Session 1: General Organisation and Osteology Flashcards
Introduction
- The head and neck region contains many structures compressed into a relatively small area. The head consists of the scalp, skull, brain and its coverings (the meninges), special sense organs, muscles, cranial nerves and their branches, viscera, glands, blood vessels and lymphatics to name but a few.
- Head injuries (e.g. fractures of the skull and face) and their complications, such as haemorrhage, infection and injury to the brain and cranial nerves are a major cause of disability and/or death.
- The neck, which extends between the lower margin of the mandible above and the suprasternal notch of the manubrium and the upper border of the clavicle below, connects the head to the thorax, abdomen, pelvis, trunk and limbs.
- Structures such as muscles, glands, major blood vessels, cranial and other principal peripheral nerves, lymphatics, trachea, oesophagus and vertebrae are crowded together in the neck.
- The upper components of the brachial plexus of nerves and blood vessels supplying the upper limb lie on the side of the neck.
- Major blood vessels (common carotid arteries and jugular veins) and nerves, that lack bony protection are commonly injured in penetrating wounds (e.g. stab injuries) of the neck. Cervical pain may be caused by inflamed lymph nodes, muscle strain and displacement/protrusion of the inter-vertebral discs. Most chronic neck pain is caused by bony abnormalities (e.g. cervical osteoarthritis and other forms of arthritis) or by local trauma.
Describe the main muscle groups in the head
The main muscles in the head are the:
- Muscles of facial expression
- Muscle of the cheek (buccinators)
- Occipitofrontalis muscle
- Muscles of mastication
The muscles of facial expression are in the subcutaneous tissue and they move the skin and change facial expressions.
Most muscles, originating from bone or fascia produce their effects by pulling the skin (they are the only group of muscles that insert into skin)
They surround the orifices of the mouth, eyes and nose and act as sphincters and dilators to open and close them. The buccinators keep the cheeks taut and aids in chewing.
They are all innervated by the facial nerve and can broadly be split into 3 groups: orbital, nasal and oral.
See Netter’s flashcards for individual muscles?
Describe the muscles of mastication
The muscles of mastication are supplied by the mandibular division of the trigeminal nerve (branch of CN V).
- Masseter
- Temporalis
- Buccinator
- Medial and Lateral pterygoid
What does the the motor branch of the facial nerve supply?
The Facial nerve (CN VII) supplies the superficial muscle of the neck and chin (platysma), muscles of facial expression, buccinators, muscles of the ear and the occipitofrontalis muscle.
It exits the cranium (origin: brainstem) and enters the substance of the parotid gland in which it divides into its extra-cranial branches:
- Temporal
- Zygomatic
- Buccal
- Mandibular
- Cervical
Two Zombies Bugger My Cat
Describe the causes and presentation of Facial Paralysis
The most common non-traumatic cause of facial paralysis is inflammation of the facial nerve near its exit from the cranium at the stylomastoid foramen. (The Stylomastoid foramen is between the styloid and mastoid processes of the temporal bone and is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery)
The inflammation causes oedema and compression of the nerve (Bell’s palsy if cause is unknown) in the intracranial facial canal, resulting in a number of structural and functional disorders.
The affected area sags, and facial expression is distorted, making it appear passive or sad.
As the branches of the facial nerve are superficial, they are subject to injury in wounds, cuts and in child-birth.
As the nerve and its branches pass through the parotid gland, they are vulnerable to injury during surgery on the gland or in disease of the gland. Parotid gland disease often causes pain in the auricle of the ear, external acoustic meatus, temporal region and the TMJ (temporomandibular joint).
Give an overview of the arterial supply of the face
Most arteries supplying the face are branches of the external carotid artery. The facial artery is the major arterial supply to the face.
The pulse of the facial artery can be palpated as the artery winds around the inferior border of the mandible. Because the artery has many anastomoses with other arteries of the face, in the event of laceration of the artery on one side of the face, it is necessary to compress both the arteries to stop bleeding.
Describe the venous drainage of the face
The facial vein froms the major venous drainage of the face and drains into the internal jugular vein. Superficial temporal vein, maxillary vein and other veins form the external jugular vein.
Both internal and external jugular veins drain into the subclavian vein.
What is meant by fascia of the neck?
Structures in the neck are compartmentalised by layers of cervical fascia that allows the structures to move and pass over one another with ease (by decreasing friction) as when swallowing or twisting the neck or speaking. The superficial fascia lies between the skin and investing three layers of deep cervical fascia.
