16 Skull Osteology, Cranial Fossas, Meninges, Sinuses & Intracranial Bleeds PDF

Skull osteology, cranial fossas, meninges, sinuses and intracranial bleeds Class Year 2, Semester 1 Lecturer DR. VIJAYALAKSHMI S B Department of Anatomy Email id: [email protected] Date 5/11/2024 1 LEARNING O...

Skull osteology, cranial fossas, meninges, sinuses and intracranial bleeds Class Year 2, Semester 1 Lecturer DR. VIJAYALAKSHMI S B Department of Anatomy Email id: [email protected] Date 5/11/2024 1 LEARNING OUTCOMES 1. Describe the osteology of the skull in frontal, posterior, superior and inferior views 2. Identify foramina in the skull and identify any structures passing through them 3. Define the anterior, middle and posterior cranial fossas 4. List the meningeal layers and describe their arrangements 5. Identify the relations of blood vessels to meninges 6. Describe the layout of the dural sinuses 7. Identify the types of intracranial bleeds their radiological appearance, and their clinical presentations 8. Discuss herniation and coning  Skull Skull = cranium + mandible Cranium = calvarium, base or fossae, facial bones Joined by sutures - fibrous joints Frontal Nasal Parietal Temporal Maxilla Zygoma Mandible  Skull bones 22 bones (paired and single) bones  Skull bones 22 bones, 8 paired + 6 unpaired (single) Facial Cranial Maxilla Occipital Mandible Frontal Palatine Sphenoid Zygomatic Ethmoid Vomer Parietal Nasal Temporal Lacrimal * Doesn’t include Nasal Conchae The small bones of the ears ! Skull – Anterior view Skull – Lateral view Skull – Posterior view  Pterion Frontal Parietal Occipital Pterion Frontal Parietal Temporal Sphenoid (greater wing) * Middle meningeal artery runs just behind this point Intracranial bleed Temporal Zygoma Sphenoid  Sutures and fontanelle Anterior fontanelle Bregma Coronal Frontal Parietal Sagittal Posterior Fontanelle Occipital Lambdoid Lambda  Calvaria SCALP DIPLOE External table Internal table  Fetal skull ▪ Cranium very large/ face small ▪ Cranium & face ossification = intramembranous ossification ▪ Base = endochondral ossification ▪ Vault – cancellous bone – diploe ▪ Bones ossified but mobile at birth ▪ Sutures fuse later ▪ Fontanelles are unossified gaps in the neonatal skull Posterior fontanelle closes by – 2 to 3 months Anterior fontanelle closes by 18 months  Fontanelles – Clinical signs Anterior fontanelle (Bregma) Posterior fontanelle Lambda Fontanelles: Clinical signs Depressed or sunken in dehydration Bulging in raised intracranial pressure  Fontanelles – Clinical signs Sunken Fontanelle Dehydration (inadequate fluids) Bulging fontanelle Raised intracranial pressure Hydrocephalus Meningitis Cranial fossae Anterior Middle Posterior  Anterior cranial fossa Formed by the following bones: Frontal Foramina present: Ethmoid ▪ Foramen caecum Crista galli ▪ Olfactory foramen Cribriform plate Sphenoid (body and lesser wings)  Middle cranial fossa Formed by the following bones: Sphenoid (body and greater wings) Sella turcica Temporal Squamous and petrous parts  Middle cranial fossa Foramina R Optic canal Superior orbital fissure Rotundum (R) Ovale (O) O Spinosum (S) S  Posterior cranial fossa Formed by the following bones: Temporal bone Petrous part Occipital Clivus Clivus Petrous part of Internal occipital Temporal bone protuberance Internal occipital protuberance  Posterior cranial fossa Foramina Internal acoustic meatus (IAM) Magnum (M) Jugular (J) Hypoglossal (H) Clivus H IAM J M Base of the skull Palatine process Foramen lacerum of maxilla Hard palate Palatine bone Zygomatic arch Vomer Pterygoid plates (M/L) Condylar fossa for TMJ Foramen ovale, spinosum, External spine of sphenoid acoustic meatus Carotid canal Styloid Stylomastoid foramen Occipital Mastoid condyle Foramen magnum Superior Nuchal line External occipital protuberence Meninges  Meninges of the brain Meninges Bone Dura (2 layers) Subdural space Arachnoid Subarachnoid space Pia  Meninges of the brain Dura (cut to expose subdural space) Surface of arachnoid Arachnoid removed to expose the brain surface covered by Pia Meninges of the spinal cord Bone Epi(peri/extra) dural space Dura No real Subdural space* (Dura and Arachnoid stick together) Arachnoid