Abscesses are focal confined collections of suppurative inflammatory material and can be thought of as having three components 1:
a central core consisting of necrotic inflammatory cells and local tissue
peripheral halo of viable neutrophils
surrounded by a 'capsule' with dilated blood vessel...
An absent septum pellucidum may rarely be an isolated finding, or more commonly be seen in association with a variety of conditions.
The septum pellucidum is partly or entirely absent in 2 or 3 individuals per 100,000 in the general population.
An absent septum pelluc...
Acute occlusion of the basilar artery may cause brainstem or thalamic ischaemia or infarction. It is a true neuro-interventional emergency and, if not treated early, brainstem infarction results in rapid deterioration in the level of consciousness and ultimately death.
Differentiating between acute and chronic infarction on a CT brain is an important skill for many health professionals particularly in the emergency setting:
acute: cytotoxic oedema
chronic: encephalomalacia; Wallerian degeneration
acute: more dense than CSF
Anoxic brain injury, also known as global hypoxic-ischaemic injury, is seen in all age groups (from antenatal to the elderly) as a result of numerous aetiologies. The pattern of injury depends on a number of factors including:
age of the patient (brain maturity)
neonatal hypoxic-ischaemic ence...
Anterior inferior cerebellar artery (AICA) territory infarcts are much less common than posterior inferior cerebellar artery (PICA) infarcts.
AICA territory infarcts are rare, comprising ~1% of ischaemic cerebellar strokes 2.
AICA stroke syndrome presents ...
Artery of Percheron territory infarct is rare, on account of the relative rarity of the artery of Percheron, and presents with a variety of signs and symptoms collectively termed the paramedian thalamic syndrome. It is a type of posterior circulation infarction.
On imaging, it is classically ch...
The atlantodental interval (ADI), as the name suggests, is the horizontal distance between the anterior arch of the atlas and the dens of the axis, used in the diagnosis of atlanto-occipital dissociation injuries and injuries of the atlas and axis.
It is the distance (in mm) between the posteri...
Basal ganglia and thalamus signal abnormalities occur in a wide variety of conditions. Ischaemia/hypoxia, metabolic disorders and toxins, particularly those that affect the respiratory chain, have a predilection for affecting the basal ganglia as they are highly metabolically active.
They can ...
Basal ganglia calcification is common and is seen in approximately 1% of all CT scans of the brain, depending on the demographics of the scanned population. It is seen more frequently in older patients and is considered a normal incidental and idiopathic finding in an elderly patient but should ...
There are many causes of basal ganglia T1 hyperintensity, but the majority relate to deposition of T1-intense elements within the basal ganglia such as:
calcium and phosphate abnormalities
acquired non-wilsonian hepatocerebral degeneration
The causes of basal ganglia T2 hyperintensity can be remembered using the mnemonic LINT:
venous infarction (internal cerebral vein thrombosis)
neurodegenerative / metabolic
Huntington disease: especially caudate heads
Basal ganglia T2 hypointensities can be caused by any of the following and is commonly remembered using the mnemonic ChOMP.
Parkinson disease: more in globus pallidus
Parkinson-plus syndrome: more in putamen
deoxyhemoglobin of hemorrhage
Basilar invagination, also called basilar impression, is a congenital or acquired craniocervical junction abnormality where the tip of the odontoid process projects above the foramen magnum.
The terms basilar invagination and basilar impression are often used interchangeably becau...
The basion-axial interval (BAI), as the name suggests, is the horizontal distance between the basion and the posterior cortex of the axis, used in the diagnosis of atlanto-occipital dissociation injuries.
It is the distance (in mm) between the basion and the superior extension of the posterior ...
The basion-dens interval (BDI), as the name suggests, is the distance between the basion and the tip of the dens, used in the diagnosis of atlanto-occipital dissociation injuries.
It is the distance from the most inferior portion of the basion to the closest point of the superior aspect of the ...
There are a number of benign metastasising tumours:
benign metastasising meningioma 1,2
benign metastasising leiomyoma 3
primary adenoma of thyroid 4
giant cell tumour of bone 5
The bicaudate index is the ratio of width of two lateral ventricles at the level of the head of the caudate nucleus to distance between outer tables of skull at the same level. It can be a useful marker of ventricular volume and in the diagnosis of hydrocephalus.
Involvement of both middle cerebellar peduncles is uncommon, but has a relatively long differential, including 1:
multiple systemic atrophy (MSA)
Birth trauma relates to those conditions caused by both physical/mechanical and hypoxic injuries.
Birth trauma occurs in ~5 per 1000 births 2.