The fascial planes determine the direction in which an infection in the neck may spread.
Describe the Platysma
The platysma is a broad, thin sheet of muscle in the subcutaneous tissue of the neck. It develops from the 2nd pharyngeal arch and is supplied by branches of the facial nerve (CN VII).
The platysma covers the anterolateral aspect of the neck. Inferiorly, the fibres diverge, leaving a gap anterior to the larynx and trachea.
Acting from its superior attachment, the platysma tenses the skin.
Acting from its inferior attachment, the platysma helps depress the mandible and draw the corners of the mouth inferiorly, as in a grimace.
Describe the Superficial Cervical Fascia
The cervical subcutaneous tissue (Superficial Cervical Fascia) is a layer of fatty connective tissue that lies between the dermis of the skin and the investing layer of deep cervical fascia. This tissue is usually thinner than in other regions, especially anteriorly.
It contains cutaneous nerves, blood and lymphatic vessels, superficial lymph nodes and variable amounts of fat.
Anterolaterally, it contains the platysma.
Describe the parts of the deep cervical fascia and its functions
The deep cervical fascia has three layers:
- Investing
- Pretracheal
- Prevertebral
It also condenses around the common carotid arteries, internal jugular veins and vagus nerves to form the carotid sheath.
The deep cervical fascia has several functions, including:
- Support
- Viscera (e.g. thyroid gland)
- Muscles, Vessels and deep Lymph Nodes
- Limit the spread of abscesses that result from infections
- Slipperiness that allows structures in the neck to move and pass over one another without difficulty
- Swallowing
- Turning the head and neck
Describe the Investing Layer
The most superficial, the investing layer surrounds the entire neck deep to the skin. It encloses:
- Sternocleidomastoid
- Trapezius
- Submandibular and Parotid Salivary Glands
Describe the Pretracheal Layer
A thin layer, limited to the anterior part of the neck. Inferiorly it extends into the thorax, where it blends with the fibrous pericardium. It forms 2 layers
- Muscular layer
- Encloses infrahyoid muscles
- Visceral layer
- Thyroid gland
- Trachea
- Oesophagus
Laterally it blends with the carotid sheaths; each carotid sheath is a tubular fibrous structure that extends from the base of the cranium to the root of the neck.
Describe the Prevertebral Layer
The innermost layer of the deep fascia, which forms a sheath for the vertebral column and the muscles associated with it. Extends from the base of the cranium to the 2nd/3rd thoracic vertebra and extends laterally as the axillary sheath that surrounds the axillary vessels and the brachial plexus.
Describe the Carotid Sheath including the contents
A tubular, fibrous structure that extends from the base of the cranium to the root of the neck. Contains:
- The common carotid artery (anteromedial)
- Internal jugular vein (more anterlateral)
- The vagus nerve (CN X)
+Deep Cervical lymph nodes
What is meant by cleavage planes?
The layers of deep cervical fascia form natural cleavage planes allowing separation of tissues during surgery.
Describe how the deep planes can determine spread of infection
The deep fascial layers determine the direction in which abscesses in the neck may spread. If an infection occurs:
- Between the Investing layer and the muscular part of the pretracheal surrounding the infrahyoid muscles, it will not spread beyond the manubrium.
- Between the Investing and visceral part of the Pretracheal layer, it can spread into the thoracic cavity anterior to the pericardium. This inferior spread can cause infection of the anterior mediastinum.
- Posterior to the prevertebral fascia: this can erode through the prevertebral fascia, and drain into the retropharyngeal space. The retropharyngeal space extends into the thorax and infection can spread to the mediastinal contents.
- Superficial infections are rare – tend to be outside (above) the deep cervical fascia e.g. cellulitis, abscesses point and are fluctuant
- Pus from an abscess lying behind the Prevertebral layer of deep cervical fascia may extend laterally in the neck.
- May perforate the fascial layer and enter the retropharyngeal space.
- This will produce a bulge (retropharyngeal abscess) in the pharynx
- Pus accumulates in the space between the prevertebral fascia and the buccopharyngeal membrane.
- This may lead to compression of the pharynx and therefore dysphagia and dyarthria (difficulty speaking)
What is the Retropharyngeal Space and Danger Space?
The retropharyngeal space is a potential space between the Prevertebral layer of fascia and the fascia surrounding the pharynx superficially. It is a midline space that consists largely of fatty areolar tissue and contains lymph nodes that drain the pharynx, nose and middle ear.
