The basal ganglia are a group of grey matter nuclei in the deep aspects of the brain that is interconnected with the cerebral cortex, thalami and brainstem.
In a strict anatomical sense, it contains three paired nuclei that together comprise the corpus striatum:
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 ...
Basal ganglia hemorrhage is a common form of intracerebral hemorrhage, and usually as a result of poorly controlled long-standing hypertension. The stigmata of chronic hypertensive encephalopathy are often present (see cerebral microhemorrhages).
Other sites of hypertensive hemorrhages are the ...
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
Hypointensity on T1 weighted images of the basal ganglia, as a general rule is in itself of limited value, and should be correlated with T2 signal, which is usually more informative. Most causes of T2 hyperintensity in the basal ganglia will result in T1 hypointensity (most are afterall due to e...
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
The basal nucleus of Meynert, also known as the nucleus basalis of Meynert, is formed by a group of cells that lies in the substantia innominata. It is rich in acetylcholine and its degeneration has been correlated to Alzheimer disease. It lies anterior to the anterior commissure.
The basal veins, also known as the veins of Rosenthal, are paired, paramedian veins which originate on the medial surface of the temporal lobe and run posteriorly and medially. Each vein passes lateral to the midbrain through the ambient cistern to drain into the vein of Galen with the internal ...
Basilar fractures of the skull, also known as base of skull fractures, are a common form of skull fracture, particularly in the setting of severe traumatic head injury, and involve the base of the skull. They may occur in isolation or often in continuity with skull vault fractures or facial frac...
The base of the skull (or skull base) forms the floor of the cranial cavity and separates the brain from the structures of the neck and face.
The base of the skull is a bony diaphragm composed of a number of bones - from anterior to posterior:
The basilar artery is part of the posterior cerebral circulation. It arises from the confluence of the left and right vertebral arteries at the base of the pons as they rise towards the base of the brain.
origin: vertebral artery confluence
course: ventral to pons in the pontine ciste...
Basilar artery aneurysms are less common than anterior circulation aneurysms, and rupture less frequently, but their critical location necessitates careful evaluation.
may present as a lobulated hyperattenuating structure anterior to the mid brain
rupture of a basil...
Basilar artery fenestration (or more simply, basilar fenestration) is the most common intracranial arterial fenestration. It refers to duplication of a portion of the artery, thought to occur due to failed fusion of plexiform primitive longitudinal neural arteries 4. Its reported prevalence is h...
Basilar artery hypoplasia is a rare vascular anomaly of the basilar artery.
Basilar artery hypoplasia is usually accompanied by one or more fo the following:
persistent carotid-vertebrobasilar anastomoses
hypoplastic V4 segments of the vertebral arteries
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...
A mnemonic to help recall the causes of basilar invagination is:
P: Paget disease of bone
F: fibrous dysplasia
R: rheumatoid arthritis, rickets
O: osteogenesis imperfecta, osteomalacia
C: Chiari I and Chiari II, cleidocranial dysostosis
The basilar venous plexus lies between the endosteal and visceral layers of the dura on the inner surface of the clivus and connects numerous regional venous structures:
cavernous sinuses (superolaterally)
superior petrosal sinuses (superolaterally)
intercavernous sinuses (superio...
The basion is the median (midline) point of the anterior margin of the foramen magnum. The apical ligament attaches to it.
It is one of the skull landmarks, craniometric points for radiological or anthropological skull measurement.
Various lines and measurements using the ...
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 ...
The basis pontis, or basilar/basal part of the pons, refers to the ventral portion of the pons, which contains white matter fibers of the corticospinal tract.
lacunar infarct in this region may result in pure motor hemiparesis, ataxic hemiparesis, or dysarthria-clumsy hand sy...
Battle sign is an eponymous term given to mastoid ecchymosis (bruising of the scalp overlying the mastoid process) and is strongly suggestive of a base of skull fracture, most commonly a petrous temporal bone fracture.
History and etymology
Mr William Henry Battle (1855-1936) was an English s...
