateral and fav...
Asthma is a relatively common condition that is characterised by at least partially reversible inflammation of the airways and reversible airway obstruction due to airway hyper-reactivity. It can be acute, subacute or chronic.
Asthma is one of the most common chronic diseases in t...
Asthma is a heterogeneous disease, usually characterised by chronic airway inflammation and airway hyperreactivity. It is defined by two main features 1:
a history of respiratory symptoms such as wheeze, shortness of breath, chest tightness and cough that vary over time and in intensity, AND
Asthmatic pulmonary eosinophilia is a form of pulmonary eosinophilia which is commonly attributed to Aspergillus fumigatus. Although many cases have not shown any allergen.
Plain radiograph - patterns
hyperinflation (in acute attacks or chronic severe asthma)
Astroblastomas are rare glial tumours usually found in the cerebral hemispheres of young adults and children.
They occur at all ages range from early childhood to 6th decade but are most commonly seen in children, adolescents, and young adults with a mean age between 10-30 years ...
Astrocytes are cells of the central nervous system which act as both physical and physiological support for the neurones that are embedded between them. They are particularly abundant in the grey matter, where they are the most abundant glial cells 1.
They are highly branched and contribute to ...
Astrocytic tumours are primary central nervous system tumours that either arises from astrocytes or appear similar to astrocytes on histology having arisen from precursor cells. They are the most common tumours arising from glial cells.
They can be divided into those that are diffuse in growth ...
Asymmetric pneumatisation of petrous apex results in asymmetric fatty bone marrow within the petrous apex. It is a common incidental finding on brain and skull base MRI.
Asymmetric pneumatisation of the petrous apex results in the presence of bon...
Asymmetric ventriculomegaly, interhemispheric cyst and dysgenesis of the corpus callosum (AVID) is a triad of congenital cerebral anomalies.
markedly asymmetric enlargement of the lateral ventricles may be the initial finding on routine fetal morphology ultrasound.
Asymmetrical mammographic density is a mammographic morphological descriptor. It is given when there is increased density in one of the breasts, on either one or both standard mammographic views but without evidence of a discrete mass. An asymmetrical density can be further characterised as:
Asymmetrical intrauterine growth restriction is a type of intrauterine growth restriction (IUGR) where some fetal biometric parameters are disproportionately lower than others, as well as falling under the 10th percentile. The parameter classically affected is the abdominal circumference (AC).
Asymmetrically large jugular bulbs are entirely normal and asymptomatic; its only significance is to distinguish it from pathology.
The size of the jugular bulbs is variable, with the right side being significantly larger than the left in two-thirds of people.
A normal but large bulb will have...
Asymmetry in breast size can arise from a number of factors.
Breasts are rarely absolutely the same size or volume. Normal variation is common. Most females have slight discrepancies in breast size. Asymmetric progressive breast enlargement is unusual but known. The role of the breas...
The American Thyroid Association (ATA) guidelines for assessment of thyroid nodules are meant to improve inter- and intra-reader consistency during assessment of thyroid nodules on ultrasound, and to facilitate communication with referring endocrinologists.
The 2015 guidelines stress the import...
Ataxia telangiectasia is a rare multisystem disorder which carries an autosomal recessive inheritance, sometimes classified as a phakomatosis. It is characterised by multiple telangiectasias, cerebellar ataxia, pulmonary infections and immunodeficiency.
On brain imaging, it usually demonstrate...
Atelectasis describes loss of lung volume secondary to collapse. It has many causes, the root of which is bronchial obstruction with absorption of distal gas. Atelectasis may be subsegmental, segmental, lobar, or involve and entire lung.
This is a summary article; read more ...
Atelencephaly (also termed atelencephalic microcephaly) is a rare and extreme disorder with only a handful of published cases. In this anomaly, the derivatives of the telencephalon are absent or dysplastic, while more caudal structures are normal or mildly deformed. It falls under the aprosencep...
Atelosteogenesis (AO) refers to a group of lethal skeletal dysplasias.
atelosteogenesis type I
atelosteogenesis type II
atelosteogenesis type III 4
Athletic pubalgia refers to pain around the pubic symphysis and can have different causes, including what has become known as sports hernia or sportman's hernia and osteitis pubis.
Athletic pubalgia is a clinical syndrome of chronic lower pelvic and groin pain, usually encountered in athletes. ...
The atlanto-axial articulation is a complex of three synovial joints, which join the atlas (C1) to the axis (C2).
paired lateral atlanto-axial joints: classified as planar-type joint between the lateral masses of C1 and C2, though somewhat more complex in shape wit...
