• Osteology • Arterial supply • Meningeal layers • Dural folds • Dural venous sinuses • Cerebrospinal fluid • Lymphatic drainage • Sympathetic supply Session Learning Ojectives
1. List and describe the meningeal layers covering the brain and associated real or potential spaces. 2. Describe the dural folds and associated dural venous sinuses, including the cavernous sinus. 3. Describe the arterial supply to and venous drainage from the brain and common types of intracranial bleeding. 4. Describe the ventricular system in the brain and the formation, distribution, and reabsorption of cerebrospinal fluid. 5. Identify and distinguish radiologic images featuring epidural, subdural, subarachnoid, and dural folds. 6. Describe the sympathetic innervation to the head and neck. 7. Map out the lymphatic drainage of the head and neck. Osteology
Cranial fossae: large depressions that form the floor of the cranial cavity • Increase in depth from anterior to posterior These bowl shaped fossae accommodate the brain • Anterior fossa: frontal lobe • Middle fossa: temporal lobe • Posterior fossa: cerebellum and brain stem Osteology Crista galli Cribriform plate Anterior Cranial Fossa Roof of orbit • Ethmoid bone • Frontal bone Sella turcica: • Sphenoid bone • Tuberculum sellae • Hypophysial fossa • Dorsum sellae Middle Cranial Fossa
Clivus • Sphenoid Squamous portion • Temporal bone Petrous portion
Foramen magnum Posterior Cranial Fossa • Temporal Internal occipital • Occipital protuberance Osteology Cribriform foramina • CN I: olfactory Foramen rotundum Optic canal • CN V2: maxillary • CN II: optic • Ophthalmic aa. Foramen ovale • CN V3: maxillary Superior orbital fissure • Lesser petrosal n. • CN III: oculomotor • CN IV: trochlear Foramen spinosum • CN V1: ophthalmic • Middle meningeal a. • CN VI: abducens Groove of greater •Superior ophthalmic v. petrosal nerve Foramen lacerum Jugular foramen • Greater petrosal n. • CN IX: glossopharyngeal • Deep petrosal n. •CN X: vagus • CN XI: accessory Internal acoustic meatus • Internal jugular vein • CN VII: facial • CN VIII: vestibulocochlear Hypoglossal canal • CN XII: hypoglossal Cranial Nerves
Note: a meningeal layer has been removed on the right side revealing nerves in the cavernous sinus Walls of the Cranial Cavity
Inner & outer tables: Diploic vv. Emissary vv. layers of compact bone Diploe: spongy bone containing red marrow • Contains diploic veins Emissary veins: connect extracranial veins to venous sinuses inside cranium Blood Supply to the Brain
Internal carotid arteries Vertebral arteries • Enter cranium through carotid canal and pass over foramen • Enter cranium through lacerum foramen magnum and • Curve through cavernous sinus merge to form basilar lateral to body of sphenoid artery Blood Supply to the Brain
Anterior communicating a. Internal carotid artery Anterior cerebral a.
Middle cerebral a.
Internal Posterior Basilar artery carotid a. communicating a.
Basilar a. Posterior Vertebral cerebral a. Circle of Willis arteries Dura mater Arachnoid mater Pia mater Cranial Meninges Membranous coverings which protect the brain, form the framework for blood vessels, and enclose fluid filled cavity Dura mater: thick outer layer adherent to the calvaria • Contains middle meningeal arteries Arachnoid mater: thin middle layer loosely applied to dura • Does not enter sulci/grooves of brain Pia mater: inner membrane adherent to surface of brain • Follows contours of brain Epidural Hemorrhage Hard blows to the head can fracture calvaria, causing tearing of the middle meningeal artery
• Blood collects between dura and skull • Typically a brief concussion is followed by a brief period of lucidity • Later as blood mass increases, compression of the brain can cause unconsciousness Epidural Hemorrhage Pterion: • Area of convergence of 4 bones • Thin bone, covered by temporalis • Vulnerable to blows to lateral skull • Fracture can lead to tears of the anterior branch of MMA Cranial Meninges Dura mater: two layers which only separate to enclose venous sinuses • Periosteal layer • Meningeal layer Arachnoid mater: Separated from the pia mater by the subarachnoid space Pia mater: inner membrane adherent to surface of brain Cranial Meninges
Periosteal layer Meningeal layer Arachnoid mater Arachnoid trabeculae Note the presence of cerebral vessels Pia mater within the subarachnoid space Subarachnoid Hemorrhages Sudden leak or rupture of a cerebral artery into subarachnoid space
