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  1. 1. SKULL BASE
  2. 2. • The skull base forms the floor of the cranial cavity that separates brain from facial structures and suprahyoid neck. • The skull base is composed of five bones: (1) ethmoid, (2) sphenoid, (3) occipital, (4) paired temporal, and (5) paired frontal bones.
  3. 3. Anterior skull base • It is formed by: • The orbital plates of the frontal bone laterally • The cribriform plate of the ethmoid bone and the crista galli in midline • Posteriorly by the lesser sphenoid wing and the anterior part of the greater wing of sphenoid
  4. 4. • The frontal and ethmoid sinuses , nasal cavity and the orbits are just inferior to the ACF. • The frontal lobes and meninges are just superior to the ACF.
  5. 5. Cribriform plate • It forms the roof of the nasal cavity and contains numerous small foramina that transmits the olfactory folia from the nasal mucosa of the olfactory bulb
  6. 6. Lateral lamella • It connects the CP with the fovea ethmoidalis. • Height difference between the CP and FE was classified by KEROS classification. • The site where the anterior ethmoid artery enters the anterior cranial fossa (lateral lamella of the cribriform plate) is the site of common bony injuries and cerebrospinal fluid(CSF) leaks.
  7. 7. Middle skull base • Formed mainly by: • 1)The sphenoid bone • 2)The temporal bone anterior to the petrous ridge.
  8. 8. Sphenoid bone • 3 compartments: – Basisphenoid: • Dorsum sella, posterior clinoids, sella turcica, tuberculum sella, sphenoid sinus • Fused to clivus in adult – Greater wing of sphenoid • Medial two-thirds and anterior wall of the middle cranial fossa floor – Lesser wing of sphenoid • Medial and superior aspects of the anterior wall of the middle cranial fossa and the anterior clinoids • Superior and medial edges of the superior orbital fissure
  9. 9. • The sphenoid bone articulates with cribriform plate throug the planum sphenoidale. • Posterior to planum sphenoidale is the sella tursica. • Anterior clinoid process is an anatomical land mark that separates the SOF from the optic canal. • (image of bos in nxt slide)
  10. 10. Superior orbital fissure Boundaries: Medial : body of sphenoid Superior: lesser wing of sphenoid Inferior: greater wing of sphenoid
  11. 11. Structures passing • Lacrimal nerve • Frontal nerve • Trochlear nerve • Superior and inferior division of Occulomotor nerve • Nasociliary nerve • Abducens nerve • Superiotr and inferior ophthalmic vein
  12. 12. Pterygopalatine fossa • Small pyramidal space situated deeply below the thwe apex of the orbit. • (image)
  13. 13. Boundaries • Anteriorly: Superomedial part of posterior surface of maxilla • (image)
  14. 14. • Posteriorly: Root of pterygoid process, adjoining part of anterior surface of greater wing of sphenoid • (imagee)
  15. 15. • Medially: Upper part of perpendicular plate of palatine bone • (image)
  16. 16. • Laterally: fossa opens into the infratemporal fossa through the pterygomaxillary fissure. • (image)
  17. 17. Communications • Anteriorly: With tje orbit, via the medial end of inferior orbital fissure • (image)
  18. 18. • Posteriorly: To the middle cranial fossa through the F. Rotundum, F. Lacerum • (image)
  19. 19. • Medialy: with the nose through the sphenopalatine foramen • Lateraly: with the infratemporal fossa through the pterygomaxillary fissure
  20. 20. • Inferiorly with the oral cavity through palatine canal
  21. 21. Pterygoid canal • Runs through the base of the pterygoid process to the back wall of pterygopalatine fossa. • Contain: Nerve, Artery, Vein of the pterygoid canal. • Nerve= Vidian Nerve(Greater P N+ Deep P N) • Many images
  22. 22. Foramen Lacerum • A triangular opening located in the middle cranial fossa anterior to the petrous apex. • It measures about 9mm in length & 7mm in breadth
  23. 23. • F lacerum is filled with connective tissue and transmits the small meningeal branches of ascending pharyngeal artery and the emissary vein from the cavernous sinus. • The internal carotid artery passes along its superior surface but doesn't traverse it.
  24. 24. Foramen ovale • Oval shaped opening in the middle cranial fossa located at hte posterior base of the greater wing of the sphenoid bone. • (image)
  25. 25. Contents • Mandibular div of trigeminal nerve • Accessory meningeal artery • Lesser petrosal nerve • Emissery veins
  26. 26. Foramen rotundum • Located in the middle cranial fossa inferomedial to the superior orbital fissure at the base of greater wing of sphenoid • It transmits maxillary maxillary nerve branch V2 of trigeminal nerve.
