Articles

Articles are a collaborative effort to provide a single canonical page on all topics relevant to the practice of radiology. As such, articles are written and edited by countless contributing members over a period of time. A global group of dedicated editors oversee accuracy, consulting with expert advisers, and constantly reviewing additions.

11,933 results found
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Anti-MOG associated encephalomyelitis

Anti-MOG associated encephalomyelitis represents a group of inflammatory demyelinating disorders united by the presence of IgG antibodies to myelin oligodendrocyte glycoprotein (MOG) that overlap with acute disseminated encephalomyelitis (ADEM), neuromyelitis optica spectrum disorder (NMOSD) and...
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Antimuscarinics in MRI protocols

Antimuscarinics decrease bowel movements in pelvic MRI, and may be used for better image acquisition. Usually, 20mg of hyoscine butylbromide IM/IV is administered prior to examination. Contraindications Myasthenia gravis Pyloric stenosis Benign prostatic hyperplasia Paralytic ileus Additi...
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Anti-neutrophil cytoplasmic antibody associated vasculitides

Anti-neutrophil cytoplasmic antibody-associated vasculitides refer to a group of heterogeneous autoimmune diseases characterized by necrotising vasculitides and positive anti-neutrophil antibody titres. They are reactive to either proteinase-3 (PR3-ANCA) - cANCA or myeloperoxidase (MPO-ANCA) - p...
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Anti-N-methyl-D-aspartic acid receptor encephalitis

Anti N-methyl-D-aspartic acid (NMDA) receptor encephalitis is an autoimmune encephalitis with antibodies against the NMDA receptors. It is sometimes considered a form of autoimmune limbic encephalitis. It usually affects young patients particularly young females, in about 60% of whom ovarian ter...
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Antiphospholipid syndrome

Antiphospholipid syndrome is a systemic autoimmune disorder. It is usually defined as the clinical complex of vascular occlusion and ischaemic events occurring in patients who have circulating antiphospholipid antibodies. Pathology Patients have circulating antiphospholipid antibodies cross-re...
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Antiphospholipid syndrome (pulmonary manifestations)

Pulmonary involvement in antiphospholipid syndrome is one of the most frequent arterial complications of antiphospholipid syndrome.  Pathology It is essentially related to pulmonary arterial microthrombosis and may cause a wide spectrum of conditions, which include 3-5: pulmonary thromboembol...
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Anti-synthetase syndrome

Anti-synthetase syndrome (ASS) is a systemic, inflammatory, autoimmune disease that is characterised by inflammatory myositis, polyarthritis associated with interstitial lung disease (ILD) and anti-synthetase autoantibodies. Pathology ASS can result from autoantibodies to eight of the aminoacy...
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Antithrombin III deficiency

Antithrombin (AT) III deficiency (now simply called antithrombin deficiency) refers to a congenital lack of the endogenous anticoagulant antithrombin. Epidemiology Antithrombin deficiency is considered the least common of the three main anticoagulant deficiencies (the other two being protein C...
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Antley-Bixler syndrome

Antley-Bixler syndrome (ABS) (or trapezoidocephaly-synostosis syndrome) is a rare, autosomal dominant or recessive condition characterised by craniosynostosis and extra-cranial synostoses. Mid-facial hypoplasia is also common. Epidemiology Very rare condition with only 50 cases described in th...
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Antoine Henri Becquerel

Antoine H Becquerel (1852-1908) was a French scientist renowned for his work and subsequent discovery into the evidence of radioactivity for which he was awarded a Nobel prize. Early life Antoine Henri Becquerel was born on the 15th December 1852 in Paris, France to a family of nobility and ac...
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Antonio Egas Moniz

Antonio Egas Moniz (1874-1955) 1 was a pioneering Portuguese neurologist that is notable in radiology history for his development of cerebral angiography in 1927. He is also known as the developer of prefrontal leucotomy (now better known as a lobotomy) ​for which he received a Nobel Prize in 1...
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Antopol-Goldman lesion