• Most result from rupture of a saccular aneurysm • Sudden onset of severe headache, stiff neck, and nausea or vomiting Ruptured • Urgent neuroimaging and aneurysm vessel ligation required Bridging Veins Cerebral veins which pierce the arachnoid mater and meningeal layer of dura to Superior drain into dural venous sinuses cerebral veins
Bridging veins Superior sagittal Subdural Hematoma sinus Extravasated blood separates the layers Bridging veins at the dura-arachnoid interface Caused by tearing of bridging veins when head trauma jerks brain in cranium • Symptoms such as mental compromise may not be seen until several days post trauma
Blood creates and fills subdural space (normally only a potential space) Shaken Baby Syndrome • Serous brain injury can result from forcefully shaking a baby or toddler • Results from tearing of the bridging veins = subdural bleed CASE 1: A MMA fighter received a CASE 2: A couple brings their baby CASE 3: A 53 year old male blow to the lateral side of the head to the ER explaining that he won’t presents to the emergency room during his last match and later stop crying, and has shown a complaining of “the worst showed the following symptoms: recent lack of interest in eating. headache of his life”, and a stiff severe headache, drowsiness, The mother tells you he recently neck. He has a history of high blood dizziness, and confusion fell and hit his head. pressure.
A. Case 2 only In which of the cases above would you B. Case 1 and 2 suspect an intracranial bleed involving C. Case 1 and 3 arterial blood? D. Case 2 and 3 E. Case 3 only CASE 1: A MMA fighter received a CASE 2: A couple brings their baby CASE 3: A 53 year old male blow to the lateral side of the head to the ER explaining that he won’t presents to the emergency room during his last match and later stop crying, and has shown a complaining of “the worst showed the following symptoms: recent lack of interest in eating. headache of his life”, and a stiff severe headache, drowsiness, The mother tells you he recently neck. He has a history of high blood dizziness, and confusion fell and hit his head. pressure.
• Fracture of pterion • Tearing of • Rupture of • Tear • • • Epidural Hematoma Subdural Hematoma Subarachnoid • Lens shaped • Crescent shaped Hemorrhage • Shift of midline • Confined to one • Appears as white that structures hemisphere fills normally black • Shift of midline subarachnoid spaces structures • Follows brain contours Dural Folds Infoldings of meningeal dura that divide the cranial cavity into compartments in order to protect the brain from undue rotation and displacement Falx cerebri
Falx cerebri: separates right and left cerebral hemispheres Tentorium cerebelli: separates occipital lobes from cerebellum Diaphragma sellae: covers pituitary gland in hypophyseal fossa Falx cerebelli: partially separates cerebellar hemispheres
Falx cerebelli Diaphragma sellae Tentorium cerebelli Dural Fold Attachments Falx cerebri: • Crista galli • Internal occipital protuberance Anterior clinoid Tentorium cerebelli: process • Clinoid processes Posterior • Superior border of petrous clinoid process portion of temporal bone • Transverse groove of occipital bone Diaphragma sellae: • Clinoid processes Occipital crest Falx cerebelli: • Occipital crest Dural Venous Sinuses Dural venous Layers of dura separate to form sinus dural venous sinuses • Walls are tough and rigid; lack smooth muscle • Lined by endothelium • Lack valves • Receive venous return from the brain (bridging veins) • Are sites of reabsorption of cerebral spinal fluid (CSF) Dural Venous Sinuses Superior sagittal sinus Inferior sagittal sinus Superior sagittal sinus: Transverse upper border of the falx cerebri sinus Inferior sagittal sinus: lower Confluence border of the falx cerebri of sinuses Straight sinus: junction of falx cerebri & tentorium cerebelli Occipital sinus: posterior attachment of falx cerebelli Confluence of sinuses: internal occipital protuberance Transverse sinus: posterior border of tentorium cerebelli Straight sinus Occipital sinus Superior sagittal sinus Dural Venous Sinuses Inferior sagittal sinus Straight sinus Formed by the union of the Straight inferior sagittal sinus with the sinus great cerebral vein Confluence of sinuses Receives blood from: • Superior sagittal sinus • Straight sinus • Occipital sinus Drains into: Confluence • Left & right transverse sinuses Occipital sinus Great cerebral vein Anterior and posterior Dural Venous Sinuses Intercavernous sinuses Sigmoid sinus: follows s-shaped groove in occipital and temporal bones Basilar sinus toward jugular foramen
