Lissencephaly type II is characterised by reduction in normal sulcation, associated with a bumpy or pebbly cortical surface (thus the term cobblestone lissencephaly), absent in lissencephaly type I. Unlike type I lissencephaly which is the result of neuronal undermigration, type II is due to ove...
The claw sign is useful in determining whether a mass arises from a solid structure or is located adjacent to it and distorts the outline.
It refers to the sharp angles on either side of the mass, which the surrounding normal parenchyma forms when the mass has arisen from the parenchyma. As suc...
The cingulate sulcus sign has been proposed as being useful as an MRI feature of idiopathic normal pressure hydrocephalus (NPH). It denotes the posterior part of the cingulate sulcus being narrower than the anterior part. The divider between the anterior and posterior parts of the sulcus being a...
Chasing the dragon sign is seen in toxic leukoencephalopathy caused by the 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...
The sphenoparietal sinus is one of the dural venous sinuses and is located along the posteroinferior ridge of the lesser wing of the sphenoid bone. It drains into the cavernous sinus and receives tributaries from:
superficial middle cerebral vein
middle meningeal vein (frontal ramus)
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 optic canal is a cylindrical canal running obliquely through the lesser wing of sphenoid bone near the base where it joins the body of sphenoid. It transmits the optic nerve and ophthalmic artery. The optic canal opens into the skull base at the optic foramen.
Non-ketotic hyperglycaemic hemichorea (NHH) is a rare cause of T1 bright basal ganglia and one of the neurological complications of non-ketotic hyperglycaemia, along with non-ketotic hyperosmolar coma and non-ketotic hyperglycaemic seizures.
NHH is most frequently reported in eld...
Rasmussen encephalitis (RE), also known as chronic focal encephalitis (not to be confused with a Rasmussen aneurysm), is a chronic inflammatory disease of unknown origin, usually affecting one brain hemisphere.
Most cases (85% cases) occur in children under the age of 10 years 1. ...
Contrast-induced neurotoxicity, also known as iodinated contrast-induced encephalopathy, is a rare complication of iodinated intravascular contrast resulting in a usually temporary neurological deficit. CT imaging findings can be dramatic, demonstrating contrast staining and oedema, but spontane...
Retinoblastoma staging can be via a number of systems with various end-points and multiple systems are often used concurrently.
Reese Ellsworth classification
The Reese Ellsworth classification is assessed with fundoscopy and aims at predicting the chance of preserving the eye with ex...
The butterfly sign refers to the normal appearance of the choroid plexuses on axial imaging of the fetal brain, commonly observed on the antenatal ultrasound. Its absence may suggest holoprosencephaly 1.
In the CNS, the term should not be confused with a butterfly glioma, which is a glioblastom...
Medical devices in the abdomen and pelvis are important to be recognised, just like medical devices of the chest. Often we ignore these devices, considering them to be incidental and non-pathological, however it is essential to be aware of potential complications.
The caput medusae sign, refers to developmental venous anomalies of the brain, where a number of veins drain centrally towards a single drain vein. The appearance is reminiscent of Medusa, a gorgon of Greek mythology, who was encountered and defeated by Perseus.
The sign is seen on both CT and ...
Internal auditory canal (IAC) diverticulum are small focal outpouching arising from the anterolateral wall of the IAC.
In one study, they were identified in 5% of petrous temporal bone CT-scan 1. In the same study, it was coexisting with otosclerosis in 1% of cases 1.
Subarachnoid haemorrhage (SAH) is bleeding into the subarachnoid space. This is usually found centrally (around the circle of Willis) but can occur in other parts of the brain.
This is a summary article; read more in our article on subarachnoid haemorrhage.
Extradural haemorrhages (EDH) represent collections of blood in the extradural (epidural) space. The haemorrhage sits between the skull superficially and the dura which overlies the brain parenchyma.
This is a summary article; read more in our article on extradural haemorrhag...
Stroke is a clinical diagnosis where an acute neurological deficit follows a cerebrovascular insult. There are two main groups of stroke: ischaemic (>80%) or haemorrhagic (<20%) 1.
This is a summary article; read more in our article on stroke.
