The Cranium, Meninges & Venous Sinuses Flashcards
Bones of the skull vault
Unpaired:
- Frontal
- Ethmoid
- Sphenoid
- Occipital
Paired:
- Temporal
- Parietal
Features of the Frontal Bone
- Supra-orbital notches
- Superior cilliary ridges
- Air sinuses (initially 2 parts, fuse in early life)
Parts of the Sphenoid Bone
- Greater & lesser wings
- Medial & lateral pterygoid plates
Features of the sphenoid bone
- Sella turcica (contains pituitary)
- Foramina:
- Optical canals
- Superior orbital fissures
- Rotundum
- Ovale
- Spinosum
Parts of the Temporal Bone
- Squamous
- Petromastoid
- Tympanic
- Styloid process
Features of the petromastoid part of the temporal bone
- Middle & inner ear
- Internal auditory meatus
- Facial canal
- Air cells (in mastoid process)
Features of squamous part of the temporal bone
- Zygomatic process
- Mandibular fossa
Features of tympanic part of the temporal bone
- External auditory meatus
- Acts as attachment for tympanic membrane
Features of the styloid process
- Attachment for ligaments and muscles
NB: CN VII emerges from the adjacent stylomastoid foramen
Features of the parietal bone
- Foramina for emissary veins
- Connect scalp veins → dural sinuses
Parts of the occipital bone
- Squamous
- Basal
Features of the occipital bone
- Superior nuchal line
- Occipital protuberance
- Occipital condyles
- Foramen magnum
- Hypoglossal canals
Discuss fractures of the skull vault
Fractures heal with fibrous tissue which may not ossify, leaving fracture lines visible on x-ray
Discuss cranial suture size and the clincal relevance
Growth of cranial suture is the result of intracranial pressure i.e. NOT genetically controlled
Clinical relevance:
- Low IC pressure = microencephaly
- High IC pressure = hydrocephaly
NB: pterion = meeting of sutures of sphenoid (greater wing), temporal, parietal & frontal bones
- A: Crista Galli
- B: Hypoglossal Canal (CN XII)
- C: Foramen Ovale (CN Vc)
- D: Foramina for Olfactory Nerves (CN I)
- E: Internal Auditory Meatus (CN VII & VIII)
- F: Optic Canal (CN II)
- G: Foramen Rotundum (Vb)
- H: Jugular Foramen (CN IX, X, XI)
- I: Superior Orbital Fissure (CN III, IV, Va & VI)
- J: Foramen Lacerum
- K: Foramen Spinosum:
Features of the anterior cranial fossa
- Foramina for olfactory filaments (cribriform plate)
- Crista galli (attachment for falx cerebri)
NB: houses frontal lobes
Features of the middle cranial fossa
- Pituitary fossa
- Clinoid processes (form sella turcica w/ fossa)
- Superior orbital fossa
- Foramen ovale
- Foramen rotundum
- Foramen spinosum
NB: houses temporal lobes laterally
Features of the posterior cranial fossa
- Internal acoustic meatus
- Jugular foramen
- Hypoglossal canal
- Foramen magnum
NB: houses occipital lobes
Define the meninges
A tri-layered connective tissue membrane structure investing the brain and spinal cord:
- Dura mater (two layers)
- Arachnoid mater
- Pia mater
Discuss the dura mater
- Dense connective tissue layer
- Two layers (single around spinal cord)
- Endosteal layer - cont. with pericranium
- Meningeal layer
- United, separated to form the dural sinuses
- Reflected to form folds
- Falx cerebri - sep. cerebral hemispheres
- Tentorium cerebelli - sep. cerebrum from cerebellum
- Falx cerebelli - sep. cerebellar hemispheres
- Diaphragma sellae covering pituitary fossa
Discuss the arachnoid mater
- Thin & non-vascular
- In cranium, it is thicker, with strands connecting it to the pia
- Subarachnoid space filled with CSF
- Cisterns form where the arachnoid bridges across larger grooves
Discuss the pia mater
- Delicate, highly vascular layer
- Invests grooves, sulci (brain) & ventral median fissure (cord)
Discuss the meningeal spaces
Spinal:
- Spinal epidural: between dura & periosteum
- Loose connective tissue, venous plexuses and lymphatics
Cranial:
- Extradural: between endosteal layer & skull
- Potential space
- Subdural: between dura & arachnoid
- Potential space
- Subarachnoid: between arachnoid & pia
- Extends to lumbar cistern (S2) in adults
Drainage of dural venous sinuses - Diagram
Define the dural venous sinuses
Complex network of venous channels draining blood from the brain and cranium
NB: Lined with vascular endothelium but lack valves/musculature
Path of the superior sagittal sinus
- Begins at the crista galli, runs in the superior margin of falx cerebri
- Forms median groove in cranial vault
- Drains to right transverse sinus
Path of the inferior sagi ttal sinus
- Runs in posteroinferior border of falx cerebri
- Joins great cerebral vein & basal vein to form straight sinus
- Straight sinus runs in falx cerebri tentorium cerebelli junction
- Continues as the left transverse sinus
Path of the transverse sinus
- Run in lateral margins of tentorium cerebelli
- Receives superior petrosal → sigmoid sinus
Path of the greater petrosal sinus
- Runs in edge of tentorium cerebelli (where TC attaches to petrous bone)
- Joins with cavernous sinus with transverse sinus
- GPS + TS form sigmoid sinus
Path of the sigmoid sinus
- Deeply grooves petrous temporal bone
- Curves forward onto occipital bone → jugular foramen
- Lies medial to mastoid air cells
- Consequences for mastoiditis
- Joins with lesser petrosal sinus to form internal jugular vein
Path of the inferior petrosal sinus
- Lies in groove between occipital and petrous temporal bones
- Joins with the sigmoid sinus
Describe the cavernous sinus
- Contains interlacing strands of connective tissue forming a cavern-like meshwork
- Lies either side of body of sphenoid
- Infections of face can spread to sinus
- Facial → superior ophthalmic → sinus
- Causes cavernous sinus thrombosis
Limits of the spinal cord
- Foramen magnum → Lower board of L1
- Tapers at end as conus medullaris
-
Filum terminale attaches conus to dural sac (S2)
- Stalk of pia
- Cauda equina = roots of spinal nerves S2-Co
- Pass caudal from conus
Discuss lumbar punctures
- Performed in L3/4 intervertebral space to collect CSF for:
- Diagnosis
- Therapeutics (spinal analgesia, chemo)
Discuss the spinal nerve roots
- Ventral aspect gives rise to motor fibres, dorsal aspect = sensory
- Join, form mixed spinal nerves of intervertebral foramina
- Covered by the meninges which fuse with epineurium as emerge from IV foramen
