Skull and Scalp Flashcards
Outline the functions of the skull.
- houses brain, special sense organs, upper airways and proximal GIT
- provides surfaces for muscular attachments
- facilitates mandibular movements for mastication and speech
The skull without the mandible is called __________.
cranium
The cranium may be subdivided into 2 regions. Name them.
Neurocranium/cranial vault
Viscerocranium/facial skeleton
The neurocranium may be subdivided into two parts, the calvaria (skull cap) and the skull base. Compare them in terms of shape and mode of ossification.
The calvaria are flat bones, formed by intramembraneous ossification (hence may be called membranous neurocranium). Most of them consist of two tables and a diploe.
The bones of the skull base are relatively thicker and are formed by endochondral ossification (hence may be called cartilaginous neurocranium).
Name the four paired paranasal sinuses. (Named according to bones that house them)
maxillary, frontal, ethmoid and sphenoid
Briefly explain three sutural morphologies.
- Interlocked (serrated): has numerous projections that interlock
- Simple (butt-end): the margins of adjacent bones are smooth and meet end-to-end
- Overlap (beveled): border of one bone overlaps the adjacent bone
Identify unique features of the fetal/neonate skull.
- presence of fontanelles
- wider and more sutures
- unilaminar calvarial bones (no diploe)
- prominent frontal and parietal eminences [Diagram]
- relatively large orbits
- contracted (relatively small) viscerocranium due to underdeveloped sinuses
- unerupted teeth and absent alveolar processes (horizontal portion of maxilla that holds the tooth roots)
- rudimentary paranasal sinuses
- cranial base is relatively narrow, short and largely cartilaginous
- ununited bony parts eg. parts of temporal bone
- short, straight and wholly cartilaginous external acoustic meatus
- undeveloped parts: glabella, mastoid process and superciliary arches
- unique mandibular morphology
What is the unique mandibular morphology in neonates? (Hint: consider symphysis menti, the mandibular angle, coronoid and condylar processes, mental foramen)
- right and left mandible is separated by symphysis menti, which is absent in adults
- mandibular angle is obtuse
- The coronoid process is slightly lower than the condylar process. As a person grows, the coronoid process elevates itself quite significantly.
- the mental foramen lies nearer to the base of mandible in children, nearer to the alveolar margin in old people, and midway in adults
What are the extents of the scalp?
Anteriorly: superciliary arches
Posteriorly: superior nuchal lines
Laterally: external acoustic meatus and zygomatic arch
List the layers of the scalp from superficial to deep.
- skin
- subcutaneous dense connective tissue
- the occipitofrontalis muscle (epicranius) and its aponeurosis (galea aponeurotica)
- subaponeurotic loose connective tissue
- pericranium (periosteum of the skull)
Name the two main arteries involved in the blood supply to the scalp as well as their branches.
- Ophthalmic branch of internal carotid artery; gives supratrochlear, supraorbital arteries
- External carotid artery; gives superficial temporal artery, posterior auricular artery, occipital artery
- [Diagram: arteries of the scalp]
They form a rich anastomosis within the dense connective tissue layer of the scalp.
Why do scalp wounds bleed profusely?
- The blood supply to the scalp is made up of many anastomoses.
- The blood vessels to the scalp are adhered to dense connective tissue, preventing the vasoconstriction that normally occurs in response to damage.
- If a deep transverse cut on the skull reaches aponeurosis, frontalis and occipitalis will contract and hence aponeurosis will pull apart.
Why do scalp wounds heal faster?
The scalp is richly vascularized.
Why are scalp wounds often related to menengitis?
(HINT: Think about the bacteria due to the scalp wound. What does it do?)
Bacteria introduced into the scalp through a scalp wound can be transported through emissary veins to the meninges where they may cause meningitis.
What is the clinical relevance of the skin of the scalp?
It has numerous sebaceous glands, hence is a common site for sebaceous cysts.
What is the clinical relevance of the aponeurosis of the scalp?