Superior petrosal sinus: along Cavernous attachment of tentorium cerebelli to sinus superior border of petrous portion of Superior temporal bone petrosal sinus
Inferior petrosal sinus: descends Inferior in groove between clivus and posterior petrosal sinus petrous portion of the temporal bone Cavernous sinus: lateral surfaces of Sigmoid sinus the body of the sphenoid Intercavernous sinuses: within diaphragma sellae Basilar sinus: beneath dura of clivus Dural Venous Sinuses Transverse sinus Continues laterally from confluence of sinuses Sigmoid sinus Basilar sinus Drains into internal jugular vein at jugular foramen Superior Superior petrosal sinus petrosal sinus Drains cavernous sinus into sigmoid Inferior sinus petrosal sinus Inferior petrosal sinus Drains cavernous sinus into IJV at Sigmoid sinus junction with sigmoid sinus Basilar sinus Connects inferior petrosal sinuses and communicates inferiorly with the C internal vertebral venous plexus Transverse sinus Multiple connections: Cavernous Sinus • Superior ophthalmic vein • Opposite cavernous sinus • Superior and inferior petrosal sinus • Basilar sinus • Pterygoid plexus
Pterygoid venous plexus Contents: Cavernous Sinus • CN III: Oculomotor • CN IV: Trochlear • CN V1: Ophthalmic • CN V2: Maxillary • CN VI: Abducens • Internal carotid artery (ICA)
Oculomotor Trochlear Ophthalmic Maxillary
Meningeal dura Periosteal dura ICA Abducens Cavernous Sinus Thrombosis • The facial vein is connected to the cavernous sinus through: • Superior ophthalmic veins • Pterygoid venous plexus • Infected pieces of clots can travel from inflamed facial vein to cavernous sinus
• Usually a patient history of sinusitis, Danger triangle of abscessed tooth or middle face infection face • Symptoms: fever, orbital swelling due to venous congestion, visual disturbances due to cranial nerve impairment
Cerebrospinal fluid: clear fluid, nearly devoid of protein, which protects and nourishes the brain • Located in ventricles and subarachnoid space • Constantly produced by choroid plexuses in ventricles ~ 500 ml/day • Reabsorbed into venous system *primarily superior sagittal sinus Ventricular System Ventricles: a communicating network of cavities in the brain which are filled with cerebrospinal fluid
Lateral Ventricles Lateral ventricle Interventricular foramen Interventricular 3rd Ventricle foramen
Cerebral aqueduct Third ventricle th 4 Ventricle Cerebral aqueduct Fourth ventricle Median and lateral (2) apertures Subarachnoid Space Anterior view Left lateral view Cerebrospinal Fluid Granular pit
CSF is absorbed into the venous system through arachnoid granulations • These projections of arachnoid membrane extend through the meningeal dura and into the dural venous sinuses and lateral lacunae • Arachnoid granulations may cause granular pits in the overlying calvaria
Lateral lacunae Arachnoid granulation
Lymphatic Drainage Lymph nodes of the head: • Located at the junction of the head and neck • Drain into the deep cervical nodes of the neck The superficial cervical lymph nodes are primary drainage locations for lymph from adjacent areas or organs Lymphatic Drainage Lymph nodes in the neck have been divided into levels Lymphatic Drainage
• Understanding the pattern of lymphatic flow is critical to identifying the location of a potential cause of enlarged cervical lymph nodes • There are two main sites in the neck where the lymphatic pathways intersect: • Jugulofacial venous junction • Jugulosubclavian venous junction Sympathetic Innervation • Sympathetic preganglionic neurons of the head and neck originate in the lateral horn of the spinal cord (T1-L2) • They exit into the sympathetic trunk and ascend to synapse in the superior cervical ganglion • Postganglionic neurons then travel with arterial plexuses • As fibers head towards their targets some fibers pass through ganglia without synapsing Sympathetic Innervation of the Head Parasympathetic Innervation • Visceral efferent fibers travel along four cranial nerves • Synapse in regional ganglia close to target Parasympathetic Innervation Lecture Summary • Osteology: foramina, fossae, landmarks • Arterial supply: circle of Willis • Meningeal layers: real/potential spaces, related intracranial bleeds • Dural folds: attachments • Dural venous sinuses: location, drainage • Cerebrospinal fluid: production, flow, reabsorption • Lymphatic drainage: groups, drainage • Sympathetic supply: pathways, innervation