In English writing the indefinite article 'a' is used in congruence with a noun of which not a particular one is indicated as opposed to 'the'. For instance 'the house' is a particular house that can be identified, whereas 'a house' does not reference one house specifically.
When the word follo...
A-rings are a type of distal oesophageal ring. They are above the B-ring and occur a few centimetres proximal to the gastro-oesophageal junction. They represent a physiological contraction of oesophageal smooth muscle covered by mucosa. A-rings are uncommonly symptomatic.
Aarskog syndrome or Aarskog–Scott syndrome (also known as the facio-digito-genital syndrome) is a rare anomaly characterized by short stature in association with a variety of structural anomalies involving mainly the face, distal extremities, and external genitalia.
Aase-Smith syndrome is an extremely rare congenital disorder.
congenital hypoplastic anaemia - fetal anaemia
cleft lip, cleft palate
hydrocephalus (due to Dandy-Walker anomaly)
The American Association for the Surgery of Trauma (AAST) injury scoring scales are the most widely accepted and used system of classifying and categorising traumatic injuries. Injury grade reflects severity, guides management, and aids in prognosis. At the time of writing (mid 2016), 32 differe...
The AAST (American Association for the Surgery of Trauma) renal injury scale 3-4 is the most widely used renal trauma grading system at the time of writing (mid 2016). Severity is assessed according to the depth of renal parenchymal damage and involvement of the urinary collecting system and ren...
The AAST (American Association for the Surgery of Trauma) liver injury scale 1994 revision is the most widely used liver injury grading system at the time of writing (mid 2016).
haematoma: subcapsular, <10% surface area
laceration: capsular tear, <1 cm parenchy...
The 1994 revision of American Association for the Surgery of Trauma (AAST) splenic injury scale is the most widely used grading system for splenic trauma at the time of writing (mid 2016).
subcapsular haematoma <10% of surface area
capsular laceration <1 cm dept...
AP supine radiograph can be performed as a standalone projection or as part of an acute abdominal series, depending on the clinical question posed, local protocol and the availability of other imaging modalities.
the patient is supine, lying on their back, either on the X-ray ...
The lateral decubitus abdominal radiograph is used to identify free intraperitoneal gas (pneumoperitoneum). It can be performed when the patient is unable to be transferred to, or other imaging modalities (e.g. CT) are not available. The most useful position for detecting free intraperitoneal ai...
The PA erect abdominal radiograph is often obtained in conjunction with the AP supine abdominal view in the acute abdominal series of radiographs. When used together it is a valuable projection in assessing air fluid levels, and free air in the abdominal cavity.
the patient is...
Abdominal adhesions are bands of scar tissue (ﬁbrous or ﬁbrous fatty), most often occurring as a complication of previous abdominal surgery.
Adhesions often occur with
multiple abdominal operations or previous postoperative intra-abdominal complications
history of intra-abdominal i...
Abdominal and pelvic anatomy encompasses the anatomy of all structures of the abdominal and pelvic cavities.
The abdominal aorta is the main blood vessel in the abdominal cavity that transmits oxygenated blood from the thoracic cavity to the organs within the abdomen and to the lower limbs.
It is a continuation of descending thoracic aorta at T12 posterior to the median arcuate ligament...
Abdominal aortic aneurysms (AAA) are focal dilatations of the abdominal aorta that are 50% greater than the proximal normal segment or that are >3 cm in maximum diameter.
Its prevalence increases with age. Males are much more commonly affected than females (with a male: female ...
Abdominal aortic aneurysms (AAA) are focal dilatations of the abdominal aorta that are 50% greater than the proximal normal segment or >3 cm in maximum diameter.
prevalence of rupture increases with age
males more commonly affected than females
prevalence is almost 1...
Abdominal aortic aneurysm (AAA) rupture is a feared complication of abdominal aortic aneurysm and is a surgical emergency. It is part of the acute aortic syndrome spectrum.
Abdominal aortic aneurysms are common and affect ~7.5% of patients aged over 65 years 6.
Abdominal aortic injuries are very rare and are much less common than thoracic aortic injury.
Aortic injury occurs in <1% of blunt trauma patients, with abdominal aortic injury representing only ~5% of all aortic injuries 1. Males are more frequently injured, with the median a...
The abdominal cavity is divided into two major compartments, the peritoneum and retroperitoneum, early in fetal development.
The parietal peritoneum is reflected over the peritoneal organs to form a series of supporting peritoneal ligaments, mesenteries and omenta. The peritoneal reflections ca...
