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 ischemia 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 edema
chronic: encephalomalacia; Wallerian degeneration
acute: more dense than CSF
AIDS-defining illnesses are conditions that in the setting of a HIV infection confirm the diagnosis of AIDS, and do not commonly occur in immunocompetent individuals 2. According to the CDC surveillance case definition 1, they are:
bacterial infections: multiple or recurrent
Anoxic brain injury, also known as global hypoxic-ischemic injury, is seen in all age groups (from antenatal to the elderly) as a result of numerous etiologies. The pattern of injury depends on a number of factors including:
age of the patient (brain maturity)
neonatal hypoxic-ischemic encepha...
Anterior inferior cerebellar artery (AICA) territory infarcts are much less common than posterior inferior cerebellar artery (PICA) infarcts. AICA generally arises from the caudal third of the basilar artery and supplies the lateral pons, inner ear, middle cerebellar peduncle and the anterior in...
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. Ischemia/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 b...
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
autoimmune encephalitis (e.g. anti-D2 dopamine antibody encephalitis)
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 metastasizing tumors:
benign metastasizing meningioma 1,2
benign metastasizing leiomyoma 3
primary adenoma of thyroid 4
giant cell tumor 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 list of differential diagnoses, 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.
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.
Localization of brain stones can help narrow the underlying etiology but...
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 shunting 1
anemias (largely associated with massive hematopoiesis)
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 are relatively common. Although a diverse range of pathologies may be seen in this region, the most common by far is an acoustic schwannoma.
Cerebellopontine angle masses can be divided into four groups, based on imaging characteristics:
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...
The differential for peripheral or ring enhancing cerebral lesions includes:
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)
Cervical spine injuries can involve the cervical vertebral column, intervertebral discs and cervical spine ligaments, and/or cervical spinal cord. The cervical spine accounts for ~50% of all spinal injuries.
5-10% of patients with blunt trauma have a cervical spine injury 1.
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 recognize 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 sign is seen in toxic leukoencephalopathy caused by the inhalation of heroin fumes.
Three stages are recognized:
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 a 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, the intracranial compartment above or the base of skull below.
When evaluating the clivus it is important to compare the marro...
This article aims to be a collection of articles that represent central nervous system infectious (CNS) diseases.
The organisms involved in CNS infections vary depending on the specific location of infection. Bacteria, viruses, fungi, parasites, and prions can all ...
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 recognized.
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-recognized, especially asymptomatic variants 1.
The clinical ...
Colpocephaly is a descriptive term for a disproportionate prominence of the occipital horns of the lateral ventricles. It can result from a wide range of congenital insults.
Patients may present with motor abnormalities, cognitive deficit, visual abnormalities, and seizur...
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 pediatric patients.
Cranial radiotherapy is used for a variety of brain tumors, either in isolation or in combination with concurrent chemotherapy. Complications from irradiation...
Congenital calvarial defects are a group of disorders characterized 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 ventriculomegaly can have a large number of syndromic associations.
fetal alcohol syndrome
Convexal subarachnoid hemorrhages (cSAH) are nontraumatic intracranial hemorrhages that occur within the surface sulci of the brain (c.f. basal cisternal distribution of aneurysmal SAH).
There are various causes of convexal subarachnoid hemorrhage, some of which include:
A coup-contrecoup injury is a term applied to head injuries and most often cerebral contusions and traumatic subarachnoid hemorrhage. 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 poi...
A 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 (bone removed) or cranio...
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 tumor
Cytotoxic lesions of the corpus callosum (CLOCCs) represent a collection of disparate conditions that can cause signal change in the corpus callosum, usually involving the splenium.
The term cytotoxic lesions of the corpus callosum (CLOCCs) has been proposed recently 12 as a more ...
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, ischemic or toxic in origin and include 1-7:
multiple sclerosis (MS)
Most tumors 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 tumor (DNET)
multinodular and vacuolatin...
Diffuse atrophy of the cerebellum refers to a progressive and irreversible reduction in cerebellar volume. It is a relatively common finding and found in a wide variety of clinical scenarios.
Diffuse cerebellar atrophy can be difficult to distinguish from global cerebellar hypopla...
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 tumors and conditions, although meningiomas are by far the most common. The differential of a dural mass includes:
primary dural lymphoma
solitary fibrous tumor of the dura
Ectopia lentis refers to subluxation or dislocation of the lens of the eye secondary to dysfunction or disruption of zonular fibers.
systemic and syndromic disorders
typically upwards and out
most common spontaneous cause 2
homocystinuria - typ...
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. Contrast this with abscesses, which arise within parenchymal tissue, rather than occupying a pre-existing anatomical space.
Colloquially, the standalone term empyema is used to refer to thoracic empyemas but there...
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)...
An enlarged posterior fossa 'CSF' space posterior to the cerebellum has a number of differentials that include:
mega cisterna magna
Careful attention to the cerebellum needs to paid as also to be considered are:
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.
Epiphora represents excessive tearing of the eye and is a common clinical presentation to ophthalmological practice. It is most frequently due to an obstruction of the nasolacrimal drainage apparatus. Less commonly, overproduction of tears may be responsible.
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 hemorrhage (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 tumors.
choroid plexus papilloma/carcinoma
cranial nerve schwannoma
solitary fibrous ...
Extraconal orbital lesions include lesions which arise from structures within the extraconal orbital space and those extending from adjacent structures into the orbits.
dermoid cyst: most common lesion in pediatrics
lacrimial gland lesions
Extraneural spread of primary intracranial neoplasm is distinctly uncommon, occurring far less frequently than CSF spread.
The most frequent neoplasms 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 tumors 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 tumor by far
astrocytoma/glioblastoma: next most common
craniopharyngioma: papillary type
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 from a number of pathologies, including:
fetal arachnoid cyst
fetal choroid plexus cyst
fetal connatal cyst
fetal porencephalic cyst
fetal interhemispheric cyst
fetal subependymal cyst
dorsal cyst of holoprosencephaly
Fetal intracranial hemorrhage may occur either within the cerebral ventricles, subdural space or infratentorial fossa.
Hemorrhages can occur in a number of situations:
mechanical trauma, e.g. maternal abdominal blunt or birth trauma
severe fetal hypoxia
background fetal thrombocyt...
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...
Grey-white differentiation refers to the appearance of the interface between cerebral and cerebellar white matter and grey matter on brain CT and MRI.
The term is most often used when trying to differentiate cytotoxic from vasogenic edema.
cytotoxic edema (see ionic edema), where there is a l...
Hiccups (or hiccoughs), medical term singultus (rarely used), are an unpleasant phenomenon, experienced by everyone on occasion, and usually self-limiting. However the much rarer intractable chronic form can be extremely debilitating.
Hiccups are a symptom that has probably been e...
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...
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 tumor, or by a combination of both. It merely deno...
Accurately determining whether hydrocephalus or atrophy (compensatory enlargement of the CSF spaces) is the cause of ventriculomegaly can be, at times, challenging in image interpretation.
Features that favor hydrocephalus include:
dilatation of the temporal horns
Hyperattenuating cerebral metastases on CT can be due to hemorrhage, calcium, or highly cellular tumors.
There is overlap between the entities, with some cerebral metastases appearing in more than one list 1-6:
hemorrhagic cerebral metastases (mnemonic)
Hypomyelinating disorders are a heterogeneous subset of white matter disorders characterized by abnormally low amounts of myelination.
In distinction to other myelin disorders, hypomyelination is a permanent deficiency in myelin deposition rather than myelin destruction (i.e. demyelination) or ...