Brudzinski sign occurs in meningitis (of any aetiology) where passive flexion of one leg causes flexion in the opposite leg. Passive flexion of the neck brings about flexion of the legs as well.
First described by Jósef Brudziñski (1874-1917), paediatrician from Warsaw, Pola...
The callosal angle has been proposed as a useful marker of patients with idiopathic normal pressure hydrocephalus (iNPH), helpful in distinguishing these patients from those with ex-vacuo ventriculomegaly (see hydrocephalus versus atrophy).
Ideally the angle should be measured on a cor...
The spinal arachnoid mater is a thin, delicate and avascular connective tissue membrane which forms the middle layer of the meninges and covers the spinal cord1.
The spinal arachnoid mater becomes continuous with the cerebral arachnoid mater as it traverses the foramen magnum and...
Butterfly gliomas are a high grade astrocytoma, usually a glioblastoma (WHO grade IV), which crosses the midline via the corpus callosum. Other white matter commissures are also occasionally involved. The term butterfly refers to the symmetric wing-like extensions across the midline.
High-velocity penetrating brain injuries, in practical terms most often due to cranial gunshot injuries, are a form of penetrating traumatic brain injuries, which are much less common than blunt traumatic brain injuries and distinguished from low-velocity penetrating brain injuries (such as stab...
Low-velocity penetrating brain injuries are relatively uncommon, far less frequently encountered than blunt traumatic brain injuries, and depending on the country more or less common than high-velocity penetrating brain injuries from gunshot wounds.
The demographics of affected i...
The superior anastomotic vein of Trolard connects the superior sagittal sinus and the superficial middle cerebral vein (of Sylvius).
Its size is dictated by the relative size of the superficial middle cerebral vein and the anastomotic vein of Labbé. The vein of Trolard is smaller than both of t...
Superficial veins of the brain predominantly drain the cerebral cortex, and include:
superior cerebral veins (or superficial cerebral veins)
inferior cerebral veins
superficial middle cerebral veins
superior anastomotic vein (of Trolard)
inferior anastomotic vein (of Labbe)
Some also inclu...
The denticulate ligaments are bilateral triangular extensions of pia mater that anchor the spinal cord to the dura mater.
They are formed by pia mater of the spinal cord coursing in-between the dorsal and ventral nerve roots bilaterally. They function to provide stability to the spinal cord wit...
The spinal cord blood supply is formed by many different vessels with an extensive collateral supply and drainage.
The spinal cord is supplied by three longitudinal arteries:
single anterior spinal artery: supplies the anterior two-thirds of the spinal cord
paired posterior s...
Incomplete hippocampal inversion unsurprisingly describes the situation where the normal inversion of the hippocampus fails to happen during development.
Incomplete hippocampal inversion is the most correct description of this finding. Hippocampal malrotation is a term used by some...
Mesial temporal sclerosis (MTS), also commonly referred to as hippocampal sclerosis, is the most common association with intractable temporal lobe epilepsy (TLE) 2-3,5. It is seen in up to 65% of autopsy studies, although significantly less on imaging.
Most patients prese...
The bright rim sign has been described in dysembryoplastic neuroepithelial tumours (DNETs) and is seen, as the name so aptly describes, as a rim of high signal around the DNET on FLAIR sequences.
US carotids is a standard test performed in the assessment of cranial arterial blood supply.
This is a summary article; we do not have a more in-depth reference article.
assessment of carotid stenosis
The lenticulostriate arteries are a collection of small perforating arteries arising from the anterior part of the circle of Willis and supplying the basal ganglia.
They are divided into:
medial lenticulostriate arteries
lateral lenticulostriate arteries
There is, however, some confusion a...
The anterior perforated substance, or substantia perforata anterior, is an area in the basal forebrain that plays an important role with regards to the blood supply of deep grey matter structures of the brain.
Located within the basal forebrain, the anterior perforated substance...
The boomerang sign refers to a boomerang-shaped splenial lesion (splenium of corpus callosum) which is seen as a hyperintense lesion on T2-WI, FLAIR and DWI 1.
This sign can be seen in:
transient lesion of the splenium
posterior reversible encephalopathy syndrome (PRES)
The orbit is a feature of the face and contains the globe and it's supporting structures, as well as many nerves and vessels.