The space is posterior to the pharynx and oesophagus, and extends from the base of the skull to a variable level between the T1 and T6 vertebral bodies.
This is the largest, most important interfascial space in the neck because it is the major route of spread of infection from the neck to the thorax.
The space runs to the diaphragm.
The true retropharyngeal space is ANTERIOR to the DANGER SPACE.
The Danger Space is bounded superiorly by the skull base, anteriorly by the alar fascia and posteriorly by the prevertebral fascia. It comes to an end at the level of the diaphragm.
The true Retropharyngeal Space is between the buccopharyngeal fascia (component of the pretracheal layer) and alar fascia.
The danger space connects the deep cervical spaces to the mediastinum – its inferior boundary is posterior mediastinum at the level of the diaphragm. It is a potential path for spread of infections from the pharynx to the mediastinum. In healthy patients it is indistinguishable from the retropharyngeal space. It is only visible when distended by fluid or pus, below the level of T1-T6 since the retropharyngeal space variably ends at this level.
Describe the SCM and Trapezius
Sternocleidomastoid Muscle
- 2 heads of origin. The sternal end arises from the anterior surface of the manubrium of the sternum. The clavicular head arises from the superior surface of the MEDIAL third of the clavicle.
- Insertion: attaches to the lateral surface of the mastoid process of the temporal bone and the lateral half of the superior nuchal line.
- Action: tilts the head to 1 side, flexes the neck and rotates the neck so the face points superiorly to the opposite side. When the muscles of both sides act together, they flex the neck.
- Innervation: spinal accessory nerve (CN XI and C2 and C3)
Trapezius
- Origin: external occipital protruberance and medial third of the superior nuchal line of the occipital bone, ligamentum nuchae and spinous processes of the 7th cervical vertebra and all 12 thoracic vertebrae.
- Insertion: superior fibers insert into the posterior border of the lateral third of the clavicle, middle fibers insert into the medial margin of the acromion and posterior border of the scapular spine. Inferior fibers converge to end in an aponeurosis inserted into the scapular spine. So superior surface of middle 1/3rd of clavicle is free of muscular attachment.
- Innervation: motor supply is from the accessory nerve (CN XI). Proprioceptive fibers are from the 3rd and 4th cervical nerves.
Describe the borders of the anterior triangle of the neck
- Anterior – Mid line of the neck from chin to the jugular notch
- Posterior – The anterior border of SCM
- Superior – Inferior border of the mandible (jawbone)
- Apex (inferior boundary) – Jugular notch in the manubrium
- Roof – Superficial cervical fascia, containing the platysma
- Floor – Pharynx, larynx, thyroid gland – visceral fascia covers the floor
Borders of half the Anterior triangle
- Superiorly: inferior border of the mandible (jawbone)
- Laterally: medial border of the sternocleidomastoid
- Medially: imaginary sagittal line down midline of neck
Describe the carotid triangle
Carotid Triangle (6)
- Carotid sheath
- Common carotid artery (birfurcates within the carotid triangle into the external and internal carotid arteries)
- Internal jugular vein
- Vagus nerve
- Deep Cervical Lymph Nodes
- Thyroid gland
- Larynx
- Pharynx
- External carotid artery and some of its branches
- Hypoglossal and Spinal accessory nerves
- Branches of cervical plexus
Borders of Carotid Triangle:
- Superior: posterior belly of the digastric muscle
- Lateral: medial border of the sternocleidomastoid muscle
- Inferior: superior belly of the omohyoid muscle
List the subdivisions of the Anterior Triangle
The anterior triangle can be further subdivided into 4 triangles
- Submandibular (digastric) triangle
- Submental triangle
- Carotid triangle
- Muscular (omotracheal) triangle
Describe the submandibular (digastric triangle)
Submandibular (digastric) Triangle (4) located underneath the body of the mandible.
- Submandibular gland
- Submandibular lymph nodes
- Hypoglossal and Mylohoid nerves
- Parts of facial artery and vein (pass through this area)
Borders of Submandibular Triangle:
- Superiorly: body of the mandible
- Anteriorly: anterior belly of the digastric muscle
- Posteriorly: posterior belly of the digastric muscle
Describe the submental triangle
Submental Triangle (5) is situated underneath the chain
- Submental lymph nodes, which filter lymph draining from the floor of the mouth and parts of the tongue
- Small veins which unite to form anterior jugular vein
Borders of Submental Triangle:
- Inferiorly: hyoid bone
- Medially: imaginary sagittal midline of the neck
- Laterally: anterior belly of the digastric
Describe the muscular (omotracheal) triangle
Muscular (omotracheal) triangle (7) situated more inferior than the triangular sub-divisions. It is slightly dubious triangle, in reality having four boundaries. The muscular triangle is unique in containing no vessels of note.