Atlanto-axial subluxation is a disorder of C1-C2 causing impairment in rotation of the neck. The anterior facet of C1 is fixed on the facet of C2. It may be associated with dislocation of the lateral mass of C1 on C2.
Down syndrome (20%)
The atlanto-occipital articulation is comprised of a pair of condyloid synovial joints that connect the occiput (C0) to the first cervical vertebra (atlas/C1).
Each joint is comprised of two concave articular surfaces on the superior aspect of the lateral mass of a...
Atlanto-occipital assimilation is the fusion of the atlas (C1) to the occiput and is one of the transitional vertebrae.
Atlanto-occipital assimilation occurs in ~0.5% (range 0.25-1%) of the population 2-4.
Atlanto-occipital is typically asymptomatic but s...
Atlanto-occipital dissociation (AOD) injuries are severe and include both atlanto-occipital dislocations and atlanto-occipital subluxations.
The tectorial membrane and alar ligaments provide the most stability to the atlanto-occipital joint, and injury to these ligaments results in i...
The atlantodental interval (ADI), as the name suggests, is the horizontal distance between the anterior arch of the atlas and the dens of the axis, used in the diagnosis of atlanto-occipital dissociation injuries and injuries of the atlas and axis.
It is the distance (in mm) between the posteri...
The atlas is the first cervical vertebra, commonly called C1. It is an atypical cervical vertebra with unique features. It articulates with the dens of the axis and the occiput, respectively allowing rotation of the head, and flexion, extension and lateral flexion of the head. Unlike the rest o...
The atoll sign in radiology can refer to:
reverse halo sign (atoll in thoracic CT)
atoll sign in liver MRI: suggestive of an inflammatory hepatic adenoma
The atoll sign in hepatic imaging has been described when a liver lesion shows a peripheral rim of high T2 signal intensity with the centre of the lesion appearing isointense to the background of non-cirrhotic liver on T2WI mimicking an atoll. It is considered a characteristic sign of an inflamm...
Atresia refers to a situation where there is underdevelopment of a structure with very rudimentary remnant tissues. This contrasts with an agenesis meaning there is no development of the structure as all. The term atresia is often used with hollow structures such as a bronchus or intestine.
Atretic parietal cephalocoeles (APC) also known as atretic cephalocele, refers to small subscalp lesions that consist of dura, fibrous tissue, and dysplastic brain tissue.
Common presentation in infants and young children.
Palpable midline parietal soft ti...
Atrial escape refers to a chest x-ray sign of massive left atrial enlargement and is an exaggerated version of the double density sign.
Normally, the right border of the left atrium is not visible. As it enlarges it forms a distinct border projecting through the right heart shadow, medial to ...
Atrial septal defects (ASD) are the second most common congenital heart defect after ventricular septal defects and the most common to become symptomatic in adulthood.
They are characterised by an abnormal opening in the atrial septum allowing communication between the right and left atria. Due...
Atrial-oesophageal fistulas are rare pathological connections between the left atrium and the oesophagus.
The presentation is non-specific. Patients may complain of fever, malaise, dysphagia or present with neurological symptoms 3.
The chief cause of atrial-...
Atrioventricular septal defects (AVSDs), also known as atrioventricular canal defects or endocardial cushion defects, comprise of a relatively wide range of defects involving the atrial septum, ventricular septum and one or both of the tricuspid or mitral valve. They can represent 2-7% of congen...
Atrophic gastritis is a chronic condition of autoimmune and non-autoimmune aetiology.
Two types of atrophic gastritis have been described 1-3:
type A: autoimmune
gastric body and fundus atrophy secondary to antiparietal cell antibodies
decreased secretion of acid and intrinsic fa...
Attenuation is the reduction in power and intensity of sound waves as they travel through tissue.
The attenuation coefficient is quantified as the measure of how easily a material can be penetrated by an x-ray beam. It quantifies how much the beam is "attenuated" (i.e. weakened) by the material it is passing through.
Atypical adenomatous hyperplasia (AAH) of the lung is a putative precursor lesion of adenocarcinoma of the lung. This entity replaces part of a spectrum of the previous bronchoalveolar carcinoma. It is defined as a peripheral focal proliferation of atypical cuboidal or columnar epithelial cells ...
Atypical callosal dysgenesis is a term used to denote an unusual pattern of dysgenesis of the corpus callosum.
