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.

65 results found
Article

Early DWI reversal in ischaemic stroke

Early DWI reversal in ischaemic stroke (also referred to as diffusion lesion reversal) is encountered early in the course of ischaemic infarction, most frequently in the setting of reperfusion within 3 to 6 hours of onset 1. In the vast majority of cases it is transient and does not represent tr...
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Eccentric target sign

The eccentric target sign is considered pathognomonic for cerebral toxoplasmosis. It is seen on postcontrast MRI/CT as a ring enhancing lesion with an eccentrically located enhancing mural nodule. It is believed that this mural nodule is an extension from the abscess wall itself with inflamed ve...
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Ecchordosis physaliphora

Ecchordosis physaliphora is a congenital benign hamartomatous lesion derived from notochord remnants, usually located in the retroclival prepontine region, but can be found anywhere from the skull base to the sacrum.  Terminology There has been some controversy as to whether intradural chordom...
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Ectopia lentis

Ectopia lentis refers to subluxation or dislocation of the lens secondary to dysfunction or disruption of zonular fibres.  Pathology Aetiology trauma systemic and syndromic disorders Marfan syndrome typically upwards and out most common spontaneous cause 2 homocystinuria -  typically dow...
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Ectopic posterior pituitary

An ectopic posterior pituitary reflects a disruption of normal embryogenesis and is one of the more common causes of pituitary dwarfism. Although it can be an isolated abnormality, numerous other congenital central nervous system malformations have been identified. Epidemiology Ectopic posteri...
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Efface

Efface is a term frequently used by radiologists, most often in the context of CSF containing spaces in the brain (sulci and ventricles). Unfortunately it is often used incorrectly.  The word efface, in general english usage, means to cause something to fade or disappear 1-2. In the context of...
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Eloquent cortex

Eloquent cortex is a term that refers to specific brain areas that directly controls function, thus damage to this areas generally produces major focal neurological deficits. Examples of eloquent cortex are:  primary motor cortex (precentral gyrus) primary somatosensory cortex (postcentral gyr...
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Embryonal tumors with multilayered rosettes (ETMR)

Embryonal tumors with multilayered rosettes (ETMR) are rare small round blue cell tumour of the central nervous system, and are one of the most aggressive brain tumours usually encountered in children.  Terminology Previously embryonal tumors with multilayered rosettes (ETMR) where known as em...
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Emergency CT head (mnemonic)

A useful mnemonic which is used to read an emergency head CT scan is: Blood Can Be Very Bad Mnemonic Using a systematic approach will help to ensure that significant neuropathology will not be missed. B: blood look for epidural hematoma, subdural hematoma, intraparenchymal hemorrhage, intra...
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Empty delta sign

The empty delta sign is CT sign of dural venous sinus thrombosis of the superior sagittal sinus, where contrast outlines a triangular filling defect (clot). It is only described with CECT-scan or MRI, not with NECT nor non-contrast MRI. Pathology The exact mechanism for this appearance is unce...
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Empty light bulb sign in brain death

In brain death, on HMPAO-Tc99m imaging there is absent or reduced flow in the internal carotid arteries and increased flow within the external carotid arteries. This leads to absent uptake in the brain with subsequent increased perfusion in the nasal region. This appearance has been called the '...
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Empty sella

An empty sella, also known as an empty pituitary fossa, is a relatively common incidental finding and posed more of a diagnostic problem before modern cross-sectional imaging. In addition to being incidental, a well-established association with benign intracranial hypertension is also recognised...
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Empty thecal sac sign

The empty thecal sac sign or empty sac sign is when the thecal sac appears empty on MRI of the lumbar spine, best seen on T2-weighted images. If the empty thecal sac sign is present, a diagnosis of adhesive arachnoiditis can be made.​ Radiographic features MRI There is usually no Gadolinium c...
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Empyema

Empyemas are purulent inflammatory collections within a body cavity. They are similar to abscesses, which arise within parenchymal tissue rather than occupying a pre-existing anatomical space. Terminology Colloquially, the term empyema is used to refer to thoracic empyemas but there are variou...
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En plaque meningioma

En plaque meningiomas refer to a specific meningioma macroscopic appearance characterised by diffuse and extensive dural involvement, usually with extracranial extension into calvarium, orbit, and soft tissues. These tumours are thought to have a collar-like or sheet-like growth along the dura m...
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Encephalitis due to herpesvirus family

Although sporadic viral encephalitis is most commonly due to herpes simplex virus 1 (HSV-1) the extended herpesvirus family consists of many other viruses many of which can also infect the central nervous system. Encephalitis due to herpesvirus family include 1:   herpes simplex virus 1 (HSV-1)...
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Encephalitis lethargica

