SS Flashcards
List the bones that make up the skull
Temporal, Frontal, Occipital, Parietal, Maxillary, Zygomatic, Nasal, Lacrimal, Ethmoid, Sphenoid, Mandible
Describe sutures and the main ones found on the skulls
What are fontanelles?
Sutures are immobile fibrous joints found only in the skull. In adults the sagittal suture is found between the 2 parietal bones superiorly and it meets with the coronal suture anteriorly and the lambdoid suture posteriorly. The coronal suture travels across the skull in the coronal plane separating the frontal bone from the parietal bones and the lamdoid suture runs across posteriorly separating the pariteal bones from the occipital bone.
The meeting point of the lambdoid sutures and sagittal suture is the lambda, and the meeting point of the coronal suture and sagittal suture is the bregma.
In babies the sutures are not yet fused and they are fontanelles instead. These are thin membranes which join the bones of the skull and become ossified throughout development. Typically the anterior fontanelle ossifies within 1-2 years while the posterior and lateral fontanelles ossify earlier.
Describe the mastoid process and its significance
The posterior belly of digastric and sternocleidomastoid muscle attaches to the mastoid process of the temporal bone.
The facial nerve runs deep to the process and therefore it is important to consider when removing the parotid gland.
The mastoid process doesn’t develop til around 10 years of age.
What is the pterion and where is it located?
What is its significance?
The pterion is an H-shaped suture formed by the joining of the temporal, parietal, sphenoid and frontal bones.
It is located 2.5cm superior to the zygomatic arch and 2.5cm posterior to the lateral margin of the orbit.
The pterion is the weakest part of the skull which can often become damaged due to trauma and often the anterior branch of the middle meningeal artery runs deep to it. Therefore damage to the pterion often results in extradural haemorrhage which may be fatal.
Where are these foramina located and what structures pass through them?
- Foramen ovale
- Foramen spinosum
- Carotid canal
- Jugular foramen
- Foramen magnum
- Hypoglossal canal
- stylomastoid foramen
- Optic canal
- Foramina of cribriform plate
- Superior orbital fissure
- Foramen rotundum
- Internal acoustic meatus
- Foramen ovale is located on the posterolateral border of the greater wing of sphenoid on the base of the skull and the mandibular division of the trigeminal nerve (V3) and lesser petrosal nerve run through it
- The foramen spinosum is posterolateral to the foramen ovale in the greater wing of the sphenoid bone and the middle meningeal artery runs through it
- The carotid canal is in the petrous part of the temporal bone on the base of the skull and contains the internal carotid artery and its associated nerve plexus
- The foramen magnum is a large opening in the base of the skull surrounded by occipital bone which contains the brainstem, vertebral arteries and nerve plexuses, spinal arteries, meninges and the roots of CN XI
- The hypoglossal canal sits anterior and superior to the occipital condyles in the occipital bone and contains the hypoglossal (XII) nerve and vessels
- The jugular foramen sits lateral to the hypoglossal canal in the occipital bone and contains the IJV and CN IX, X and XI
- The sytlomastoid foramen is located between the mastoid and styloid processes at the base of the skull and carries the Facial (VII) nerve
- The optic canals sit anterior to the anterior clinoid processes in the lesser wing of the sphenoid in the anterior cranial fossa. The Optic (II) nerve and ophthalmic artery run through here to enter the orbit.
- The olfactory foramina of the cribriform plate are small perforations in the anterior cranial fossa allowing the passage of Olfactory (I) nerve fibres from the olfactory bulb sitting on the cribriform plate of the ethmoid bone and into the nasal mucosa
- The superior orbital fissure sits just lateral to the optic canals and separates the greater and lesser wings of the sphenoid bone allowing passage of CN III, IV, V1, VI and the ophthalmic vein between the middle cranial fossa and the orbit
- The foramen rotundum is located posterior to the medial end of the superior orbital fissure within the middle cranial fossa and allows the passage of V2 into the pterygopalatine fossa
- The internal acoustic meatus is located in the petrous part of the temporal bone within the posterior cranial fossa and it allows the passage of CN VII and VIII and the labyrinthine artery
Describe the external ear, its main components and structure, its innervation and its clinical relevance
The external ear is made up of the auricle and external acoustic meatus. The concha is the deepest part of the auricle forming the external boundary of the external acoustic meatus which extends approximately 2.5cm to the tympanic membrane, although it does not have a straight course. The lateral third of the external acoustic meatus is cartilaginous and the medial two thirds are bony and it is lined by a mucous membrane.
