Neuroanat 3_Ventricular system and cerebrospinal fluid_2022_Student.pptx

Ventricular system and cerebrospinal fluid Professor Andrew Dilley Previous lecture • Anatomy of the cerebral hemispheres • Anatomy of the limbic system • Anatomy of the basal ganglia • Structure of the meninges • Dural venous sinuses Ventricular system Ventricular system • Series of cerebros...

Ventricular system and cerebrospinal fluid Professor Andrew Dilley Previous lecture • Anatomy of the cerebral hemispheres • Anatomy of the limbic system • Anatomy of the basal ganglia • Structure of the meninges • Dural venous sinuses Ventricular system Ventricular system • Series of cerebrospinal fluid-filled interconnected spaces • Continuous with the subarachnoid space and central canal Neuralation • Neuroectoderm forms neural tube Ectoderm Neural crest cells Mantle layer Lumen Ependymal layer Embryonic day 24 • Lumen of neural tube becomes ventricles and central canal • Ependymal layer lines ventricles and central canal Development of the ventricles • Lumen expands at cranial end to form each ventricle • There is a ventricle associated with each part of the brain Lateral ventricles Surrounded by: Telencephalon (cerebral hemispheres) Third ventricle Diencephalon (thalamus/hypothalamus) Mesencephalon (midbrain) Fourth ventricle Metencephalon (pons/cerebellum) Myelencephalon (medulla) Central canal Embryonic day 36 Lumen occupies most of the space of the developing brain Lateral ventricles • Two lateral ventricles - One for each cerebral hemisphere • Very large C-shape • Divided into: Body Anterior horn Posterior horn Inferior horn Body (Parietal lobe) Anterior horn (Frontal lobe) • Each part corresponds to a different lobe Inferior horn (Temporal lobe) Posterior horn (Occipital lobe) Lateral ventricles on MRI Horizontal: Coronal: Anterior Lateral ventricles On T1-weighted MRI, CSF appears dark Lateral ventricle borders • Septum pellucidum separates bodies of lateral ventricles • Corpus callosum sits in roof Corpus callosum Septum pellucidum Lateral ventricle borders • Caudate nucleus sits in lateral wall • Hippocampus sits in floor of inferior horn Caudate nucleus Rostral Coronal Hippocampus Horizontal Interventricular foramen • Lateral ventricles communicate with the third ventricle through the interventricular foramen • Also called Foramen of Monro Lateral ventricles Septum pellucidum Interventricular Foramen (Foramen of Monro) Third ventricle Third ventricle • Third ventricle appears as a slit-like cleft • Thalami sit in lateral walls Mammillary bodies • Fornix forms roof Hippocampus Thalamus Fornix Third ventricle Coronal Horizontal Summary of associated structures Corpus callosum Septum pellucidum Rostral Caudate nucleus Fornix Lentiform nucleus Thalamus Coronal Caudate nucleus Hippocampus Horizontal Cerebral aqueduct • Third ventricle communicates with fourth ventricle through the cerebral aqueduct • Also called Aqueduct of Sylvius Third ventricle Fourth ventricle • Surrounded by the midbrain Cerebral aqueduct (Aqueduct of Sylvius) Fourth ventricle • Fourth ventricle is surrounded by hindbrain: Cerebral aqueduct (aqueduct of Sylvius) - Cerebellum posterior - Pons and medulla anterior - Cerebellar peduncles lateral Midbrain Pons Medulla Superior medullary velum Fourth Roof ventricle Inferior medullary velum • Continuous with the central canal of the spinal cord and subarachnoid space Fourth ventricle communication • Three foramina exit into subarachnoid space: Posterior surface of brainstem - Two Foramina of Luschka (lateral) - One Foramen of Magendie (middle) Colliculi (midbrain) - Into the Cisterna Magna Cerebellar peduncles Foramen of Luschka Foramen of Magendie Coronal Note the diamond shape in coronal view Cerebrospinal fluid Function of cerebrospinal fluid • Cerebrospinal fluid (CSF) is functionally important • Lots of different functions: 1. Hydraulic buffer to cushion brain against trauma 2. Vehicle for removal of metabolites from CNS 3. Stable ionic environment for neuronal function 4. Transport of neurotransmitters and chemicals Choroid plexus • Cerebrospinal fluid is produced by the choroid plexus • Filters blood from branches of internal carotid and basilar arteries • Choroid plexus present throughout ventricles: Corpus callosum Choroid plexus (Lateral ventricle) Fornix Thalamus Choroid plexus (Third ventricle) Coronal section Choroid plexus (Fourth ventricle) Structure of the choroid plexus • Very simple structure • Capillary network surrounded by cuboidal epithelium • During CSF production: 1. Blood filtered through fenestrated capillaries 2. Components transported through cuboidal epithelium into ventricles Structure of the choroid plexus BRAIN PARENCHYMA Ependymal lining of ventricle VENTRICLE Fenestrated capillaries (Filter) Connective tissue core Cuboidal epithelium (Transport) CSF Tight junctions between epithelial cells - Prevent