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.

1,984 results found
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Gerstmann-Straussler-Scheinker disease

Gerstmann-Straussler-Scheinker disease is a very rare type of human transmissible spongiform encephalopathy. It manifests with dementia and/or ataxia and is due to a mutation in the prion protein (PRNP) gene, which is inherited in an autosomal dominant pattern. 
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Giant cell glioblastoma

Giant cell glioblastoma is a variant of glioblastoma (along with epithelioid glioblastoma and giant cell glioblastoma) recognised in the current (2016) WHO classification of CNS tumours 7. This tumour was previously called monstrocellular tumour due to the macro size of its cells. Epidemiology ...
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Giant cerebral aneurysm

Giant cerebral aneurysms are ones that measure >25 mm in greatest dimension.  Epidemiology Giant cerebral aneurysms account for ~5% of all intracranial aneurysms 1,3. They occur in the 5th-7th decades and are more common in females 2. Clinical presentation Patients can present with symptoms ...
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Gigantism

Gigantism is a nonspecific term that refers to enlargement of normal body proportions and can be divided into generalised gigantism (i.e. of the whole body) or localised gigantism (i.e. affection only part of the body).  Localised gigantism is due to a variety of causes, and is discussed separa...
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Ginkgo leaf sign (spinal meningioma)

The ginkgo leaf sign of spinal meningiomas (not to be confused with the ginkgo leaf sign of subcutaneous emphysema) has been described as a useful MRI sign in distinguishing a spinal meningioma from neurogenic tumour (e.g. spinal schwannoma).  It is seen on axial post contrast T1 imaging, with ...
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Glasgow coma scale

The Glasgow coma scale (GCS) was developed in 1974 1 to describe the level of consciousness specifically in patients with head injury although it is now used widely as a shorthand for all manner of presentations and has generally been validated, although concerns about its use in certain scenari...
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Glial cells

Glial cells, or neuroglia, are cells that surround the neurones of the central nervous system embedded between them, providing both structural and physiological support 1-3.  Together they account for almost half of the total mass 1 and 90% of all cells of the central nervous system 3. Glial ce...
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Glial fibrillary acid protein (GFAP)

Glial fibrillary acid protein (GFAP) is a commonly used target for immunohistochemistry and is positive in many glial cells and tumours of glial origin. GFAP is the building block for intermediate filaments which are abundant in the cytoplasms particularly of astrocytes. 
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Glioblastoma

Glioblastoma (GBM) is the most common adult primary intracranial neoplasm (see brain tumours), accounting for 15% of all intracranial neoplasms and approximately 50% of all astrocytomas. GBMs are high grade astrocytomas; they are therefore generally aggressive, largely resistant to therapy, and ...
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Glioblastoma NOS

Glioblastoma NOS (not otherwise specified) is a diagnosis in the current (2016) WHO classification of CNS tumours and denotes a diffuse glioma with astrocytic features and anaplasia, microvascular proliferation and/or necrosis consistent with a WHO grade IV glioblastoma but with inconclusive or ...
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Glioblastoma vs cerebral metastasis

Differentiating a glioblastoma (GBM) from a cerebral metastasis is a frequent challenge, with profound surgical, workup and treatment implications. Unfortunately distinguishing between the two entities is not always straightforward.  This article addresses helpful imaging features to aid in dis...
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Glioma treatment response assessment in clinical trials

Glioma treatment response assessment in clinical trials has undergone numerous revisions with a number of criteria having been developed over the years. This has been necessary as a result of a number of factors: improved understanding of tumour biology (e.g. appreciating importance of non-enha...
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Gliomatosis cerebri

Gliomatosis cerebri is a rare growth pattern of diffuse gliomas that involves at least three lobes by definition. There often is an important discordance between clinical and radiological findings, as it may be clinically silent while it appears as a very extensive process radiologically. Impor...
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Gliosarcoma