The external ear may be effected by allergy, swimmer’s ear in which there is infection of the mucosa, or surfer’s ear in which there is growth of the bony part which occludes the canal.
The auricle is supplied by the lesser occipital, greater auricular and a branch of V3, so infection of the auricle may cause head and neck pain. The deeper parts of the auricle may also be supplied by CN VII and X.
The external acoustic meatus is supplied by CN V3, X, VII
The tympanic membrane is supplied by V3, VII, X and IX on its outer surface and IX on its inner surface.
Describe the middle ear and its main features as well as its main clinical relevance
The middle ear is an air-filled cavity stretching from the tympanic membrane to the inner ear which sits in the petrous part of the temporal bone and is lined by mucosa.
Has 2 parts: tympanic cavity and epitympanic recess and is connected to the nasal cavity by the pharyngotympanic tube.
The middle ear is clinically important due to the high prevalence of middle ear infections in children and babies which have potential to spread intracranially via venous drainage systems. Middle ear infection may also spread to the mastoid antrum via an aditus in the posterior wall of the middle ear and this can lead to mastoiditis which is an emergency situation in which prevention of meningitis must occur through antibiotics, pus drainage, and surgery.
Middle ear: Roof/Tegmental wall
The tegmen tympani bone separates the middle cranial fossa and the middle ear and care should be taken not to go through here in surgery
Middle ear: Floor/Jugular wall
The floor of the middle ear separates the middle ear from the internal jugular vein which sits below. In the medial aspect of the floor of the middle ear the tympanic branch of CN IX (which travels through the jugular foramen along with the IJV) emerges and joins the tympanic plexus over the promontory on the medial wall.
Middle ear: Lateral wall/Tympanic membrane
-Clinical relevance (ear examination)
The lateral wall of the middle ear is formed mainly by the tympanic membrane which separates the middle ear from the external acoustic meatus.
The external acoustic meatus and tympanic membrane can be assessed with an otoscope in an ear examination. It is important to avoid damaging the chorda tympani nerve which runs superiorly behind the tympanic membrane within the middle ear as this supplies taste to the anterior two thirds of the tongue.
When examining the external acoustic meatus the ear should be lifted up in adults and down in babies in order to straighten the canal.
We can then observe the tympanic membrane to determine whether someone has a middle ear infection. We should normally be able to see the lateral process and handle of the malleus and the cone of light and should be able to distinguish the pars flacida. With infection we may not be able to see some of these structures and the membrane may lose its translucence.
Middle ear: Medial wall/Labyrinthine wall
The medial wall of the middle ear has many features. The promontory is a prominence of the cochlea of the inner ear which bulges into the middle ear and is lined by mucosa and covered by the tympanic plexus.
The sympathetic chain which travels with the internal carotid artery gives off a branch from the internal carotid plexus which runs through the anterior wall of the middle ear to join the tympanic plexus. The tympanic branch of CN IX joins the tympanic plexus via the medial floor of the middle ear. The lesser petrosal nerve comes off the tympanic plexus and exits the middle ear via the anterior wall.
The round and oval windows connect the middle and inner ears.
The prominence of the facial (VII) nerve is a bony canal which exits through the medial wall. CN VII gives off the chorda tympani before entering this canal and this enters through the posterior wall before running superiorly in the middle ear, deep to the tympanic membrane and going on to supply taste to the tip of the tongue.
The prominence of the lateral semi-circular canal runs just superior to this prominence.
Middle ear: Anterior wall/Carotid wall
The anterior wall separates the middle ear from the internal carotid artery.
