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Skull Base Foramina

Created: 10/9/2010
Updated: 10/9/2010

• Extend across the brains and spinal cord
• Dura, Arachnoid and Pia Mata (applied to each other)

o Dura

 Dura parts in endocranium makes a cleft with double folds/ reduplication to form the
 Dural Venous Sinuses that lead to the jugular bulb and jugular veins
 Falx = Longest dural fold and hemisects the brain
 Tenetorium = Largest and separates the cerebellum from the cerebrum
 Dural sac
• S2 in adults
• S4 in child until 2 years old

o Arachnoid mata with Pia Mata
 Subarachnoid space; encloses the Circles of Willis therefore SA haemorrhage
• Huge in the posterior fossa aka “Basal Cisterns”

☼ Blood supply to the Brain
• Internal carotid and External carotid circulations anastamose on the scalp – hence huge potential for blood loss in scalp injuires!
• Cerebral circulation – Circle of Willis

• Internal carotid artery
o Enters the skill via the Carotid Canal
o Anterior Circulation and Middle cerebral Artery

• Middle Meningeal artery
o Branch of Maxillary branch of External Carotid
o Enter skull via tiny foramen spinosum
o Runs along inner aspect of the pterion (weak point of skull above the ear)
o Talk and die Extradurals

• Vertebral arteries
o Branch of Subclavian
o Enters via foramen magnum
o Posterior circulation of Circle of Willis as form the basilar artery

Venous Drainage of the Brain
• Dural venous sinuses drain into the big posterior S shaped sigmoid sinuses that empty into the internal jugular veins bilaterally

☼ Cavernous Sinus (MCQ)
o Large Dural Venous Sinus, roughly behind the eye
o Applied to the body of the sphenoid bone


o Pituitary gland sits medial to it
o In it runs
 Internal carotid artery with SNS fibres hitchhiking to form the ophthalamic artery in SA space
 Abducens IV nerve
 Lateral walls of the sinus run cranial nerves III, IV, Va and Vb

o Important clinically in facial infections/ orbital cellulitis leading to cavernous sinus thrombosis
 Horner’s syndrome, diplopia on lateral gaze and probable meningitis

☼ CSF Flow (MCQ/ Viva)
• 150 – 200 ml/ day
• 25ml in spine
• Produced by choroid plexus of the ventricles
• Absorbed by arachnoid granulations, little venous out pouches of the dural venous sinuses

• Lateral Ventricles  Foramen of Monroe III ventricle - Sylvian aqueduct IV ventricle  Lateral Foramina of Lushka x2  Midline foramen of Magendie  spinal cord

☼ Trigeminal Nerve (My viva, December 2008!, SAQs 2010)
• Fifth Cranial nerve in 3 divisions
o Va Ophthalmic
o Vb Maxillary
o Vc Mandibular
• Sensory to face, nose and scalp with 3 x large sensory nuclei
• Motor
o Muscles of mastication only  1 x small motor nucleus
o Secretory visceral motor to parotid and salivary glands

• Trigeminal Nuclei
o Motor in the Pons
o Sensory
 Sensation = Sensory 1  Lateral to motor nucleus in pons
 Proprioception = Sensory II  Midbrain above the pons
 Pain and Temperature Sensory III  Longest and in spinal tract below the pons

• Emergences from the skull
o V1  Superior orbital Fissure
 Branches: Lacrimal and Frontal nerves
o V2  Foramen Rotundum and then Infraorbital fissure to form Zygomatic nerve and Infraorbital nerve

• V3 Foramen ovale
 Mental foramen  Mental nerve chin skin

• Ganglion (Chronic Pain Trigeminal Neuralgia)
o Gasserian Ganglion
 Found in the apex of the petrous temporal bone ~ behind the zygoma
 Covered with an invagination of dura aka Meckle's cave (of Meckle's diverticulum fame, a busy man)
 Sensory nerves pass through the ganglion
 Motor nerves of Vc pass UNDER the ganglion and synapse in other ganglia in the face

• Motor to masticators
• PNS hitchhiking to the Otic ganglion to supply the parotid gland secretions
• Sensory branch to lingular nerve to tongue on the Chorda Tympani
o NB Taste to tongue is provided by anterior 2/3 Facial Nerve on the Chorda Tympani, posterior 1/3 taste by Glossopharyngeal

