Correlative Clinical Anatomy of the Head

Joel G. Soria, MD

Development of the skull

The base of the skull develops by endochondral ossification

The brain and cranial nerves develop before the skull, so when the chondrocranium develops, its components form around the nerves and form foramina.

The chondrocranium ossifies from a number of centers.

The last piece of cartilage to ossify is between the body of the sphenoid bone and the occipital bone, just anterior to the foramen magnum: this is the spheno-occipital synchondrosis. Its epiphyseal plate exists for the growth in length of the base of the skull and it ossifies at age 25.

THE HEAD Osteology of the skull

Introduction: superior part of the body that is attached to the trunk by the neck

Composition: the brain and its protective coverings, the ears, and the face

The Cranium Introduction:

The cranium (skull) is the skeleton of the head

Parts: � the neurocranium / Cranial Vault � the viscerocranium / Facial Bones

The Head

The head is formed mainly by the skull with the brain and its covering meninges enclosed in the cranial cavity.

The special senses, the eye and the ear, lie within the skull bones or in the cavities bounded by them.

The brain gives rise to 12 pairs of cranial nerves, which leave the brain and pass through foramina and fissures in the skull.

All the cranial nerves are distributed to structures in the head and neck, except the 10th, which also supplies structures in the chest and abdomen.

Bony Anatomy

Bones of the Skull

The skull is composed of several separate bones united at immobile joints called sutures. The connective tissue between the bones is called a sutural ligament. The mandible is an exception to this rule, for it is united to the skull by the mobile temporomandibular joint.

The bones of the skull can be divided into those of the cranium and those of the face. The vault is the upper part of the cranium, and the base of the skull is the lowest part of the cranium.

Skull

divided into CRANIUM (neurocranium) and FACIAL BONES (viscerocranium)

Cranium

Consists of 8 bones, which form the calvarium and the cranial base – Calvarium composed of external and internal tables of compact bone separated by a layer of spongy bone (diploe) – Cranial base articulates with the atlas, the bones of the facial skeleton, and the mandible

Frontal bone: 1

 Parietal bones: 2

Occipital bone: 1

Temporal bones: 2

Sphenoid bone: 1

Ethmoid bone: 1

Craniumfacial bones

Zygomatic bones: 2

 Maxillae: 2

 Nasal bones: 2

Lacrimal bones: 2

 Vomer:1

 Palatine bones: 2

Inferior conchae: 2

Mandible: 1

Cranium

A - Frontal B - Parietal (2) C - Occipital D- Temporal (2) E - Sphenoid F - Ethmoid

Quick Hints CRANIAL BONES

All cranial bones are

unpaireD EXCEPT

PARIETAL and

TEMPORAL bone

Memory Aide CRANIUM

what are the bones

that compose the

cranium

S

T

E

P

O

F

STEP OFF MY SKULL

PHENOID

EMPORAL

THMOID

ARIETAL

CCIPITAL

ACIAL

Memory Aide CRANIUM

Suture

Bones of the cranium are joined by sutures

coronal suture (A) - frontal bones and parietal bones

sagittal suture (B) - parietal bones

lambdoidal suture (C) - parietal bones and occipital bone

Pterion

Junction of the frontal, parietal, sphenoid and temporal bones

Thinnest part of the calvarium

Superficial to the anterior branch of the middle meningeal artery

Clinical Correlate SKULL FRACTURE AT PTERION

lateral skull fracture at the pterion may lacerate the middle meningeal artery

– result: epidural hematoma – CT scan: biconvex lens-

shaped hematoma

–  Hx/PE: initial lucid asymptomatic interval, followed by deterioration

fontanelles

At birth, the anterior fontanelle is a diamond-shaped area between the 2 frontal bones and the 2 parietal bones.

It pulsates and bulges when the baby cries.

It closes by 18 months to 2 years and is then known as the bregma

anterior fontanelle

triangular in form and situated at the junction of the sagittal suture and lambdoidal suture

Generally closes in 6–8 weeks from birth.

A delay in closure is associated with congenital hypothyroidism.