The lesser petrosal nerve comes off the tympanic plexus and leaves the middle ear via the anterior wall.
The branch of the internal carotid plexus which joins the tympanic plexus enters through the anterior wall.
The chorda tympani nerve leaves through the anterior wall.
The tensor tympani muscle runs through this wall.
The pharyngotympanic tube connects the nasopharynx and middle ear via this wall. This tube has a bony part and soft gelatinous part and is not well developed in babies. It is responsible for equalising air pressure between the oral cavity and middle ear and can become blocked leading to trapping of bacteria in the middle ear.
Middle ear: Posterior wall/Mastoid wall
The posterior wall separates the middle ear from the mastoid air cells inferiorly and connects the middle ear to the mastoid antrum superiorly via an aditus.
The continuation of the mucosa between the middle ear and mastoid antrum via the aditus means that middle ear infection may spread and cause mastoiditis.
The tendon to the stapedius muscle and the chorda tympani nerve enter the middle ear via the posterior wall.
What are some of the contents of the middle ear and what is the main neurovascular supply?
The malleus, incus and stapes bones form the ossicular chain and are all joined at synovial joints.
The tensor tympani muscle and stapedius are in the middle ear.
Nerves within the middle ear include the chorda tympani (branch of CN VII), tympanic plexus (formed by branch of CN IX, and the caroticotympanic nerves of the internal carotid plexus.
The external carotid artery gives branches to the external acoustic meatus and middle ear.
Describe the basic organisation of the cranial dura mater
Made up of 2 layers, an outer periosteal layer and an inner meningeal layer. The periosteal layer seals the whole skull covering the internal and external surface. Only the inner meningeal layer continues down to cover the spinal cord, so the dura mater of the spinal cord differs to that of the cranium.
Describe the dural partitions
The dura partitions the different parts of the brain. The falx cerebri separates the 2 cerebral hemispheres.
The tentorium cerebelli separates the cerebrum from the cerebellum.
The falx cerebelli divides the 2 cerebellar hemispheres.
The infundibulum is a membrane which partially covers the pituitary gland
Blood supply to the cranial dura mater
The meningeal arteries run in grooves on the interior surface of the skull within the outer periosteal layer of the dura mater.
The main arterial supply to the dura comes from the meningeal arteries, mainly the middle meningeal, which travels through the foramen spinosum and divides into anterior and posterior branches. The anterior branch crosses the pterion.
Innervation of cranial dura mater
Falx cerebri innervated by V1
Tentorium cerebelli innervated by V1
Dura mater innervated by V1, V2 and V3, X and C1-C3
Intracranial venous sinuses
These sinuses form between the periosteal and meningeal layers of the dura
The inferior sagittal sinus drains into the straight sinus that meets the superior sagittal sinus at the confluence of the sinuses.
From the confluence the transverse sinuses extend out laterally and become the sigmoid sinuses.
The sigmoid sinus eventually becomes the IJV which exits the skull through the jugular foramen
Contents, location and clinical relevance of the cavernous sinus
The internal carotid artery and Abducent (VI) nerve run within the cavernous sinus.
CN III, IV, V1 and V2 run along the wall of the cavernous sinus.
The cavernous sinuses are located either side of the sella turcica and are important due to their contents.
An infection in the orbit may be carried back to the cavernous sinus via the ophthalmic vein. Therefore it is important to consider a baby that presents with periorbital cellulitis as this infection may pass into the cavernous sinus, causing a thrombus which may compromise the internal carotid artery or other cranial nerve structures in the sinus.
Where does blood accumulate in racoon eyes?
A skull fracture may result in a patient presenting with racoon eyes. This occurs when blood accumulates between the periosteal layer of the dura and the skin of the eyelids
Venous drainage of the skull
small venous networks drain into larger veins which drain into venous sinuses which eventually lead to the IJV
Emissary veins run through the bony skull connecting the outside of the skull and dural venous sinuses (this means a laceration of the skull can cause infection which can enter the cranial cavity via the emissary veins)
Diploic veins drain the bony part of the skull into the sinuses
Cerebral veins drain from the cerebrum into the sinuses.