Encephalitis lethargica (EL) is a rare disease that is also known as von Economo encephalitis. It affects the midbrain and basal ganglia, and the exact aetiology is unknown.  Clinical presentation Symptoms are initially that of pharyngitis followed by lethargy, extrapyramidal movements (parkin...
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Encephalocoele

Encephalocoeles, also known as meningoencephalocele, are a type of cephalocoele where brain tissue herniates out through a defect in the cranium.  Terminology They should be distinguished from cranial meningoceles in which the lesion contains only meninges and extracranial brain herniation, in...
Article

Encephalocraniocutaneous lipomatosis

Encephalocraniocutaneous lipomatosis (ECCL), also known as Haberland syndrome, is a rare congenital neurocutaneous syndrome characterised by unilateral lipomas of the cranium, face, and neck, ipsilateral lipodermoids of the eye, and ipsilateral brain anomalies. The clinical features of ECCL ove...
Article

Encephalomalacia

Encephalomalacia is term given to describe softening or loss of brain parenchyma with or without surrounding gliosis, as a late manifestation of injury.  Clinical presentation asymptomatic  serve as a focus of seizure Pathology Encephalomalacia is the end result of liquefactive necrosis of ...
Article

Endolymphatic sac tumour

Endolymphatic sac tumours (ELST) are very rare, locally invasive tumors of endolymphatic sac. Early detection of ELST is very important, because early surgical intervention may prevent further hearing loss. ELSTs do not metastasise, but are highly locally aggressive.  Epidemiology Mean age at ...
Article

Enlarged posterior fossa 'CSF' space

An enlarged posterior fossa 'CSF' space posterior to the cerebellum has a number of differentials that include: mega cisterna magna epidermoid cyst arachnoid cyst Careful attention to the cerebellum needs to paid as also to be considered are: cerebellar atrophy Dandy-Walker malformations ...
Article

Enterovirus 71

Enterovirus 71 is one of the viruses that causes hand-foot-and-mouth disease in children. It is an enterovirus, one of the picornaviruses. Infection with enterovirus 71 predominantly results in a vesicular rash of the hands and feet that follows a prodrome of symptoms including fever, vomiting ...
Article

Entorhinal cortex

The entorhinal cortex (Brodman area 28) is located in the mesial temporal lobe and acts as the interface between the hippocampus and the neocortex. It has been considered part of the hippocampal formation (along with Ammon’s horn, subiculum and presubiculum), but is difficult to precisely locali...
Article

Eosinophilia myalgia syndrome

Eosinophilia myalgia syndrome (EMS) is a fatal neurological condition caused by ingestion of improperly manufactured L-tryptophan.  Impurities and/or metabolites that block histamine degradation result in peripheral blood eosinophilia and myalgia.   In the brain, cortical and basal ganglia atro...
Article

Ependymal cyst

Ependymal cysts are rare benign neuroepithelial cysts lined by ependymal cells. Most are small and asymptomatic and only cause symptoms if large. On imaging these cysts are essentially indistinguishable from other intraventricular simple cysts (e.g. intraventricular arachnoid cysts). Epidemiol...
Article

Ependymal rosette

Ependymal rosette corresponds to an histologic architectural pattern that provides strong evidence of ependymal differentiation (ependymoma). It is characterised by a halo or spoke-wheel arrangement of cells surrounding an empty tubule lumen. Differential diagnosis It must be differentiated fr...
Article

Ependymitis granularis

Ependymitis granularis sounds far more worrying than it actually is. The term refers to symmetrical foci of periventricular high T2 and FLAIR signal hyperintensity anterior and lateral to the frontal horns. It is just an anatomical variant, usually small, less than 1 cm, and have a triangular mo...
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Ependymoma

Ependymomas represent a relatively broad group of glial tumours which share common origin from differentiated ependymal cells lining the ventricles of the brain or the central canal of the spinal cord. They account for ~5% of all neuroepithelial neoplasms, ~10% of all paediatric brain tumours an...
Article

Ependymoma RELA fusion-positive

Ependymoma RELA fusion-positive is a recently accepted variant of ependymoma, only recognized in the 2016 update to the WHO classification of CNS tumours.  It has been found that this variant is responsible for the majority of supratentorial ependymomas in childhood 1. 
Article

Ependymoma vs astrocytoma of the spinal cord

A number of factors are useful when differentiating between spinal cord ependymoma and spinal cord astrocytoma of the spinal cord.  Ependymoma child or adult more central in location bony remodeling is common low T1 signal well defined enhancement syrinx is more common haemorrhage is mor...
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Epidermoid cyst