In the adult, the orbit has a volume of approximately 30 mL, of which the globe occupies 6.5 mL. It has a roof, floor, medial and lateral wall. The orbit ...
The cavernous sinuses are paired dural venous sinuses.
The cavernous sinus (CS) is located on either side of the pituitary fossa and body of the sphenoid bone between the endosteal and meningeal layers of the dura. The normal lateral wall should be either straight or concave.
The trigeminal nerve is the fifth cranial nerve and its primary role is relaying sensory information from the face and head, although it does provide motor control to the muscles of mastication. It is both large and complicated and has multiple brainstem nuclei (sensory and motor) as well as man...
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 inferior orbital fissure (IOF) lies in the floor of the orbit inferior to the superior orbital fissure and it is bounded superiorly by the greater wing of sphenoid, inferiorly by maxilla and orbital process of palatine bone and laterally by the zygomatic bone. It opens into posterolateral as...
Transalar (transsphenoidal) herniation describes herniation of brain matter in and around the middle cranial fossa across the greater sphenoid wing and can be ascending or descending. Compression of structures against the sphenoid bone results in symptoms.
Transalar herniation is not...
The middle meningeal artery branches off the first part of the maxillary artery. It passes vertically through the roots of the auriculotemporal nerve and enters the middle cranial fossa via the foramen spinosum. Here it gives off two branches - superior tympanic branch and ganglionic branch - be...
The WHO classification of CNS tumours is the most widely accepted system for classifying CNS tumours and was based on the histological characteristics of the tumour. Although the most recent version of the 'blue book' is the 4th edition from 2007, an update has been released in 2016 3, which sho...
Spindle cell oncocytomas (SCO) of the pituitary gland, also referred as adenohypophysis spindle cell oncocytomas, are rare, relatively benign (WHO grade I), and nonfunctional tumours commonly showing clinical and radiologic presentations mostly indistinguishable from the much more common non-sec...
The superior orbital fissure is the communication between the cavernous sinus and the apex of the orbit. It is straddled by the tendinous ring which is the common origin of the four rectus muscles (extraocular muscles).
medial: body of sphenoid
superior: lesser wing ...
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 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 bare orbit sign, is described as a characteristic appearance of the orbit, seen when the innominate line is absent. The innominate line is a projection of the greater wing of the sphenoid, and its absence or destruction is responsible for this appearance.
It is the classical frontal radiogr...
The sphenopetrosal suture is the cranial suture connecting the greater wing of sphenoid with the petrous part of temporal bone in the middle cranial fossa. This fissure forms part of the posterior wall of the foramen lacerum.
The interseptal distance (ISD) is a measurement used to assess septal area atrophy as a marker for neurodegenerative conditions in patients with memory problems 1.
It is proposed that atrophy of the septal nuclei can commonly be seen in conditions associated with hippocampal atrophy, particular...
Hypertrophic olivary degeneration (HOD) is a rare condition characterised by unique pattern of trans-synaptic degeneration. It is caused by a lesion in the triangle of Guillain and Mollaret, resulting in hypertrophy of the inferior olivary nucleus. The three corners of the triangle are:
Hemimegalencephaly is a rare congenital disorder of cortical formation with hamartomatous overgrowth all or a part of a cerebral hemisphere. This results from either increased proliferation or decreased apoptosis (or both) of developing neurons 2.
Hemimegalencephaly is a cryptogen...
The superior cerebellar artery (SCA) arises from the distal basilar artery, just below the posterior cerebral artery (PCA) and typically supplies:
whole superior surface of the cerebellar hemispheres down to the great horizontal fissure
most of the cerebellar ...
The pontine branches are the small arterial branches of the basilar artery that supply the pons and structures adjacent to the pons.
There are usually 3-5 paired arterial branches which are located in the mid-basilar region between the anterior inferior cerebellar artery and the superior cerebe...
The anterior inferior cerebellar artery (AICA) is one of three vessels that provides arterial blood supply to the cerebellum. It has a variable origin, course and supply, with up to 40% of specimens not having an identifiable standard AICA. The amount of tissue supplied by the AICA is variable (...
The basilar artery is part of the posterior cerebral circulation. It artery 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 pontin...
