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...
Extraventricular neurocytomas, previously known as cerebral neurocytomas, are rare WHO grade II primary CNS neoplasms usually arising in the cerebral hemispheres. They are, as the name implies, extraventricular versions of central neurocytomas.
These tumours are reported at essen...
The extreme capsule is a series of white matter tracts in the brain that run between the claustrum and insular cortex.
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).
The eye of the tiger sign is most classically associated with Pantothenate kinase-associate...
Fabry disease is a multisystem disorder which results from an X-linked inborn error of metabolism. The disease is characterised by a deficiency in hydrolase alpha-galactosidase activity with a resultant abnormal accumulation of globotriaosylceramide (Gb3) in various organ systems. In men, the co...
The facial colliculus is an elevation on the floor of the fourth ventricle and is not formed by the facial nerve nucleus, but by the fibres of the facial nerve arching backwards around the abducens nerve (CN VI) nucleus before turning forwards once more in the caudal pons.
Facial colliculus syndrome refers to a constellation of neurological signs due to a lesion at the facial colliculus, involving:
abducens nerve (CN VI) nucleus
facial nerve (CN VII) fibres at the genu
medial longitudinal fasciculus
lower motor neuron facial nerve palsy ...
The facial nerve is one of the key cranial nerves with a complex and broad range of functions.
Although at first glance it is the motor nerve of facial expression which begins as a trunk and emerges from the parotid gland as five branches (see facial nerve branches mnemonic), it has taste and p...
There are many mnemonics to recall the branches of the facial nerve (superior to inferior) as they exit the anterior border of the parotid gland. Examples include:
Tall Zulus Bear Many Children
Two Zulus Bit My Cat
Two Zebras Bit My Coccyx
Ten Zebras Buggered My Car
To Zanzibar By Motor Car...
Facial nerve choristomas are rare, being characterised by non-neoplastic proliferation of smooth muscle cells and fibrous tissue. Facial nerve choristomas presumably can occur anywhere along the course of the facial nerve (CN VII), although the only cases reported are in the internal acoustic me...
Facial nerve schwannoma (FNS), also known as facial nerve neuroma/neurilemoma, is a schwannoma that arises from the facial nerve. They are generally uncommon, and when involving the temporal bone, make up less than 1% of all temporal bone tumours.
FNS is a rare tumour 2.
Helpful mnemonics for remembering the segments of the facial nerve include:
I Love Going To Makeover Parties 1
I Love Grinning, Then Making Pouts
both grinning and pouting are performed by muscles which are innervated by the facial nerve
I Must Learn To Make (facial) Expressions
Facial palsy refers to the neurological syndrome of facial paralysis. It can result from a broad range of physiological insults to the facial nerve or its central nervous system origins. The most common causes of this is Bell palsy.
While facial palsy refers to the clinical presen...
The facial-cavernous anastomoses are the communications of the facial and deep facial veins with the cavernous sinus.
At the medial canthus of the eye there is a communication with the ophthalmic veins, which drain into the cavernous sinus. Blood from the frontal scalp normally f...
Fahr syndrome, also known as bilateral striatopallidodentate calcinosis, is characterised by abnormal vascular calcium deposition, particularly in the basal ganglia, cerebellar dentate nuclei, and white matter, with subsequent atrophy.
It can be either primary (usually autosomal dominant) or se...
The falx cerebelli is a small infolding of the dura in the sagittal plane over the floor of the posterior cranial fossa. It partially separates the two cerebellar hemispheres 1.
The falx cerebelli is attached posteriorly in the midline to the internal occipital crest of the occip...
The falx cerebri is the largest of the four main folds (or septa) of the intracranial dura mater, separating the cerebral hemispheres 1.
The falx cerebri is a double-fold of dura mater that descends through the interhemispheric fissure in the midline of the brain to separate the...
In discussing mineralisation of the falx cerebri, many radiology textbooks use the term falx calcification and make no mention of falx ossification.
Ossification of dural folds is relatively unusual; one study suggested a prevalence of falx ossification of 0.7% 1. Even though, os...
Familial multiple cavernous malformation syndrome(s) are uncommon, accounting for only a minority of cavernous malformations.
It has been more frequently reported in patients of Hispanic descent 1.
The presentation is most commonly with seizures (38-55%) 1 ...