Antopol-Goldman lesions are very rare presentations of subepithelial haemorrhage in the renal pelvis, presenting as discrete mass-like haematomas. Pathology The cause of these lesions is uncertain, although long-term anticoagulation, non-steroidal anti-inflammatory drug (NSAID) overuse, trauma...
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Antral follicle count

Antral follicle count (AFC) or basal antral follicle count is a test performed to check a female individual's ovarian reserve.  Principle A female is born with a lifetime supply of eggs and as she enters puberty these eggs develop. During and after puberty these follicles develop and are relea...
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Antral nipple sign

The antral nipple sign refers to redundant pyloric mucosa protruding into the gastric antrum and is seen in pyloric stenosis. See also cervix sign of pyloric stenosis target sign of pyloric stenosis shoulder sign of pyloric stenosis
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Antral pad sign

The antral pad sign is a feature seen on a spot radiograph of the upper gastrointestinal tract obtained with orally-administered contrast material. It refers to the extrinsic impression or indentation on the posteroinferior aspect of the antrum. The impression is generally arcuate and smooth, an...
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Antrochoanal polyp

Antrochoanal polyps (ACP) are solitary sinonasal polyps that arise within the maxillary sinus. They pass to the nasopharynx through the sinus ostium and posterior nasal cavity, enlarging the latter two. Similar, less common, polyps can arise in the sphenoid sinus extending into the nasopharynx:...
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Antrolith

An antrolith is a calcified mass within the maxillary sinus. The origin of the nidus of calcification may be extrinsic (foreign body in sinus) or intrinsic (stagnant mucus, fungal ball). Most antroliths are small and asympotomatic. Larger ones may present as sinusitis with symptoms like pain a...
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AO classification of proximal humeral fractures

The AO classification of proximal humeral fractures, along with the Neer classification, is one of the most frequently used systems for classifying proximal humeral fractures.  The AO classification divides proximal humeral fractures into three groups, A, B and C, each with subgroups, and place...
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AO classification of sacral injuries

The AO classification of sacral injuries aims to simplify and universalise the process of classifying sacral injuries and improve interobserver and intraobserver reliability. The AO sacral classification is broken into three subsections that follow a hierarchical structure similar to the AO cla...
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AO classification of subaxial injuries

The AO classification of subaxial injuries aims to simplify and universalise the classification of subaxial cervical spine fractures and improve interobserver and intraobserver reliability. The AO subaxial cervical spine injury classification involves four criteria based on morphology, facet in...
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AO classification of thoracolumbar injuries

The AO classification of thoracolumbar injuries aims to simplify and universalise the process of classifying spinal injuries and improve interobserver and intraobserver reliability 3. The AOSpine thoracolumbar classification system consists of only three classes of thoracolumbar injuries. Unlik...
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Aorta

The aorta, the great artery, is the largest artery of the human body and carries oxygenated blood ejected from the left ventricle to the systemic circulation. It is divided into: thoracic aorta ascending aorta aortic arch descending aorta abdominal aorta It has branches from each section a...
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Aortic aneurysm

The broad term aortic aneurysm is usually reserved for pathology discussion. More specific anatomic and radiologic discussion is based on the location of the aneurysm: thoracic aortic aneurysm abdominal aortic aneurysm
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Aortic annulus

The aortic annulus is a fibrous ring at the aortic orifice to the front and right of the atrioventricular aortic valve and is considered the transition point between the left ventricle and aortic root. The annulus is part of the fibrous skeleton of the heart. It is at the level of the sinus of V...
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Aortic arch

The aortic arch represents the direct continuation of the ascending aorta and represents a key area for a review of normal variant anatomy and a wide range of pathological processes that range from congenital anomalies to traumatic injury. Summary origin: continuation of the ascending aorta at...
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Aortic arch branches (mnemonic)