Briefly describe the arachnoid and the pia mater
The arachnoid mater is a thin, avascular membrane which has trabeculae and a subarachnoid space beneath it.
It does not enter grooves or fissures of the cerebrum.
The arachnoid granulations in the subarachnoid space drain CSF into the venous sinuses.
The cerebral arteries and veins run in the subarachnoid space
The pia mater is a thin layer which invests around the surface of the brain and down all the grooves of the cerebrum.
Extradural haemorrhage
- Where it occurs
- Likely damaged vascular structure
- Likely cause
- CT appearance
Extradural haemorrhage typically occurs due to damage of the meningeal arteries, usually the middle meningeal, resulting in a bleed between the periosteal layer of the dura mater and the skull.
It is usually associated with skull fracture and appears more discrete and lens-shaped on the CT scan.
Subdural haemorrhage
Subdural haemorrhage occurs within the meningeal layer of the dura mater.
It often results due to damage to venous structures, typically the cerebral veins which cross the meningeal layer of the dura as they travel from the subarachnoid space to the venous sinuses.
They require relatively little force to occur, may occur in patients with cerebral atrophy or who are on anti-coagulants. Chronic subdural haemorrhage is more common but acute cases can occur following high velocity trauma.
Subarachnoid haemorrhage
Subarachnoid haemorrhage occurs within the subarachnoid space typically due to damage of the cerebral arteries which run in the subarachnoid space (but cerebral veins can also cause subarachnoid haemorrhage).
They usually occur due to a cerebral artery aneurysm within the circle of willis.
It results in sudden severe headache, vomiting, and frequent loss of consciousness,
A subarachnoid haemorrhage appears more diffuse on CT scan.
List the bones making up the orbit
Frontal bone Zygomatic bone Maxillary bone Lacrimal bone Ethmoid bone Sphenoid bone Palatine bone
List the bones making up the roof, floor and walls of the orbit
Roof = Frontal bone
Floor = Maxilla and zygomatic bones
Lateral wall = Frontal and zygomatic bones
Medial wall = Lacrimal, ethmoid and maxilla
List the layers of the eyelids from superficial to deep
skin subcutaneuous tissue orbicularis oculi orbital septum tarsus conjunctiva
Describe the significance of the skin and subcutaneous tissue of the eyelids
There is the presence of a potential space in the subcutaneous tissue which can accumulate blood.
A skull fracture may damage the periosteal layer of the dura leading to bleeding into this potential space between the dura and skin of the eyelids, leading to racoon eyes
Describe the voluntary muscle of the eyelids and its clinical significance
The orbicularis oculi muscle has an orbital part and a palpebral part which goes to the eyelid.
It is innervated by the facial (VII) nerve.
Therefore any damage to the facial (VII) nerve will cause inability of the upper eyelid to close/blink on the ipsilateral side, and the lower eyelid will droop away.
This is associated with corneal ulcers and spillage of tears. Therefore it is important to consider the facial nerve in surgical procedures to ensure it is not damaged.
Orbital septum
A continuation of the periosteal layer of the cranial dura which runs in the upper and lower eyelids
Tarsus, Levator Palpebrae Superioris and Superior Tarsal muscles
The tarsus is a fibrocartilage structure on the eyelid.
The LPS and superior tarsal muscle both attach to the tarsus but have different innervation.
LPS is innervated by CN III
The superior tarsus is a smooth muscle and is innervated by SNS fibres
The LPS and superior tarsus muscle are involved in raising the eyelid. Therefore a loss of function in either of these muscles may result in drooping of the upper eyelid.
A partial ptosis results if superior tarsus function is lost, while a complete ptosis results if LPS function is lost
Patient’s often present with Horner’s syndrome with partial ptosis when the SNS chain is cut in some procedures
Tarsus glands
Glands embedded in tarsus which secrete oily substance
Glands at base of eyelashes in eyelids are sweat glands
Blockage or infection of these glands can cause bumps in the eyelid
Stye/hordeolum may occur due to blockage of sweat glands at base of eyelashes and is usually painful.