Bat wing 4th ventricle sign refers to the morphology of the fourth ventricle in the Joubert anomaly and related syndromes. The absence of a vermis with apposed cerebellar hemispheres gives the fourth ventricle an appearance reminiscent of a bat with its wings outstretched.
It is best demonstrat...
Behavioral variant frontotemporal lobar degeneration (bvFTLD), also known as behavioral variant frontotemporal dementia, is one of the clinical neurodegenerative diseases associated with frontotemporal lobar degeneration (FTLD).
In the older literature, it is also referred to as P...
Behçet disease is a multisystemic and chronic inflammatory vasculitis of unknown etiology.
The mean age at which Behçet disease occurs is 20-30 years. The disease is most prevalent in the Mediterranean region, Middle East and East Asia. The highest incidence has been reported in T...
CNS manifestations of Behçet disease, also known as neuro-Behçet disease, corresponds to the neurological involvement of the systemic vasculitis Behçet disease and has a variety of manifestations.
For a discussion of the disease, in general, please refer to Behçet disease article.
Bell palsy, also known as idiopathic peripheral facial paralysis, is characterized by rapid onset facial nerve paralysis, often with resolution in 6-8 weeks. As there are numerous causes of facial nerve palsy, many acute in onset, it is currently a diagnosis of exclusion supported by a typical p...
Benedikt syndrome, or paramedian midbrain syndrome, is a midbrain stroke syndrome that involves the fascicles of the oculomotor nerve and the red nucleus.
ipsilateral CN III palsy 1-4
crossed hemiataxia 1-4
crossed choreoathetosis 1-4
It is usually caused by...
Benign enhancing foramen magnum lesions have been anecdotally seen by radiologists for years but only recently described as an incidental finding in a typical location in the foramen magnum just behind the vertebral artery. Although the precise nature of this finding has not been entirely elucid...
Benign enlargement of the subarachnoid spaces in infancy (BESS or BESSI) also known as benign external hydrocephalus (BEH) is, as per the name, a benign enlargement of the subarachnoid spaces in infants. It usually involves the frontal lobe subarachnoid spaces, and it is characterized clinically...
Benign metastasizing meningiomas are a rare occurrence, encountered as a complication of a tiny fraction of all meningiomas diagnosed. It refers to spread of the tumor via metastases to distant sites, analogous to benign metastasizing leiomyoma from uterine fibroids.
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
Benign notochordal cell tumors are vertebral lesions that are usually asymptomatic and discovered incidentally on imaging of the head or spine. As this is a poorly-recognized entity, it can often be confused with aggressive vertebral lesions, such as a chordoma, when it is seen on imaging.
Benign paroxysmal positional vertigo (BPPV) is one of the most common causes of vertigo. It occurs secondary to change in posture and typically is associated with nystagmus. The etiology is thought to be due to changes of position of the otoliths in the inner ear, most commonly into the posterio...
Benign regressive post-infectious neurological disorders (BRPINDs) refer to a group of neurological disorders and must be differentiated from the more malignant and progressive post-infectious neurological disorders such as SSPE (subacute sclerosing panencephalomyelitis) or rubella panencephalit...
Beta-propeller protein-associated neurodegeneration (BPAN) is a rare subtype of neurodegeneration with brain iron accumulation disease (NBIA).
It was previously known as static encephalopathy with neurodegeneration in childhood (SENDA), but it was renamed after the underlying genetic abnormalit...
Betz cells are pyramidal cell neurons located within the fifth layer of the primary motor cortex. They are some of the largest in the central nervous system, sometimes reaching 100 µm in diameter and send their axons down the corticospinal tracts to the anterior horn cells of the spinal cord.
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.
Bickers Adams Edwards syndrome is a rare x-linked disorder with profound intellectual disability, adducted thumb and large head which is comprising of a constellation of congenital CNS anomalies including :
congenital aqueductal stenosis
corpus callosum agenesis
absence of the medullary pyra...