There are a wide range of conditions related to birth trauma, ranging from superficial and minor injuries through t...
Brain stones, also known as cerebral calculi, refers to large intracranial calcifications that may be solitary or multiple.
If symptomatic, patients most commonly present with seizures.
Localisation of brain stones can help narrow the underlying aetiology bu...
Calcification of the globe has many causes, varying from the benign to malignant. When calcification is seen of the posterior half of the globe, it could relate to any of the layers (scleral, choroidal or retinal), as it is not possible to separate them out on CT.
drusen: 1% population...
Calvarial thickening can occur from a number of causes. These include
chronic ventricular shunting1
anaemias (largely associated with massive haematopoiesis)
Carotid artery stenosis also referred as extracranial carotid artery stenosis, is usually caused by an atherosclerotic process and is one of the major causes of stroke and transient ischemic attack (TIA) 1.
This article refers to stenosis involving carotid bulb and the proximal segment of inte...
A cavernous sinus mass has a wide differential including:
orbital apical inflammation with cavernous sinus involvement (Tolosa-Hunt syndrome)
any of the cranial nerves traversing the cavernous sinus: III, IV, V (V1 and V2) and VI
trigeminal schwannoma is ...
The central nervous system curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core central nervous system knowledge.
Topics pertaining to the intracranial content (brain, pituitary, dura, intracranial vasculatures). There will be...
Cerebellopontine angle (CPA) masses frequently occur, many of which are relatively specific for the region.
Cerebellopontine angle masses can be divided into four groups, based on imaging characteristics:
mass with high T1 signal on MRI
mass with CSF intensity/den...
Cerebral arteriovenous fistulae (CAVF) are cerebral vascular malformations or acquired conditions in which there is an abnormal direct communication between a venous and an arterial channel without the presence of a true nidus.
dural arteriovenous fistula (DAVF)
caroticocavernous fistula (CCF...
Cerebral atrophy is the morphological presentation of brain parenchymal volume loss that is frequently seen on cross sectional imaging. Rather than being a primary diagnosis, it is the common endpoint for range disease processes that affect the central nervous system. Though often no identifiabl...
Cerebral herniation, also referred to as acquired intracranial herniation, refers to shift of cerebral tissue from its normal location, into an adjacent space as a result of mass effect.
There are a number of different patterns of cerebral herniation which describe the type of herni...
Cerebral intraparenchymal hyperattenuations have been increasingly recognised on CT scans following mechanical thrombectomy for treatment of thromboembolic ischaemic stroke. It is a term that encompasses both contrast staining and petechial haemorrhagic change, and is used as distinguishing betw...
The differential for peripheral or ring enhancing cerebral lesions includes:
subacute infarct /haemorrhage /contusion
demyelination (incomplete ring)
tumefactive demyelinating lesion (incomplete ring)
Vascular malformations of the central nervous system can be divided, as they can elsewhere, into high and low flow malformations.
arteriovenous malformation (AVM)
cerebral AVM (pial/parenchymal AVM)
cerebral proliferative angiopathy
dural arteriovenous fistula (DAVF)
Chamberlain line is a line joining the back of hard palate with the opisthion on a lateral view of the craniocervical junction.
It helps to recognise basilar invagination which is said to be present if the tip of the dens is >3 mm above this line.
McGregor developed a modificatio...
"Chasing the dragon" is a sign seen in toxic leukoencephalopathy caused by inhalation of heroin fumes.
Three stages are recognised:
cerebellar signs and motor restlessness
pyramidal and pseudobulbar signs
spasms, hypotonic paresis, and ultimately death
Only a minorit...
Chorioretinitis refers to inflammation of the retina and choroid. As a delayed sequelae, it is one of the causes of calcification of the globe. It is often considered a form of posterior uveitis.
various congenital infections such as 2-3
rubella: ocular rubella
There are many signs in radiology that are related to Christmas:
snowcap sign in avascular necrosis
in total anomalous pulmonary venous return
in pituitary macroadenomas
snowstorm appearance in complete hydatidiform and testicular microlithiasis
holly leaf sign in calcified pl...
There are several viral and prion infections which can result in a chronic encephalitis with slow progression into brain atrophy. These have very poor prognosis with no effective treatment. Some of these include:
progressive multifocal leukoencephalitis
subacute sclerosing panencephalitis
The differential of a mass involving or arising from the clivus is a relatively narrow one and can be divided into whether the lesion arises from the skull base itself, from the intracranial compartment or from below the base of skull.
When evaluating the clivus it is important to compare the...