Gliosarcomas are a variant of glioblastoma (along with epithelioid glioblastoma and giant cell glioblastoma) recognised in the current (2016) WHO classification of CNS tumours 9. They are highly malignant (WHO grade IV) primary intra-axial neoplasms with both glial and mesenchymal elements. Ter...
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Gliosis

Gliosis is the focal proliferation of glial cells in the CNS in response to insult. By strict definition, gliosis is not synonymous with encephalomalacia which is the end result of liquefactive necrosis of brain parenchyma following an insult. Radiologically they share similar features and is of...
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Global cortical atrophy scale

The global cortical atrophy (GCA) scale, also known as the Pasquier scale, is a qualitative rating system developed to assess cerebral atrophy, especially in the context of neurodegenerative diseases. It evaluates atrophy in 13 brain regions assessed separately in each hemisphere and resulting i...
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Globe

The globes or simply, the eyes are paired spherical sensory organs, located anteriorly on the face within the orbits, which house the visual apparatus. Gross anatomy Location The globe is suspended by the bulbar sheath in the anterior third of the bony orbit.  Size Each globe is an approxim...
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Globe rupture

Globe rupture is an ophthalmologic emergency. A ruptured globe or an open-globe injury must be assessed in any patient who has suffered orbital trauma because open-globe injuries are a major cause of blindness. In a blunt trauma, ruptures are most common at the insertions of the intraocular mus...
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Globus pallidus

The globus pallidus (plural: globus pallidi) is a paired structure and one of the nuclei that make up the basal ganglia. It is a subcortical structure at the base of the forebrain and in anatomical relation to the caudate nucleus and putamen. It forms the lentiform nucleus with the putamen. Eac...
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Glomus tympanicum paraganglioma

Glomus tympanicum paragangliomas (chemodectomas) are the most common middle ear tumour.  Epidemiology There is a female predominance (M:F = 1:3); presentation is most common when patients are more than 40 years old 1,2.  Clinical presentation May be incidental but symptomatic masses produce ...
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Glossopharyngeal nerve

The glossopharyngeal nerve is the ninth (IX) of the twelve pairs of cranial nerves. It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve and has sensory, motor, and autonomic components. Gross anatomy Origin The sensory ganglion cells lie in the supe...
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Glossopharyngeal neuralgia

Glossopharyngeal neuralgia is due to irritation of the glossopharyngeal nerve and presents with repeated episodes of severe pain in the tongue, throat, ear, and tonsils, which can last from a few seconds to a few minutes. It is far less common than trigeminal neuralgia. Epidemiology Glossophar...
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Glutamine-Glutamate peak

Glutamate-Glutamine (Glx) peak is one of the regions assessed on MR spectroscopy, and resonates between 2.2 and 2.4 ppm chemical shift. It overlaps with the GABA peak and cannot be routinely separated from each other.
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Glutaric aciduria type 1

Glutaric aciduria type 1 is a leukodystrophy that can be subclassified as an organic acidopathy. It has a highly variable clinical presentation, and laboratory investigations are not always diagnostic. Imaging, therefore, has an important role to play as the MRI features can be characteristic. ...
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Glymphatic pathway

The glymphatic pathway has only recently been described and functionally represents the brain’s lymphatic system, although no anatomical structure equivalent to the peripheral lymphatic system is present within the brain parenchyma. It is believed to be a crucial normal homeostatic feature allow...
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Gomez-Lopez-Hernandez syndrome

Gomez-Lopez-Hernandez syndrome, also known as cerebellotrigeminal-dermal dysplasia, is a rare phakomatosis characterised by rhombencephalosynapsis, parietal-occipital scalp alopecia, brachycephaly, facial malformations and trigeminal anesthesia.  History and etymology It is named after Manuel ...
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Gradenigo syndrome

Gradenigo syndrome consists of the triad of: petrous apicitis abducens nerve palsy, secondary to involvement of the nerve as it passes through Dorello canal retro-orbital pain, or pain in the cutaneous distribution of the frontal and maxillary divisions of the trigeminal nerve, due to extensi...
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Grading of brachial plexus injuries