Bickerstaff encephalitis is a rare immune-mediated condition believed to be one of a number of conditions sharing a similar immunological mechanism, and collectively termed anti-GQ1b IgG antibody syndrome.
Bickerstaff encephalitis is often seen following varicella zoste...
The Biffl scale or grade illustrates the spectrum of blunt cerebrovascular injury (BCVI) seen on angiography (both CTA and DSA). Some authors refer to the grading scale as the Denver scale, which is not to be confused with the Denver criteria, a series of clinical indications and risk factors fo...
The bifid postcentral gyrus sign, also known as the pars deflection sign, is a landmark useful for identifying the central sulcus on cross-sectional imaging.
The medial aspect of the postcentral gyrus splits in two before meeting the interhemispheric fissure. The two legs straddle the pars marg...
Big black brain is a radiologic pattern unique to infants and toddlers in the context of traumatic brain injury, most frequently due to abusive head trauma.
The CT presentation is a parenchymal hypodensity and uniform loss of gray-white differentiation in the entire hemisphere, associated with...
Bilateral frontoparietal polymicrogyria (BFPP) is a rare genetic condition consisting of extensive bilateral perisylvian polymicrogyria.
As is the case with many areas of medicine transitioning from phenotypical to molecular/genetic definitions, it has been postulated what bilateral frontopari...
Bilateral megalencephaly refers to megalencephaly affecting both cerebral hemispheres.
neurofibromatosis type 1 (NF1)
tuberous sclerosis (TS)
Involvement of both middle cerebellar peduncles is uncommon, but has a relatively long list of differential diagnoses, including 1:
multiple systemic atrophy (MSA)
Bilateral thalamic gliomas are rare but characteristic low-grade astrocytomas that occur in both children and young adults.
Presentation may vary with age. Young children with bilateral thalamic glioma often have signs of increased intracranial pressure and movement disor...
Bilateral thinning of the parietal bones, also known as biparietal osteodystrophy, is an uncommon, slowly progressive acquired disease of middle-aged people with slight female predilection. It is typically an incidental finding.
The etiology is unknown but is thought to be an age-re...
Bill bar is a bony anatomical landmark that divides the superior compartment of the internal acoustic meatus into an anterior and posterior compartment. Anterior to Bill bar, in the anterior superior quadrant, are the facial nerve (CN VII) and nervus intermedius, and posterior to it, in the post...
Bing-Neel syndrome is an extremely rare neurological complication of Waldenström macroglobulinemia where there is malignant lymphocyte infiltration into the central nervous system (CNS).
The exact incidence is unknown, however, in one study of patients with Waldenström macroglobul...
Biotin deficiency is very rare. Biotin is a vitamin which acts as an enzymatic cofactor with a key role in energy production and the synthesis of fats. Biotin is present in a diverse range of cereals, nuts, seeds and eggs. Hence, true deficiency is unusual. It has been observed in the following ...
Biotinidase deficiency is a rare autosomal recessive condition in which the body is unable to break down the conjugated form of biotin (vitamin B7), resulting in low levels of bioavailable biotin, and clinical biotin deficiency.
Profound deficiency (<10% of normal level) is estima...
Biotin-thiamine-responsive basal ganglia disease (BTBGD) is a rare neurometabolic syndrome caused by defective thiamine transporter 2 (THTR2) activity due to mutations in the solute carrier family 19 member 3 gene (SLC19A3).
The presentation of biotin-thiamine-responsive basal ga...
Birth trauma (a.k.a. birth injury) relates to those conditions caused by both physical/mechanical and hypoxic injuries.
Birth trauma occurs in ~5 per 1000 births 2.
Bilateral thalamic lesions are usually seen in combination with basal ganglia, white matter and sometimes cortical lesions. Symmetrical bilateral involvement of the thalami has a broad differential diagnosis:
deep cerebral vein thrombosis and dural venous sinus thrombosis:
Neuroanatomy of the bladder is complex, described here is a summary of the co-ordination of micturition.
