CT Brain anatomy Flashcards
What is the clinical significance of Sphenoid sinuses?
In the context of trauma, a fluid level in the sphenoid sinus may be a sign of a basal skull fracture
Is a sphenoid sinus septated or not?
it can be single or septated
What is a common incidental finding of maxillary sinuses on CT?
Mucosal thickening
What are the meninges and what are there three layers?
thin layers of tissue found between brain and the inner table of the skull.
- dura mater
-
arachnoid
- these two are an anatomical unit only seperated by pathology
- pia mater
what do we call the thick infoldings of the meninges?
Falx cerebri and tentorium cerebelli
- Tentorium Cerebelli: seperateates cerebellum from cerebrum. Anchored by petrous bones
- Falx Cerebri: lies in the midline and seperates the cerebral hemispheres
Clinical significance of the Tentorium cerebelli and falx cerebri
Tentorium Cerebelli: in the context of subarachnoid haemorrhage or subdural haematoma the tent may become more dense due to layering of blood
Falx cerebri: pathological processes may cause ‘mass effect with deviation to one side
Both can be a source of meningiomas
What makes us sure we are looking at a meningioma on CT?
- CSF cleft sign
- A dural tail
- Sunburst or spoke wheel appearance of the vessels
- White matter buckling sign
- arterial narrowing
Where is CSF found, why does it help us?
CSF Spaces aka ‘extra-axial spaces’
- Sulci
- fissues
- basal cisterns
- Ventricles
it helps us assess whether the brain volume is normal
Where are the lateral ventricles and what do they contain?
- Paired, one in each hemisphere
- Contain the choroid plexus which produces CSF
- Chroid plexus is nearly always calcified in adults
Where is the third ventricle and how does it communicate with the lateral ventricles?
Located centrally, communicates with tehe tird ventricle via small holes ‘foramina of monro’
Where is the fourth ventricle and how does it communicate with the third ventricle?
Located in the posterior fossa between the brain stem and cerebellum.
Communicates with the third ventricle above via a very narrow canal, the aqeduct of sylvius
Point of the Basal cisterns?
They contain CSF that surrounds the brainstem structures
What causes the differences in density of the brain parenchyma?
How does this impact CT
White matter has a high content of myelinated axons
Grey matter has relatively few axons and higher number of cell bodies.
As myeline is a fatty substance of lower density it appears blacker than grey matter on CT
- Grey appears grey*
- White appears black*
Important grey matter structres visible on CT: quick description of each
cortex, insula, basal ganglia and thalamus
Cortex: formed in gyri (folds) over the entire brain surface
Insula: inner surface found deep to the sylvian fissue
Basal Ganglia: Caudate nucleus + lentiform nucleus
Thalamus
Loss of definition of the insular cortex may mean what?
May be an early sign of acute infarct involving the MCA territory
Insults (eg thalamic stroke) to the thalamus may result in?
Thalamic Pain Syndrome or Dejerine–Roussy syndrome
Preceeding unilateral parasthesia then replaced by
- Burning and tingling of varying severity (often severe and dehabilitating)
- Hypersensitivity: usually dysaesthesia or allodynia
What is allodynia and dysaesthesia?
Allodynia: pain from a stimuus that would not usually cause pain
Dysaesthesia: neuropathic pain, can be any combination of itching, tingling, burning, or searing experienced spontaneously or from stimuli.
White matter structures of the brain
Internal capsules: white matter tracts which connect with the corona radiata and white matter or the cerebral hemispheres superioriorally and the brainstem inferiorally
The corpus callosum is a white matter tract located in the midline, it arches over the lateral ventricles and connects the two hemispheres white matter (glenu and splenium)
Parts of the internal capsules?
Has an anterior and a posterior limb which cnnects at the ‘genu’
When would we worry abou the internal capsules?
These heavily axonated structrues are supplied by perforating branches of the MCA.
These vessels are smal and susceptible to lacunar infarcts
Even a small insult to the internal capsule can have a profound affect on motor and sensory funciton
When can the connecting nature of the corpus pallosum be a dangerous thing?
Malignant lesions of the brain can grow from one brain hemisphere to the other via the corpus callosum
**elsewhere the falx acts as a relative barrier to direct invasion
The posterior fossa accomodates the ….
cerebellum and brain stem
seperated from cerebral hemisoheres by tentorium cerebelli
What are the cerebral vascular territories of the brain?
Can we see these of CT?
Different areas of the brain are supplied by the anterior, middle and posterior cerebral arteries in a predictable manner
Posterior fossa structures are supplied by the vertebrobasilar arteries
Vascular structures are not well visualised on CT but knowing the areas they supply is helpful
What is special about the vascular supply to the insula and basal ganglia?
Multiple tiny perforating branches of the MCA supply this region!