Fat embolism syndrome (FES) is a rare clinical condition caused by circulating fat emboli leading to a multisystemic dysfunction. The classical clinical triad consists of:
It occurs in ~2.5% (range 0.5-4%) of th...
Fatal familial insomnia is an extremely rare autosomally inherited prion disease 1. Unlike other prion diseases, it does not exhibit spongiform changes. The main pathological findings are gliosis in the inferior olivary nuclei and thalami.
A fatty falx cerebri is a common finding, seen (according to one study) 7.3% of patients, and is explained by fat being a normal feature of the extradural neural axis compartment located between the two visceral layers of the falx.
A fatty falx is an incidental finding and should not be mistak...
The Fazekas scale is used to simply quantify the amount of white matter T2 hyperintense lesions usually attributed to chronic small vessel ischaemia, although clearly not all such lesions are due to this.
This classification was proposed by Fazekas et al. in 1987 1 and at the time of writing (l...
FCD may refer to:
focal cortical dysplasia (of the brain)
fibrous cortical defect (of the bone)
Feingold syndrome is characterised by the combination of:
alimentary tract atresias especially oesophageal atresia
Fetal brain tumours are uncommon and tends to have very different pathological spectrum than that observed in adults; in order of decreasing frequency:
fetal intracranial teratoma: most common tumour by far
astrocytoma/glioblastoma: next most common
craniopharyngioma: papillary type
Fetal hydrocephalus often refers to an extension of fetal ventriculomegaly where the ventricular dilatation is more severe. It is usually defined when the fetal lateral ventricular diameter is greater than 15 mm 1.
The estimated incidence is 0.5-3% per 1000 live births. There may ...
A fetal interhemispheric cyst refers to an interhemishperic cyst diagnosed in utero. It is seen as a cystic collection located in the interhemispheric fissure, with or without communication with the ventricular system.
agenesis of the corpus callosum: strong association...
Fetal intracranial calcification refers to intracranial calcification detected in utero. This can arise from a number of pathologies which include:
in utero infections
fetal toxoplasmosis infection: calcification tends to be randomly distributed
fetal cytomegalovirus infection1: calcificatio...
Fetal intracranial cystic lesions can arise number of pathologies, including:
fetal arachnoid cyst
fetal choroid plexus cyst
fetal connatal cyst
fetal porencephalic cyst
fetal interhemispheric cyst
fetal sub ependymal cyst
dorsal cyst of holoprosencephaly
Blake pouch cyst...
Fetal intracranial haemorrhage may occur either within the cerebral ventricles, subdural space or infratentorial fossa.
Haemorrhages can occur in a number of situations:
mechanical trauma, e.g. maternal abdominal blunt or birth trauma
severe fetal hypoxia
background fetal thromboc...
A fetal (origin of the) posterior cerebral artery is a common variant in the posterior cerebral circulation, estimated to occur in 20-30% of individuals 2.
The posterior communicating artery (PCOM) is larger than the P1 segment of the posterior cerebral artery (PCA) and supplies the bulk of the...
Fetal schizencephaly refers to schizencephaly diagnosed in utero. Usually only open lips types can be diagnosed antenatally.
may show a unilateral or bilateral defect extending from the pial surface to the ventricular wall
there may be other feature...
Fetal ventriculomegaly refers to the presence of dilated cerebral ventricles in utero.
Important in itself, it is also associated with other CNS anomalies.
Using the current sonographic cut-off criteria (see radiographic features below), the estimated prevalence may be at ~0.9% o...
Fetal ventriculomegaly (ventricle width >10 mm) is an important finding in itself and it is also associated with other central nervous system abnormalities. For more information, see the main article fetal ventriculomegaly.
Fetal ventriculomegaly can be thought of in ter...
Fibrillary astrocytomas are the most common type of diffuse low grade astrocytoma and as of the 2016 update to WHO classification of CNS tumours it no longer exists as a distinct entity, having been incorporated into the generic term diffuse astrocytoma 6.
Unlike the other variant...
Fibrocartilaginous embolism (also known as nucleus pulposus embolism) is a rare cause of spinal cord ischaemia due to embolisation of nucleus pulposus material from intervertebral disc in a retrograde direction to a spinal artery or vein.
Fibrocartilaginous embolism is a diagnosis of suspicion....