- Sternothyroid
- Sternohyoid
- Thryoid glands
- Parathyroid glands
- Pharnyx
Boundaries of the muscular triangle:
- Superiorly: hyoid bone
- Medially: imaginary midline of the neck
- Supero-laterally: superior belly of the omhyoid muscle
- Infero-laterally: inferior portion of the sternocleidomastoid
Describe the borders of the Posterior Triangle of the Neck
Anterior triangle is associated with structures coursing between head and trachea. The posterior triangle is significantly smaller and associated with structures coursing between thorax/neck and upper limb.
- Anterior – Posterior border of SCM
- Posterior – Anterior border of Trapezius
- Inferiorly – Middle third of the clavicle, between Trapezius and SCM
- Apex – Where SCM and Trapezius meet on the superior nuchal line of the occipital bone
- Roof – Investing layer of deep cervical fascia
- Floor – Muscles covered by the Prevertebral layer of deep cervical fascia. The muscles are: Splenius captitis, Levator scapulae, Anterior, Middle and Posterior Scalene
Describe the subdivisions of the Posterior Triangle
Occipital Triangle (2) superior, larger part
- Spinal Accessory Nerve (CN XI) crosses the triangle in an oblique, inferoposterior direction within the investing layer of fascia. It lies relatively superficially in the posterior triangle, and is at danger of injury
- Trunks of Brachial Plexus
- Part of external jugular vein
- Posterior branches of cervical plexus
- Cervicodorsal trunk
- Cervical lymph node
Omoclavicular (subclavian) triangle (3)
- 3rd part Subclavian Artery (distal portion of the subclavian artery)
- Part of Subclavian Vein
- Suprascapular artery
- Supraclavicular lymph nodes
What are the types of connective tissue?
Loose: superficial fascia, adipose tissue
Deep regular: muscle, tendon/aponeurosis
Dense irregular: dermis, deep fascia
What is meant by the Parapharyngeal Space?
Parapharyngeal Space: (potential space) aka Lateral Pharyngeal Space
- Consists largely of fatty areolar tissue and contains branches of the trigeminal nerve as well as deep vessels: internal maxillary artery, ascending pharyngeal artery. It also contains the pterygoid venous plexus.
- The parapharyngeal space is shaped like a pyramid, inverted with its base at the skull base, with its apex inferiorly pointing to the greater cornu of the hyoid bone.
- It is continuous with the retropharyngeal space and also communicates with other cervical and cranial fascial spaces, as well as the mediastinum.
- Lesions can affect the carotid sheath structures e.g. thrombosis in internal jugular vein
Describe the hyoid muscles
In the anterolateral part of the neck, the hyoid bone (level C4) provides attachments for the Suprahyoid Muscles superiorly, and the Infrahyoid Muscles inferiorly.
These hyoid muscles steady or move the hyoid and larynx e.g. elevate hyoid and larynx during swallowing
Describe the Suprahyoid Muscles
- Mylohyoid
- Geniohyoid
- Stylohyoid
- Digastric Muscles
- Two bellies (Anterior and Posterior)
- Joined by an intermediate tendon
- Fibrous sling, from Pretracheal layer of Deep Cervical Fascia allows the tendon to slide anteriorly and posteriorly
Together the Suprahyoid muscles constitute the substance of the floor of the mouth, supporting the hyoid in providing a base from which the tongue functions. They also elevate the hyoid and larynx in relation to swallowing and tone production.
Describe the Infrahyoid Muscles
Superficial Plane
- Sternohyoid
- Omohyoid
- Has two bellies (Superior and Inferior)
- Joined by an intermediate tendon
- Fascial sling for the tendon connects to the clavicle
Deep Plane
- Sternothyroid
- Thyrohyoid
Often called the strap muscles because of their ribbon-like appearance, the Infrahyoid muscles anchor the hyoid, sternum, clavicle and scapula, and depress the hyoid and larynx during swallowing and speaking.
They also work with the Suprahyoid muscles to steady the hyoid, providing a firm base for the tongue.
Describe the arterial supply of the head and neck
The head and neck receives the majority of its blood supply through the carotid and vertebral arteries.
