Anatomy and pattern recognition of the skull, facial bones and teeth

Question 1

Bony anatomy of the skull and associated joints

Answer 1

Bone classification of the skull

Cranial bones - mainly flat for cranium
parietal bones, temporal bones, frontal bone, occipital bone, ethmoidal bone and Sphenoid bone

Facial bone - irregular
mandible, maxillary bones, zygomatic bones and orbit

Question 2

Bones of the skull

Answer 2

Most complex bony structure,

the skull can be divide into 2 sets of bones, those of the cranium (cranial bones) and Facial bones.

Most of the skull bones are flat.

Skull bones in the adult are firmly locked by sutures. Main sutures are Sagittal, Coronal and Lambdoid sutures. Additional small sutures sphenoparietal, frontozygomatic and occipitomastoid,

The interior of the skull is divided into 3 fossae, anterior, middle and posterior.

Provide points of entry and exit to the skull through foramina and fossae.

Question 3

What are the Cranial bones?

Answer 3

Cranial bones provide:
muscle attachment.
protection for the brain, and organs of hearing and balance.

Cranium formed by 8 cranial bones:
Paired:
parietal bones (2)
temporal bones (2)
Unpaired:
Frontal bone (1)
Occipital bone (1)
Ethmoidal bone (1)
Sphenoid bone (1)

Question 4

What are the Parietal bones?

Answer 4

Form large part of the roof of the cranium (superior and lateral aspect of the skull). Curved and rectangular in shape. The 4 largest sutures occur where the parietal bones articulate.

Articulation:
Frontal bone – Coronal suture
Parietal bone – Sagittal suture
Occipital bone – Lambdoid suture
Temporal bone and Greater wing of sphenoid – Squamous suture

Features
Internally contains grooves for middle meningeal arteries.
Temporal ridges (superior and inferior)
Sagittal sulcus

Question 5

What is the occipital bone?

Answer 5

Forms posterior wall of the skull
Internally forms the posterior cranial fossa
Divided into 3 parts - Squamous, lateral and basilar
Features
Foramen magnum

Externally
External occipital protruberence
External occipital crest
Occipital condyle
Superior nuchal line
Median nuchal line
Inferior nuchal line

Internally
Internal occipital protruberence
Internal occipital crest
Transverse sulcus - groove for transverse sinus.
Groove for sigmoid sinus
Jugular process

Articulates with
Parietal bone
Temporal bone
Sphenoid bone
1st cervical vertebra

Question 6

What are the temporal bones?

Answer 6

Form the infero–lateral aspects of the skull.

Contains three main regions
Squamous,
Tympanic,
Petromastoid
mastoid,
petrous.

Squamous region

Thin portion of bone.
Articulates with
the parietal bone.
The sphenoid
the mandible

Features
Zygomatic process, with the zygomatic bone forms the zygomatic arch.
Articular fossa
Articular tubercule

Tympanic region

Feature
External auditory meatus.
Styloid process

Question 7

Temporal bones: Squamous region

Answer 7

Thin portion of bone.
Articulates with
the parietal bone.
The sphenoid
the mandible

Features
Zygomatic process, with the zygomatic bone forms the zygomatic arch.
Articular fossa
Articular tubercule

Question 8

Temporal bones: Tympanic region

Answer 8

Feature
External auditory meatus.
Styloid process

Question 9

Temporal bones: Mastoid part

Answer 9

Features

Mastoid process
Mastoid notch
Mastoid foramen
Sigmoid sulcus

Question 10

Temporal bones: Petrous

Answer 10

Looks like a miniature mountain ridge.
Posterior slope lies in the posterior cranial fossa. Anterior slope is in the middle cranial fossa

Articulates with the
Occipital bone posteriorly
Sphenoid bone anteriorly

Features
Contains middle and inner ear cavities. Housing organs of hearing and balance.
Arcuate eminence
Internal auditory meatus
Stylomastoid foramina
Carotid canal
Jugular fossa
Foramen lacerum

Question 11

What is the Sphenoid bone?