Fibrous meningiomas (also known as fibroblastic meningiomas) are the second most common histological subtype of meningioma, found in ~50% of all meningiomas, usually along with meningothelial histology (40%) or in isolation (7%). They are, for some reason, the most common intraventricular mening...
The following lesions may resemble a figure of eight (sometimes referred to as snowman shaped):
supracardiac variety of total anomalous pulmonary venous return 1
pituitary macroadenoma with suprasellar extension 2
intraspinal neurofibroma with extraspinal extension through neural foramina
The Fisher scale is the initial and best known system of classifying the amount of subarachnoid haemorrhage on CT scans, and is useful in predicting the occurrence and severity of cerebral vasospasm, highest in grade 3 2.
Numerous other scales have been proposed, incorporating various paramete...
The flat floor of fourth ventricle sign is useful in detecting a pontine mass and is a sign of mass effect. The normal floor of the fourth ventricle (remember that the floor is anterior) normally slopes upwards towards the midline, with the facial colliculi visible on either side.
It is a non-...
Flavivirus encephalitis include a number of entities which characteristically involve the basal ganglia and thalami.
Typically these conditions present with a prodrome which is nonspecific but indicative of a viral infection. Symptoms include fever, myalgia, rash, rigors...
The presence of Flexner-Wintersteiner rosette is characteristic for retinoblastoma but is also seen in pineoblastoma and medulloepitheliomas.
Flow-diverter stents are relatively new and important devices in the management of intracranial aneurysms, especially ones that are large, broad-necked or fusiform.
In a multi-centre study in Italy, Briganti et al reported an overall morbidity rate of 3.7% and a mortality rate o...
Focal areas of signal intensity (FASI), alternatively called focal abnormal signal intensity or unidentified bright objects, are bright areas on T2-weighted images commonly identified in the basal ganglia (often the globus pallidus), thalamus, brainstem (pons), cerebellum, and subcortical white ...
Focal brainstem gliomas are a relatively uncommon type of brainstem glioma, which carry a more favorable prognosis compared to the more common diffuse brainstem glioma. The name is a reflection of the imaging findings, which demonstrate a sharply demarcated mass with relatively frequent enhancem...
Focal calvarial thinning can result from a number of causes. They include:
bilateral thinning of the parietal bones (normal variant) most common
mega cisterna magna
peripherally located tumors (e.g. oligodendroglioma)
Focal cortical dysplasias (FCD) represent a heterogeneous group of disorders of cortical formation, which may demonstrate both architectural and proliferative features. They are one of the most common causes of epilepsy and can be associated with hippocampal sclerosis and cortical glioneuronal n...
Fogging phenomenon is seen on non contrast CT of the brain and represents a transient phase of the evolution of cerebral infarct where the region of cortical infarction regains a near-normal appearance.
During the first week following a c...
Foix-Alajouanine syndrome refers to presentation of spinal AVMs with progressive neurological deterioration.
Initially, patients have a spastic paraplegia which progresses to flaccidity, loss of sphincter control and ascending sensory level. It is thought to be due to venous hypertension.
The foramen caecum is located in the anterior cranial fossa, anterior to the cribriform plate of the ethmoid bone and posterior to the frontal bone, within the frontoethmoidal suture. It lies at a variable distance from the crista galli.
The foramen caecum is frequently found in infants, uncomm...
Foramen caecum can refer to a number of different anatomical structures:
foramen caecum (tongue)
foramen caecum (anterior cranial fossa)
The foramen lacerum is a triangular opening located in the middle cranial fossa anterior to the petrous apex, which forms its posterior border. Its anterior border is formed by the body of the sphenoid bone at the junction of greater wing and pterygoid process and medial border is formed by the ...
The foramen magnum is the largest foramen of the skull and is part of the occipital bone 1. It is oval in shape with a large antero-posterior diameter 2.
The foramen magnum is found in the most inferior part of the posterior cranial fossa 3. It is traversed by vital structures in...
The foramen of Magendie (also called median aperture) is one of the foramina in the ventricular system and links the fourth ventricle and the cisterna magna. It is one of the three ways that cerebrospinal fluid (CSF) can leave the fourth ventricle and enter the subarachnoid space.
Foramen ovale is an oval shaped opening in the middle cranial fossa located at the posterior base of the greater wing of the sphenoid bone, lateral to the lingula. It transmits the mandibular division of the trigeminal nerve (CN Vc), accessory meningeal artery, emissary veins between the caverno...