According to CT myelography, brachial plexus injuries can be classified into six types 1: N type: normal root sleeve and nerve roots A1 type: slightly deformed root sleeves and nerve roots as compared to unaffected site A2 type: obliteration of the tip of root sleeves and deformed thickened n...
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Granular cell tumour of the pituitary region

Granular cell tumour of the pituitary region, also known as a pituitary choristoma, are rare low-grade tumours of the posterior pituitary and infundibulum.  Terminology Care must be taken when reading older literature as granular cell tumours of the pituitary region, and alternative names incl...
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Granulocytic sarcoma

Granulocytic sarcoma (also called myeloid sarcoma and chloroma) is a rare neoplasm comprised of myeloid precursor cells. It can occur in association with: acute myeloid leukaemia (AML) chronic myeloid leukaemia (CML) other myeloproliferative disorders such as myelofibrosis with myeloid meta...
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Granulomatosis with polyangiitis

Granulomatosis with polyangiitis (GPA), previously known as Wegener granulomatosis, is a multisystem systemic necrotising non-caseating granulomatous vasculitis affecting small to medium sized arteries, capillaries and veins, with a predilection for the respiratory system and kidneys 3. This ar...
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Granulomatosis with polyangiitis (CNS manifestations)

CNS manifestations of granulomatosis with polyangiitis (GPA) (previously known as Wegener's granulomatosis) are rare. Granulomatosis with polyangiitis (Wegener granulomatosis), is a multi-system systemic necrotizing non-caseating granulomatous vasculitis affecting small to medium-sized arteries,...
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Granulomatous amoebic encephalitis

Granulomatous amoebic encephalitis (GAE), also referred to as cerebral amoebiasis, is a rare and usually fatal subacute-chronic CNS infection in immunocompromised patients caused by free-living amoebae such as Acanthamoeba spp (main cause), Balamuthia mandrillaris and Sappinia pedata. This is a...
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Greater palatine foramen

The greater palatine foramen is the opening in the posterior hard palate of the greater palatine canal, which is formed between the articulation of maxillary bone and the greater palatine sulcus of palatine bone. The canal is also known as the pterygopalatine canal. A small accessory canal branc...
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Greater superficial petrosal nerve

The greater (superficial) petrosal nerve originates at the geniculate ganglion, where the nervus intermedius and facial nerve join. It contains mainly preganglionic parasympathetic fibers and some sensory taste afferent from the soft palate. It arises at the geniculate ganglion, passes through ...
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Grey matter heterotopia

The grey matter heterotopias are a relatively common group of conditions characterised by interruption of normal neuronal migration from near the ventricle to the cortex, thus resulting in "normal neurons in abnormal locations" 2. They are a subset of disorders of cortical formation 3-4. Grey m...
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Ground glass density nodule

A ground glass density nodule (GGN) is a circumscribed area of increased pulmonary attenuation with preservation of the bronchial and vascular margins. A GGN can be: partly solid (part of the ground-glass opacity completely obscures the parenchyma) non-solid (no completely obscured areas) - pu...
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Growing teratoma syndrome

Growing teratoma syndrome is a rare complication after treatment for metastatic (or in the case of intracranial disease, primary) non-seminomatous germ cell tumours (NSGCT). It was first described in the paediatric population with treated germ cell neoplasms, and represents enlarging masses at ...
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Guillain-Barré syndrome

Guillain-Barré syndrome (GBS) is defined as a heterogeneous group of autoimmune polyradiculopathies, involving sensory, motor and autonomic nerves. It is the most common cause of rapidly progressive flaccid paralysis. It is believed to be one of a number of related conditions, sharing a similar ...
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Gyrus rectus

The gyrus rectus, or straight gyrus, is located at the medial most margin of the inferior surface of frontal lobe 1,2. Its function is unclear but it may be involved in higher cognitive function (e.g. personality) 3. Gross anatomy The gyrus rectus is bounded medially by the interhemispheric fi...
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Habenula