Posterior inferior cerebellar artery (PICA) is one of the three vessels that provide arterial supply to the cerebellum. It is the most variable and tortuous cerebellar artery.
Its origin is highly variable:
~20% arise extracranially, inferior to the foramen magnum
The posterior communicating artery (PCOM or P Comm) makes up the posterior linkage in the circle of Willis.
The PCOM originates from the posterior aspect of the C7 (communicating) segment of the internal carotid artery and extends posteriormedially to anastomose with the ...
The middle cerebral artery (MCA) is one of the three major paired arteries that supply blood to the brain. The MCA arises from the internal carotid artery (ICA) as the larger of the two main terminal branches (the other being the anterior cerebral artery), coursing laterally into the lateral sul...
The anterior communicating artery (ACOM) arises from the anterior cerebral artery and acts as an anastomosis between the left and right anterior cerebral circulation. Approximately 4 mm in length, it demarcates the junction between the A1 and A2 segments of the anterior cerebral artery.
The posterior cerebral arteries (PCA) are the terminal branches of the basilar artery and supply the occipital lobes and posteromedial temporal lobes.
origin: terminal branches of the basilar artery
course: from basilar towards occiput
posterior communicating artery
The anterior cerebral artery along with the middle cerebral artery forms at the termination of the internal carotid artery. It is the smaller of the two, and arches anteromedially to pass anterior to the genu of the corpus callosum, dividing as it does so into its two major branches; pericallosa...
Traumatic brain injuries (TBI) are common and come with a large cost to both society and the individual. Imaging, particularly CT, plays a key role in accurate diagnosis, classification and follow-up.
They can be broadly divided into closed and penetrating head injuries 4:
closed head injury
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 give the fourth ventricle an appearance reminiscent of a bat with its wings outstretched.
It is best demonstrate...
The optic tracts are the posterior continuation of the optic nerves after the medial (temporal field) fibers decussate at the optic chiasma.
The optic tracts course posterolaterally through the ambient cistern from the chiasma to the lateral geniculate nucleus of the thalamus. Mo...
The optic chiasm or chiasma is the midline structure where the nasal (medial) fibres of the optic nerves decussate to continue posteriorly as the optic tracts. It lies in the chiasmatic cistern and along with the pituitary stalk, is completely encircled by the circle of Willis.
Midline shift is a finding described on transverse (axial) slices from CT and MRI studies. It describes the situation where the midline of the intracranial anatomy is no longer in the midline and is the result of pushing or pulling forces within either side of the intracranial compartment.
Thyroid-associated orbitopathy (TAO) is the most common cause of proptosis in adults and is most frequently associated with Graves disease.
On imaging, it is characterised by enlargement of the extraocular muscles' bellies (frequently: inferior rectus > medial rectus > superior rectus) sparing...
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.
The olfactory system transmits smell from detection of odorants at the olfactory epithelium in the nasal cavity to the primary olfactory cortex. It is phylogenetically the most ancient sensory tract and terminates on primitive cortical areas.
Primary olfactory neurons are bipola...
The globes or simply, the eyes are paired spherical sensory organs, located anteriorly on the face within the orbits, which house the visual apparatus.
The globe is suspended by the bulbar sheath in the anterior third of the bony orbit.
Each globe is an approxim...
Diffuse axonal injury (DAI) is a severe form of traumatic brain injury due to shearing forces. It is a potentially difficult diagnosis to make on imaging alone, especially on CT as the finding can be subtle, however, it has the potential to result in severe neurological impairment.
The visual system transmits visual information from the retina within the eyes to the primary visual cortex of the occipital lobe as well as the pretectal nuclei and superior colliculi of the midbrain.
Below the visual pathway is described from distal to proximal in a single hemi...
Intracranial metastatic melanoma is the third most common brain metastasis.
For a broad discussion about the primary tumour or brain metastasis in general, please refer to the articles:
A population-based study of 169,444 cancer patients ...
Acute disseminated encephalomyelitis (ADEM), as the name would suggest, is featured by a monophasic acute inflammation and demyelination of white matter typically following a recent (1-2 weeks prior) viral infection or vaccination 4,6. Grey matter, especially that of the basal ganglia, is also o...