The foramen rotundum is located in the middle cranial fossa, inferomedial to the superior orbital fissure at the base of greater wing of the sphenoid bone. Its medial border is formed by lateral wall of sphenoid sinus. It runs downwards and laterally in an oblique path and joins the middle crani...
The foramen spinosum is located in the posteromedial part of greater wing of sphenoid bone posterolateral to foramen ovale which connects the middle cranial fossa with the infratemporal fossa. It transmits the middle meningeal artery, middle meningeal vein, and (usually) the nervus spinosus.
The forceps major, also known as the posterior forceps, is a fibre bundle which connects the occipital lobes and crosses the midline via the splenium of the corpus callosum.
The forceps minor, also known as the anterior forceps, is a fibre bundle which connects the lateral and medial surfaces of the frontal lobes and crosses the midline via the genu of the corpus callosum.
The fornix is the main efferent system of the hippocampus and an important part of the limbic system. It is one of the commissural fibres connecting the cerebral hemispheres.
Roughly C-shaped, the fornix extends from the hippocampus to the mamillary bodies of the hypothalamus and...
The fossa of Rosenmüller, also known as the posterolateral or pharyngeal recess, is the most common site of origin for nasopharyngeal carcinoma.
It is located superior and posterior to the torus tubarius (the posterior projection of the cartilaginous portion of the eustachian tub...
The fourth ventricle is one of the components of the ventricular system in the brain, along with the lateral and third ventricles. It extends from the cerebral aqueduct (of Sylvius) to the obex and is filled with CSF.
CSF enters the ventricle via the cerebral aqueduct and leaves via one of four...
A fourth ventriculocoele is large posterior fossa cyst which remodels, thins and eventually erodes through the occipital bone to form an occipital encephalocoele.
It may be classified as part of the Dandy-Walker continuum, but this is controversial.
A foveola pharyngica recess is one of the variants of the inferior median clival canal, thought to represent a remnant of the notocord. It represents a blind ending recess in the anteroinferior surface (nasopharyngeal) surface of the clivus 1,2.
Determining fracture type is really important when looking at a fracture and trying to describe it. Fractures can broadly be split into complete and incomplete fractures.
This is a summary article. For more information, you can read a more in-depth reference articles: complet...
Fracture-a-la-signature (or signature fracture) is another term used to described a depressed skull fracture.
Fracture-a-la-signature derives its name from forensic medicine because the size and shape of a depressed skull fracture may give information on the type of weapon used. It can be a si...
Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive degenerative movement disorder resulting from a fragile X “premutation”, defined as 55-200 CGG repeats in the 5’-untranslated region of the FMR1 gene 1. The premutation can expand in subsequent generations (during oogenesis) to...
Friedreich ataxia (FA) is the most common inherited progressive ataxia. It carries an autosomal recessive inheritance 1.
Thought to have an estimated prevalence of ~1:50,000. There is no recognised gender predilection.
Typically present in childhood to adolescence. Those with a h...
Frontal horn width to intercaudate distance ratio (FH/CC) is used in assessing patients with suspected Huntington's disease.
On the same axial plane obtained on the ACPC (anterior commissure and posterior commissure) line, the ratio between the distance between the caudate heads (where they ar...
The frontal lobe is by far the largest of the four lobes of the cerebrum, and is responsible for many of the functions which produce voluntary and purposeful action.
The frontal lobe is the largest lobe accounting for 41% of the total neocortical volume 8. The frontal lobe resid...
The frontal pole is one of the three poles of the brain (along with the occipital pole and temporal pole), and corresponds to the anterior most rounded point of the frontal lobe.
It does not have easily defined boundaries, but is roughly equivalent to the frontopolar cortex, which in turn is co...
Frontoethmoidal encephalocoeles are second only to occipital encephalocoeles in terms of frequency, representing approximately 15% of all encephalocoeles. They represent meninges or brain tissue herniating through cranial defect in the anterior cranial fossa and typically result in facial defor...
The frontolacimal suture is the cranial suture between the frontal and lacrimal bones.
The frontopolar artery is a branch of the A2 segment of the anterior cerebral artery (ACA), commonly arising after the medial frontobasal artery and coursing obliquely across the medial surface of the cerebral hemisphere towards the frontal pole.