Abdominal ectopic pregnancies are an extremely rare type of ectopic pregnancy.
They are thought to represent ~1% of all ectopic pregnancies 6 with an estimated incidence of 1:1000-10,000 births.
It is often thought that they most frequently result from a tubal rupture ...
Abdominal herniations may be congenital or acquired and come with varying eponyms. They are distinguished primarily based on location and content. 75-80% of all hernias occur in the inguinal region.
Content of the hernia is variable, and may include:
small bowel loops
mobile colon segments (s...
An opacity projecting over the abdomen has a broad differential. Possibilities to consider include:
ingested, e.g. coins, batteries, bones, etc.
artifacts, e.g. object attached to the cloth of the patient like a safety pin or button
iatrogenic, e.g. haemostatic clips, gastric ...
This mnemonic helps to remember the relative echogenicity of abdominal organs on ultrasound:
Darling Parents So Love Kids
From most to least echogenic:
Abdominal paracentesis, more commonly referred to as an ascitic tap, is a procedure that can be performed to collect peritoneal fluid for analysis or as a therapeutic intervention.
diagnostic: especially for newly diagnosed ascites
determine aetiology of ascites
assess for bacter...
AP supine radiograph for neonates is a mobile examination performed on the neonatal unit. It can be taken as a standalone projection or as part of a series including a left lateral decubitus x-ray in cases of suspected perforation.
the patient is supine, lying on their back i...
The lateral view abdominal radiograph is a useful problem-solving view that can complement frontal views of the abdomen. It is different than the lateral decubitus view of the abdomen and looks more like a lateral lumbar spine view.
the patient may be either erect or recumbent...
Abdominal radiography can be useful in many settings. Before the advent of computerised tomography (CT) imaging, it was a primary means of investigating gastrointestinal pathology (and often allowed indirect evaluation of other abdominal viscera).
Although abdominal radiography has...
The abdomen, when looking from in front, is divided into nine regions by imaginary planes (two vertical and two horizontal) forming abdominal surface anatomy. The nine regions are of clinical importance when examining and describing pathologies related to the abdomen. The horizontal planes are o...
Abdominoschisis refers to a split or in the abdominal wall. Some authors use the term synonymously with a gastroschisis. When the defect continues into the thoracic region it is termed a thoraco-abdominoschisis. A large abdominoschisis is considered part of the limb body wall complex 2.
The abducens nerve is the sixth cranial nerve. It courses from its nucleus located in the dorsal pons to its innervation of the lateral rectus muscle and can be divided into four parts:
nucleus and intraparenchymal portion
cavernous sinus portion
The abductor digiti minimi muscle overlies the opponens digiti minimi.
origin: pisiform, the pisohamate ligament, and tendon of flexor carpi ulnaris
insertion: 5th proximal phalanx
action: abducts 5th finger at metacarpophalangeal joint
arterial supply: ulnar artery
The abductor digiti minimi muscle is on the lateral side of the foot and contributes to the large lateral plantar eminence on the sole.
origin: lateral and medial processes of calcaneal tuberosity, and band of connective tissue connecting calcaneus with base of metatarsal V
The abductor hallucis muscle forms the medial margin of the foot and contributes to a soft tissue bulge on the medial side of the sole.
origin: medial process of calcaneal tuberosity
insertion: medial side of base of proximal phlanx of great toe
action: abducts and flexes great toe a...
The abductor pollicis brevis is a thin subcutaneous muscle laterally placed in the thenar eminence of the hand.
origin: mainly from the flexor retinaculum, few fibres origin from the tubercles of scaphoid and trapezium and tendon of abductor pollicis longus. Accessory slips may spring from the ...
The abductor pollicis longus (APL) is a muscle found in the deep posterior compartment of the forearm. As it descends, it becomes superficial and passes under the extensor retinaculum and through the 1st extensor compartment of the wrist before attaching distally.
origin: posterior sur...
The ABER position is related to imaging of the shoulder joint and is a mnemonic for ABduction and External Rotation.
In this position, labral tears are conspicuous by tightening the inferior glenohumeral labroligamentous complex (which are also the most important glenohumeral ligaments in preve...
Abernethy malformations are rare vascular anomalies of the splanchnic venous system. They comprise of congenital portosystemic shunts and result from persistence of the embryonic vessels.
Type I malformations are thought only to occur in females with type II having a male predile...