The habenula is part of the epithalamus and receives input from the brain via the stria medullaris. It outputs to many midbrain areas involved in releasing neuromodulators, such as dopamine, norepinephrine, and serotonin. The habenula was traditionally divided into lateral (limbic) and medial (...
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Haemangioblastoma (central nervous system)

Haemangioblastomas are tumours of vascular origin and occur both sporadically and in patients with von Hippel Lindau (vHL). They are WHO grade I tumours that can occur in the central nervous system or elsewhere in the body, including kidneys, liver, and pancreas. These tumours generally present...
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Haematocrit effect

The haematocrit effect with fluid-fluid levels is the result by layering of heavier cellular elements of blood located dependent to liquid supernatant may be seen on CT or MRI. It is most frequently seen in the setting of anticoagulation therapy or coagulopathy. See also signal flare phenomenon
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Haematomyelia

Haematomyelia refers to the presence of intramedullary haemorrhage or haematoma within the spinal cord. This is distinct from extramedullary haemorrhage, such as that seen in epidural haematomas. Although this can occur in the setting of trauma, the term is generally used to signify non-traumat...
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Haemorrhagic infarct vs intracerebral haemorrhage

Haemorrhagic infarct or haemorrhagic transformation of an infarct is seen to occur secondary to the breakdown of the lamina of the microvessels. Intracerebral haemorrhage (ICH) may overlap with a haemorrhagic infarct and hence needs to be differentiated as the line of treatment will vary. Diff...
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Haemorrhagic intracranial metastases

Haemorrhagic intracranial metastases are considered to represent between 3-14% of all cerebral metastases (c.f. 1-3% of gliomas are haemorrhagic). These classically originate from: melanoma: melanoma metastases to brain renal cell carcinoma choriocarcinoma thyroid carcinoma: papillary carci...
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Haemorrhagic intracranial tumours

Various types of brain tumours may cause haemorrhage. Increased tumour vascularisation with dilated, thin-walled vessels and tumour necrosis are the most important mechanisms of haemorrhage. The list includes: glioblastoma pituitary adenoma ependymoma central neurocytoma choroid plexus carc...
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Haemorrhagic metastases (mnemonic)

A mnemonic for primary malignancies responsible for haemorrhagic metastases is: MR CT BB Mnemonic M: melanoma: metastatic melanoma to brain R: renal cell carcinoma C: choriocarcinoma T: thyroid carcinoma, teratoma B: bronchogenic carcinoma B: breast carcinoma
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Haemorrhagic transformation of ischaemic infarct

Haemorrhagic transformation is a complication of cerebral ischaemic infarction and can significantly worsen prognosis. Terminology It should be noted that the term haemorrhagic transformation is a little variably used and collectively refers to two different processes, which have different inc...
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Haemosiderin cap sign

The haemosiderin cap sign refers to an MR imaging feature in some spinal tumours where a cap of T2 hypointense haemosiderin is above and/or below the tumour due to previous haemorrhage.  It is most often associated with spinal cord ependymomas, being seen in 20-33% of these cases 1. The sign, h...
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HANAC syndrome

Hereditary angiopathy with nephropathy, aneurysms, and muscle cramps (HANAC) syndrome is an autosomal dominant monogenic COL4A1-related disorder. Epidemiology The exact prevalence is unknown. Clinical presentation The cardinal features of HANAC syndrome are helpfully described in the name of...
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Harlequin eye deformity

The harlequin eye deformity may seen in unilateral (plagiocephaly) or bilateral (brachycephaly) coronal suture synostosis, and refers to the elevation of the superolateral corner of the orbit.
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Heerfordt syndrome

Heerfordt(-Waldenström) syndrome or uveoparotid fever is a variant of sarcoidosis, comprising of: fever parotid enlargement facial palsy ocular involvement (anterior uveitis) Epidemiology The exact prevalence is unknown, as only isolated case reports exist. Neurologic involvement may occur...
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Hemiconvulsion-hemiplegia epilepsy syndrome

