Anatomy- Skull Features

anatomy of the skull
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  Anatomy of the base of the skull, the pituitary fossa and the cavernous sinus  Divisions of the fossae    Anterior vs middle o   Anterior border is the brim of the frontal bone o   posterior border of the anterior cranial fossa: lesser wing sphenoid o   Anterior clinoid processes lie “above” the optic canals   o   Lesser wing sphenoid “sits” in the lateral sulcus of the cortex      Middle vs posterior o   anterior: dorsum sellae (median rectangular plate) and the posterior clinoid processes (foot of the bed) o   lateral: superior ridge of the petrous temporal bone Contents of the fossae      Anterior cranial fossa o   Crista galli    Expansion of the ethmoid bone    Attaches the anterior aspect of the falx cerebri (dura) o   Cribiform plate    Penetrations of the olfactory nerves o   Ethmoidal foraminae    Anterior and posterior ethmoidal nerves    Seen from orbit o   Orbital plate of the frontal bone forms most of the floor    Middle cranial fossa (median) o   4 clinoid processes  –  wings of sphenoid, dorsum sellae o   Optical canal and associated groove o   The sella turcica (hypophyseal fossa)  –   the “turkish saddle”       Body of the sphenoid bone    Pituitary gland sits here, covered by dura sella o   Foramen lacerum    Not a true foramen, nothing traverses it entirely (things enter and exit via canals in the the walls of the foramen)    Apertures for the    Carotid canal (ICA)    Pterygoid canal (greater petrosal nerve)    Greater petrosal nerve (of CNVII) passes into foramen lacerum --> pterygoid canal --> pterygopalatine fossa o   Superior orbital fissure    III, IV, V1, VI o   Foramen rotundum    V2 --> pterygopalatine fossa o   Foramen ovale    V3    Lesser petrosal nerve --> infratemporal fossa (parasympathetic to otic ganglion) o   Foramen spinosum    Middle meningeal --> infratemporal fossa o   Cavernous sinus  –  see later    Posterior cranial fossa o   Foramen magnum    Most inferior portion of the PCF o   Hypoglossal canal     Exit of the hypoglossal nerve, within walls of foramen magnum o   Jugular foramen    Exit of vagus, glossopharyngeal, and accessory nerves    Figure 8 shape for the formation site of the IJV (saggital sinus, inferior petrosal sinus) o   Internal auditory meatus    Exit of facial nerve and vestibulocochlear nerves o   Clivus    Basal portion of the occipital bone and the body of the sphenoid o   Internal occipital crest    Attaches the posterior portion of the falx cerebri Pituitary gland  (middle cranial fossa)    2 embryological srcins o   Oral cavity (pharyngeal tissue) o   Hypothalamus (neural tissue)    Two outgrowths of each tissue develop at ~day 42 o   Rathke’s pouch (oral)   o   Neurohypophyseal bud (neual)    The outgrowth from the oral cavity grows towards the neurohypophyeal bud and by ~day60, loses its connection to the oral cavity o   Piece of tissue that was part of the GIT is loosely attached to the outbud of the developing hypothalamus    Therefore the pituitary has the following strucures o   Anterior lobe  –  associated with CNS via vascular connections o   Posterior lobe  –  associated with CNS via neural connections    Bone forms around the bud at ~3 months Cavernous sinus  (middle cranial fossa)    Lies between 2 layers of dura    Joined in the midline, allowing passage of venous blood across the midline o   Anterior intercavernouse sinus o   Posterior intercavernous sinus     BETWEEN the layers o   III, VI, V1, VI (sometimes some V2)    Note the abducent CNVI lies close to the ICA o   Internal carotid artery    Heads anteriorly within the cavernous sinus, doubles back on itself to pierce the dura and branches to supply intracranial branches o   Sympathetic plexii (for structures of the head)    OUTSIDE the layers (between bone and bony dural surface) o   Middle meningeal artery o   Petrosal nerves (parasympathetics)    INSIDE both layers (brain side) o   Optic chiasm, optic nerve o   Pituitary gland (intradural structure) o   Temporal lobe of cortex    Important: pituitary has close association with the ICA, abducent, and venous drainage of the eye. Things that happen to the pituitary have the potential to affect structures of the cavernous sinus.    Image: o   * sphenoidal sinus (air) o   A = pituitary, arrow = infundibulum o   C = optic chiasm o   I = ICA both in the cavernous sinus and intracranial portion More anterior view (towards anterior clinoid process)
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