Aberrant arachnoid granulations (AbAG) are arachnoid granulations that penetrated the dura but failed to migrate normally in the venous sinus. They are most often located in the greater wing of the sphenoid bone. Occasionally, they are seen at the posterior temporal bone wall.
Aberrant internal carotid artery is a variant of the internal carotid artery (ICA) and represents a collateral pathway resulting from involution of the normal cervical portion (first embryonic segment) of the ICA 5.
There is consequent enlargement of the usually small collaterals which course t...
Aberrant left pulmonary artery, also known as pulmonary sling, represents an anatomical variant characterised by the left pulmonary artery arising from the right pulmonary artery and passing above the right main bronchus and in between the trachea and oesophagus to reach the left lung. It may le...
Aberrant right subclavian arteries (ARSA), also known as arteria lusoria, are the commonest of the aortic arch anomalies 2.
The estimated incidence is 0.5-2%.
They are often asymptomatic, but around 10% of people may complain of tracheo-oesophageal symptom...
Aberrations in the Normal Development and Involution of the breast (ANDI) is an all encompassing term that is used to describe a wide spectrum of the benign breast diseases. As the name suggests, it is based on the theory that most of the encountered benign breast disorders are essentially minor...
Abnormal bowel wall attenuation patterns on CT scan can be grouped under five categories:
water halo sign
fat halo sign
The first three patterns are seen on contrast studies.
It is defined as uniform enhancement of th...
A mnemonic used for abnormal collection of barium anywhere in the body :
Abnormal ductus venosus waveforms can arise in a number of conditions ranging from aneuploidy to vascular malformations and fetal tumours.
Abnormal waveforms in fetal ductus venosus flow assessment can occur in a number of situations:
Down syndrome: around 80...
Abnormal intra-abdominal gas may be seen on a chest or abdominal radiograph, or CT or MRI.
abnormally located bowel, e.g. Chilaiditi syndrome (bowel interposed between liver and hemidiaphragm), inguinal hernia
Abnormal renal rotation (renal malrotation) refers to an anatomical variation in the position of the kidneys, in particular to anomalous orientation of the renal hilum. It may occur unilaterally or bilaterally. It is almost always an asymptomatic incidental finding.
An eccentrically located gestational sac towards the fundus of uterus is the normal sonographic appearance; however an abnormally eccentric gestational sac on ultrasound may be apparent due to a number of causes
interstitial ectopic pregnancy 1
normally implanted pregnancy in a
An abnormally low sac position can result from several possibilities which include
impending / ongoing miscarriage
cervical ectopic pregnancy
fundal fibroid or other mass compressing the sac downward
Abnormally thickened endometrium on imaging may occur for a number of reasons which may be categorised based on whether or not they are related to pregnancy. Aetiologies may also be classified based on whether the patient is premenopausal or postmenopausal.
The ABR certifying exam is the second of two exams necessary for certification in diagnostic and interventional radiology in the United States of America (the first is the core exam). It is taken 15 months after the end of the PGY 5 year (or three months after a one year PGY 6 fellowship).
The ABR core exam is the first of two exams necessary for certification in diagnostic and interventional radiology in the United States of America. It is taken at the end of the PGY 4 year of radiology residency training.
The exam is computer-based and occurs in two sessions (7.5 hours and 6 ho...
Abscesses are focal confined collections of suppurative inflammatory material and can be thought of as having three components 1:
central core comprised of necrotic inflammatory cells and local tissue
peripheral halo of viable neutrophils
surrounded by a 'capsule' with dilated blood vessels a...
The absent bow tie sign represents the loss of the normal appearance of the menisci on parasagittal MRI images, and is suggestive of meniscal injury.
Normally the medal and lateral menisci appear as low signal bow-tie-shaped structures between the femoral condyles and tibial plateaux. As the no...
Agenesis of the ductus venosus (ADV) is a rare fetal vascular anomaly. According to the data obtained from the screening tests performed at 11-14 weeks of pregnancy, its incidence is reported to be 1/2500 (12).
In the literature review on ductus venosus agenesis, Acherman et.al (13) ...
An absent infrarenal inferior vena cava (IVC) can be congenital due to failure of development of the posterior cardinal and supracardinal veins, or acquired as result of intrauterine or perinatal inferior vena cava thrombosis.
It is an extremely rare anomaly.
In fetal sonographic assessment, an absent nasal bone is a feature which can sometimes be used as an adjunctive marker for fetal aneuploidy.
