anatomy of the Cranial fossae of the skull.pptx

1. Cranial Fossae

The cranial base is divided into three fossae: anterior, middle, and posterior, each accommodating specific brain parts and housing important neurovascular structures.

Anterior Cranial Fossa holds the frontal lobes and is formed mainly by the frontal, ethmoid, and sphenoid bones. Notable features include the crista galli and cribriform plate of the ethmoid, which transmits olfactory nerves. Clinically, this fossa is prone to fractures, possibly causing cerebrospinal fluid (CSF) rhinorrhea, anosmia, or periorbital bruising ("black eye").

Middle Cranial Fossa resembles a butterfly in shape, with a central part housing the pituitary gland (in the sella turcica) and lateral parts accommodating the temporal lobes. It includes foramina for cranial nerves and blood vessels: optic canal (CN II), superior orbital fissure (CN III, IV, V1, VI), foramen rotundum (V2), foramen ovale (V3), foramen spinosum (middle meningeal vessels), and foramen lacerum. Fractures here often lead to CSF leakage from the ear and possible cranial nerve damage, especially VII and VIII.

Posterior Cranial Fossa is the largest and deepest, containing the cerebellum, pons, and medulla. Key features include the foramen magnum, internal acoustic meatus (CN VII, VIII), jugular foramen (CN IX, X, XI), and hypoglossal canal (CN XII). The floor is formed by the occipital and temporal bones. Fractures here may damage the vestibular nerve, causing balance issues, especially in acoustic neuroma cases.

1. Cranial fossae

2. CRANIAL FOSSAE Anterior cranial fossa Middle cranial fossa Posterior cranial fossa The internal surface of the cranial base has three distinct depressions/ fossae that lies at different levels forming the bowl-shaped floor of the cranial cavity that accommodates the brain. The fossae increase in depth from anterior to posterior

3. ANTERIOR CRANIAL FOSSA Anterior cranial fossa accommodates the frontal lobe of the brain Anterior cranial fossa is formed: Boundaries: Anteriorly & laterally: frontal bone Middle: ethmoid bone Posteriorly : body and lesser wing of sphenoid bone Floor: orbital plate of the frontal bone

4. Features seen Frontal crest – a median bony extension of the frontal bone Crista galli – a midline ridge of bone posterior to the foramen ceacum that projects superiorly from the ethmoid On either side of the crista galli is the sievelike cribiform plate of the ethmoid

5. Foramina Two skull foramina located in the anterior fossa : Foramen caecum – Emissary veins Foramen of the  cribriform  plate  - olfactory nerve (CNI ) Anterior & posterior foramina- vessels /nerves

6. Applied anatomy The  cribriform plate  of the ethmoid is the thinnest part of the anterior cranial fossa , and therefore most likely to fracture. Anosmia  – the olfactory nerve fibres run through the cribriform plate, and can be ‘sheared’, resulting in loss of sense of smell. Fracture of the anterior cranial fossa may cause bleeding and discharge of cerebrospinal fluid through the nose. It may also cause a condition called black eye which is produced by seeping of blood into the eyelid

7. MIDDLE CRANIAL FOSSA The middle cranial fossa is butterfly shaped fossa located, centrally in the cranial floor posteroinferior to the anterior fossa with a middle part accommodating the pituitary gland and two lateral parts accommodating the temporal lobes of the brain

8. Middle Cranial Fossa Boundaries Anteriorly Posterior border of the lesser wing of sphenoid bone, anterior clinoid process & anterior margin of the sulcus chiasmaticus Laterally Greater wings of sphenoid bone and squamous part of temporal bone & anteroinferior angle of the parietal bone

9. Middle Cranial Fossa Boundaries Posteriorly : petrous part of temporal bone; dorsum sellae of the sphenoid bone Floor: Body of sphenoid, Greater wing of sphenoid and Squamous and Petrous parts of temporal bone

10. Features seen Sella turcica surrounded by anterior and posterior clinoid processes Sella turcica acts to hold and support the pituitary gland, and consists of three parts: is composed of three part namely Tuberculum sellae Hypophyseal fossa Dorsum sellae

11. The  tuberculum sellae  (horn of the saddle) is a vertical elevation of bone. It forms the anterior wall of the sella turcica , and the posterior aspect of the chiasmatic sulcus (a groove running between the right and left optic canals). The  hypophyseal fossa  or  pituitary fossa  (seat of the saddle) sits in the middle of the sella turcica . It is a depression in the body of the sphenoid, which holds the pituitary gland.

12. The  dorsum sellae  (back of the saddle) forms the posterior wall of the sella turcica . It is a large square of bone, pointing upwards and forwards. It separates the middle cranial fossa from the posterior cranial fossa .