The ECA supplies the areas of the head and neck external to the cranium. After arising from the common carotid artery, it travels up to the neck, posterior to the mandibular neck and anterior to the lobule of the ear. The artery ends within the parotid gland, dividing into the superficial temporal artery and the maxillary artery. Before terminating, the ECA gives off six branches:
- Superior thyroid artery
- Lingual artery
- Facial artery
- Ascending pharyngeal artery
- Occipital artery
- Posterior auricular artery
The maxillary aetery supplies the deep structures of the face while the facial and superficial temporal arteries generally supply superficial areas of the face.
The ICA do not supply any structures in the neck, entering the cranial cavity via the carotid canal in the petrous part of the temporal bone. Within the cranial cavity, the ICA supplies the brain, eyes and forehead.
The right and left vertebral arteries arise from the subclavian arteries, medial to the anterior scalene muscle. They then ascend up the posterior side of the neck, through holes in the transverse processes of the cervical vertebrae, known as foramen transversarium. The vertebral arteries enter the cranial cavity via the foramen magnum and converge to give rise to the basilar arteries. The vertebral arteries supply no branches to the neck, or extra-cranial structures.
The neck is also supplied by arteries other than the carotids. The right and left subclavian arteries give rise to the thyrocervical trunk which has branches:
- 1st branch> inferior thyroid artery supplies the thyroid gland
- Ascending cervical artery arises from the ineferior thyroid artery as it turns medially in the neck, to supply the posterior prevertebral muscles.
- The transverse cervical artery is the next branch of the thyrocervical trunk and it crosses the base of the carotid triangle to supply the trapezius and rhomboid muscles.
- Lastly, the suprascapular artery arises and the supplies the posterior shoulder area
Describe the cranium including the 8 cranial bones
The 8 cranial bones form the calvaria (aka calvarium, pl. calvaria) (the vault /roof of the skull / cranial cap) and the cranial base.
The 8 cranial bones are: ethmoid, frontal, occipital, 2x parietal, 1x sphenoid and 2x temporal.
The superior portions of the frontal, occipital and two parietal bones make up the calvarium.
The bones of the calvarium consist of 2 layers of compact bone separated by a layer of bone marrow, the diploe.
The frontal, sphenoid, ethmoid, occipital, parietal and temporal bones make up the cranial base. The bones of the cranial base articulate with the 1st cervical vertebra (the atlas), the facial bones and the mandible.
These bones form an almost closed box containing the brain. Foramen magnum is the only major opening of the box of the head (where the spinal cord passes through)
How are the cranial bones joined together?
The bones of the cranium are joined by sutures (coronal, sagittal and lambdoid).
- Their edges are often serrated and the direction serrations travel in are random.
- This allows them to interlock firmly.
- It also makes it less likely for them to be easily unlocked by force applied in one direction – need force applied in multiple directions at one time to unlock sutures
- The coronal separates the frontal and parietal bones.
- The Bregma is the anatomical point at which the coronal suture is intersected perpendicularly by the sagittal suture.
- The Lambda is rounded and corresponds with the point of meeting of the saggital and lambdoid suture
What are fontanelles?
- Fontanelles are an anatomical feature of the human skull comprising any of the soft membranous gaps (sutures) between the cranial bones that make up the calvaria.
- Fortanelles allow for rapid stretching and deformation of the neurocranium as the brain expands faster than the surrounding bone can grow.
- During infancy, the anterior fontanelle (aka frontal fontanelle) is at the junction of the sagittal suture, coronal suture and frontal suture.
- The posterior fontanelle (aka occipital fontanelle) is situated at the junction of the sagittal suture and lambdoidal suture. It generally closes in 6-8 weeks from birth whilst the frontal fontanelle persists until ~18 months after birth.
Describe the cranial floor
- The floor of the cranial base is also known as the cranial fossa and has 3 distinct depressions (anterior, middle and posterior).
- The inferior surface of the cranial floor contains lots of openings where cranial blood vessels and nerves enter or leave including the foramina magnum.
- The foramina of the cranial floor lessen the weight of the skull and allows for pass of anatomical structures between extra- and intra-cranial compartments (communication)
- Thus, the cranial base is liable to fracture in high energy impacts to the head.
- Sensory nerves, arterial supply to brain and meninges, sympathetic fibres ( some to special sense organs e.g. eyes), venous blood (some sections) and also infections sometimes enter the cranial cavity through foramina (sometimes infections from outside to inside enter through nutrient foramina)
- Cranial motor nerves, parasympathetic outflow, veins (venous blood), lymphatics and infections can exit the cranial cavity through foramina.