A useful mnemonic to remember the major branches of the aortic arch is: ABC'S ​Mnemonic A: arch of aorta B: brachiocephalic trunk C: left common carotid artery S: left subclavian artery  
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Aortic dissection

Aortic dissection is the most common form of the acute aortic syndromes and a type of arterial dissection. It occurs when blood enters the medial layer of the aortic wall through a tear or penetrating ulcer in the intima and tracks along the media, forming a second blood-filled channel within th...
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Aortic dissection detection risk score

The aortic dissection detection risk score (ADD-RS) is a clinical decision tool that aids in grading the pretest probability of an acute aortic dissection. Scores range from 0-3, where 0 is classed as low risk, 1 is moderate risk and 2-3 is high risk 1. Criteria The three domains in which pati...
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Aortic dissection detection risk score plus d-dimer

The use of the aortic dissection detection risk score plus d-dimer is a proposed standardised strategy of safely ruling out the diagnosis of an acute aortic syndrome. Similar to how the pulmonary embolism rule-out criteria (PERC) negates the need for further workup of a pulmonary embolism.  Int...
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Aortic hiatus

The aortic hiatus is one the three major apertures through the diaphragm and lies at the level of T12. Strictly speaking, it is not a real aperture in the diaphragm, but an osseoaponeurotic opening between it and the vertebral column.  The hiatus is situated slightly to the left of the midline ...
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Aortic intramural haematoma

Aortic intramural haematoma (IMH) is an atypical form of aortic dissection due to haemorrhage into the wall from the vasa vasorum without an intimal tear. It is part of the acute aortic syndrome spectrum. Epidemiology Typically aortic intramural haematomas are seen in older hypertensive patien...
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Aortic isthmus

The aortic isthmus is the part of the aorta just distal to the origin of the left subclavian artery at the site of the ductus arteriosus. This portion of the aorta is partly constricted in the fetus because of the lack of flow within the aortic sac and ascending aorta. It marks the partial sepa...
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Aortic knob

The aortic knob or knuckle refers to the frontal chest x-ray appearance of the distal aortic arch as it curves posterolaterally to continue as the descending thoracic aorta. It appears as a laterally-projecting bulge, as the medial aspect of the aorta cannot be seen separate from the mediastinum...
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Aortic nipple

An aortic nipple is seen in about 10% of PA chest x-rays on the lateral surface of the aortic arch/aortic knob. It represents the left superior intercostal vein. When prominent, superior vena cava obstruction should be considered as the left superior intercostal vein serves as a collateral path...
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Aortic pseudoaneurysm

Aortic pseudoaneurysms typically occur as a result of trauma, a subset of traumatic aortic injury. They can be acute or chronic. Pathology Aortic pseudoaneurysms are contained ruptures of the aorta in which the majority of the aortic wall has been breached, and luminal blood is held in only by...
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Aortic-pulmonary stripe

The aortic-pulmonary stripe is an uncommon feature of frontal chest radiographs and was first described by Keats in 1972 1. It is formed by the interface of the pleural surface of the anterior segment of the left upper lobe contacting the mediastinal fat that is anterolateral to the pulmonary t...
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Aortic root

The aortic root is the first part of the aorta and connects the heart to the systemic circulation.  Gross anatomy The aortic root lies between the junction of the aortic valve and ascending aorta. It has several subparts 1: three aortic valve leaflets and leaflet attachments three aortic sin...
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Aortic root abscess

An aortic root abscess is a serious complication of infective endocarditis. Radiographic features General Abscesses tend to be saccular in shape, range from 1 to 3 cm in diameter. Depending on sinus of origin, extended beneath the main and right pulmonary arteries or into the interventricular...
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Aortic spindle

Aortic spindles are an anatomical variant of the proximal descending thoracic aorta. It occurs just distal to the aortic isthmus and has a circumferential smooth bulging appearance.  Differential diagnosis ductus diverticulum: not circumferential aortic pseudoaneurysm thoracic aortic aneurysm
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Aortic transection