The bladder acts as a reservoir normally storing 400-500 mL of urine under low pressure (<15 cmH2O) before voluntary voiding can occur at a socially-convenient time. Bladder filling and empt...
Blake's pouch cyst is a cystic appearing structure that represents posterior ballooning of the inferior medullary velum into the cisterna magna, below and posterior to the vermis, that communicates with an open fourth ventricle. It is caused by a failure of the regression of Blake's pouch second...
The blend sign refers to a CT appearance of early intracranial hematoma growth. It is defined as blending of a hypoattenuating area and a hyperattenuating region with a well-defined margin.
The blood-brain barrier (BBB) forms a physical resistance to the passage of lipophobic substances from cerebral capillaries into the brain and is a key reason why there is no CSF enhancement following intravenous contrast media on CT and MRI.
The blood-brain barrier is formed by ...
The blood supply of the meninges generally concerns the blood supply of the outer layer of dura mater rather than the inner layer of dura mater, arachnoid or pia mater which do not require a large blood supply. There are several arteries that supply the dura in the anterior, middle, and posterio...
Blumcke et al. proposed the most recent (2011) 2 and now widely adopted consensus classification system for focal cortical dysplasia, which shares many features with the previously described classifications system by Palmini (2004) and Barkovich (2005).
Unfortunately, as is the case with many ...
Blunt cerebrovascular injury (BCVI) is an uncommon but serious consequence of blunt trauma to the head and neck.
It is often part of multi-trauma with a significant series of blunt trauma CTA reporting an incidence of approximately 1% 3. A large systematic review and meta-analysis...
Bochdalek's flower basket is the eponymous name for the incidental finding of protrusion of the choroid plexus through the foramina of Luschka. This is a relatively common finding.
It is an important normal variant to recognize as the presence of protruding calcified choroid tissue in the fourt...
Blood oxygenation level dependent (BOLD) imaging is the standard technique used to generate images in functional MRI (fMRI) studies, and relies on regional differences in cerebral blood flow to delineate regional activity.
Blood flow in the brain is highly locally controlled in response to oxy...
Boomerang sign may refer to:
boomerang sign (peroneus brevis tear)
boomerang sign (medial meniscal tear)
boomerang sign (splenium)
History and etymology
Boomerang is of course a curved projectile used originally by the Australian Aborigines, one of its various uses was as a hunting weapon 1.
The boomerang sign refers to a boomerang-shaped region of cytotoxic edema in the splenium of the corpus callosum typically seen in cytotoxic lesions of the corpus callosum (CLOCCs) 1-4.
boomerang sign in peroneus brevis split syndrome
boomerang sign in horizontal meniscal flap tear
The Borden classification of dural arteriovenous fistulas (DAVF) groups these lesions into three types based upon the site of venous drainage and the presence or absence of cortical venous drainage. It was first proposed in 1995 1. At the time of writing (July 2016), it is probably less popular ...
The Boston criteria were first proposed in 1995 in order to standardize the diagnosis of cerebral amyloid angiopathy (CAA) 1. They comprise of combined clinical, imaging and pathological parameters.
The criteria are divided into four tiers and are as 3-4:
full post-mortem examin...
Bouthillier et al. described (in 1996) 1 a seven segment internal carotid artery (ICA) classification system. It remains the most widely used system for describing ICA segments at the time of writing (mid-2016).
There are a few other classifications systems including those proposed by Fisher (1...
Brachial plexus injuries are a spectrum of upper limb neurological deficits secondary to partial or complete injury to the brachial plexus, which provides the nerve supply of upper limb muscles.
Trauma, usually by motor vehicle accidents, involves severe traction on the ...
Mnemonics for brachial plexus root subdivisions include:
Rad Techs Drink Cold Beer
Robbie T Drinks Cold Beer
Rugby Teams Drink Cold Beers
Reach To Drink Cold Beer
Read That Damn Cadaver Book
Really Tired, Don't Care Now (nerve instead of branch)
Red Toucans Don't Come Back
The bracket sign of the pars marginalis, also known as the pars bracket sign, refers to the appearances of the superior most extent of the pars marginalis of the cingulate sulcus on axial imaging. It forms two roughly symmetric brackets, open anteriorly. The next sulcus anteriorly is the central...