Wounds on the scalp gape when the aponeurosis is cut transversely. Occipitalis and frontalis will contract hence pulling apart the aponeurosis. This may also contribute to profuse bleeding.
What is caput succedaneum?
This is the swelling/edema of the scalp of a newborn, most often brought by pressure from the uterus or vaginal wall during a head-first delivery. There is reduced venous return, hence accumulation of fluid within the scalp tissues.
State the clinical relevance of the anterior fontanelle in neonatal skulls.
- It can indicate the degree of intercranial pressure (if elevated, anterior fontanelle will bulge and hence we see that in meningitis or in hydrocephaly).
- It can be used as an acoustic window to perform cranial ultrasound.
- It permits access to the superior sagittal sinus.
- Through its lateral angle a needle may be passed into the lateral ventricles of the brain.
What are the regions of the foetal skull?
- Face
- Brow
- Vertex (best type of presentation for delivery since the suboccipito-bregmatic diameter [9.5 cm] is less than diameter of maternal pelvis [10 cm] hence less tedious in terms of vaginal delivery)
- Occiput
Appreciate these regions on a diagram.
Base of the cranial cavity is divided into 3 different fossae. Name them.
Anterior fossa
Middle fossa
Posterior fossa
What does the cranial cavity house?
the brain, meninges, the intracranial portions of cranial nerves, blood vessels and CSF
How can the skull be used as identification in medical legal aspects?
- Determination of sex
- Determination of chronological age
- Determination of racial origin
- Facial approximation
State the sensory innervation of the scalp.
Anterior division receives innervation from CN V
Ophthalmic nerve,
- Supratrochlear nerve
- Supraorbital nerve
Maxillary nerve,
- Zygomaticotemporal nerve
Mandibular nerve,
- Auriculotemporal nerve
Posterior division receives innervation from cervical nerves.
- greater occipital nerve (from dorsal rami of C2)
- third occipital nerve (from dorsal rami of C3)
- lesser occipital and greater auricular (from cervical plexus)
- The cribriform plate is a part of which bone?
- Name the structure that passes through the cribriform plate.
- ethmoid bone
- CN I (olfactory nerve)
Which bone forms the optic canal? Name the structures that pass through the optic canal.
- lesser wing of sphenoid bone
- ophthalmic artery, CN II (optic nerve)
- State the boundaries of the superior orbital fissure.
- What structures pass through the superior orbital fissure?
- greater and lesser wings of sphenoid
- CN III (oculomotor nerve)
- CN IV (trochlear nerve)
- CN VI (abducens nerve)
- CN V1 (ophthalmic nerve - first division of trigeminal nerve)
- superior ophthalmic vein
- State the boundaries of the inferior orbital fissure.
- State the structures that pass through the inferior orbital fissure.
- greater wing of sphenoid bone, zygomatic bone and maxillary bone
- zygomatic nerve [this is a branch of the maxillary division of the trigeminal nerve]
- infraorbital nerve and vessels [infraorbital nerve is the terminal branch of the maxillary nerve]
What structure passes through foramen rotundum?
Maxillary nerve (CN V2) (second division of trigeminal nerve)
What structures pass through foramen ovale?
- Mandibular nerve (third division of trigeminal nerve- CN V3)
- Accessory meningeal artery
- Lesser petrosal nerve (branch of CN IX - glossopharyngeal)
- Emissary vein
Acronym: MALE
What structures pass through the carotid canal?
internal carotid artery
internal carotid nerve plexus
What structures pass through the internal acoustic meatus?
- CN VII - facial nerve
- CN VIII - vestibulocochlear nerve
- Labyrinthine artery
Which structures pass through the jugular foramen? (7)
- CN IX - glossopharyngeal nerve
- CN X - vagus nerve
- CN XI - accessory nerve
- internal jugular vein
- inferior petrosal sinus
- sigmoid sinus
- posterior meningeal artery
Which structure passes through the hypoglossal canal?
CN XII - hypoglossal nerve
Which structures pass through foramen magnum (5)?