  27. 27. Foramen spinosum • Located in the posteromedial part of the greater wing of sphenoid bone posterolateral to the foramen ovale.
  28. 28. • Connects middle cranial fossa with the infratemporal fossa. • Transmits : 1) Middle meningeal artery • 2)Middle meningeal vein • 3)Nervous spinosus
  29. 29. Sella tursica • . The sella turcica is a depression in the superior surface of the body of sphenoid bone for pituitary gland. It is bordered anteriorly by tuberculum sellae and posteriorly by dorsum sellae. Floor of the sella is formed by the sphenoid sinus. The roof of the sella turcica is formed by a fold of dura called diaphragma sellae, which is pierced by the pituitary stalk.
  30. 30. Cavernous sinus (CS) • The CS extends from the orbital apex and superior orbital fissure anteriorly to the Meckel’s cave. • The CS connects the superior and inferior ophthalmic veins, pterygoid plexus, and Sylvian vein to superior and inferior petrosal sinuses.
  31. 31. • The internal carotid artery (ICA) is the medial most structure inside the CS. • Cranial nerves III and IV and the first and second divisions of the cranial nerve V (from superior to inferior) are located in the lateral dural wall of the CS. • Cranial nerve VI courses in the central part of the CS inferolateral to the ICA.
  32. 32. Posterior skull base • Formed mainly by: • 1)The occipital bone • 2)Parts of the temporal and sphenoid bone
  33. 33. Carotid canal • Passage in the petrous temporal bone and transmits Internal carotid artery and the sympathetic plexus. • Its inferior opening is called carotid foramen and its situated anterior to the jugular fossa and medial to the tympanic plate. • Canal is initially directed superiorly ,then turns anteromedially to reach upto petrous apex.
  34. 34. Jugular formen • The jugular foramen is seen at the posterior end of petro-occipital suture. Anteriorly the caroticojugular spine separates the jugular foramen from the inferior carotid opening..
  35. 35. • Fibrous or bony septum divides jugular foramen into anteromedial pars nervosa and posterolateral pars vascularis. • Pars nervosa is smaller and more consistent in size, and transmits cranial nerve IX (glossopharyngeal nerve) with its tympanic branch (Jacobson nerve) and the inferior petrosal sinus. • The pars vascularis is larger and more variable in size, transmitting the internal jugular vein, cranial nerve X (vagus nerve) with its auricular branch (Arnold nerve), cranial nerve XI (accessory nerve), and the posterior meningeal artery.
  36. 36. • The right jugular foramen is larger than the left in 75% of the population. • When the roof of the jugular bulb is seen above the level of floor of internal auditory canal, it is called a high-riding jugular bulb, which is more common on the right side. • This is a dangerous variant and compromises the exposure during translabyrinthine surgery
  37. 37. Hypoglossal canal • Located anteromedial to the jugular foramen • Content; Hypoglossal nerve • Hypoglossal canal lies in close proximity to the jugular foramen • Along the medial aspect, an osseous bony bar called the jugular tubercle separates the jugular foramen from the hypoglossal canal.
  38. 38. Communication pathways
  39. 39. Relation of skull base to the deep facial spaces • The deep facial spaces are in close contact with the base skull. • Infections and tumours of these spaces often extend up to the skull base. • Para pharyngeal, masticator, carotid, and retropharyngeal spaces are seen in close contact with the skull base along their cephalad aspect.
  40. 40. Parapharyngeal space • Parapharyngeal space extends caudally to the submandibular space and cranially abuts the base skull. It contains fat within, which acts as a medium for infection. Tumors can easily traverse across the fat within the parapharyngeal space.
  41. 41. Masticator space • Masticator space connects the mandible to the skull base. Odontogenic infections and oropharyngeal squamous cell carcinoma can tract along masticator space to the base skull. Intracranial extension of the tumor can occur via third division of trigeminal nerve, mandibular nerve (perineural spread) through the foramen ovale.
  42. 42. Carotid space • Vascular lesions such as jugular vein thrombosis and neural tumors such as schwanoma, neurofibroma, and paraganglioma are seen in the carotid space. These lesions usually spread longitudinally along the length of the neck with subsequent extension into the jugular foramina in the skull base.