Chalazion occurs when the duct draining the oily secretions of the tarsus glands is blocked and it usually doesn’t cause pain
Conjunctiva
Protected by inner surface of eyelid but may be effected in conjunctivitis
Supplied by ophthalmic, facial and superficial temporal arteries
Supplied by V1 to upper eyelids and V2 to lower eyelids
List the extrinsic muscles of the eye
Superior, medial, lateral and inferior rectus muscles
Superior and inferior oblique muscles
Common tendinous ring and structures passing through it
A ring formed from the periorbital part of the dura where the superior, inferior, medial and lateral rectus muscles attach which surrounds the optic canal and part of the superior orbital fissure.
The structures passing through the common tendinous ring include: the ophthalmic artery and optic (II) nerve (in the optic canal), the superior and inferior divisions of CN III, CN VI, Nasociliary nerve.
These structures may all be affected as a result of infection causing narrowing of the ring
Lacrimal apparatus
Lacrimal gland sits superolaterally in the orbit around the tendon of LPS and secretes tears
Lacrimal sac sits in lacrimal fossa medially and drains the tears
The puncta acts as a pump which pumps the tears through the lacrimal canaliculi into the lacrimal sac which leads to the nose
Arterial supply and venous drainage in orbit
Ophthalmic artery with many branches (to lacrimal gland, lacrimal duct and retina)
Ophthalmic veins
Innervation in orbit
CN II, III, IV, V1, VI
- intracranial injury such as trauma, increased ICP, infection may effect these nerves.
- An increase in ICP will affect CN VI first causing medial deviation of eyes and inability to move eyes laterally from midline
- damage to CN IV means you cannot look down and in
CN III supplies all extrinsic eye muscles except Lateral rectus which is supplied by CN VI and superior oblique which is supplied by CN IV
The superior branch of CN III supplies LPS and superior rectus
The inferior branch supplies inferior and medial rectus, inferior oblique and ciliary ganglion
If there is no ptosis this indicates the superior branch of CN III should be fine
CN V1 has 3 branches - lacrimal, frontal, nasociliary
Danger triangle of face
From commisures of mouth on nasion
Ophthalmic vein communicates with facial veins and cavernous sinus and therefore this provides a pathway for spread of infection from the face to the cranial cavity
The existence of communications between the facial vein and cavernous sinus and direction of blood flow is important for the spread of infection from the face
Describe the superficial cervical fascia
The superficial cervical fascia lies between the skin and the investing layer of the deep fascia.
It contains fatty subcutaneous tissue and the platysma muscle, a thin sheet of skeletal muscle originating from the thorax and blending with the mandible and lower facial muscles. It is innervated by the cervical branch of the facial (VII) nerve.
Investing layer of deep fascia
Lies deep to the superficial fascia being the most superficial layer of the deep fascia surrounding the neck.
It invests around the peripheral muscles of the neck including the trapezius, SCM and infrahyoid muscles.
Pretracheal layer of deep fascia
Middle layer of deep fascia enclosing the larynx/trachea, pharynx/oesophagus and the thyroid gland
Prevertebral layer of deep fascia
Deep layer of deep fascia which encompasses the vertebral column and paravertebral muscles. Anterior to the vertebral bodies the fascia splits into 2 layers.
Carotid sheath
Sheath formed by contributions from the investing, pretracheal and prevertebral layers of the deep cervical fascia which covers the internal carotid artery, internal jugular vein and vagus (X) nerve
Pretracheal space
The potential space between the investing layer of the deep fascia and the pretracheal layer which extends from the pharynx down to the anterior mediastinum
Retropharyngeal space
Potential space between posterior border of pretracheal fascia and the prevertebral fascia extending from base of skull to upper part of posterior mediastinum
Prevertebral space
Potential space where the prevertebral fascia has split into 2 anterior to the vertebral bodies which extends from the base of the skull to the diaphragm.