- medulla oblongata
- vertebral arteries and venous plexus
- meninges
- spinal roots of accessory nerves
- meningeal branches of vertebral arteries
Name the structure that passes through foramen cecum.
It transmits the emissary vein from the nose to the superior sagittal sinus.
State the boundaries of the anterior cranial fossa.
- anteriorly and laterally: inner surface of frontal bone
- midline: ethmoid bone
- posteriorly: body (medially) and lesser wings (laterally) of sphenoid
State the boundaries of the middle cranial fossa.
- At the midline, the boundary between the middle and anterior cranial fossae is the prechiasmatic groove (a smooth groove stretching between the optic canals across the body of the sphenoid).
- Anteriorly, the middle cranial fossa is separated from the anterior cranial fossa by the posterior border of the lesser wings of the sphenoid bone.
- The posterior border is formed by the superior border of the petrous part of the temporal bone.
State the boundaries of the posterior cranial fossa.
- anteriorly: superior border of the petrous part of the temporal bone
- posteriorly: internal surface of the squamous part of the occipital bone
- floor: basilar, condylar, and squamous parts of the occipital bone and the mastoid part of the temporal bone
State the contents of the anterior cranial fossa.
- The frontal lobe
- Olfactory bulbs and tracts
State the contents of the middle cranial fossa.
- Temporal lobes of the brain
- Hypophysis cerebri (pituitary gland)
- Parietal lobe
- Trigeminal ganglion
- Optic nerve and chiasma
- CN III - VI
State the contents of the posterior cranial fossa.
- occipital lobe
- pons
- medulla
- cerebellum
- cranial nerves VII - XII
What structures pass through foramen spinosum.
- middle meningeal artery and vein
- meningeal branch of mandibular nerve
Arrange the following foramina in the order in which they occur from anterior to posterior: optic canal, foramen cecum, superior orbital fissure, cribriform plate.
foramen cecum, cribriform plate, optic canal, superior orbital fissure
[Diagram: foramina of the skull]
Arrange the following foramina in the order in which they occur from anterior to posterior: foramen rotundum, foramen spinosum, foramen ovale
foramen rotundum, foramen ovale, foramen spinosum
[Diagram: foramina of the skull]
Arrange the following foramina in the order in which they occur from anterior to posterior: hypoglossal canal, carotid canal, jugular foramen, foramen magnum, internal acoustic meatus
carotid canal, internal acoustic meatus, jugular foramen, hypoglossal canal, foramen magnum
[Diagram: foramina of the skull]
What type of joint is formed by sutures of the skull?
Synarthroses
What do each of the four fontanelles become when they close?
Anterior fontanelle - bregma
Posterior fontanelle - lambda
Sphenoid fontanelle - pterion
Mastoid fontanelle - asterion
[Diagram: fontanelles]
In a neonate, why are sutures more and wider?
This is to allow some degree of compression during birth since the head is passing through the birth canal.
The metopic suture/frontal suture close in the first _____ years.
2
Name the fontanelles of the neonate skull and state the ages when they close.
- Anterior fontanelle - 2 yrs
- Posterior fontanelle - 2 months
- Sphenoidal fontanelles (paired) - 3 months
- Mastoid fontanelles (paired) - 1 yr
a) The largest transverse diameter in a neonatal skull is the biparietal diameter. TRUE or FALSE?
b) The biparietal diameter is the distance between ____________________.
a) TRUE
b) 2 parietal tuberosities [Diagram]
The pterion is a neurological landmark found at the junction of which bones ?
frontal, sphenoid, parietal and the squamous part of temporal bone
[Diagram]
The asterion is a neurological landmark found at the junction of which bones?
Temporal, occipital and parietal bones
[Diagram]
The inferior petrosal sinus and the sigmoid sinus form which vein?
Internal jugular vein
[Diagram]
Which structure passes through the stylomastoid foramen?
facial nerve (CN VII)
Which structures pass through the incisive foramen?