What is the pterion? What are the consequences of a fracture at this point?
The bone is very thick in some areas e.g. occipital and frontal bones.
The pterion, which lies on the lateral aspect of the skull, is the thinnest part of the calvaria, and is an area of clinical importance.
It is a H-shaped junction between temporal, parietal, frontal and sphenoid bones.
A fracture here can lacerate an underlying artery (the anterior middle meningeal artery), resulting in an extradural haemotoma and raised intracranial pressure. Blood will then collect in between the dura mater and the skull, causing a dangerous increase in intra-cranial pressure. This is known as an extradural haematoma.
The increase in intra-cranial pressure causes a variety of symptoms; nausea, vomiting, seizures, bradycardia and limb weakness. It is treated by diuretics in minor cases, and drilling burr holes into the skull in the more extreme hemorrhages.
Describe the frontal bone and the ethmoid bone? What are the consequences of a cribiform plate fracture?
- The frontal bone forms the anterior part of the skull vault. Anteriorly and inferiorly, it forms the upper border of the orbital margins and it also forms the roof of the orbit.
- The ethmoid is found in the midline of the anterior cranial fossa.
In the midline of the ethmoid bone, the crista galli (latin for cock’s comb) is situated. On either side of the crista galli is the cribriform plate. It is a sheet of bone which contains numerous small foramina – these transmit olfactory nerve fibres (CN I) into the nasal cavity.
The ethmoid also contains the anterior and posterior ethmoidal foramen. Other features include the ethmoid bulla (an elevation above the curved fissure on the lateral wall of the middle meatus) and ethmoid air cells (ethmoidal sinuses)
The cribriform plate of the ethmoid is the thinnest part of the anterior cranial fossa, and therefore most likely to fracture. There are two major consequences of cribriform plate fracture:
- Anosmia – the olfactory nerve fibres run through the cribriform plate, and can be ‘sheared’, resulting in loss of sense of smell.
- CSF rhinorrhoea - the fragments of bone can tear the meningeal coverings of the brain, causing the leakage of cerebrospinal fluid into the nasal cavity. This is visible as a clear fluid.
Describe the Sphenoid bone
The Sphenoid Bone is very important in forming the base of the cranium. Its parts are:
- A central part or body – sphenoidal sinus is found here. The body forms all of the median part of the middle cranial fossa and on it: the optic groove, tuberculum sellae, sella turcica (where the pituitary gland is), dorsum sellae with the posterior clinoid process, the clivus (where the pons part of the brainstem sits)
- 2 wings – greater wing and lesser wing
- Pterygoid Process – downwardly projecting process
Describe the Temporal bone
The Temporal Bone is important in the senses of hearing and balance
6 parts (if all parts are named individually) 4 parts identified (if conjugate names are used)
- Squamous
- Mastoid: 2 important parts (Mastoid process and mastoid air cells). The air cells act as an reservoir of air, equalising the pressure within the middle ear in the case of auditory tube dysfunction. The mastoid air cells can also become infected, known as mastoiditis.
- Tympanic
- Styloid Process
- Zygomatic Process
- Petrous part (strongest bone in the body, contains the inner ear)
Middle ear infections (otitis media) can spread to the mastoid air cells. Due to their porous nature, they are a suitable site for pathogenic replication. The mastoid process itself can get infected, and this can spread to the middle cranial fossa, and into the brain, causing meningitis. If mastoiditis is suspected, the pus must be drained from the air cells. When doing so, care must be taken not the damage the nearby facial nerve.
The temporal bone is relatively strong, and thus it is usually only fractured as a result of blunt trauma to the skull. It has a varied presentation. Ear-related disorders are commonly seen, such as vertigo or hearing loss. As the facial nerve travels through the temporal bone, it can be damaged, with paralysis resulting. Other symptoms include bleeding from the ear and bruising around the mastoid process (which is palpable just behind the ear)
Describe the Occiput
The Occipital Bone is also known as the Occiput
Consists of 4 parts arranged around the foramen magnum
- Squamous: forms the posterior part of the vault
- Condylar (x2 i.e. left and right) forms most of the edges of foramen magnum
- Basilar: forms the anterior part of the foramen magnum
Compare the neonatal skull to the adult skull
- In the neonate, cranial sutures are wide. Adjacent cranial bones held together largely by thick connective tissue matrix ‘tissue islands’. The wide membranous tissue islands in the vicnicity of what will become Bregma and Lambda in the adult are known as fontanelles.