Intradural spinal mass lesions are relatively uncommon, compared to intracranial or extradural masses, and can be challenging to diagnose. Additionally, the need for a pre-operative/non-operative diagnosis is in many ways greater as biopsy of lesions within the cord has the potential of devastat...
Spinal haemangioblastomas are the third most common intramedullary spinal neoplasm, representing 2-6% of all intramedullary tumours 1,4,7.
This article specifically relates to spinal hemangioblastomas. For a discussion on intracranial hemangioblastomas and a general discussion of the pathology ...
The primitive arteries in the brain can be remembered by the following mnemonic:
P: posterior inferior cerebellar (PICA)
A: anterior choroidal
The meningohypophyseal trunk and anterior choroidal and posterior ...
Mnemonics for brachial plexus root subdivisions include:
Red Tits Don't Come Back
Robbie T Drinks Cold Beer
Rugby Teams Drink Cold Beers
or Rad Techs Drink Cold Beer
Read That Damn Cadaver Book
Really Tired, Don't Care Now (nerve instead of branch)
Where the first letter of each word rep...
A useful mnemonic for remembering the differentials for pituitary region masses is:
S: sarcoid, sellar tumour (pituitary adenoma)
T: teratoma or tuberculosis (and other granulomatous diseases)
C: craniopharyngioma, cleft cyst (Rathke), ...
The symptoms of normal pressure hydrocephalus (NPH) can be recalled with this mnemonic:
wet, wacky, wobbly
wet: urinary incontinence
wacky: dementia (memory disturbance)
wobbly: gait disturbance
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
A mnemonic to remember the order in which extraocular muscles are involved in thyroid-associated orbitopathy (TAO) is:
I: inferior rectus
M: medial rectus
S: superior rectus
L: lateral rectus
There is some debate about this however. Some claim superior rectu...
A handy mnemonic to recall cortically-based brain tumours is:
P: pleomorphic xanthoastrocytoma
D: dysembryoplastic neuroepithelial tumour (DNET); desmoplastic infantile astrocytoma and ganglioglioma
A useful mnemonic to help remember the parts of the corpus callosum, from anterior to posterior, is:
Remember Genu Before Splenium
Remember G Before S (as G comes before S alphabetically)
B: body (trunk)
A useful mnemonic to remember the causes of corpus callosum hyperintensity is:
I MADE A PHD
I: infections (e.g. tuberculosis, varicella, rotavirus, HSV)
M: Marchiafava-Bignami syndrome
A: AIDS encephalopathy
D: diffuse axonal injury and diffuse vascular injury
Convenient mnemonics for the causes of cerebral ring enhancing lesions are:
MAGIC DR or DR MAGIC
DR MAGIC L
MAGIC DR or DR MAGIC
I: infarct (subacute phase)
D: demyelinating disease
R: radiation necrosis or re...
Mnemonics for the common cerebellopontine angle masses include:
AMEN or MEAN
A: acoustic schwannoma (~80%)
M: meningioma (~10%)
E: ependymoma (~5%)
N: neuroepithelial cyst (arachnoid/epidermoid) (~5%)
acoustic schwannoma much more commo...
The structures inside and beside the cavernous sinus and their relative positions can be recalled with the following mnemonic:
O TOM CAT
Consider a coronal view of the cavernous sinus.
'O TOM' are the first letters of components of the lateral wall of cavernous sinus considered vertically, fr...
The complications of acute bacterial meningitis can be remembered using the mnemonic:
C: cerebritis / cranial nerve lesion
E: extra-axial collection: empyema and hygroma
Spinal muscular atrophy (SMA) is a type of congenital neuromuscular disease affecting anterior horn cells of the brainstem and spinal cord.
This disorder affects 1 in 6000-10000 infants 1.
The condition typically affects infants and young children, presenti...
A useful mnemonic to remember the nine lobules of the cerebellar vermis is:
Like Cats Catching Dogs For The Party Up North
C: central lobule
Tethered spinal cord syndrome, also known as an occult spinal dysraphism sequence, is a neurological disorder caused by tissue attachments that limit the movement of the spinal cord within the spinal column.
The condition is closely linked to spina bifida, and as such pre...