The frontopolar cortex is located at the frontal pole of each frontal lobe, and is comprised of three roughly horizontal gyri: superior, middle and inferior frontopolar gyri.
It contains Brodmann area 10, which is thought to contribute to many aspects of cognition 1,2.
Despite many studies re...
Frontotemporal dementia (FTD) is a confusing term used inconsistently in the literature and is thus best avoided. The following are some of the conditions sometimes denoted by this term:
frontotemporal lobar degeneration (FTLD) 1
behavioural variant of FTLD 2
Pick disease (an anti...
Frontotemporal lobar degeneration (FTLD) is the pathological description of a group of neurodegenerative disorders characterised by focal atrophy of the frontal and temporal cortices. The conditions grouped under this term vary from publication to publication, depending on whether clinical, path...
Fukuyama congenital muscular dystrophy (FCMD) is a form of congenital muscular dystrophy.
FCMD is almost exclusively found in Japan where it has an incidence of 2-4 per 100,000 infants and is the second most common muscular dystrophy after Duchenne muscular dystrophy 1,2. However,...
Functional magnetic resonance imaging (fMRI) is a technique used to obtain functional information by visualising cortical activity. fMRI detects subtle alteration in blood flow in response to stimuli or actions. It is used in two broad ways:
typically in pre-surgical patients...
The fusiform gyrus, also known as the temporo-occipital gyrus is a structure that lies on the basal surface of the temporal and occipital lobes. It forms part of Brodmann area 37, along with the inferior and medial temporal gyri. As its name suggests, it is composed of a temporal or anterior por...
Fusiform intracranial aneurysms are a type of intracranial aneurysms with an elongated fusiform shape caused by atherosclerotic disease most common in the vertebrobasilar circulation.
3%-13% of all intracranial aneurysms
They can be incidental or asymptomat...
The Galassi classification of middle cranial fossa arachnoid cysts is used to classify arachnoid cysts in the middle cranial fossa, which account for 50-60% of all arachnoid cysts 1. Galassi et al published this classification in 1982, and at the time of writing (June 2016) it remains the most ...
Gamma-aminobutyric acid (GABA) is the principle inhibitory neurotransmitter in the central nervous system 1 and as such, is one of the compounds examined in MR spectroscopy. It is present in the human brain at a concentration of about 1 mM, a whole order of magnitude lower than some of the more...
Gangliocytomas are rare indolent CNS tumours (WHO grade I), primarily encountered in children, and frequently discovered as the cause of epilepsy. They differ from gangliogliomas by the absence of neoplastic glial cells, although both tumours are defined by the presence of displaced ganglion cel...
Ganglioneurocytomas are rare variants of extraventricular neurocytomas, themselves an uncommon variant of central neurocytomas (intraventricular).
They are recognised in the current (2016) WHO classification of CNS tumours when an extraventricular neurocytoma demonstrates a distinctive and defi...
Ganglioneuromas are fully differentiated neuronal tumours that do not contain immature elements and potentially occur anywhere along the peripheral autonomic ganglion sites.
On imaging, usually, they present as well-defined solid masses and can be quite large at presentation. Generally, they a...
Gemistocytic astrocytoma is a histologic subtype of low grade astrocytoma, with a poorer prognosis than other matched WHO grade tumours, and with no specific imaging features.
For a general discussion of clinical presentation, epidemiology, treatment please refer to the article on low grade as...
The geniculate ganglion contains fibres for taste and somatic sensation and is located in the petrous temporal bone.
It is located at the first genu of the facial nerve at the anterior most part of the Fallopian canal at the junction between the labyrinthine and tympanic segment...
Germinal matrix haemorrhages, also know as periventricular-intraventricular haemorrhages (PVIH), correspond to the most common type of intracranial haemorrhage in neonates and are related to a perinatal stress affecting the highly vascularised subependymal germinal matrix. The majority of cases ...
The term germinoma usually refers to a tumour of the brain (WHO Classification of CNS tumours), but can also refer to similar tumours of the ovary and testis.
dysgerminoma of the ovary
seminoma of the testis
All three tumours share similar histology.
Gerstmann syndrome, also known as angular gyrus syndrome, is a dominant hemisphere stroke syndrome consisting of four components:
agraphia or dysgraphia
acalculia or dyscalculia
Pure Gerstmann syndrome is said to be without aphasia.
History and ety...
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.