- nasopalatine nerve
- sphenopalatine artery
- [Diagram]
What is the clinical significance of the pterion?
The pterion overlies the anterior division of the middle meningeal artery, which ruptures following a blow in this region to form an extradural hematoma (a clot between the skull bone and the dura matter). If the clot is big, it may compress the brain leading to unconsciousness or even death. [Diagram] [Radiograph]
Further notes: Symptoms of an Epidural Hematoma
~ Brief loss of consciousness: after a head trauma, there is a brief loss of consciousness.
~ Alertness followed by decline: this is followed by a period of alertness that may last several hours before a subsequent loss of consciousness and decline in brain function.
~ Other symptoms include: severe headache, dizziness, nausea and vomiting, confusion, paralysis and enlarged pupil in one eye [the medical term for unequal pupil size is anisocoria].
Identify the most dangerous layer of the scalp giving 2 reasons.
Loose areolar connective tissue
REASONS:
1. Presence of emissary veins connecting the scalp veins and the intracranial venous sinuses. Scalp infections can spread through the emissary veins to the intracranial venous sinuses to cause venous sinus thrombosis.
2. Blood or pus can spread to the eye lids and the root of the nose (i.e. periorbital region) because of the attachment of the frontalis into the skin and not to the bone.
3. [Diagram]
Identify the layer of the scalp that constitutes the plane of avulsion giving a reason.
Loose areolar connective tissue layer
Reason: The superficial 3 layers usually peel off as a unit with their blood vessels (the superficial 3 layers are referred to as scalp proper).
Identify 4 weak points of the skull.
Pterion (weakest)
Orbital roof
Cribriform plate
Squamous temporal
Acronym: POCS
State the lymphatic drainage of the scalp.
- Posterior ½ of the scalp drain to occipital and posterior auricular nodes.
- Anterior ½ drain to the parotid nodes.
- The lymph eventually reaches the submandibular and deep cervical nodes.
What are emissary veins?
These are valveless veins that connect the superficial veins of the scalp with the diploic veins of the skull bones and, through them, with the intracranial venous sinuses.
A clinical relevance of the pericranium is Pott’s puffy tumor. Briefly describe what it entails and why would “tumor” be a misnomer.
[Clinical presentation of Pott’s puffy tumor]
It is a rare clinical entity characterized by a subperiosteal abscess associated with osteomyelitis. (Especially on the frontal bone)
The word “tumor” refers to cancerous growth causing swelling. Here, the swelling on the forehead is caused by the abscess but it is not a cancerous growth. Hence a misnomer.
Side note:
osteomyelitis: infection of a bone
At what age does the diploe form?
4 yrs
At what age does the mandibular symphysis (symphysis menti) close?
1 year
a) What is craniosynostosis?
b) Give examples of craniosynostosis.
a) It occurs when the fetal skull and facial bones fuse too soon in utero disrupting normal bone growth. Abnormal fusion of different sutures leads to unusual patterns of growth on the skull.
b) Scaphocephaly/dolichocephaly: fusion of the sagittal suture
[Scaphocephaly (1)] [Scaphocephaly (2)]
Plagiocephaly: flattening of one side; unilateral coronal suture fusion, rotational growth
[Plagiocephaly (1)] [Plagiocephaly (2)]
Brachycephaly/steeple (tower skull) flat head: fusion of the coronal suture
[Brachycephaly]
Trigonocephaly: fusion of the metopic suture
[Trigonocephaly (1)] [Trigonocephaly (2)]
Oxycephaly or turricephaly: fusion of coronal and any other suture
Pansynostosis: premature closure of three or more cranial sutures, presents as microcephaly
Kleeblattschaedel: a severe form of pansynostosis that prevents as bulging of the different bones of the cranial vault
[Kleeblattschaedel]
The styloid and mastoid processes are parts of the ________ bone.
temporal
Name the foramen traversed by each of the following arteries.
1. accessory meningeal artery
2. middle meningeal artery
3. posterior meningeal artery
- foramen ovale
- foramen spinosum
- jugular foramen