An aortic transection  (also known as a traumatic aortic rupture) is a type of traumatic aortic injury. It is considered the second most common cause of death associated with motor vehicle accidents. Pathology It occurs from a near-complete tear through "all the layers" of the aorta due to tra...
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Aortic valve

The aortic valve is one of the four cardiac valves. It is the semilunar valve that allows blood to exit the left ventricle. It opens during systole and closes during diastole. The valve has left, right and posterior cusps, the bases of which attach around the valve orifice to a fibrous ring or a...
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Aortic valve regurgitation

Aortic valve regurgitation, also known as aortic valve insufficiency or aortic valve incompetence, is a valvulopathy that describes leaking of the aortic valve during diastole that causes blood to flow in the reverse direction from the aorta and into the left ventricle. Epidemiology Aortic reg...
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Aortic valve stenosis

Aortic valve stenosis is the most common valvulopathy and describes narrowing of the opening of the aortic valve between the aorta and the left ventricle. Epidemiology Aortic stenosis is the most common valvulopathy, present in up to one-quarter of all patients with chronic valvular heart dise...
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Aortitis

Aortitis refers to a general descriptor that involves a broad category of infectious and non-infectious conditions where there is inflammation (i.e. vasculitis) of the aortic wall. Clinical presentation The presentation is non-specific with fever, pain and weight loss.  Pathology  Aetiology ...
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Aortocaval fistula

Aortocaval fistula is a rare and devastating complication of abdominal aortic aneurysm (AAA), wherein the aneurysm erodes into the inferior vena cava. Epidemiology Spontaneous rupture of an abdominal aortic aneurysm into the adjacent inferior vena cava occurs in <1% of all aneurysms and in ~3...
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Aortoenteric fistula

Aortoenteric fistula is an uncommon catastrophic cause of gastrointestinal haemorrhage. Aortic fistulas can be primary (associated with complicated abdominal aortic aneurysm) or secondary (associated with graft repair). Epidemiology The annual incidence of primary aortoenteric fistulas is thou...
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Aortoiliac occlusive disease

Aortoiliac occlusive disease refers to complete occlusion of the aorta distal to the renal arteries. Terminology When the clinical triad of impotence, pelvis and thigh claudication, and absence of the femoral pulses are present, it may also be called Leriche syndrome, which usually affects you...
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Aorto-left renal vein fistula

Aorto-left renal vein fistula is an extremely rare complication of abdominal aortic aneurysm rupture. The initial clinical presentation is often non-specific, however, characteristic imaging findings, if recognised early, can lead to prompt diagnosis and assist in surgical planning.  Epidemiolo...
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Aortopulmonary septal defect

Aortopulmonary septal defect (APSD), also known as aortopulmonary window (APW), is a congenital anomaly where there is an abnormal communication between the proximal aorta and the pulmonary trunk in the presence of separate aortic and pulmonary valves. Terminology APSD should not be confused w...
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Aortopulmonary window (radiograph)

The aortopulmonary (aortic-pulmonary or AP) window (also known as APW, but see 'Terminology' below) is a radiological mediastinal space seen on frontal chest radiographs. Terminology The term "aortopulmonary window" (also called an aortopulmonary septal defect) can also refer to a rare form of...
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Aortosternal venous compression

Aortosternal venous compression refers to compression of the brachiocephalic vein as a result of its position between the sternum and the aorta(or regional arteries). It can occur with normal as well as variant anatomy (aberrant right subclavian artery 1). Clinical presentation It is asymptoma...
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Aorto-ventricular tunnel

Aorto-ventricular tunnel (AVT) is an extremely rare form of congenital heart disease, representing an anomalous extracardiac communication between the ascending aorta and the left or right ventricles. Terminology In most cases the anomalous communication is between the aorta and the left ventr...
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APACHE score

