Cavernous Sinus

ANATOMY:
  • There are 2 Cavernous Sinuses on either side of Sella tursica irregular form larger behind than front.
  • Extends from sphenoid fissure to petrous apex.
  • It is a true dural venous sinus creating a cavity bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica.
OSSEOUS RELATIONSHIP:
  • Related to sphenoid bone and sella tursica.
  • On each side of fossa is S shaped groove lodges Internal carotid artery
  • Fibrous or osseous bridge exist between Anterior, Middle or Posterior Compartment
  • Connection between AC and MC makes distal end of carotid sulcus to carotico-clinoid foramen
CAROTID CANAL:
  • Located at anterolateral aspect of petrous bone.
  • Part of the canal wall is formed by the posterior part of greater wing of sphenoid
  • Canal contains horizontal segment of Internal Carotid Artery(ICA) and sympathetic fibres.
  • At posterior and medial wall canal is separated from cochlea by a thin plate of bone.
  • Internal Carotid Artery courses anteriorly and medially within petrous bone to emerge near petrous apex.
  • At the most distal end under V3 ICA is covered only by dura or thin layer of cartilage.
  • Foramen rotundum situated most anterior and internal part of greater wing of sphenoid bone.
  • Foramen ovale and Foramen Spinosum is situated posteriolateral to this.
  • Eustachian tube and Tensor tympani are located anterior and parallel to horizontal segment of ICA below floor of Middle cranial fossa(MCF).
  • Geniculate ganglion of 7th nerve located in the floor of MCF is usually covered by a layer of bone
ARTERIAL COMPARTMENT:
  • ICA enters the skull through carotid canal located medial to styloid anteromedial to jugular foramen.
  • Vertical segment of ICA 
  1. Jugular fossa posteriorly 
  2. Eustachian tube anteriorly 
  3. Tympanic bone anterolaterally 
  • Horizontal segment of ICA is related to otic apparatus and 7th N.
  • Branches are
  1. Caroticotympanic artery
  2. Vidian or Pterygoid artery( usually from Int: Maxillary Artery)
  • ICA enters intracranial cavity passing between lingula of sphenoid and petrous apex where it is surrounded by venous plexus and symp fibres.
  • INTRACAVERNOUS ICA(5 Parts)
  1. Posterior Vertical Segment
  2.  MENINGO HYPOPHYSEAL TRUNK
  3. branches. 
  • Tentorial Artery
  • Inferior Hypophyseal Artery
  • Dorsal Meningeal Artery
  1. Horizontal Segment
  2. Anterior vertical segment
  3. vertical segment
  • Artery of Inferior CS arises from central third of horizontal segment courses laterally with 6th N
  • Mc Connel`s Capsular Artery -arises from medial aspect of hori seg
  • Courses towards the pituitary gland
  • Ophthalmic Artery arises from CS in 8 % cases
  • Persistent Trigeminal Artery present in 2% cases
VENOUS COMPARTMENT
  • Divided into medial, lateral anteroinferior and posterosuperior compartments.
  • As afferents each CS receives spheno parietal sinus, frontal trunk of middle meningeal, superior & inferior ophthalmic vein, superficial middle cerebral vein, inferior cerebral vein
  • Superior opthalmic vein connects facial vein to cavernous sinus
  • Veins communicating the cavernous sinus to pterygoid plexus pass through fossa of vesalius
  • On efferent side, CS drains into Inferior Petrosal sinus.
NEURAL COMPARTMENT
  • III,IV,V1,V2 lie between 2 dural layers that form lateral wall of CS.
  • Superficial layer of lateral wall is a thick layer formed by the duramater.
  • This layer continues anteriorly over the superior surface of Anterior clinoid process(ACP) enveloping ICA to form distal dural ring.
  • The inner layer has a reticular consistency and incomplete in 40% of cases.
  • Through the inner layer run III,IV and V1.
  • The inner layer extents anteriorly and inferiorly to ACP surrounds anterior loop of ICA and forms the proximl ring and also anterior loop of CS.
  • III N pierces CS in the middle of occulomotor trigone in the upper part of lateral wall of CS.
  • Courses anteriorly and leaves the CS on nhe inferolateral surface of ACP
  • IV th N enters posterolateral to III N courses anterolateroinferior to enter the Superior Orbital Fissure.
  • V1 enters the lower part of lateral wall of CS runs anteriorly and upwards to pass through SOF
  • VI enters CS through Dorello`s canal and courses inside the sinus lateral to ICA.
  • This canal is limited superiorly by petroclinoid ligament also known as Gruber`s ligament
Exam Question
  • Structures passing through cavernous sinus are internal carotid artery & abducent nerve
  • As afferents each CS receives spheno parietal sinus, frontal trunk of middle meningeal, superior & inferior ophthalmic vein, superficial middle cerebral vein, inferior cerebral vein
  • III , IV, V1, V2, VI are the cranial nerves that travels through the cavernous sinus
  • Superior ophthalmic vein directly communicates with cavernous sinus
  • Abducent nerve & internal carotid artery Are the direct content of cavernous sinus
  • Facial vein is connected to cavernous sinus via superior opthalmic vein
  • Veins communicating the cavernous sinus to pterygoid plexus pass through fossa of vesalius

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