Hemiconvulsion-hemiplegia epilepsy syndrome (HHE) is a clinical syndrome of infancy or early childhood that is associated with seizures, cerebral hemiatrophy and transient or permanent epilepsy. It refers to the characteristic holohemispheric global atrophy of one hemisphere, that is independen...
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Hemifacial hypertrophy

Hemifacial hyperplasia or hemifacial hypertrophy is a rare developmental anomaly characterised by asymmetric growth of hard and soft tissues of the face 1. Epidemiology These asymmetries are often noted at birth and are usually accentuated with increasing age, especially around puberty 2. The...
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Hemifacial spasm

Hemifacial spasm (HFS), similar to trigeminal neuralgia (CN V) and glossopharyngeal neuralgia (CN IX), is characterised by episodic discharges of the facial nerve (CN VII). As in the two other aforementioned conditions, irritation of the nerve at the root exit zone by an aberrant vascular struc...
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Hemimedullary syndrome

Hemimedullary syndrome, also known as Reinhold syndrome, occurs as a result of the occlusion of the ipsilateral vertebral artery proximal to the posterior inferior cerebellar artery and its anterior spinal artery branches 1-3. This situation causes lateral medullary infarct and medial medullary ...
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Hemimegalencephaly

Hemimegalencephaly is a rare congenital disorder of cortical formation with hamartomatous overgrowth all or a part of a cerebral hemisphere. This results from either increased proliferation or decreased apoptosis (or both) of developing neurons 2. Epidemiology Hemimegalencephaly is a cryptogen...
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Hepatic encephalopathy

Hepatic encephalopathy (also known as portosystemic encephalopathy) refers to a spectrum of neuropsychiatric abnormalities occurring in patients with liver dysfunction and portal hypertension. It results from exposure of the brain to excessive amounts of ammonia. Terminology Hepatic encephalop...
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Hereditary haemorrhagic telangiectasia

Hereditary haemorrhagic telangiectasia (HHT) is also known as Osler-Weber-Rendu syndrome. Epidemiology Worldwide prevalence ~1.5 per 100,000. Wide geographic variability with much higher incidence in certain regions, e.g. 1 in 200 in Dutch Antilles, 1 in 3500 in France. Clinical presentation ...
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Hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) refers to a heterogeneous group of neurodegenerative conditions characterised by progressive degeneration of the corticospinal tracts and posterior column of the spinal cord. Clinical presentation Patients often tend to have progressive lower extremity weakn...
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Herpes simplex encephalitis

Herpes simplex (HSV) encephalitis is the most common cause of fatal sporadic fulminant necrotizing viral encephalitis and has characteristic imaging findings.  Two subtypes are recognised which differ in demographics, virus and pattern of involvement. They are 1: neonatal herpes encephalitis ...
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Heschl's gyrus

Heschl's gyrus, also known as transverse temporal gyrus, is part of the temporal lobe and contains the primary auditory cortex (Brodmann area 41). It is entirely hidden within the Sylvian fissure, with the planum temporale and superior temporal gyrus located lateral to it. 
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High riding jugular bulb

A high riding jugular bulb is distinguished from an asymmetrically large jugular bulb by its dome (roof) reaching above the internal acoustic meatus (IAM). It need not be larger than the contralateral bulb, but usually is. A run of the mill high riding jugular bulb has an intact sigmoid plate -...
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High-grade glioma

High-grade glioma is a relatively vague term, and in some ways is best avoided, unless one deliberately wants to be vague/inclusive. It has often (especially in older literature) been used to denote both anaplastic gliomas (WHO grade III) and glioblastomas (WHO grade IV), always including astroc...
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High-velocity penetrating brain injury

High-velocity penetrating brain injuries, in practical terms most often due to cranial gunshot injuries, are a form of penetrating traumatic brain injuries, which are much less common than blunt traumatic brain injuries and distinguished from low-velocity penetrating brain injuries (such as stab...
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Hippocampal sulcus remnant cyst