This article aims to be a collection of articles that represent the central nervous system infectious diseases. There will be some overlap between articles as they are listed and discussed in a mixture of anatomical and aetiological classification.
It is important to remember tha...
CNS lymphoma refers to the involvement of the central nervous system with lymphoma. It can be broadly divided into primary and secondary, with a number of special types of also recognised.
primary CNS lymphoma (PCNSL)
MALT lymphoma of the dura 5
secondary CNS lymphoma...
Cochlear implants (CI) are a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. Unlike conventional hearing aids, the cochlear implant does not amplify sound, but works by directly stimulating any functioning audi...
COL4A1-related disorders are a group of autosomal dominant disorders caused by a mutation in the COL4A1 gene.
The exact prevalence is unknown, but the group of disorders is considered to be under-recognised, especially asymptomatic variants 1.
The clinical ...
Colpocephaly is a descriptive term to a disproportionate prominence of the occipital horns of the lateral ventricles. It can result from a wide range of congenital insults.
Patient may present with motor abnormalities, cognitive deficit, visual abnormalities, and seizures...
Communicating hydrocephalus is a type of hydrocephalus where CSF is able to leave the ventricular system.
Communicating hydrocephalus is commonly used as the opposite of obstructive hydrocephalus which leads to much unnecessary confusion, as most causes of communicating hydrocepha...
Complications of cranial radiation therapy are fairly common, particularly in long term survivors, and especially in paediatric patients.
Cranial radiotherapy is used for a variety for a brain tumours, either in isolation or in combination with concurrent chemotherapy. Complications from irradi...
Congenital calvarial defects are a group of disorders characterised by congenital calvarial bone defects that vary in severity.
CT with 3D shaded surface reformats is the best imaging tool as it demonstrates calvarial defects and bone margins:
Congenital muscular dystrophies (CMD) are a heterogeneous group of autosomal recessive myopathies presenting at birth with hypotonia, delayed motor development, and early onset of progressive muscle weakness, confirmed with a dystrophic pattern on muscle biopsy.
Congenital ventriculomegaly can have large number of syndromic associations
fetal alcohol syndrome
Convexal subarachnoid haemorrhages (cSAH) are nontraumatic intracranial haemorrhages that occur within the surface sulci of the brain (c.f. basal cisternal distribution of aneurysmal SAH). There are various causes of convexal SAH, some of which include:
dural venous sinus thromboses
A coup-contrecoup injury is a term applied to head injuries and most often cerebral contusions and traumatic subarachnoid haemorrhage. It refers to the common pattern of injury whereby damage is located both at the site of impact (often less marked) and on the opposite side of the head to the po...
Cranioplasty is the surgical intervention to repair cranial defects, and is mostly performed after traumatic injuries. The procedure is performed using different materials and techniques, with no consensus about the best option. Methyl-methacrylate is the prosthetic material most extensively use...
Craniotomy is a surgical procedure where a piece of calvarial bone is removed to allow intracranial exposure. The bone flap is replaced at the end of the procedure, usually secured with microplates and screws. If the bone flap is not replaced it is either a craniectomy or cranioplasty.
A cystic spinal lesion can result from a number of disease entities. They include
Dandy walker malformation
certain skeletal dysplasias 2
tricho-rhino-phalangeal syndrome type I
due to a tumour
Deep brain stimulation is used in a variety of clinical settings, predominantly in patients with poorly controlled movement disorders. Although effective, its exact mode of function continues to be poorly understood 2.
Careful patient selection and target selection are essential if the proced...
Demyelinating disorders are a subgroup of white matter disorders characterized by the destruction or damage of normally myelinated structures. These disorders may be inflammatory, infective, ischaemic or toxic in origin and include 1-7:
multiple sclerosis (MS)
Most tumours of the CNS can potentially occur in the temporal lobe, but entities with a predilection for being diagnosed in this location include:
pleomorphic xanthoastrocytoma (PXA)
dysembryoplastic neuroepithelial tumour (DNET)
Diffuse atrophy of the cerebellum refers to degeneration/reduction from a previously normal cerebellar volume.
Cerebellar atrophy slightly differs from cerebellar hypoplasia meaning the cerebellum was not well formed to start with.
Diffuse atrophy can result ...
Dopaminergic pathways include:
Dural arteriovenous shunts (DAVS) are rare congenital arteriovenous malformations (CAVMs). On the basis of clinical and anatomical features DAVS have three different types:
dural sinus malformations (DSMs)
infantile or juvenile DAVS (IDAVS)
adult DAVS (ADAVS)
Dural ectasia refers to ballooning or widening of the dural sac which can result in posterior vertebral scalloping and is associated with herniation of nerve root sleeves.