13. The  sella turcica is surrounded by the anterior and posterior  clinoid processes .  The anterior clinoid processes arise from the lesser wings of sphenoid , while the posterior clinoid processes are the superolateral projections of the dorsum sellae . They serve as attachment points for the  tentorium cerebelli , a membranous sheet that divides the brain

14. Foramina  The middle cranial fossa contains 6 foramina namely Optic canal Superior orbital fissure Foramen rotundum Foramen ovale Foramen spinosum   Foramen lacerum

15. Optic canals The  optic canals  are situated anteriorly in the middle cranial fossa . They transmit the optic nerves (CN II) and ophthalmic arteries into the orbital cavities. The optic canals are connected by the  chiasmatic sulcus , a depressed groove running transversely between the two.

16. The  superior orbital fissure The  superior orbital fissure  opens anteriorly into the orbit. It transmits the Oculomotor nerve ( cn iii) Trochlear nerve (CN IV) Opthalmic branch of the trigeminal nerve (CN V1) Abducens nerve (CN VI) Opthalmic veins and sympathetic fibres .

17. The  foramen rotundum lies posterior to superior orbital fossa It  opens into the pterygopalatine fossa   It transmits the maxillary branch of the trigeminal nerve (CN V2).

18. The   foramen ovale   lies posterolateral to foramen rotundum and opens into the infratemporal fossa It transmits the: O – optic ganglion V- CNV3 - mandibular branch of the trigeminal nerve A - accessory meningeal artery. L - lesser petrosal nerve (occasionally) E - Emissary veins

19. The  foramen spinosum  lies posterolateral to foramen ovale and also opens into the infratemporal fossa . It transmits the: Middle meningeal artery Middle meningeal vein Meningeal branch of CN V3.  

20. Applied anatomy The Middle cranial fossa is most commonly fractured. Fracture of the middle cranial fossa produces Bleeding and discharge of CSF through the ear Bleeding through the nose or mouth may occur due to involvement of the sphenoid bone VII & VIII cranial nerves may be damaged if the fracture also passes through the internal acoustic meatus. If semicircular canal is damaged, vertigo may occur

21. Posterior CRANIAL FOSSA The posterior fossa is the most posterior, largest and deepest of the 3 fossae . Lodges the cerebellum, pons and medulla oblongata

22. Posterior Cranial Fossa Posterior cranial fossa Boundaries; Anteromedially : superior border of petrous temporal bone & dorsum sellae Anterolateral : mastiod part of temporal & mastoid angle of the parietal bone

23. Posterior Cranial Fossa Posterior cranial fossa Boundaries ; Posteriorly : squamous part of occipital bone The floor  consists of the mastoid part of the temporal bone and the squamous , condylar and basilar parts of the occipital bone.

24. Posterior Cranial Fossa Posterior cranial fossa Boundaries; Foramen magnum form the central part of the floor . Posterolaterally to the foramen magnum lies the  cerebellar fossae . These are bilateral depressions that house the cerebellum. They are divided medially by a ridge of bone, the  internal occipital crest . Internal occipital crest ends in the Internal occipital protuberance (confluence of sinuses

25. Foramina There are 4 foramina found in the posterior cranial fossa Internal acoustic meatus Jugular foramen  Hypoglossal canal Foramen magnum

26. Internal acoustic meatus The  internal acoustic meatus   is an oval opening in the posterior aspect of the petrous part of the temporal bone . It transmits F acial nerve Vestibulocochlear nerve L abyrinthine vessels

27. Foramen magnum A large opening, the  foramen magnum,  lies centrally in the floor of the posterior cranial fossa . It is the largest foramen in the skull. It transmits the Medulla of the brain Meninges , Vertebral arteries, Spinal root of accessory nerve (ascending) Dural veins Anterior and posterior spinal arteries. Anteriorly an incline, known as the  clivus , connects the foramen magnum with the dorsum sellae .

28. Jugular foramen The  jugular foramina  are situated either side of the foramen magnum. Each transmits the Glossopharyngeal nerve- CN IX Vagus nerve – CN X Spinal accessory nerve –CN XI (descending) Internal jugular vein Inferior petrosal sinus, Sigmoid sinus Meningeal branches of the ascending pharyngeal and occipital arteries.

29. Hypoglossal canal Immediately superior to the anterolateral margin of the foramen magnum is the  hypoglossal canal . It  transmits the hypoglossal nerve through the occipital bone.

30. Applied anatomy Fracture of the posterior cranial fossa causes bruising over the mastoid region extending over the sternocledomastoid muscle . Vestibular nerves are most likely to be damaged (compressed), resulting in problems with balance in a common type of brain tumour , an acoustic neuroma , which often arises in the posterior aspect of the internal acoustic meatus . If undetected an acoustic neuroma will continue to grow and will eventually cause damage to the facial and cochlear nerves.