Subarachnoid space Pia  Cranial Dura Two layers Outer periosteal layer intimately attached to the bone no space between dura and bone Inner meningeal layer Venous sinuses lie between these two layers No valves  sinuses, not veins Meninges Bone Dura (2 layers) Subdural space Arachnoid Subarachnoid space Pia  Cranial Dura Outermost, thickest, tough, fibrous membrane Consists of two connective tissue layers: an external periosteal layer and an inner meningeal layer Two layers adhering to each other except at the ‘Dural folds’ containing venous blood. Also contains the meningeal arteries. Periosteal layer attached to the inner surface of the skull bone forms a component of the periosteum. Often tears with skull-base fractures. In the skull, epidural space is a “Potential” space In the vertebral column, there is “True” epidural space  Cranial Dura Meningeal layer Smooth, avascular, lined by mesothelium Continuous with spinal dura at the foramen magnum Forms folds/septa – to reduce or prevent displacement of the brain when the head moves 1. Falx cerebri – separates two cerebral hemispheres 2. Tentorium cerebelli - separates occipital lobe from cerebellum 3. Falx cerebelli – partially separates the cerebellar hemispheres 4. Diaphragma sellae - Roof of pituitary across the fossa. Cranial dura - innervation  Dural sinuses Dura outer layer (periosteal) Meninges Dura inner layer (meningeal)  Dural sinuses Superior sagittal sinus Runs in upper part of the falx cerebri to the internal occipital protuberance Inferior sagittal sinus Runs in the free edge of the falx cerebri, Great cerebral vein (of Galen) enters to form straight sinus Straight sinus runs in tentorium cerebelli to the confluence of sinuses Superior sagittal sinus Confluence Inferior sagittal sinus Straight sinus Transverse sinus Great cerebral vein (cut)  Dural sinuses Confluence of sinuses can be variable, however – Superior sagittal sinus typically drains to the right transverse sinus – Inferior sagittal sinus goes into the left transverse sinus Superior petrosal sinus Transverse sinus Runs in the groove, receives superior petrosal sinus, becomes sigmoid sinus Sigmoid sinus To jugular bulb, in the jugular foramen, becomes internal jugular vein Sigmoid sinus Transverse sinus  Dural sinuses Petrosal sinuses: Superior and Inferior run along superior and inferior borders of the petrous temporal bone. Connect Cavernous sinuses with Sigmoid sinuses.  Cavernous sinus Either side of body of sphenoid - Surrounding pituitary gland Important relations to Internal Carotid Artery & cranial nerves!!! Sphenoparietal sinus Ophthalmic veins Superior petrosal sinus runs to transverse/sigmoid sinus Inferior petrosal sinus runs to jugular bulb Ophthalmic veins (orbit  superior orbital fissure) Sphenoparietal sinus (along lesser wing of sphenoid) Cavernous sinuses  Cavernous sinus Sympathetic plexus Dura mater Cavernous sinus thrombosis “Danger triangle” Rare but life-threatening, can complicate due to facial, sinus, and orbital infections Basilar plexus – thrombosis here may cause brainstem infarction Fever, headache, periorbital swelling Arachnoid and subarachnoid space Arachnoid mater- Impermeable layer between dura and pia mater. Adherent to dura. Separated from pia mater by subarachnoid space containing CSF circulating around the arachnoid trabeculae –spider-leg-like strands of connective tissue and blood vessels. Arachnoid villi and granulations drain CSF into dural sinuses. Subarachnoid space and CSF The Subarachnoid space is filled with CSF and surrounds brain and spinal cord. Has an important protective function as it acts like a water cushion surrounding the whole CNS This space is in direct continuity with the fourth ventricle and is the place where CSF flows in from the IV ventricle. One important key feature that distinguishes the Subarachnoid space of the cerebral meninges from the one around the spinal cord is that around the spinal cord, its width is more regular, whereas around the brain, it is quite irregular, and enlarges at certain locations, forming cisterns Netter Presenter Image, Copyright Icon Learning System. All rights reserved  Arachnoid and subarachnoid space Subarachnoid cisterns