Patients with dural ectasia may present with low back pain or radicular pain in the buttocks or legs...
Pachymeningeal enhancement, also known as dura-arachnoid enhancement 4, refers to a dural and outer layer of arachnoid pattern of enhancement seen following contrast administration and may occur in the conditions listed below:
Dural masses can be the result of a number of different tumours and conditions, although meningiomas are by far the most common. The differential of a dural mass includes:
primary dural lymphoma
solitary fibrous tumour of the dura
Ectopia lentis refers to subluxation or dislocation of the lens of the eye secondary to dysfunction or disruption of zonular fibres.
systemic and syndromic disorders
typically upwards and out
most common spontaneous cause 2
homocystinuria - ty...
Elevated prolactin can be due to a number of causes, including elevated production/secretion as well as reduced inhibition.
Prolactin is controlled by numerous homeostatic mechanisms, with tonic secretion of prolactin inhibitory hormone (dopamine) by the hypothalamus having a dominant effect 1...
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.
Colloquially, the term empyema is used to refer to thoracic empyemas but there are variou...
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)...
Enlargement of sella turcica can be seen in situations including the following:
empty sella syndrome
slight globular enlargement of the sella with no erosion, destruction or posterior displacement of dorsum sellae
enlargement with erosion of anterior cortex of dorsu...
The term epidermoid cyst can refer to a:
epidermal inclusion cyst
intracranial epidermoid cyst
splenic epidermoid cyst
spinal epidermoid cyst
testicular epidermoid cyst
Epilepsy is a common neurological disorder that has a 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.
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...
External ventricular drains (EVDs) are a common neurosurgical procedure used to monitor and treat raised intracranial pressure in the acute setting.
Treatment and prognosis
intracranial haemorrhage (e.g. subdural, intraventricular)
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.
Often it is trivially easy to distinguish an intra-axial from an extra-axial mass. In many cases,...
Extra-axial masses of the intracranial compartment have a wide range of differentials, ranging from benign developmental cysts to malignant tumours.
choroid plexus papilloma/carcinoma
cranial nerve schwannoma
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:
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...
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 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...
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...
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)
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...
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...
The CNS manifestations of HIV/AIDS (neuroAIDS) occur secondary to a wide range of neurodegenerative, infectious, inflammatory, or neoplastic processes.
Since the introduction of highly active antiretroviral therapy (HAART) in 1996, there has been a shift in the epidemiology of CN...
Accurately determining the cause of ventriculomegaly between hydrocephalus and atrophy (compensatory enlargement of the CSF spaces) can be, at times, challenging in image interpretation.
Features that favour hydrocephalus include:
dilatation of the temporal horns
Hyperattenuating cerebral metastases on CT can be due to haemorrhage, calcium, or highly cellular tumours.
There is overlap between the entities, with some cerebral metastases appearing in more than one list 1-6:
haemorrhagic cerebral metastases (mnemonic)
Hypomyelinating disorders are a subset of white matter disorders characterised by abnormally low amounts of myelination. Clinically, they may be subcategorized into those with and without typical peripheral nervous system involvement (usually determined by nerve conduction studies). These includ...
Hypothalamic lesions are numerous representing some entities that are unique to the hypothalamus, as well as many lesions that can be seen elsewhere within the brain. Additionally, due to it's proximity to the optic chiasm, third ventricle and pituitary region, many lesions of these locations ca...
Hypoxic-ischaemic encephalopathy in adults and older children (i.e. not neonates), also known as global hypoxic-ischaemic injury, is seen in many settings and often has devastating neurological sequelae.
For a discussion of neonatal hypoxia, refer to neonatal hypoxic-ischaemic encephalopathy.
IgG4-related disease (IgG4-RD) is a systemic disease that is characterised by extensive IgG4-positive plasma cells and T-lymphocyte infiltration of various organs.
This condition has been known by many other names in the past, such as IgG4-related sclerosing disease, IgG4-related s...
Gunshot injuries often require imaging assessment, and this evaluation has both clinical relevance (assessment of organ damage, surgical planning and prognostication), and often also forensic implications.
Incidence of gunshot injuries to the head is increasing in some countries, ...
Intracranial arterial beading represents alternating areas of constriction in the intracranial arteries that gives the appearance of beads strung together.
The various conditions where this is seen are:
cerebral vasospasm post sub...
Intracranial lesions or processes can be described according to which intracranial compartment they occur within.
The simplest division is into 3 compartments:
extra-axial: external to the brain parenchyma
intra-axial: within the brain parenchyma
intraventricular: within the ventricular sys...