It is assessed on a midline sagittal view. In this section the nasal bone is often seen as a bright echogen...
An absent patella is a rare finding and can be found with an equally rare set of associations:
surgical removal of patella (patellectomy)
nail patella syndrome 2
popliteal pterygium syndrome
proximal focal femoral deficiency (PFFD)
Meier-Gorlin syndrome 3
An absent septum pellucidum may rarely be an isolated finding, or more commonly be seen in association with a variety of conditions.
The septum pellucidum is partly or entirely absent in 2 or 3 individuals per 100,000 in the general population.
An absent septum pelluc...
An absent thumb can have many associations. They include:
Fanconi anaemia (pancytopenia-dysmelia syndrome)
phocomelia (e.g. thalidomide embryopathy)
Poland syndrome (pectoral muscle aplasia and syndactyly)
Absent end diastolic flow (AEDF) in an umbilical artery Doppler assessment is a useful feature which indicates underlying fetal vascular stress if detected in mid or late pregnancy. It is often classified as Class II in severity in abnormal umbilical arterial Dopplers 9.
Absence of the yolk sac in the presence of an embryo on a transvaginal ultrasound is considered abnormal, and in general is associated with subsequent embryonic death.
Absorbed dose is a measure of the energy deposited in a medium by ionizing radiation. It is equal to the energy deposited per unit mass of medium, and so has the unit J/kg or gray (Gy) where 1Gy = 1Jkg-1.
The absorbed dose is not a good indicator of the likely biological effect. 1 Gy of alpha r...
The anterior commissure (AC) - posterior commissure (PC) line, also referred as the bicommissural line, has been adopted as a convenient standard by the neuroimaging community, and in most instances is the reference plane for axial imaging in everyday scanning. The creation of a standard image p...
Acardiac twins (or recipient twins) are haemodynamically disadvantaged non-viable twins that undergo secondary atrophy in association with a twin reversed arterial perfusion sequence.
Acardiac twinning is thought to affect 1 in 100 monozygotic twin pregnancies and 1 in 35,000 preg...
There are a number of accepted abbreviations that we use on Radiopaedia.org. We would like the site to be as standardised as possible and we have therefore chosen our accepted abbreviations and would ask that where possible these are used:
e.g. not eg./e.g/eg (short for "exempli gratia&quo...
The accessory appendicular artery (or artery of Seshachalam) or is a branch of the posterior caecal artery, which in turn arises from the ileocolic artery, and runs in the mesoappendix.
The exact prevalence of this accessory artery and its impact upon the risk of appendicitis varies among studi...
Accessory breast tissue is a relatively common congenital condition in which abnormal accessory breast tissue is seen in addition to the presence of normal breast tissue. This normal variant can present as a mass anywhere along the course of the embryologic mammary streak (axilla to the inguinal...
Accessory fissures of the lung usually occur at the borders of bronchopulmonary segments. They are common normal variants but are less commonly seen on imaging.
Some of the more common accessory fissure include 1:
azygos fissure: most commonly seen accessory fissure
inferior accessory fissur...
Accessory gallbladders are a rare anatomical variant occurring in 0.03% of cases (approximately 1 in 3000 people). They can arise from either the left or right hepatic ducts or both. Accessory gallbladders arise from a bifid diverticulum of the hepatic duct in the 5th or 6th week of development ...
The accessory (or superior) hemiazygos vein forms part of the azygos system and along with the hemiazygos vein, it is partially analogous to the right-sided azygos vein. It drains the left superior hemithorax.
Origin and course
The accessory hemiazygos vein is formed by the con...
An accessory left atrial appendage is a frequent fortuitous finding in cardiac imaging, encountered in ~10% of patients. They are more often seen as a small diverticular structure projecting from the right upper side of the left atrial wall.
it must not be confused with ...
The accessory middle cerebral artery is a variant of the middle cerebral artery (MCA) that arises from the anterior cerebral artery (ACA). It is different from a duplicated middle cerebral artery, in which the duplicated vessel originates also from the distal end of the internal carotid artery (...
Accessory navicular syndrome occurs when a type II accessory navicular (or "os tibiale externum") becomes painful due to movement across the pseudojoint between the ossicle and the navicular bone.
The syndrome presents on MRI with bone marrow oedema signal (hypointense T1, hyperintens...
The parietal and occipital bones in particular are common regions for accessory sutures because of their multiple ossification centres.