Enlargement of subarachnoid spaces at several places in the cranial cavity Includes cerebellomedullary cistern, cisterna magna, chiasmatic cistern Suspected pathological sites in the brain can be visualized through these cisterns by use of radiological procedures  Arachnoid Granulations (Villi) Projections of arachnoid mater protruding into venous sinuses Largest ones – along superior sagittal sinus (often visible on specimens) Cerebrospinal fluid reabsorbed into venous circulation  Pia mater Meningitis – inflammation of the Delicate layer pia Adheres to the surface of Permeable to water & small the brain solutes Dips into gyri and sulci May secrete small amount of Macroscopically CSF invisible, except filum Mainly produced by choroid terminale plexuses  Intracranial bleeding 1. Extradural (EDH) 1 2 2. Subdural (SDH) 3 3. Subarachnoid (SAH) 4 4. Intracerebral or intraparenchymal (ICH) 5 5. Intraventricular (IVH)  Extradural hemorrhage High-pressure arterial bleeding in a tightly closed space Cause: A skull fracture tearing (arterial) vessels in the extradural space Where? Usually in temporal / temporo-parietal region Middle meningeal artery (anterior branch) behind pterion Lies extra-dural – runs in the groove or even a tunnel of bone Occasionally results from damage to sagittal/transverse sinus  Extradural hemorrhage Does not cross skull suture line because endosteum is attached to suture membrane. Biconvex Hematoma in Extra-dural ‘space’ between 2 layers of cranial dura. Appearance Area of increased density Biconvex (Lentiform) in shape Spread limited by dural adhesion to the skull Clinical features May have a short period of LOC Loss of consciousness Lucid interval Then rapid deterioration  Extradural Extraduralhemorrhage bleeding Epidural hematoma Subtentorial herniation of Compression of temporal lobe ipsilateral crus cerebri* III Nerve compression Hutchinson pupil/ “blown pupil” Contralateral Babinski  Subdural hemorrhage Appearance Area of increased density Acutely – then becomes hypodense at 1-2 months Crescent or sickle shape Cerebral or ventricular shift https://www.radiologymasterclass.co.uk/gallery/ct_brain/ct_brain_images/subdural_acute_chronic_ct_brain  Subarachnoid hemorrhage Harder to see sometimes! Blood in subarachnoid space May be widely distributed throughout the cisterns and fissures or in the ventricular system May be from an aneurysm in the circle of Willis (Berry Aneurysm) Symptoms Severity of symptoms is related to the severity of the bleed Usually – sudden onset headache “blow to head” Transient or prolonged LOC Nausea/vomiting  Meningeal bleedings - summary Site Source Example: Possible presentation of named example Extra-dural Arterial Trauma - middle meningeal Blow to temple, loss of artery (ant. branch) at pterion consciousness, followed by lucid internal, then deterioration Sub-dural Venous Cerebral atrophy with Elderly patient with stumble/fall, but stretched cerebral veins – no direct blow. Gradual increase in minimal trauma needed to confusion over 2 – 3 days. shear or tear these Sub-arachnoid Arterial Ruptured berry aneurysm on Sudden, severe headache (? during Circle of Willis episode of raised blood pressure) – like a blow to the back of the head  Herniation Can occur in bleeding, tumours, or other space-occupying lesions Compression of Cerebral cortex → Confusion Herniation (coning) of structures → Compression at various levels UNCUS What you must NOT do if intracranial pressure is raised: LUMBAR PUNCTURE CEREBELLAR TONSIL !!!!!! https://www.wikiwand.com/en/Brain_herniation  Uncus Herniation Uncus of the temporal lobe can be pushed through the tentorial notch. This presses on III, particularly the efferent parasympathetic fibres, causing a sluggish light reflex. UNCUS CEREBELLAR TONSIL https://www.wikiwand.com/en/Brain_herniation  Cerebellar tonsil herniation Cerebellar tonsil can be pushed into the foramen magnum, pressing on the medulla and abnormal function of the cardiorespiratory centre causes: BP to rise pulse rate to fall cycles of apnoea and tachypnea/hyperventilation UNCUS → Cheyne-Stokes respiration CEREBELLAR TONSIL https://www.wikiwand.com/en/Brain_herniation  PRACTICE REFERENCES QUESTIONS