The bracket sign refers to a radiographic appearance seen with the tubulonodular variety of pericallosal lipoma. It reflects calcification seen at the periphery of the midline lipoma. It is best seen on coronal imaging and historically was identified on frontal radiographs.
It should not be con...
The brain is the vital neurological organ composed of:
The brain is housed in the skull and bathed in cerebrospinal fluid. It is continuous with the cervical spinal cord at the cervicomedullary junction.
Brain abscess is a potentially life-threatening condition requiring rapid treatment, and prompt radiological identification. Fortunately, MRI is usually able to convincingly make the diagnosis, distinguishing abscesses from other ring-enhancing lesions.
Demographics reflect at-ri...
Brain death refers to the irreversible end of all brain activity and is usually assessed clinically. Radiographic testing may be used as additional support for a clinical diagnosis of brain death, such as when clinical tests are impossible to perform, e.g. ocular trauma, precluding brainstem fun...
Brain development occurs from the three vesicles of the embryo's neural tube.
By approximately 4.5 to 5 menstrual weeks, the primitive neural plate has developed. The neural plate then divides into the neural crest and...
MRI protocol for brain infection assessment is a group of MRI sequences put together to best approach CNS infections in general.
Note: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologist's an...
This is a basic article for medical students and other non-radiologists
Brain mass lesions are a broad collection of pathological processes that result in changes on brain imaging (usually CT or MRI). They are a very disparate group of conditions ranging from infection (abscess) to brain tumors...
Brain metastases are estimated to account for approximately 25-50% of intracranial tumors in hospitalized patients. Due to great variation in imaging appearances, these metastases present a common diagnostic challenge which can importantly affect the management approach for individual patients.
Brain morphometry is the act of measuring various dimensions (typically volume) of parts of the brain. Historically, this was only performed post-mortem.
In modern practice, this is performed in vivo using MRI. A volumetric scan of the brain (typically T1 weighted) is obtained and segmented i...
Brain screen protocol is a simple non-contrast MRI protocol comprising a group of basic MRI sequences as a useful approach when imaging the brain when no particular condition is being sought (e.g. headache). The protocol is designed to obtain a good general overview of the brain. Additionally, t...
The brainstem is the most caudal part of the brain. It adjoins, is structurally continuous with the spinal cord and consists of the:
pons (part of the metencephalon)
medulla oblongata (myelencephalon)
The brainstem provides the main motor and sensory innervation to t...
Brainstem gliomas consist of a heterogeneous group which vary greatly in histology and prognosis.
It should be noted that if not otherwise specified the term brainstem glioma usually refers to the most common histology, the diffuse brainstem glioma, and in children is most likely a...
The brainstem nuclei are the nuclei in the brainstem. These include:
cranial nerve nuclei
Brainstem stroke syndromes, also known as crossed brainstem syndromes, refer to a group of syndromes that occur secondary to lesions, most commonly infarcts, of the brainstem.
Although many different brainstem stroke syndromes have been classically described, the majority appear e...
The brain MRI stereotactic study, also known as frame-based stereotactic MRI study or conventional brain MRI stereotaxis, is a localization MRI protocol that delineates an intracranial structure or lesion in relation to a three-dimension coordinate system allowing precise surgical access to them...
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...
MRI protocol for brain trauma is a group of MRI sequences put together to best approach traumatic brain injury, especially diffuse axonal injury.
Note: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software...
MRI protocol for brain tumor assessment is a group of MRI sequences put together to best approach CNS tumors in general.
Note: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologist's and referr...
Brain tumors arise from the normal constituents of the brain and its coverings (meninges). Spinal tumors are considered separately.
As a general rule, brain tumors increase in frequency with age, with individual exceptions (e.g. pilocytic astrocytoma, the vast majority of which a...