The Acute Physiology and Chronic Health Evaluation (APACHE) score is a illness severity score commonly used in critical care medicine to predict mortality upon admission to an intensive care unit.  Criteria It involves two sections - one assessing the severity of the acute illness and another ...
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Apert syndrome

Apert syndrome (also known as type I acrocephalosyndactyly) is a syndrome that is predominantly characterised by skull and limb malformations. Epidemiology The estimated incidence is at 1:65-80,000 pregnancies. Pathology Thought to occur from a defect on the fibroblast growth factor receptor...
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Apgar score

Apgar score was originally described by Virginia Apgar (American anaesthesiologist, 1909-1974) in 1952. Helpfully, her surname is also a useful mnemonic for remembering the 5 factors: each is graded as 0, 1 or 2 with a total possible score of 10. The lower the score the worse the prognosis. Th...
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Aphthoid ulceration

Aphthoid ulcers are shallow ulcers of the gastrointestinal mucosa. Pathology Aetiology infective inflammatory conditions Yersinia enterocolitis amoebic enterocolitis cytomegalovirus enterocolitis noninfective inflammatory conditions Crohn disease idiopathic granulomatous gastritis vasc...
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Apical hypertrophic cardiomyopathy

Apical hypertrophic cardiomyopathy (AHCM) (also known as Yamaguchi syndrome) is a rare form of hypertrophic cardiomyopathy which usually involves the apex of the left ventricle and rarely involves the right ventricular apex or both apices. Epidemiology Historically, this condition was thought ...
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Apical ligament

The apical ligament is a small ligament that joins the apex (tip) of the dens of C2 to the anterior margin (basion) of the foramen magnum. It is the weak, fibrous remnant of the notochord and does not contribute significant stability. The more posterior alar and cruciate ligaments are stronger ...
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Apical lung disease (mnemonic)

A handy mnemonic to remember common apical lung diseases is: SET CARP or CARPETS Mnemonic S: sarcoidosis E: eosinophilic pneumonia T: tuberculosis C: cystic fibrosis A: ankylosing spondylitis R: radiation pneumonitis P: pneumoconiosis
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Apical pleural cap

Apical pleural cap refers to a curved density at the lung apex seen on chest radiograph. Epidemiology The frequency of apical pleural thickening increases with age 3. Pathology It arises from a number of causes: pleural thickening/scarring idiopathic: chronic ischaemic aetiology is favoure...
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Apical zone

The apical zone is one of the four chest radiograph zones and an important location for missed diagnoses when reporting a frontal chest radiograph and makes up one of the "check areas". It is sometimes thought of as a subdivision of the upper zone.  Radiographic features Plain radiograph port...
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Aplastic anaemia

Aplastic anaemia is a rare haematopoietic stem-cell disorder. The condition results in pancytopaenia and hypocellular bone marrow. Most cases are acquired, however there are unusual inherited forms. Pathophysiology Aplastic anaemia manifests as a marked reduction in the number of pluripotent h...
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Apocrine carcinoma of the breast

Apocrine carcinoma of the breast is a rare variant of breast cancer. The diagnosis is mainly pathological as it is difficult to differentiate from other forms of breast cancer on imaging. Epidemiology It accounts for about 4% of all cases. It is seen most often in females in the age group of 5...
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Apocrine metaplasia of the breast

Apocrine metaplasia of the breast is a benign breast condition and is sometimes considered part of or associated with fibrocystic change. It is a common finding in the female breast, particularly after the age of 25, and many regard it as a normal component of the breast. Epidemiology Seen mos...
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Apophyseal avulsion fractures of the pelvis and hip

Apophyseal avulsion fractures of the pelvis and hip are relatively common among physically active adolescents and young adults. Epidemiology Pelvic and hip apophyseal injuries typically occur in the 14 to 25 year age range. Mechanism Kicking sports, such as soccer, and gymnastics are frequen...
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Apophysis