Hippocampal sulcus remnant cysts are remnants of incomplete involution of the embryonic hippocampal fissure, and are an incidental finding.   Epidemiology They are seen in more than ~25% (range 10-40%) of the adult population 1,3. Radiographic features MRI They consist of small (1-2 mm) cys...
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Hippocampus

The hippocampus is an important component of the human brain, situated in the temporal lobe. It plays a role in information processing and the reproductive cycle and is involved in Alzheimer disease. Gross anatomy Location The hippocampus lies in the hippocampal sulcus immediately below the f...
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Hirayama disease

Hirayama disease, also termed non-progressive juvenile spinal muscular atrophy of the distal upper limbs, is a type of cervical myelopathy related to flexion movements of the neck. It is considered a benign motor neurone disorder with a stationary stage after a progressive course. Epidemiology ...
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History of imaging the pituitary region

The history of imaging the pituitary region encompasses many different modalities and has greatly evolved over the years, including plain radiographs, pneumoencephalography, angiography, CT and MRI. The pituitary gland is situated in the central skull base, closely related to the sphenoid sinus,...
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HIV associated dementia

HIV associated dementia (HAD), previously referred to as AIDS dementia complex (ADC), corresponds to a neurological clinical syndrome seen in patients with HIV infection. The associated imaging appearance is generally referred to as HIV encephalopathy. Terminology The terms HIV dementia comple...
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HIV associated neurocognitive disorders

HIV associated neurocognitive disorders (HAND), which is a new term emerged from an international conference in 2006 1, correspond to a group of clinical syndromes related to the HIV infection in the cells of the nervous system expressing different degrees of impairment of cognition and associat...
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HIV vacuolar myelopathy

HIV vacuolar myelopathy is the most common chronic myelopathy associated with HIV infection and is typically seen in the late stages of the disease. Clinical presentation Patients tend to have slowly progressive weakness of the lower extremities, gait disorders, sensory abnormalities in the lo...
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HIV/AIDS

Acquired immunodeficiency syndrome (AIDS) is an immunosuppressed state, caused by infection with the human immunodeficiency virus (HIV). It is characterised by opportunistic infections, neoplasms and neurological manifestations. Epidemiology According to the United Nations programme on HIV/AID...
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HIV/AIDS (CNS manifestations)

The CNS manifestations of HIV/AIDS (neuroAIDS) occur secondary to a wide range of neurodegenerative, infectious, inflammatory, or neoplastic processes.  Epidemiology Since the introduction of highly active antiretroviral therapy (HAART) in 1996, there has been a shift in the epidemiology of CN...
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Hockey stick sign (Creutzfeldt-Jakob disease)

The hockey stick sign refers to the hyperintense signal involving the pulvinar and dorsomedial thalamic nuclei bilaterally on FLAIR, in cases of variant Creutzfeldt-Jakob disease, which has the shape of a hockey stick. See also pulvinar sign (Creutzfeldt-Jakob disease) hockey stick sign (thyr...
Article

Holocord presentation

Holocord presentation refers to a process which involves the spinal cord, from cervicomedullary junction to the tip of the conus. It does not relate to a specific condition nor does it distinguish between involvement by cystic expansion or solid tumour, or by a combination of both. It merely den...
Article

Holoprosencephaly

Holoprosencephaly (HPE) is a rare congenital brain malformation resulting from incomplete separation of the two hemispheres. Classically three subtypes have been recognised, however additional entities are now included in the spectrum of the disease. The three main subtypes, in order of decreas...
Article

Homer Wright rosettes

Homer Wright rosettes are differentiated tumour cells grouped around a central region containing neuropil (therefore its association with tumors of neuronal origin). Pathology Examples of tumours where these can be seen include: medulloblastoma (the presence of Homer Wright rosettes in a post...
Article

Horizontal gaze palsy with progressive scoliosis

HGPPS is a rare autosomal recessive AR congenital anomaly caused by mutation of ROBO3 gene on chromosome 11. Clinical presentation Abnormal horizontal gaze while normal vertical gaze and kyphoscoliosis. Horizontal gaze requires the action of ipsilateral abducent nerve and contralateral oculomo...
Article