The term epidermoid cyst can refer to a: epidermal inclusion cyst intracranial epidermoid cyst splenic epidermoid cyst spinal epidermoid cyst testicular epidermoid cyst
Article

Epidural angiolipoma

Epidural angiolipomas are rare benign tumours composed of mature adipocytes and abnormal vessels.  Epidemiology Epidural angiolipomas are more frequently encountered in women, and typically in middle age (40-50 years of age) 1.  Clinical presentation In keeping with the slow growth of these ...
Article

Epidural blood patch

Epidural blood patch is a treatment option for patients with craniospinal hypotension or post lumbar puncture headaches. The procedure can be done blind or under fluoroscopic or CT guidance, and is performed predominantly by radiologists and anaesthetists.  Indications craniospinal hypotension...
Article

Epidural empyema

Epidemiology and demography Epidural empyemas are relatively rare, but acount for ca. 30% of all intracranial infections. They can appear at every age with no sex preference. Etiology The most common pathogens are streptococci, Haemophilus influenzae, Staphylococcus aureus and Staphylococcus ...
Article

Epidural lipomatosis

Epidural lipomatosis refers to an excessive accumulation of fat within the spinal epidural space, typically in the lumbar region, such that the thecal sac is compressed, and in some instances results in compressive symptoms.  Epidemiology Demographic of affected individuals reflects the underl...
Article

Epilepsy

Epilepsy is a common neurological disorder that has varied presentation, and requires two or more unprovoked seizures at least 24 hours apart for diagnosis. MRI is the modality of choice for epilepsy, most often investigating for an underlying cause, especially in adults.  Epidemiology Epileps...
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Epithalamus

The epithalamus is a dorsal posterior segment of the diencephalon which includes the habenula, the stria medullaris and the pineal gland. Its function is the connection between the limbic system to other parts of the brain.
Article

Epithelioid glioblastoma

Epithelioid glioblastoma is a variant of glioblastoma (along with gliosarcoma and giant cell glioblastoma) only recently added to the WHO classification of CNS tumours as part of the 2016 update 1.  Note: whether or not epithelioid glioblastomas are distinct from rhabdoid glioblastomas is at pr...
Article

Erdheim-Chester disease

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell, non-familial multisystemic granulomatosis, with widespread manifestations and of highly variable severity. The most common presenting symptom is bone pain. Epidemiology Erdheim-Chester disease is a rare, non-inherited disease of midd...
Article

État criblé

État criblé, also known as status cribrosum, is a term that describes the diffusely widened perivascular spaces (Virchow-Robin spaces) in the basal ganglia, especially in the corpus striatum. It is usually symmetrical, with the perivascular spaces showing CSF signal and without diffusion restric...
Article

État lacunaire

État lacunaire is a term describing the presence of multiple lacunar infarcts, which are ischemic strokes due to occlusion of penetrating cerebral arterioles, especially in the basal ganglia. The term has been strongly described as a pathological substrate for a multi-infarct vascular dementia 4...
Article

Evans' index

The Evans' index is the ratio of maximum width of the frontal horns of the lateral ventricles and maximal internal diameter of skull at the same level employed in axial CT and MRI images. This ratio varies with the age and sex. It is useful as a marker of ventricular volume and thus has been pr...
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Exencephaly

Exencephaly is a lethal congenital fetal brain developmental anomaly (neural tube defect). Pathology It is characterised by calvarial absence and loss of fetal brain tissue to variable degrees and is considered a precursor to anencephaly 3 in the acrania-exencephaly-anencephaly sequence. Mark...
Article

External auditory canal atresia

External auditory canal atresia (EACA) is characterised by complete or incomplete bony atresia of the external auditory canal (EAC) and, especially when seen in the setting of an associated syndrome, a dysplastic auricle and abnormal middle ear cavity. Epidemiology The incidence is 1 in 10,000...
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External capsule

The external capsule is a series of white matter tracts in the brain. They are situated between the putamen and claustrum.
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External petrosal nerve

The external petrosal nerve is one of the three branches from the geniculate ganglion. It carries sympathetic fibers to the middle meningeal artery.
Article

External ventricular drain

External ventricular drains (EVDs) are a common neurosurgical procedure used to monitor and treat raised intracranial pressure in the acute setting.  Treatment and prognosis Complications infection EVD malfunction EVD malposition intracranial haemorrhage (e.g. subdural, intraventricular) ...
Article

Extra-axial

Extra-axial is a descriptive term to denote lesions that are external to the brain parenchyma, in contrast to intra-axial which describes lesions within the brain substance.  Radiographic features Often it is trivially easy to distinguish an intra-axial from an extra-axial mass. In many cases,...
Article