Answer 11

Butterfly-shaped bone. Spans the with of the middle cranial fossa. Forms the central wedge and as such considered key stone of the cranium.

Articulates with all the other cranial bones

The sphenoid bone consists of:
Body centrally (contains sphenoid sinus) Posterior aspect forms the dorsum sellea that culminate to the posterior cliniod processes
Greater wing of sphenoid
Lesser wing of sphenoid project posteriorly to form the anterior clinoid processes
Pterygoid processes – project inferiorly from body, anchor muscle for chewing

Features.
Sella turcica (Pituitary fossa) Hollowed out forming a deep depression.
Anterior clinoid processes
Posterior clinoid processes
Optic foramina
Optic groove
Foramen ovale
Foramen spinosum
Foramen rotundum
Superior orbital fissure
Pterygoid canal

Question 12

`what is the Ethmoid bone?

Answer 12

Delicate bone. Contains ethmoid sinuses

Features
Cribiform plate – forms roof of nasal cavity. Punctured by tiny holes called olfactory foramina allow the passage of olfactory nerves to the smell receptors in the nasal cavity in the brain.
Perpendicular plate – forms superior part of nasal septum.
Lateral mass – either side of the perpendicular plate containing ethmoid sinuses
Crista gali – projects superiorly from the cribiform plate is a process. Dura mater outer covering of the brain is attached to this area, helps secure the brain.

Articulates with
Sphenoid bone
Frontal bone
Lacrimal bone
Palatine bone
Vomer
Nasal bone
Maxilla

Question 13

What are facial bones?

Answer 13

Form the framework of the face:
Contain cavities for the sense organs (sight, taste, smell)
Provide opening for food; and air entry and exit
Secure teeth
Act as an attachment for muscle.

Bones:
Inferior nasal concha (Paired) – forms part of nasal cavity

The vomer (Single) – forms part of nasal septum

The Nasal bone (Paired) – forms the bridge of the nose

The Lacrimal bone (Paired) – form part of orbit

Palatine bone (Paired) – forms part of nasal cavity and a small part of the orbit. Posterior part of hard palate

Mandible (Paired)
Maxillary bones (Paired)
Zygomatic bones (Paired)

Question 14

what are maxillary bones?

Answer 14

All facial bones with the exception of the mandible articulate with it.
Form the upper jaw and the central portion of the facial skeleton

Features
Alveolar margin - contains sockets in which the upper teeth are embedded.

Palatine process – forms anterior part of the hard palate

Frontal process – articulates with the frontal bone

Maxillary sinus – air filled cavity within the maxillary bone. Largest of the paranasal sinuses

Zygomatic process – articulates with the zygomatic bone

Infra orbital foramina – permits nerves (zygomatic and maxillary to pass) and blood vessels to the face.

Anterior nasal spine – located immediately below the nasal aperture.

Question 15

What are zygomatic bones?

Answer 15

Irregular shape. Form the cheek commonly referred to as the “cheek bone”.

Features
Frontal process - articulates with frontal bone.
Temporal process – zygomatic process of the temporal bone.
Also articulates with the maxillary bone inferiorly.

Question 16

What is an orbit?

Answer 16

Formed by:
Frontal bone
Maxillary bone
Ethmoid bone
Lacrimal bone
Palatine bone
Lesser wing of sphenoid
Greater wing of sphenoid
Zygomatic bone

Features:
Superior orbital fissure
Inferior orbital fissure –
Optic foramina – passage of optic nerve

Question 17

What is the mandible?

Answer 17

U shaped bone. Largest strongest bone of the face.

Features
Body
Ramus
Mandibular angle
Mandibular notch
Coronoid process
Mandibular condyle

Alveolar margin - contains sockets in which the lower teeth are embedded.

Symphysis Menti or Mandibular symphysis – Line of fusion of the two mandibular bones.

Mental foramina

Mandibular foramina – located on medial surface of each ramus.

