Head – Ventricular System

Ventricular System

Discuss the anatomy of the cavernous sinus (8 marks).

DESCRIPTION

• Parasagittal space beside sphenoid body in middle cranial fossa containing cranial nerves 3-6; extradural portion of internal carotid artery and an interconnected plexus of venous sinuses.

SHAPE

• From apex of orbit to apex of petrous temporal bone
• Spindle-shaped on lateral view
• Each end pointed
• 5mL capacity on each side; approx 2cm long; 1cm wide
• Numerous fibrous septa – blood spaces divided into numerous cave
• 3x major venous spaces described: Postero-superior, Anteroinferior, Medial (all in relation to cavernous ICA)

BOUNDARIES

Roof – dura lateral to the adjoining diaphragma sellae (medially); tentorium cerebelli attached to anterior clinoid process (lateral).

• Attached to: anterior, middle and posterior clinoid processes
• Pierced by ICA anteriorly
• Pierced by CN3 and 4 (close to tentorial edge)

Anterior –

• Greater wing of sphenoid
• Superior orbital fissure
• Narrow strip

Lateral – layer of dura extending from roof down to floor of middle cranial fossa

• CN 3, 4, V1 and V2 run forward

Floor – narrow strip of endosteum along base of greater wing of sphenoid

• Orifices: f. Rotundum; carotid canal (from f.lacerum)

Medial wall- endosteum of sphenoid body;

• inner layer of dura mater covering lateral pituitary fossa

Posterior – inner layer of dura extending up from posterior cranial fossa; joins with roof

• Narrow strip
• Raised portions; separated from periosteum extend posteriorly as superior and inferior petrosal sinuses 

RELATIONS

• Superior: intradural internal carotid artery; uncus of temporal lobe; MCA; optic chiasm
• Anterior: apex of orbit
• Lateral: medial surface of temporal lobe; middle cranial fossa;
• Floor: trigeminal cave and ganglion
• Medial: sphenoid body; pituitary fossa; pituitary gland and stalk; sphenoid air cells
• Posterior:  cerebral peduncle and upper pons

CONTENTS

Nerves

• CN3 – Oculomotor
  • Pierces roof dura – medial to raised edge from free margin of tentorium
  • Passes along lateral wall in an inferomedial direction
  • Lies medial to other nerves
  • Splits into superior and inferior divisions
    • Superior joined by SNS branch to Levator Palpebrae Superioris
  • Exits via SOF (intratendinous)
• CN4 – Trochlear
  • Pierces roof – posterior to CN3 (and inferior)
  • Courses anteriorly; crossing to become superior and lateral to CN3
  • Exits via SOF (extratendinous) to supply superior oblique muscle
• CN6 – Abducens (most medial)
  • Enters posterior cavernous sinus [Dorello’s canal – below petrosphenoidal ligament within dural tunnel]
  • Inferior to proximal cavernous ICA
  • Forward on lateral aspect of ICA; medial to CNV1 and V2
  • Exits via SOF (intratendinous)
• CN5 – Trigeminal (Most lateral)
  • V1 division – Ophthalmic
    • Courses anteriorly towards SOF
    • Divides into 3 branches at anterior cavernous sinus
    • Exits SOF (intratendinous – nasociliary; extratendinous – lacrimal, frontal nn.)
  • V2 division – Maxillary
    • Runs horizontally forwards on lower lateral wall
    • Exits via foramen rotundum
  • V3 division – Mandibular
    • NOT a content of cavernous sinus
    • Through foramen ovale inferiorly into infratemporal fossa 

Arteries

• ICA – foramen lacerum; through carotid canal
  • Enters posterior part of sinus
  • Arches upwards and forwards; grooving medial wall
  • Curved superiorly to pierce roof medial to anterior clinoid process
• Accompanied by sympathetic plexus (internal carotid nerve)
  • From superior cervical ganglion
    • Gives off long ciliary nerves –> dilator pupillae;
    • SNS to ciliary ganglion; branch to Levator palpebrae superioris

Veins

• Two cavernous sinuses communicate via inter-cavernous sinus
  • Small plexus; between dural layers; connects to diaphragma sellae veins
• Venous Connections to brain, meninges, orbit, superior and inferior petrosal sinus, pterygoid venous channels (listed below)

VENOUS CONNECTIONS

• From brain:

• • Superficial middle cerebral vein – pierces roof near carotid artery
  • Inferior cerebral veins

• From meninges

• • Sphenoparietal sinus – venous blood from temporal bones (middle meningeal artery territory); under lesser wing of sphenoid – enters roof
  • Middle meningeal veins

• Orbit:

• • Superior ophthalmic vein – from SOF; connects to facial vein
  • Inferior ophthalmic vein – from IOF – connected to pterygoid plexus
  • Central vein of retina

• Communications

• • Pterygoid venous plexus – emissary vein through f. Ovale or venous foramen (of Versalius) or via f.lacerum
  • Internal vertebral venous plexus – via basilar plexus of veins

• Draining channels

• • Superior petrosal sinus – top of posterior wall – courses posteriorly along upper border of petrous bone to transverse sinus
  • Inferior petrosal sinus – larger; primary venous drainage from cavernous sinus. From posterior wall beneath petroclinoid ligament.
    • Courses down along suture (between apex of petrous bone and side of clivus) towards jugular foramen
    • Drains into internal jugular vein
• NOTE: blood can flow in either direction based on local venous pressures
  • Modified by pulsation of cavernous ICA
  • Gravity + head position

VARIANTS

• Foramen of Versalius – present in 20% – transmits emissary vein to pterygoid plexus
• Cavernous ICA branches (Tran-dinh 1987; Krisht 1994)
  • Ophthalmic artery with cavernous origin (7-15.6%)
  • Posterior trunk or Meningohypophyseal trunk (100%)
    • Gives inf hypophyseal, clival, marginal tentorial, basal tentorial aa.
    • Supplies proximal CN6
  • Lateral trunk or Inferolateral Trunk(65-84%) – Supplies all intracavernous cranial nerves (except proximal CN6)
    • Ant br: anterior lateral wall of cavernous sinus.
    • Post br: supplies posterior lateral wall of cavernous sinus. & anastomosis with middle meningeal artery
  • Medial group (28-50%)
    • Capsular arteries; osseous branches

Extra information: Summary of nerve relations in cavernous sinus

• No nerve lies lateral to 5th and its branches
• No nerve lies medial to 6th
• The 4th runs parallel with 5th at a higher level
• The 3rd slopes downwards crossing medial to both