The apophyses (singular: apophysis) are the normal bony outgrowths that arise from separate ossification centres and eventually fuse with the bone in time. The apophysis is a site of tendon or ligament attachment, as compared to the epiphysis which contributes to a joint. When unfused, they can...
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Apophysis of the proximal 5th metatarsal

The apophysis of the proximal 5th metatarsal lies laterally and is oriented longitudinally parallel to the shaft. Apophysis of the fifth metatarsal base appears on plain radiographs at age 12 for boys and 10 for girls. Fusion of the apophysis to the metatarsal base usually occurs within the fol...
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Apostrophe use and eponyms

Apostrophes are used according to standard English grammar rules. They are used for possessives and to indicate missing letters.  When using a possessive it's usually by adding "'s" at the end, e.g. "the patient's disease". Apostrophes should not be used for pluralisation, e.g. "apostrophes" an...
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Apparent diffusion coefficient

Apparent diffusion coefficient (ADC) is a measure of the magnitude of diffusion (of water molecules) within tissue, and is commonly clinically calculated using MRI with diffusion weighted imaging (DWI) 1.  Basics Diffusion-weighted imaging (DWI) is widely appreciated as an indispensable tool i...
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Appendiceal carcinoid

Appendiceal carcinoids are rare overall but represent the most common tumour of the appendix. The appendix is also one of the most common (but not the most common) locations for gastrointestinal carcinoid tumours.  Clinical presentation Appendiceal carcinoids can present as the obstructive cau...
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Appendiceal intussusception

Appendiceal intussusception happens when appendix segment is pulled into itself or into the cecum. This condition can mimic various chronic and acute abdominal conditions. It is an important entity to recognise since it could be mistaken for a caecal mass. Epidemiology Appendiceal intussuscept...
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Appendiceal mucocele

Appendiceal mucoceles occur when there is an abnormal accumulation of mucin causing abnormal distention of the vermiform appendix due to various neoplastic or non-neoplastic causes. Epidemiology The reported prevalence at appendectomy is 0.2-0.3%. They are thought to typically present in middl...
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Appendicitis

Appendicitis is inflammation of the vermiform appendix. It is a very common condition in general radiology practice and is one of the main reasons for abdominal surgery in young patients. CT is the most sensitive modality to detect appendicitis. Epidemiology Acute appendicitis is typically a d...
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Appendicitis (summary)

This is a basic article for medical students and other non-radiologists Appendicitis occurs when there is inflammation of the vermiform appendix. It is a very common condition and is a major cause of abdominal surgery in young patients. CT is the most sensitive modality to detect appendicitis a...
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Appendicolith

An appendicolith is a calcified deposit within the appendix. They are present in a large number of children with acute appendicitis and may be an incidental finding on an abdominal radiograph or CT. Incidence may be increased among patients with a retrocaecal appendix. Overall they are seen in 1...
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Appendicular abscess

Appendicular abscess is considered the most common complication of acute appendicitis, in particular after a perforated appendix.  Radiographic features Appendicular abscesses can arise either in the peritoneal cavity or the retroperitoneal space. Ultrasound Ultrasound is the first investiga...
Article

Appendicular artery

The appendicular artery is a branch of the ileal or posterior caecal branch of the ileocolic artery, which is from the superior mesenteric artery. It courses posteriorly to the terminal ileum in the free wall of the mesoappendix to supply the appendix.
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Appendicular films (early clinical)

This is a basic article for medical students and other non-radiologists Appendicular films are x-rays taken of the bones and joints of the arms and legs. I've used this term to separate the x-rays taken as part of an assessment of non-acute disease from trauma films which represent x-rays taken...
Article

Appendicular skeleton

The appendicular skeleton is the portion of the bony skeleton that includes and supports the limbs (the appendages). It includes the pectoral girdle and the bony pelvis, connected to the axial skeleton centrally and is composed of 126 bones in total.  Appendicular bones form from cartilage, by ...
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Appendix