Extra-axial masses

There is a wide range of extra-axial masses, ranging from benign developmental cysts to malignant tumours.  Differential diagnosis neoplasms chordoma choroid plexus papilloma/carcinoma cranial nerve schwannoma meninges meningioma solitary fibrous tumour hemangiopericytoma metastases l...
Article

Extra-ventricular neurocytoma

Extra-ventricular neurocytomas are extremely rare WHO grade II primary CNS neoplasms.  Pathology The tumours are of neuronal origin and are similar to the comparatively much more common intra ventricular neurocytomas. Radiographic features Due to there rarity most features are derived from c...
Article

Extracranial brain herniation

Extracranial brain herniation refers to herniation of brain tissue outside the calvarium through a skull bone defect, which may be post traumatic or post surgery. Unlike encephalocoeles, brain herniation is surrounded by the meninges.  The herniated brain tissue requires surgical reduction as i...
Article

Extracranial meningioma

Extracranial meningiomas, also known as primary extradural meningiomas or ectopic meningioma, are a rare location-specific type of meningioma that arise outside the dural covering of the brain and spinal cord. They are essentially extracranial tumours, most often occurring in the head and neck, ...
Article

Extradural haematoma vs subdural haematoma

Differentiating extradural (EDH) from subdural (SDH) haemorrhage in the head is usually straightforward, but occasionally it can be challenging. SDHs are more common and there are a few distinguishing features which are usually reliable. Pathology History and mechanism of injury Extradural ha...
Article

Extradural haemorrhage

Extradural haematoma (EDH), also known as an epidural haematoma, is a collection of blood that forms between the inner surface of the skull and outer layer of the dura, which is the periosteum. They are commonly associated with a history of trauma and associated skull fracture. The source of ble...
Article

Extradural haemorrhage (summary)

Extradural haemorrhages (EDHs) represent collections of blood in the extradural (epidural) space. The haemorrhage sits between the skull superficially and the dura which overlies the brain parenchyma. Summary Epidemiology Patients with extradural haemorrhages are usually young and have a hist...
Article

Extradural neural axis compartment

Extradural neural axis compartment (EDNAC) exists from the tip of the coccyx all the way to the back of the globe, and yet it is relatively unknown as a concept. It is bounded externally by the periosteum of the vertebrae and sacrum inferiorly and the skull superiorly, and the visceral layer of ...
Article

Extradural space

The extradural (epidural) space is a potential space between the cranial bones and the endosteal layer of the dura mater, which is otherwise adherent to the cranial bone 1.  Gross Anatomy The extradural space is a potential space inside the cranial vault and is not normally appreciable unless ...
Article

Extraneural spread of intracranial neoplasms

Extraneural spread of primary intracranial neoplasms is distinctly uncommon, occurring far less frequently than CSF spread.  The most frequent neoplsams to do so, in decreasing order of frequency are: glioblastoma (GBM) meningioma medulloblastoma
Article

Extraocular muscle involvement in thyroid associated orbitopathy (mnemonic)

A mnemonic to  remember the order in which extraocular muscles are involved in thyroid associated orbitopathy (TAO) is: I'M SLOW Mnemonic I: inferior rectus M: medial rectus S: superior rectus L: lateral rectus O: obliques There is some debate about this however. Some claim superior rect...
Article

Extrapontine myelinolysis

Extrapontine myelinolysis (EPM) is one of the complications occurring secondary to rapid correction of hyponatraemia, and is, along with central pontine myelinolysis encompassed by the more recent term osmotic demyelination syndrome. In the vast majority of cases it is associated with central p...
Article

Extrapulmonary tuberculosis

Extrapulmonary tuberculosis (TB) refers to the haematogenous spread of Mycobacterium tuberculosis. Pathology Extrapulmonary tubercuosis can occur as a primary form of the disease, i.e. direct infection of an extrapulmonary organ without the presence of primary pulmonary tuberculosis or it can...
Article

Extrapyramidal system

The extrapyramidal system is the part of the motor system involved in modulation and regulation of movement. As its name suggests, it is distinct from the motor fibres that are relayed through the pyramids of the medulla oblongata (corticospinal and corticobulbar tracts). It is composed of nerv...
Article

Extreme capsule

The extreme capsule is a series of white matter tracts in the brain that run between the claustrum and insular cortex.
Article

Eye of tiger sign

The eye of the tiger sign refers to abnormal low T2 signal on MRI (due to abnormal accumulation of iron) in the globus pallidus with a longitudinal stripe of high signal (due to gliosis and spongiosis) that can be seen in: Hallervorden-Spatz syndrome: classical but not 100% pathognomonic progr...

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