- Neonatal precursor to Bregma is called the Anterior Fontanelle
- Neonatal precursor to Lambda is called the Posterior Fontanelle
- Sutures between adjacent cranial bones are open in the newborn and closed in the adult. Open sutures allow for movement between bones in the newborn.
- In the adult, Lambda and Bregma are pin-point landmarks. In newborns, they do not really exist. Instead they present as membranous island gaps that bridge adjacent cranial bones of the newborn.
- The open sutures at birth allow for cranial bones to be pushed together during the birthing process. The serrated bone edges temporarily interlock during the birthing process. The interlocking sutures protect the brain from injury.
Neonatal Skull at Pre-Term Birth
- Cranial sutures are too wide open at pre-term stages of foetal development.
- If birth should occur prematurely, pressures from the birthing process do not result in interlocking of the cranial bones.
- Thus there is a high probability of brain damage from the trauma of the normal birthing process.
Describe the mandible
The mandible, commonly known as the jaw, is an innominate bone (crosses midline) and comprises of 2 separate bones (the left and right mandibles) therefore it is a bilateral bony structure.
It is formed by union of left and right mandibles which are joined by a midline fibrous joint (the mental symphisis)
The mandibular branch (the only branch with motor function) of the trigeminal nerve (Cranial nerve 5) travels through the mandibular foramen. The mandibular branch innervates the muscles of mastication (masseter, temporalis, medial pterygoid and lateral pterygoid)
Describe Cervical Vertebrae including typical features
Cervical vertebrae 1 to 7 form the bony skeleton of the neck and lie between the skull and thorax. They bear less weight than vertebrae in the other regions of the body.
Spinal roots exit above corresponding vertebra apart from C8 which exits below C7 (inferiorly)
Typical Cervical Vertebrae features include:
- Triangular Vertebral foramen
- Bifid spinous process (the spinous process splits into 2 distally)
- Transverse foramina (for the vertebral artery, vein and plexus of sympathetic nerves – however there are 2 vertebrae where this is not the case.
- C7: the vertebral artery runs around the vertebra, instead of passing through the transverse foramen. The vertebral vein and associated nerves are still present in the foramen.
- Atlas: the vertebral artery runs along the groove for the vertebral artery instead of through the transverse foramina (although some texts say the vertebra; artery runs through the transverse foramina and then across the posterior arch and through the suboccipital triangle before entering the foramen magnum)
C1, C2 and C7 are atypical. Describe the atlas
The ring-shaped first cervical vertebra (the atlas) supports the skull at the atlanto-occipital joint. No body or spinous process.
The atlanto-occipital joint between the lateral masses of C1 and the occipital condyles permitting nodding of the head, such as the neck flexion and extension that occurs ‘the yes movement’
These joints are synovial condyloid joints. Anterior and posterior atlanto-occipital membranes help prevent excessive movement of these joints.
The anterior articular facet articulates with the dens of the axis.
The atlas also has lateral masses on either side of the vertebral arch, which provide an attachment for the transverse ligament of the atlas.
The posterior arch has a groove for the vertebral artery and C1 spinal nerve.
Describe the axis
The second cervical vertebra (the axis) is the strongest of the cervical vertebra because C1, carrying the skull, rotates on it. The odontoid process (the dens) of the axis projecting superiorly from its body is held in position by a transverse ligament of the atlas that prevents horizontal displacement of the atlas. Spinous process is bifid.
C2 articulates anteriorly with anterior arch of the atlas (allows ‘no’ movement) and posterior with the transverse ligament of the atlas.
The dens articulates with the articular facet of the atlas, in doing so creating the medial atlanto-axial joint. This allows for rotation of the head independently of the torso. This is a pivot type synovial joint.
There are 2 lateral atlanto-axial joints which are formed by the articulation between the inferior facets of the lateral masses of C1 and the superior facets of C2. These are plane type synovial joints.
Describe the joints and foramina of the cervical vertebral column
- There are 2 joints that are present throughout the vertebral column. Firstly, the joint of the vertebral bodies which are the symphyses (secondary cartilaginous joints). The articulating surfaces of the adjacent vertebral bodies are joined by intervertebral discs. The second joint occurs at vertebral arches, formed by the superior and inferior articular processes of adjacent vertebrae. This is a plane type synovial joint.
- The cervical vertebrae 3 to 7 are characterised by a large vertebral canal because of the cervical enlargement of the spinal cord for the innervations of the upper limb.