The appendix or vermiform appendix is a blind muscular tube that arises from the caecum, which is the first part of the large bowel. Gross anatomy The appendix arises from the posteromedial surface of the caecum, approximately 2-3 cm inferiorly to the ileocaecal valve, where the taeniae coli c...
Article

Appleby procedure

The Appleby procedure is a type of pancreatic cancer resection.  For some patients with pancreatic cancer involving the body and tail of the pancreas, involvement of the coeliac axis is a classic contraindication to pancreaticoduodenectomy (Whipple procedure).  With the Appleby procedure, ther...
Article

Apple core sign (colon)

The apple core sign, also known as a napkin ring sign (bowel), is most frequently associated with constriction of the lumen of the colon by a stenosing annular colorectal carcinoma. Differential diagnosis The appearance of the apple-core lesion of the colon also can be caused by other diseases...
Article

Apple core sign (femur)

The apple core sign has been used to describe the circumferential erosion of the femoral neck seen in synovial chondromatosis. Although this is the most common process that may lead to an apple core erosion of the femoral neck, this has also been observed with: pigmented villonodular synovitis ...
Article

Apple-peel intestinal atresia

Apple-peel intestinal atresia, also known as type IIIb or Christmas tree intestinal atresia, is a rare form of small bowel atresia in which the duodenum or proximal jejunum ends in a blind pouch and the distal small bowel wraps around its vascular supply in a spiral resembling an apple peel. Oft...
Article

Applying to radiology training (UK)

Application to radiology training in the UK is through a national process. There is one application track for posts in England, Wales and Scotland and another for training in Northern Ireland.  In 2015, there were 211 posts in England, Scotland and Wales. Applications are open to those who are ...
Article

Apraxia

Apraxia is the inability to perform tasks which the patient has perviously learned and has no physical impairment which would preclude them from performing them 1.  Typically apraxia stems from damage to the parietal lobes. 
Article

April Fools'

The Radiopaedia editors have a recurring commitment to prank the collective radiology community each year on April 1, an informal holiday known as April Fools' day. Sometimes months in the planning and creation, the pseudo-pathologies depicted on imaging are an exciting annual project the editor...
Article

Aprosencephaly

Aprosencephaly is an extremely rare anomaly fetal cerebral development the derivatives of the telencephalon as well as the diancephalon are absent or dysplastic, while more caudal structures are normal or mildly deformed. It falls under the aprosencephaly / atelencephaly spectrum (AAS)  See als...
Article

Aquaporin

Aquaporin is a family of transmembrane water channels found throughout the body of both humans and many other species, facilitating the passage of water, cations and gasses 1.  At least 13 types of aquaporin have been described, and these are variably expressed.  Aquaporin 4 Aquaporin 4 (AQP4...
Article

Aqueduct stenosis

Aqueductal stenosis (AS) is a the most common cause of congenital obstructive hydrocephalus, but can also be seen in adults as an acquired abnormality.  Epidemiology Congenital aqueductal stenosis has an estimated incidence is at ~1:5000 births although the reported range varies greatly (3.7:1...
Article

Arachnoid cyst

Arachnoid cysts are relatively common benign and asymptomatic lesions occurring in association with the central nervous system, both within the intracranial compartment (most common) as well as within the spinal canal. They are usually located within the subarachnoid space and contain CSF.  On ...
Article

Arachnoid cyst (fetal presentation)

A fetal arachnoid cyst is term given when an arachnoid cyst is diagnosed in utero. For a general discussion of arachnoid cysts refer to the parent article. Pathology They can be classified as being primary or secondary 2. primary (congenital) arachnoid cysts: result from a benign accumulation...
Article

Arachnoid granulation

Arachnoid granulations, also known as a Pacchionian granulation, are projections of the arachnoid membrane (villi) into the dural sinuses that allow CSF entrance from the subarachnoid space into the venous system. Epidemiology They increase in size and number with age and are seen in approxima...

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