• Bony orbit
o Pyramidal shaped
 Apex Optic foramen
 Floor Maxillary antrum with
 Roof Frontal and sphenoid sinuses
 Medial Ethmoid sinus
 Lateral  Zygoma

☼ Superior Orbital Fissure (MCQ/Viva)

o Luscious French Tarts Sit Naked In Anticipation
 Lacrimal nerve V1
 Frontal nerve V1
 Trochlear nerve IV
 Superior ophthalmic nerve III

 Nasocilary nerve V1
 Inferior ophthalmic nerve III
 Abducens VI

• Inferior orbital fissure
o Continuous with Superior Orbital Fissure
o Vb branches and Infraorbital artery emerge from it

• Nerve Supply to the Eye
 Long and short cilary nerves hitch hike on the Internal Carotid artery from superior cervical ganglion Dilate the pupil
 Via oculomotor nerve III and are preganglionic  cilary ganglion (posterior part of orbit) to the postganglionic cilary nerve  constrict pupil
 Cilary Ganglion
 Not the same as the cilary body which is circumfrential in the eye and contain the cilary muscles which
o Trigeminal nerve V1
 Supplies corneal and conjunctiva sensation

• Anatomy of Coning and the Blown Pupil
o III nerve runs along the edge of the Tentorium, which forms a fibrous floor to the skull base under the cerebrum
o As the cerebrum herniates down the nerve gets compressed
o PNS fibres travel with the III nerve (craniosacral outflow) Pupil dilates
o III nerve palsy (LR6SO4O3)  Eye down and out

o Uncal herniation (medial part of temporal lobe)
 ipsilateral blown pupil
 contralateral hemiplegia  corticospinal tracts cross at the foramen magnum

Layers continuous with the muscle layers of the Thorax
• Skin
• Fat
• External oblique muscle
o Extends from 5th to 12th Ribs to the anterior half of iliac crest
o Becomes aponeurosis towards midline
o Lower border rolls under and forms the Inguinal Ligament
o Hole in the lower border above the pubic crest is the superficial inguinal ring and the exit of the inguinal canal
• Internal oblique muscle and aponeurosis
• Neurovascular layer  T.A.Plane Blocks
• Transversus Abdominus (T.A) muscle
• Transversalis fascia
• Extraperitoneal fat
• Peritoneum

• Nerve Supply
o Thoracoabdominal nerves
 Anterior primary rami of T7 – T11
o Lateral cutaneous branches of T7 – T10
o Subcostal nerve
 Large anterior primary ramus of T12 spinal nerve
o Iliohypogastric and Ilioinguinal nerves
 L1/2 from Lumbar Plexus

o Dermatomes
 T7 – T9 above umbilicus
 T10 peri umbilicus
 T11 – L1/2 inferior to umbilicus

☼ TAP blocks: Lumbar Triangle of Petit
Muscular interspace boundaries by
• Latissimus Dorsi
• External Oblique
• Iliac crest
• Pass needle through triangle to pop through the Internal Oblique into the Neurovascular plane
• Lumbar triangle of Petit is the site of lumbar hernias…


C2 1 finger breadth below mastoid process
Cervical block
C3 Hyoid

C4 Upper border thyroid
Bifurcation of carotid

C6 Cricoid cartilage
Trachea commences Chaissaignac Tubercle
vertebral artery enters transverse foramen
Stellate ganglion blocks
Brachial plexus block

C7 Stellate ganglion
Vertebrae prominens

T2 Suprasternal notch

T4/5 Manubriosternal Angle of Louis
Bifurcation of trachea
Arch of the aorta

T7 Angle of scapula
Thoracic epidural;
T8 IVC through diaphragm
Vein goes through tendinous part so not compressed)
T10 Oesophagus and Vagi on it pass through diaphragm
T12 Aorta through diaphragm (artery through muscular part as non compressible)
L1 Coeliac plexus
Renal arteries come off aorta
Coeliac plexus blocks
L1/2 End of adult spinal cord

L4 Tuffiers’ line (iliac crests)
Lumbar epidurals
S2 Dura ends in adult

S4 Dura end in child
S5 Sacral hiatus Caudal



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