Horner syndrome

Horner syndrome classically presents as an ipsilateral blepharoptosis, pupillary miosis and facial anhydrosis due disruption at some point of the oculosympathetic pathway. The ptosis is due to interruption of the sympathetic control of the levator palpebrae superioris muscle, which controls elev...
Article

Hot cross bun sign (pons)

The hot cross bun sign refers to the MRI appearance of the pons in a variety of neurodegenerative diseases.  T2 hyperintensity forms a cross on axial images through the pons, representing selective degeneration of pontocerebellar tracts. It has been described in 1: multiple-system atrophy (MSA...
Article

Hot nose sign

The hot nose sign refers to increased perfusion in the nasal region on nuclear medicine cerebral perfusion studies in the setting of brain death. The absent or reduced flow in the internal carotid arteries is thought to lead to increased flow within the external carotid arteries and subsequent i...
Article

HTLV-1-associated myelopathy

HTLV-1-associated myelopathy (also known as tropical spastic paraparesis) is primarily seen in Japan, Melanesia and the Caribbean and presents with chronic spastic paraparesis.  Terminology This condition has been independently described in Japan (HTLV-1 associated myelopathy) and in the Carib...
Article

Human herpesvirus 6 encephalitis

Human herpesvirus 6 (HHV-6) encephalitis is a rare CNS infection due the virus reactivation in immunosuppressed patients, especially in those following a hematopoietic cell transplant who develop a characteristic limbic encephalitis syndrome with MRI signal intensity abnormalities of the mesial ...
Article

Hummingbird sign (midbrain)

The hummingbird sign, also known as the penguin sign, refers to the appearance of the brainstem in patients with progressive supranuclear palsy (PSP).  The atrophy of the midbrain results in a profile of the brainstem (in the sagittal plane) in which the preserved pons forms the body of the bir...
Article

Hunt and Hess grading system

The Hunt and Hess scale describes the severity of subarachnoid haemorrhage, and is used as a predictor of survival. grade 1 asymptomatic or minimal headache and slight neck stiffness 70% survival grade 2 moderate to severe headache; neck stiffness; no neurologic deficit except cranial nerve...
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Hunter's angle

Hunter's angle (HA) is a term coined from a neurosurgeon, Hunter Sheldon, at Huntington Medical Research Institutes. He placed his comb on the spectrum at approximately a 45° angle and connected several of the peaks. If the angle and peaks roughly corresponded to the 45° angle, the curve was con...
Article

Huntington disease

Huntington disease (HD), also known as Huntington chorea, is an autosomal dominant neurodegenerative disease, and one of the trinucleotide repeat disorders and caused by a loss of GABAergic neurons of the basal ganglia, especially atrophy of the caudate nucleus and putamen. Huntington disease is...
Article

Hutchinson pupil

Hutchinson pupil is a fixed and dilated pupil caused by compression of the oculomotor nerve (CN III) as a result of uncal herniation. It should not be confused with any of the following: Hutchinson's triad Hutchinson freckle Hutchinson teeth Hutchinson's sign Hutchinson syndrome History a...
Article

Hutchinson sign (disambiguation)

The Hutchinson sign can refer to two signs.  Hutchinson sign (ophthalmology) Relates to involvement of the tip of the nose from facial herpes zoster. It implies involvement of the external nasal branch of the nasociliary nerve (branch of the ophthalmic division of the trigeminal nerve) and thu...
Article

Hydatid disease

Hydatid cysts result from infection by the Echinococcus, and can result in cyst formation anywhere in the body.  Pathology There are two main strains which are 1,2: Echinococcus granulosus: commoner pastoral: dog is a main host; most common form  sylvatic: wolf is a main host  Echinococcus...
Article

Hydranencephaly

Hydranencephaly is a rare encephalopathy that occurs in-utero. It is characterised by destruction of the cerebral hemispheres which are transformed into a membranous sac containing cerebrospinal fluid and the remnants of cortex and white matter 1. Porencephaly is considered a less severe degree...

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