The development of the corpus callosum occurs between the 12th and 16-20th weeks of gestation 2-3. It begins with the genu and then continues posteriorly along the body to the splenium...
Of the cervical vertebrae, the atlas (C1), axis (C2) and vertebra prominens (C7) are considered atypical cervical vertebrae.
The atlas (C1) lacks a body or spinous process. It has an anterior and posterior arches with lateral masses. Its superior articular surfaces articulate with the occiput a...
Atypical choroid plexus papillomas are WHO grade II tumours derived from choroid plexus epithelium with intermediate clinical and pathological features between the much more common, and more indolent, WHO grade I choroid plexus papilloma and the more aggressive WHO III choroid plexus carcinoma.
Atypical ductal hyperplasia (ADH) is a histologically borderline lesion that has some, but not all the features of ductal carcinoma in situ (DCIS). Sometimes the distinction between ADH and DCIS is simply on the basis of the number of ducts involved.
Atypical ductal hyperplasia is a...
Atypical ectopic pregnancy generally refers to an ectopic pregnancy which occurs outside the fallopian tube.
interstitial ectopic: 3% (often also termed cornual ectopic), also essentially a type of tubal ectopic
cornual ectopic (<1%)
ovarian ectopic: 0.5-1% (ovarian pregna...
Atypical lobular hyperplasia (ALH) is a pre-malignant lesion of the breast which falls at the milder end of the spectrum of lobular neoplasia. It is therefore considered a part of borderline breast disease.
It is usually asymptomatic and mammographically occult and is in...
Of the five lumbar vertebrae, L5 is considered atypical due to its shape. The remaining lumbar vertebrae are largely typical.
For a basic anatomic description of the structure a generic vertebra, see vertebrae.
Atypical meningioma refers to a more aggressive form of meningioma and denotes a WHO grade II tumour (along with two histological variants clear cell meningioma and chordoid meningioma). Atypical meningiomas account for 20-30% of all meningiomas 1,3.
It should be noted that epidemiology, clini...
Atypical pneumonia refers to the radiological pattern associated with patchy inflammatory changes, often confined to the pulmonary interstitium, most commonly associated with atypical bacterial aetiologies such as Mycoplasma pneumoniae, Chlamydophila pneumoniae and Legionella pneumophilia. Viral...
Owing to their features, the first, eleventh and twelfth ribs are considered atypical ribs.
Of all ribs, the first is the strongest, broadest and most curved. Ribs eleven and twelve are unique, among other reasons, by not being attached to the sternum.
Atypical small acinar proliferations (ASAP) are premalignant lesions of the prostate, which can be found in as many as 5% of prostate biopsies. They are suspicious glands without adequate histologic atypia to establish a definitive diagnosis of prostate cancer. Some studies showed that there is ...
Atypical teratoid/rhabdoid tumours (AT/RTs) are an uncommon WHO Grade IV tumour, which in the vast majority of cases occurs in young children less than two years of age. It most frequently presents as a posterior fossa mass.
AT/RTs were until relatively recently classed as medulloblastomas, al...
T1 and T9 to T12 are considered atypical vertebrae. T1 bears some resemblance to low cervical vertebrae. T9 has no inferior demifacet. T10 often, but not always, shares features with T11 and T12.
For a basic anatomic description of the structure a generic vertebra, see vertebrae.
The aubergine sign (also known as egg-plant sign or deformity) is a clinical sign of a fractured penis. Haemorrhage beyond the tunica albuginea produces swelling and bruising of the penis simulating the appearance of an aubergine.
This mnemonic helps when remembering the ascending order of structures that corresponds to each waveform in an auditory brainstem response (ABR) tracing:
E: eighth nerve action potential (wave I)
C: cochlear nucleus (wave II)
O: olivary complex (superior) (wave III)
The term Aunt Minnie is radiological shorthand for a lesion/finding which has characteristic appearances and cannot, within reason, be anything but one thing.
The term was coined by Ed Neuhauser, Chief of Radiology at Boston Children’s Hospital, and popularised by Ben Felson in his 1960 classi...
An auricular pseudocyst is a rare and benign cystic swelling resulting from intracartilaginous accumulation of fluid within the pinna.
While it can occur at any age and in either gender, it typically presents in middle aged males with a mean age of presentation being around 35-40 ...
The auriculotemporal nerve is a sensory branch of the posterior division of the mandibular division of the trigeminal nerve.
The auriculotemporal nerve divides posteriorly from the posterior division of the mandibular division before dividing into two roots separate to encircle t...
