Meninges and Ventricles

Transcription

1 Meninges and Ventricles Irene Yu, class of 2019

2 LEARNING OBJECTIVES Describe the meningeal layers, the dural infolds, and the spaces they create. Name the contents of the subarachnoid space. Describe the subarachnoid cisterns. Describe the types of hemorrhages that affect meningeal spaces and their causes and symptoms. Describe each part of the ventricular system and the path of CSF to the dural sinuses. Describe how CSF is produced, its composition, function, and how it leaves the ventricular system and subarachnoid space. Define hydrocephalus. Describe its causes, symptoms, and types. Describe how meningitis can cause hydrocephalus Describe the treatments available for hydrocephalus. Chris Cohan PhD Dept of Pathology and Anat Sci Jacobs School of Medicine

3 Meninges 3 layers of connective tissue surrounding brain and spinal cord: 1. Dura outermost layer dense fibrous connective tissue blood supply middle meningeal artery; supplied by CN V Skull: outer layer -periosteum of skull; Inner meningeal Spinal cord: only has the meningeal layer Dural infolds: falx cerebrei; tentorium cerebelli forms supra- and subtentorial compartments. Sinuses for venous blood drainage

4 Falx Cerebri Dural Infolds and Sinuses Tentorium Cerebelli front front Tentorium removed Atlas of Human Intracranial Anatomy, M. Waddington

5 Dural Infolds and Sinuses Superior sagittal sinus front Inferior sagittal sinus Atlas of Human Intracranial Anatomy, M. Waddington

6 Meninges 3 layers of connective tissue surrounding brain and spinal cord: 2. Arachnoid middle, delicate, avascular loosely adheres to dura Spidery web-like processes extend to pia. 3. Pia highly vascularized layer on surface of brain and spinal cord arachnoid dura meninges removed dura arachnoid Atlas of Human Intracranial Anatomy, M. Waddington

7 Meningeal Compartments Real or potential spaces exist between meningeal layers. Some contain important constituents. They accumulate blood during hemorrhage, displacing the brain, and causing life-threatening herniation. Each type of hemorrhage creates a characteristic shape that can be identified in CT/MRI images (to be shown in Neuroimaging Session). 1. Epidural potential space 2. Subdural potential space 3. Subarachnoid real space

8 Meningeal Compartments Introduction of any mass into the cranial cavity causes increased intracranial pressure and herniation of the brain due to the closed compartment of the skull. Increased intracranial pressure is transmitted through the subarachnoid space to the eye where it causes papilledema (swelling of the optic nerve as it leaves the retina). Papilledema can be confirmed with a fundoscopic exam. normal papilledema Enlarged and elevated optic disc with fuzzy margin Herniation is a life-threatening condition as it quickly impairs autonomic centers in the brainstem.

9 Meningeal Compartments 1. Epidural potential space between periosteal layer of dura and skull. epidural hemorrhage results from skull fracture that ruptures middle meningeal artery life-threatening condition Impressions made by branches of middle meningeal artery dura

10 Meningeal Compartments 2. Subdural potential space between dura and arachnoid subdural hemorrhage results from tearing of bridging veins that traverse area between arachnoid and dura as veins empty into sinuses. potentially life-threatening condition

11 Meningeal Compartments 3. Subarachnoid real space containing spinal rootlets, blood vessels, cerebrospinal fluid (CSF) The pia and arachnoid are often considered together as the leptomeninges. The pia is densely attached to the surface of the brain, while the arachnoid forms a continuous sheet immediately subjacent to the dura. Pia and arachnoid are connected by delicate strands of arachnoid trabeculae. Subarachnoid hemorrhage can result from trauma (most common) or aneurysms (non-traumatic). typically worst headache of your life blood follows contour of gyri and sulci as pia is closely adherent to brain. life-threatening condition

12 Ventricles Spaces within brain that produce and circulate cerebrospinal fluid: lateral ventricles (2) one in each hemisphere 3 rd ventricle midline in hemisphere Interventricular foramen connects lateral and 3 rd ventricle 4 th ventricle on posterior surface of brainstem pons and medulla form its floor cerebellum forms its roof Cerebral Aqueduct connects 3 rd and 4 th ventricles narrow opening in midbrain Central Canal of spinal cord extension of ventricles Filled with CSF Function brain and spinal cord are suspended in CSF; collects metabolites from brain.

13 Lateral Ventricles Interventricular foramen lateral Cerebral aqueduct Lateral Ventricles separated by thin membrane septum pellucidum extends through each lobe as frontal horn, body, occipital horn, temporal horn body 4th 3 rd Septum pellucidum (membrane) Frontal horn Trigone/atrium convergence of body, occipital, and temporal horns Occipital horn Temporal horn

14 Lateral Ventricles Gross unstained Horizontal MRI

15 Midline Walls thalamus + hypothalamus Roof formed by choroid plexus and pia membrane. 3 rd Ventricle Cerebral aqueduct Interventricular foramen 3 rd coronal horizontal Horizontal MRI

16 rhombus-shaped extends over pons and medulla cerebral aqueduct connects to 3 rd ventricle 4 th Ventricle Cerebral aqueduct Interventricular foramen lateral 4th 3 rd Septum pellucidum (membrane) 4 th ventricle

17 Choroid Plexus the organ that secretes CSF clear, filtrate of blood found in each ventricle but NOT cerebral aqueduct Volume = 150 ml; production = 500 ml/day Glomus enlarged portion in trigone becomes calcified and is radiological landmark Ventricles

18 Ventricles Choroid plexus on MRI images

19 Ventricles CSF flows through ventricular system lateral ventricle to interventricular foramen to 3 rd to cerebral aqueduct to 4 th CSF exits ventricular system through 3 holes in the 4 th ventricle: 1 foramen of Magendie (Midline), 2 foramina of Lutschka (Lateral) CSF fills the subarachnoid space around brain and spinal cord. Foramen of Magendie Foramina of Lutschka

20 MRI showing CSF in subarachnoid space. MRI protocols typically subtract CSF from images to increase visibility. * * Cisterna magna * Subarachnoid space *Subarachnoid cisterns are enlarged areas of the subarachnoid space. They are radiologically important in showing presence of blood.

21 Ventricles CSF empties into the superior sagittal sinus Arachnoid Granulations/Villi protrusions of arachnoid membrane into the sinus Dural sinuses empty into internal jugular vein. Meningitis can affect filtration through arachnoid granulations and result in chronic impaired flow of CFS into the sinus.

22 Hydrocephalus Hydrocephalus is caused by impaired flow of CSF through ventricles, subarachnoid space, or into dural sinuses. Normal pressure is mm H 2 O reclining. results in dangerous increase in intracranial pressure and consequently papilledema Types 1. Obstructive (non-communicating) results from blockage within the ventricular system. Cerebral aqueduct is most susceptible due to narrow size. 2. Non-obstructive (communicating) reduced flow due to blockage in subarachnoid space or arachnoid granulations. 3. Ex vacuo compensatory increase in ventricle size as brain atrophy occurs. 4. Normal pressure hydrocephalus - impaired flow through subarachnoid space or arachnoid granulations with no increase in pressure 5. Benign intracranial hypertension

23 Hydrocephalus Enlarged Ventricles due to hydrocephalus:

24 Hydrocephalus Treatment A shunt can be inserted into the lateral ventricles to drain CSF to another place where it can be absorbed. Shunts are prone to clogging and infection. In some cases, a hole can be made in the thin floor of the hypothalamus/3 rd ventricle to allow CSF to drain directly into the subarachnoid space.