Oblique (ridge) line
Mylohyoid line
Mylohyoid groove
Submandibular fossa
Sublingual fossa

Question 18

Ligaments

Answer 18

Fibrous capsule
Temperomandibular ligament
Sphenomandibular ligament
Stylomandibular ligament

Blood supply –
Branches of the superficial temporal and maxillary arteries
Nerve supply –
Branches of the mandibular part of the trigeminal nerve

Question 18

What is the Temporomandibular joint (TMJ)?

Answer 18

Type
Synovial condylar joint

Articular surfaces
Temporal bone: - anterior part of the mandibular fossa
Head of the mandible.

Special feature
Articular disc

Question 18

Muscles responsible for Movements of the TMJ

Answer 18

Temporalis muscle
Masseter muscle
Medial pterygoid muscle
Lateral pterygoid muscle
Platysma muscle
Suprahyoid muscles
Geniohyoid muscle
Mylohyoid muscle
Stylohyoid muscle
Digastric muscle
Infrahyoid muscle

Movements:
Depression
Elevation
Protrusion
Retraction
Lateral movement

Question 19

What are the function of your teeth?

Answer 19

to
Cut - incisors
Tear - canines
Grind food – molar and premolar

Question 19

Teeth description

Answer 19

Primary and permanent dentitions have formed by
age 21

Primary – 20 deciduous teeth that erupt at intervals
between 6 and 24 months

Permanent – enlarge and develop causing the root
of deciduous teeth to be resorbed and fall out
between the ages of 6 and 12 years

All but the third molars have erupted by the end of adolescence
There are usually 32 permanent teeth

Tooth structure consists of 3 divisions
Crown
Root
Neck

And consists of 3 componants
Enamel
Dentin
Pulp cavity

Question 20

Skull – depressed skull fracture: description, causes, symptoms, diagnosis, complications, treatment, differential diagnosis

Answer 20

Description
Nearly always the result of trauma
Part of the skull is pressed into the brain

Causes
Trauma

Symptoms
Recent trauma and head wound

Diagnosis
Plain film is almost never the primary imaging now
CT is the modality of choice. The fracture will be shown in detail along with any soft tissue injuries

Complications
Damage to underlying brain can cause haematomas, haemorrhages and CSF leaks

Treatment
Surgical management1

Differential diagnosis

Question 21

Osteomas: description, causes, symptoms, diagnosis, complications, treatment, differential diagnosis

Answer 21

Description
Benign primary bone tumour

Causes
Can be associated with some syndromes but aetiology is unknown

Symptoms
May present as a slow growing mass

Diagnosis
Mainly occur in the paranasal sinuses, skull vault and nasal bone

Complications
Pain and disfigurement

Treatment
They are benign and are only removed if there are causing complications

Differential diagnosis
Any other cause of bony growth including Pagets

Diagnosis
Plain film
Appear as round lesions.
CT
Appear as round hyperdense lesions.
MRI
Appearances depend on the amount of bone marrow within the osteoma but on T1 normally give low signal

Question 22

Skull fractures: description, causes, symptoms, diagnosis, complications, treatment, differential diagnosis

Answer 22

Description
Fracture of a skull vault bone. They are a marker of the severity of the injury. They can be classified as a base of skull fracture or skull vault fracture

Causes
Trauma

Symptoms
Depends on mechanism of injury

Diagnosis
Plain film is rarely used now.
CT is the first line investigation
CT is excellent at assessing the bony anatomy and allowing 3D reconstruction

Complications
Dependant on the underlying damage to the brain

Treatment
Conservative or surgical depending on severity

Question 23

Paget’s disease: description, causes, symptoms, diagnosis, complications, treatment, differential diagnosis

Answer 23

Description
Common metabolic bone disorder which results in extensive bone remodelling

Causes
Unknown. More common as you age

Symptoms
Localised pain
Increased bone size
Decreased range of motion

Diagnosis
Bloods can show elevated levels indicative of Paget’s

Complications
Pathological fractures and OA

Treatment
Medication to reduce bone growth and improve pain
Painkillers

Differential diagnosis
More rare bone disorders

Diagnosis in detail
Plain film and CT
Will see large, well defined lytic lesions in the skull. Sometimes sclerotic areas are also seen
Skull appears to fall over the facial bones