Autoimmune encephalitis (also known as autoimmune limbic encephalitis) is an antibody-mediated autoimmune-mediated inflammation of the brain, typically involving the limbic system, although all parts of the brain can be involved.
Autoimmune encephalitis can be divided broadly into two groups, ...
Autoimmune hepatitis is a rare type of chronic hepatitis, currently classified as "type 1" or "type 2". It may eventually lead to cirrhosis. The role of imaging is primarily to exclude other diagnoses and evaluate for complications.
It may occur in children or adults, but most pat...
Autoimmune pancreatitis (AIP) is a form of chronic pancreatitis associated with autoimmune manifestations on clinical, histological, and laboratory grounds 1.
Distinguishing this entity from other forms of chronic pancreatitis (such as alcohol-induced) is important as steroid treatment is effec...
There are several sets of diagnostic criteria for autoimmune pancreatitis (AIP), with some overlap and contradictions.
At the time of writing (July 2016), these are the most widely used sets of diagnostic criteria.
Asian 2008 AIP diagnostic criteria
both criteria I to be fulfilled
Autoimmune thyroiditises (AIT) refers to a group of conditions where there is inflammation involving the thyroid gland related to thyroid antibodies.
They are most common thyroid disease group in the paediatric population 5.
Entities that fall under this category inclu...
An automatic full-field volumetric breast ultrasound scanner (AFFBUS) is a developing technology which was initiated to overcome the drawback of dense breast and to get a three-dimensional view of the breast.
Automatic ultrasound imaging ac...
Autosomal dominant osteopetrosis is the less severe type of osteopetrosis and should be considered and compared with the other subtype: autosomal recessive osteopetrosis. The autosomal dominant (AD) type is less severe than its autosomal recessive (AR) mate. Hence, it is also given the name "ben...
Autosomal dominant polycystic kidney disease (ADPKD), also sometimes more vaguely referred to as "adult polycystic kidney disease", is as the name would suggest, a hereditary form of adult cystic renal disease.
Autosomal dominant polycystic kidney disease is one of the most commo...
Infantile autosomal recessive osteopetrosis is a subtype of osteopetrosis, a bone disease of dysfunctional osteoclasts that results in the overgrowth of bone. It is a more severe form that tends to present earlier. Hence, it is referred to as "infantile" and "malignant" compared to its autosomal...
Autosomal recessive polycystic kidney disease (ARPKD) is one of many paediatric cystic renal diseases.
On imaging, it usually presents on ultrasound with enlarged echogenic kidneys with multiple small cysts. Liver involvement with coarse echotexture, biliary tract cystic changes, and portal hyp...
Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a rare autosomal recessive spastic ataxia unique to the region of Charlevoix-Saguenay, in the Province of Quebec, Canada. It is due to a mutation on the SACS gene locus q12 of chromosome 13. It has been reported in other regio...
Autosplenectomy denotes spontaneous infarction of the spleen with resulting hyposplenism.
Autosplenectomy is most frequently encountered in patients with homozygous sickle cell disease, although it has also been reported in pneumococcal septicaemia 1, and SLE 2. The demographics t...
The AVAglio criteria were developed to assess response to first-line treatment of glioblastoma, treated with radiotherapy and temozolomide with or without bevacizumab 1-2. These were adapted from the older Macdonald criteria, but have since been superseded by they RANO criteria (2010) 1.
Avascular necrosis (AVN), or more correctly "osteonecrosis", is a generic term referring to an ischaemic death of the constituents of bone. AVN has a wide variety of causes and can affect nearly any bone in the body. Most sites of involvement have an eponym associated with avascular necrosis of ...
Mnemonics for the causes of avascular necrosis (AVN) or more correctly osteonecrosis:
Most common causes:
T: trauma (e.g. femoral neck fracture, hip dislocation, scaphoid fracture)
A: alcohol abuse
S: sickle cell dise...
Avascular necrosis of the hip is more common than other sites, presumably due to a combination of precarious blood supply and high loading when standing.
The most common presenting symptom is a pain in the region of affected hip, thigh, groin, and buttock. Although few p...
The avascular plane of Brodel is the section of renal parenchyma between 2/3 anterior and 1/3 posterior kidney on the cross-section that is relatively avascular. The reason for its relative avascularity is that it represents the plane where the anterior and posterior segmental renal artery branc...
Aviator astragalus is an antiquated reference to a pattern of isolated fracture/dislocation injury of the talus. Fractures included under this name include compression fractures of the talar neck, fractures of the body, posterior process or fracture dislocation injuries. The talar neck is the mo...