Posterior fontanelle

bregma

superior aspect of the skull anterior to the vertex

︎  junction of the frontal and sagittal sutures

LAMBDA

posterior aspect of the skull superior to the external occipital protuberance

 junction of the sagittal and lambdoid sutures

Facial Skelton

Formed by 14 bones enclose the orbits, nasal

cavity, oral cavity, and paranasal sinuses

Facial Bones

A - Zygomatic (2) B - Maxillae (2) C - Nasal bones (2) D - Lacrimal (2) E - Vomer F - Palatine (2) G - Inf concha (2) ︎ H - Mandible

Quick Hints CRANIAL BONES

All Facial bones are

unpaireD EXCEPT

vomer and mandible.

Cranial base

Divided into 3 shallow compartments: A - anterior cranial fossa B - middle cranial fossa C - posterior cranial fossa

Contain foramina and fissures that transmit blood vessels, and cranial nerves and their branches

Anterior cranial fossa

Anterior cranial fossa

APERTURE BONE CONTENTS Perforations in cribriform

plate Ethmoid CN I

middle cranial fossa

F. RotundumF. Ovale

F. Spinosum

Optic Canal

F. Spinosum

Superior orbital fissure

middle cranial fossa

APERTURE BONE CONTENTS

Optic canal Lesser wing of sphenoid

CN II, ophthalmic artery

Superior orbital fissure

Between lesser and greater wings of sphenoid

CN III, IV, V1, VI, superior ophthalmic vein

F. rotundum

Greater wing of sphenoid

CN V2

F. ovale CN V3, lesser petrosal nerve

F. spinosum Middle meningeal artery

Foramen lacerum

Petrous temporal and sphenoid

Internal carotid artery

posterior cranial fossa

posterior cranial fossa

Memory Aide CRANIUM

Through which skull

openings do the branches

of the trigeminal nerve

(CN V) EXIT ?

Memory Aide CRANIUM

S-R-O

foramen Spinosum = V1 (ophthalmic) foramen Rotundum = V2 (maxillary) foramen Ovale = V3 (MANDIBULAR)

Clinical Correlate NEONATAL SKULL

Disproportionately large cranium relative to the face

Growth of maxillary sinus, mandible and maxilla facilitates increase in length

Absent mastoid process at birth (develops in first 2 years of life)

Clinical Correlate FONTANELLE

unossified membranous intervals (fontanelles)

– anterior fontanelle • diamond-shaped• closed by 18 mos

– posterior fontanelle• triangle-shaped• closed by end of first year

︎ depressed in dehydration

︎ bulging in increased ICP

︎ ping-pong ball-like

Clinical Correlate BASILAR SKULL FRACTURE

most common in the middle cranial fossa

︎ clinical manifestations – epistaxis

– CSF otorrhea

– CSF rhinorrhea

– hemotympanum

– Raccoon eyes • periorbital ecchymoses

– Battle sign • mastoid

Clinical Correlate NASAL FRACTURE

mostcommonfacialfracture– becauseoftheprominenceofthenose

︎ mostaresimpleandarereducedunderlocalanesthesia

Clinical Correlate MAXILLOFACIAL FRACTURE

Clinical manifestations – extensive facial swelling – midface mobility– teeth malocclusion – CSF rhinorrhea– diplopia ︎ Classified using the Le Fort System

Clinical Correlate MAXILLOFACIAL FRACTURE

Clinical Correlate MAXILLOFACIAL FRACTURE

Clinical Correlate MAXILLOFACIAL FRACTURE

Clinical Correlate BLOWOUT FRACTURE

Trauma may tear the orbital floor, causing displacement into the maxillary sinus

︎ damaged structures– paper thin portion of the

ethmoid (lamina papyracea) – infraorbital nerve

• altered sensation to the skin of the cheek, upper lips and gums

Clinical Correlate BLOWOUT FRACTURE

depressed fractures– most dangerous type– pond fracture in children ︎ comminuted fractures– broken into several pieces ︎ linear fractures –  most frequent type –  at the point of impact (coup) or opposite (countercoup)