- The spinous processes of C3 to C6 are short and bifid. (C6’s longer but not as long C7)
- C7 (vertebra prominens) is characterised by a larger, longer spinous process that can be palpated on the back of the neck. The spinous process does not bifurcate. C7 also has large transverse processes (but only vertebral veins and nerves pass through). C7 looks more like a thoracic vertebra.
- The foramina in the transverse processes of the cervical vertebrae transmit the vertebral arteries on their way to supply the brain; the transverse processes end laterally in 2 projections (anterior and posterior tubercles). The anterior tubercles of C6 are called carotid tubercles because the common carotid arteries may be compressed against them to control bleeding from these vessels.
- Lines to follow when assessing integrity: anterior, posterior and spinolaminar
Describe the ligaments of the spine
- Anterior Longitudinal Ligament: Strong, broad, fibrous band that covers and connects the anterolateral aspects of the vertebral BODIES and IV discs. The ligament extends from the pelvic surface of the sacrum to the anterior tubercle of C1 and the occipital bone anterior to the foramen magnum. This ligament maintains the stability of the IV joints and limits extension of the vertebral column.
- Posterior Longitudinal Ligament: Much narrower, somewhat weaker band. The ligament runs within the vertebral canal along the posterior aspect of the vertebral bodies, attached mainly to the IV discs from C2 to the sacrum. This ligament helps prevent hyperflexion of the vertebral column and posterior herniation of the IV discs. It is well innervated with nociceptive (pain) nerve endings.
- Ligamenta Flava: the laminae of adjacent vertebral arches are joined by broad, pale, yellow elastic fibrous tissue which extend almost vertically from the lamina above to the lamina below. The ligamenta flava resist separation of the vertebral laminae by arresting abrupt flexion of the vertebral column and thereby preventing injury to the IV discs.
- Interspinous and Supraspinous ligaments: adjacent spinous processes are united by weak, almost membranous interspinous ligaments and strong fibrous supraspinous ligaments. The supraspinous ligaments merges superiorly with the nuchal ligament.
- Nuchal ligament: the strong median ligament of the neck is a continuation of the supraspinous ligament from C7 upwards, composed of thickened fibroelastic tissue extending from the external occipital protuberance and posterior border of the foramen magnum to the spinous processes of the cervical vertebrae. Because of the shortness of the C3-C5 spinous processes, the nuchal ligament substitutes for bone in providing muscular attachments (for the rhomboids and trapezius).
- Transverse ligament of the atlas: connects the lateral masses of the atlas and in doing so anchors the dens in place.
Describe Fracture of the Dens
- Fracture of the dens may occur in a fall on the head; displacement of the fractured dens may injure the spinal cord, causing quadriplegia (paralysis of all limbs) or may injure the medulla of the brainstem, causing death. This type of facture can be viewed by an X-ray view of an open mouth (gaps change)
- Fractures of the dens make up around 40% of the axis and are most commonly caused by traffic collisions and falls.
- Often these fractures are unstable and are at high risk of avascular necrosis, due to the isolation of the distal fragment from any blood supply. As a result, fractures of the dens often take a long time to heal.
Describe a Burst fracture (Jefferson)
- Burst fracture of C1. A typical mechanism of injury is dividng head first into shallow water (head fall first from height – vertical fall onto an extended neck). This can compress the lateral masses of the atlas between the occipital condyles and the axis. This causes them to be driven apart, fracturing one or both of the anterior/posterior arches.
- If the fall occurs with enough force, the transverse ligament of the atlas may also be ruptured. Since the vertebral foramen is large, it is unlikely that there will be damage to the spinal cord at the C1 level. However there may be damage further down the vertebral column. Usually pain but no neurological symptoms. Damage to the arteries may occur.
Describe a Hangman’s fracture
Hangman Fracture (aka traumatic spondylolisthesis of axis) is a result of hyperextension and distraction.
The pars interarticularis, a bony column between the superior and inferior articular facets of the axis, is fractured. This fracture is virtually never seen in suicidal hanging (asphyxiation being the usual mode of death.
Major trauma such as a high speed motor vehicle acid is in fact the most common association, especially in fatal cases. Its name originates from the mechanism of sudden deceleration that occurs in traditional hanging.
Radiographic features include bilateral lamina and pedicle fracture at C2.
Such an injury is likely to be lethal, as either the fracture fragments or the force involved are likely to rupture the spinal cord, causing deep unconsciousness, respiratory and cardiac failure and death.