The occipital bone has complex development, ossifying from six centres. The foramen magnum is surrounded by four ossification centres. On each side are the exo...
The accessory ossicle of the anterior arch of the atlas is a normal variant and is best appreciated on a lateral cervical/sagittal study. It is observed as a circular and corticated osseous density that articulates with the inferior aspect of the anterior arch of the atlas.
It is not associate...
Accessory ossicles are secondary ossification centres that are separate from the adjacent bone. In most cases, they are congenital in origin, although they may occur as a result of trauma or local degenerative disease 2:
shoulder & elbow
os supratrochleare dorsale
Accessory ossicles of the feet are common developmental variants with almost 40 having been described. The more common ones include:
os tibiale externum (accessory navicular)
os calcaneus secundaris
Accessory ossicles of the wrist are commonly seen on plain radiographs of the wrist and associated cross-sectional imaging. Over 20 were originally described 2, although the more common include 1:
lunula: between TFCC and triquetrum
os styloideum (carpal boss): on dorsal surface of 2nd or 3rd ...
Accessory ossicles of the wrist can be easily recalled with the mnemonic:
O: os styloideum (carpal boss)
T: (os) triangulare
T: (os) trapezium secondarium
E: (os) epilunate
O: os hamuli proprium
Accessory parotid glands are a normal variant and represent ectopic salivary tissue present away and separate from the main parotid gland 1.
Accessory parotid glands are not rare and are seen in ~20% of the general population 2.
Located on the masseter muscle, ante...
Accessory peroneal muscles are a group of accessory muscles that can occur in the foot region as a normal variant in some individuals. The peroneal compartment is known as the lateral compartment of the leg.
Peroneus quartus muscle
Originally, several accessory muscles were distinguished in th...
Accessory renal arteries are a common variant and are present in ~25% (range 20-30%) of the population.
Sometimes, the term extrarenal artery may be used 2 with a further subclassification of:
aberrant renal artery: supplying the superior and/or inferior pole of the kidney
accessory renal art...
An accessory right inferior hepatic vein is the most common variation of the hepatic veins. It is present in up to 48% of the population and drains the posterior part of the right lobe (mainly segments 6 and 7) directly into the inferior vena cava.
Variations in hepatic vascular anatomy are pa...
The accessory soleus muscle is an anatomical variant characterised by an additional distinct muscle encountered along a normal soleus muscle. It is uncommon with a prevalence of ~3% (range 0.7-5.5%).
The accessory soleus muscle arises from the deep surface of the soleus or from t...
An accessory superior acetabular notch is a normal variant of the acetabulum, which can be seen on radiographs. It may lead to diagnostic confusion, especially in younger patients.
appear as bilateral symmetric fluid-filled pits in the roof of the acetabulum with sh...
The accordion sign is seen on CT examinations of the abdomen and refers to the similarity between the thickened oedematous wall of pseudomembranous colitis to that of an accordion. The appearance arises as a result of oral contrast being trapped between oedematous haustral folds and pseudomembra...
Ace-of-spades sign refers to the pathognomonic configuration of the left ventricle as seen in apical hypertrophy 1-3. It consists of marked ventricular wall thickening at the apex resulting in cavity narrowing at the apex with a relatively normal appearance of the mid-ventricular to basal wall a...
The acetabular angle is a radiographic measurement used when evaluating potential developmental dysplasia of the hip (DDH). It is most useful in patients who have started to ossify the epiphysis since ossification diminishes the usefulness of ultrasound.
The angle is formed by a horizontal lin...
The acetabular foramen is formed by the bony margins of the acetabular notch and completed by the transverse ligament of the hip. From its margins (both transverse ligament and acetabular notch) arises the ligamentum teres. Through it pass nutrient vessels to the femoral head epiphysis.
Acetabular labral tears, as the name implies, are tears involving the acetabular labrum of the hip.
With the increasing use of hip arthroscopy in orthopaedic surgery since the 1970s pathologies of the acetabular labrum as a possible cause of chronic hip and groin pain have become more familia...
Acetabular labrum acts to deepen the acetabulum and increase contact between the pelvis and the femoral head. Its exact biomechanical role remains to be fully elucidated.
The acetabular labrum is a C-shaped fibrocartilaginous structure with an opening anteroinferiorly at the site...
The acetablar notch is a depression in the margin of the acetabulum located anteroinferiorly. It is bridged by the transverse ligament, and thus forms the acteabular foramen. The ligamentum teres has part of its origin from the acetabular notch.