MRI
Bone has a speckled appearance with low signal intensity.
Nuclear medicine
Bone scintigraphy with Technicism is very sensitive but not specific

Question 24

Skull metastases: description, causes, symptoms, diagnosis, complications, treatment, differential diagnosis

Answer 24

Description
Secondary cancer deposits in the bony skull

Causes0
Common in patients with skeletal metastatic disease
Cancers that most frequently metastasize are
Breast, lung, prostate, renal cell, multiple myeloma

Symptoms
Can cause pressure on the brain leading to seizures
In 90% of cases there will be bony metastases elsewhere

Diagnosis
Lytic lesions are the most common, but breast and prostate primary may result in sclerotic lesions.

Complications
May cause seizures or vision issues

Treatment
Many patients are at end of life so palliative care is given. Radiotherapy, chemotherapy and surgery can be used.

Differential diagnosis
Nonmalignant disease or Paget’s

Question 24

What is Le Fort fractures?

Answer 24

Description
Fractures of the midface – which separate the midface from the skull base.

This includes fractures of the pterygoid plates and:
Nasal fossa
Inferior orbital rim
Zygomatic arch

Causes
trauma
Symptoms
Pain and visible facial injury

Question 24

Multiple myeloma: description, causes, symptoms, diagnosis, complications, treatment, differential diagnosis

Answer 24

Description
Is a malignant bone neoplasm and the most common in adults

Causes
Unknown but more common in older age

Symptoms
Bone pain, anaemia, renal failure

Diagnosis – see across

Complications
Pathological fractures

Treatment
Incurable

Differential diagnosis
Metastases

Diagnosis
Radiography has a role in both diagnosis and management

It can diagnose, assess for complications and assess disease progression

Common appearances on plain film are lots of round lytic bone lesions and osteopaenia.

Plain film – a skeletal survey is often performed for diagnosis and monitoring.

However more than 40% bone destruction is needed for it to be seen so it has a high false negative rate

CT is more accurate – specificity of 90%, and sensitivity of 70%. Normally done as a low dose scan

MRI whole body is more sensitive but what are the possible issues with this?

PET-CT can help work out the disease distribution.1

Question 25

Orbital blow out fractures: description, causes, symptoms, diagnosis, complications, treatment, differential diagnosis

Answer 25

Description
Describes a fracture of one of the walls of the orbit.

Causes
Typically, a fist or ball direct hit

Symptoms
Air around the eye (orbital emphysema)
Numbness in the area
The eye may be slightly displaced.

Diagnosis
Plain film is not recommended due to poor sensitivity
CT is the most used modality. Does not require contrast. CT can assess the fracture and the presence of bleeding.

Complications
Damage to the eye

Treatment
Generally now conservative management
Surgery if it’s a significant injury with risk of long term vision problems

Question 26

Dental abscess: description, causes, symptoms, diagnosis, complications, treatment.

Answer 26

description: Acute infection of the periapical tissue around the tooth root

causes: Damaged tooth enamel allowing bacteria into the tooth

symptoms: Pain and swelling.
Infection symptoms

diagnosis: In the early stage (up to the first 10 days) there may be no imaging findings
OPG / CT may show a lucency at the tooth root

complications: Can result in loss of the tooth
Infection can spread to the neck / brain

treatment: Antibiotics

Question 27

Mandible fracture: description, causes, symptoms, diagnosis, complications, treatment, differential diagnosis

Answer 27

description: One of the most common facial fractures (60-70%).

causes: Trauma, commonly road traffic collisions

symptoms: Patient may be unable to close or open their mouth. Pain.

diagnosis: Facial bones and OPG’s are common imaging methods, although CT is becoming more common as a first line imaging method.
MRI is the best imaging method for assessing the soft tissue damage.

complications:

treatment: Conservative
If the mandible is displaced the patient may need surgery with / without fixation

differential diagnosis