macromolecules from entering CSF - Permeable to water and CO2 - Forms blood-CSF barrier Cuboidal epithelium • Specialized ependymal cells • Microvilli present to increase surface area • Actively transport CSF components - Or by facilitated diffusion (i.e. aided by carrier proteins) • Bidirectional (transport of chemicals into circulation) Cerebrospinal fluid composition • Cerebrospinal fluid differs in composition compared to blood plasma: Component CSF Blood Plasma pH 7.33 7.41 Na+ (mmol/l) 144 – 152 135 – 145 K+ (mmol/l) 2.0 – 3.0 3.8 – 5.0 Ca2+ (mmol/l) 1.1 – 1.3 2.2 – 2.6 Cl- (mmol/l) 123 – 128 95 – 105 Glucose (mmol/l) 2.5 – 4.5 3.0 – 5.0 Protein (g/l) 0.2 – 0.4 ↓ 60 – 80 Low protein in CSF • Differences maintained by active transport process • Very few cells (0-3 lymphocytes/cubic mm) • CSF composition Ideal for physiological functioning of neurons CSF circulation within ventricles Lateral ventricles Interventricular foramen Third ventricle Cerebral aqueduct Fourth ventricle Luschka and Magendie foramina Cisterna magna (subarachnoid space) • CSF passes out of ventricles into the subarachnoid space CSF circulation within subarachnoid space Arachnoid granulations Superior sagittal sinus Over cerebral hemispheres Over cerebellum/cerebral hemispheres Up ventral spinal subarachnoid space Cisterna magna Down dorsal spinal subarachnoid space Central canal – usually blocked in adults Subarachnoid space • Lies between pia and arachnoid Lateral ventricle • Subarachnoid space follows contours of brain • CSF in contact with brain parenchyma Fourth ventricle Cisterna magna • Important for transfer of electrolytes into brain and removal of metabolites T2-w MRI (CSF appears white) Arachnoid granulations • Herniations of arachnoid membrane (villi) through dura mater into venous sinuses • Mainly within the superior sagittal and transverse venous sinuses Superior sagittal sinus Arachnoid granulation Dura Arachnoid Pia Subarachnoid space Endosteal and meningeal layers of dura separate around sinuses Transverse sinus • Important for removal of excess cerebrospinal fluid and metabolites Arachnoid granulations Superior view into superior sagittal sinus (dura removed) Note arachnoid granulations Absorption of cerebrospinal fluid • CSF pressure in subarachnoid space exceeds pressure in venous sinuses • Prevents blood pooling in subarachnoid space In disease • If venous pressure exceeds CSF pressure - Tips of arachnoid granulations close off Act as one-way valves Subarachnoid space: ~180 mmH2O Venous sinus: ~80 mmH2O Cerebrospinal fluid volume • 600 – 700ml CSF produced per day (~0.5 ml/min) • Mean volume in adults is 150ml (range 140 – 270ml) - Only 25ml in ventricles • Continuously moving • Important for transport of chemicals • CSF is replaced four times each day • Excess absorbed by arachnoid granulations Cerebrospinal fluid in disease Colour of cerebrospinal fluid in disease • CSF normally clear sterile fluid • Discoloured in some pathological states: Yellow/orange/pink (Xanthocromia) E.g. Subarachnoid haemorrhage - Lysis of red blood cells, oxyhaemoglobin released Cloudy/Turbid E.g. Bacterial meningitis - Leukocytes increased - Indicative of infection Cerebrospinal fluid sampling • Taken by lumbar puncture • At lumbar cistern - No spinal cord L3/4 adults L4/5 children Hydrocephalus • Dilation of brain ventricles • Due to blocked CSF circulation, impaired absorption, or over secretion • Increased intracranial (CSF) pressure • Pressure on surrounding tissues affects neurological function - Symptoms include: headaches, vomiting, visual disturbances, papilledema (swelling of optic disc), seizures, altered cognition, balance and coordination problems • Can be congenital or acquired Non-communicating hydrocephalus • Blockage within the ventricular system - Due to tumour, cyst, stenosis (e.g. narrowing of cerebral aqueduct) • CSF does not circulate over surface of brain Surgery: Insert shunt to reduce intracranial pressure T2 MRI of lateral ventricles of a patient with non-communicating hydrocephalus Dandy-Walker syndrome • Congenital malformation of the cerebellum (1:30,000 births) • Obstruction within foramina of fourth ventricle: - Symmetrical dilation of lateral, third and fourth ventricles • In infancy, child’s head may become enlarged: T2 MRI of patient with DandyWalker syndrome International Journal of Recent Surgical and Medical Sciences Communicating hydrocephalus • Obstruction in the arachnoid villi • Movement of CSF into venous sinuses is impeded - E.g. Impaired absorption following subarachnoid haemorrhage, trauma or bacterial meningitis T2 MRI long-standing communicating hydrocephalus Summary • Ventricles of brain • Cerebrospinal fluid production • Circulation and absorption of cerebrospinal fluid • Function of cerebrospinal fluid • Disorders of the ventricular system and cerebrospinal fluid Next Lecture: Ascending and descending tracts