Norma basalis (skull base)Norma basalis (skull base)Dr kifayat khan

o Mphil Anatomyo IBMS KMU

o Kaif_ayubian@hotmail.com

Objectives Objectives To identifies the bones of

the skull base (inferior view) as well as their boundaries.

To know the important anatomic structures passing in and out of base of skull

BoundriesBoundries

bounded in front by the incisor teeth in the maxillæ.

laterally by the alveolar arch, the lower border of the zygomatic bone, the zygomatic arch and an imaginary line extending from it to the mastoid process and extremity of the superior nuchal line of the occipital.

Base of skull is formed by the following bones

1) Hard palate formed by Palatine processes of the maxillæ and palatine bones

2) The vomer3) Sphnoid bone with

I. the pterygoid processesII. the under surfaces of the

great wingsIII. spinous processes

4) Temporal bone with squamæ and mastoid and petrous portions

5) Occipital bone

1)Hard palate 1)Hard palate Bounded in front and laterally

by the alveolar arch Has two bones,palatine process

of maxilla and palatine bone Two palatine process of

maxilla are joined by median palatine suture

And with palatine bone by transverse palatine suture

Posterior most limit is posterior nasal spine

ForamenForamen behind the incisor teeth is the

incisive foramen Posteriorolatrally is the

greater palatine foramen, for the transmission of the descending palatine vessels and anterior palatine nerve

Behind is lesser palatine foramina

2) vomer2) vomer Above the hard palate are the

choanæ (posterior nasal apertures ) separated by the vomer.

Each is bounded above by the body of the sphenoid, below by the horizontal part of the palatine bone, and laterally by the medial pterygoid plate of the sphenoid.

At the superior border of the vomer may be seen the expanded alæ of this bone

3)Sphenoid bone3)Sphenoid bone It has

Lateral and medial pterygoid process

The under surfaces of the great wings

Lateral to medial plate is scaphoid fossa, for the origin of the Tensor veli palatini, and at its lower extremity the hamulus, around which the tendon of this muscle turns.

The lateral pterygoid plate forms the medial boundary of the infratemporal fossa.

The great wing of sphenoid bone have 3 foramens I. Foramen ovale II. Foramen spinosumIII. Foramen Rotendum

i) Foramen Ovale Located at the base of the lateral

pterygoid plate Transmit

1. Mandibular Nerve (CN V3)2. Accessory meningeal nerve3. Lesser petrosal nerve4. Emissary vein (Cavernous sinus to pterygoid plexus)

ii) Foramen spinosum It is an aperture in the

greater wing of the sphenoid posterolateral to foramen ovale.

Transmit :- 1. Middle meningeal artery &

vein. 2. Emissary vein.3. Nervous spinosus

(Meningeal branch of mandibular nerve)

iii) Foramen rotendum

Is actually a canal in the base of the greater sphenoid wing, is situated just inferior and lateral to the superior orbital fissure. The canal transmits the maxillary nerve ( V2) and emissary veins.

iv) Foramen Lacerum It is located at the base of medial pterygoid plate, at the junction of sphenoid ,petrous temporal apex, medially by basilar portion of the occipital boneStructures passing whole length

Meningeal branch of Ascending pharyngeal artery

Emissary veinOther structures partially traversing

Internal carotid artery Greater petrosal nerve.

Petrous part of temporal bone has

carotid canal for ICA and sympathetic plexus.

Its apex forms boundary of foramen lacerum

Medial to the styloid process,its petrous part overlay the jugular foramen.

Jugular foramen transmits inferior petrosal sinus the glossopharyngeal Vagus nerve accessory nerves the transverse sinus

5) Occipital bone5) Occipital bone Behind the nasal cavities is the

basilar portion of the occipital bone, with pharyngeal tubercle

The foramen magnum Located behind basi-occipit

bounded laterally by the occipital condyles

transmits the medulla oblongata

the accessory nerves the vertebral arteries the anterior and posterior

spinal arteries

The occipital condyles lies lateral to foramen magnum

They articulate with the atlas.

hypoglossal canal Located Superior to the occipital

condyle Transmission hypoglossal nerve meningeal artery.

Behind the foramen magnum is the external occipital crest ending above at the external occipital protuberance, while on either side are the superior and inferior nuchal line

References References 1. Imaging of skull base: Pictorial essay Abhijit A Raut , Prashant S Naphade,

and Ashish Chawla. Indian J Radiol Imaging. 2012 Oct­Dec; 22(4): 305–316.

2. Imaging of the Anterior Skull Base :Hemant Parmar,MD, SachinGujar,MD et.al. Neuroimag Clin N Am 19 (2009) 427–439.

3. CT and MR Imaging of the Central Skul Base. Part 1: Techniques, Embryologic Development, and Anatomy. Fredj Lame, MD, Lyn Nadel, MD, Ira F. Braun, MD. RadloGraphics 190; 10:59 1­602

4. Imaging of the Central Skull Base Alexandra Borges, MD. Neuroimaging Clinics of North America Volume 19, Issue 3, August 2009, Pages 441–468.

5. Skull base embryology: a multidisciplinary review. Di Ieva A1, Bruner E, Haider T et.al Childs Nerv Syst. 2014 Jun;30(6):991­1000.

6. Som and curtin.

7. http://www.med.wayne.edu/diagRadiology/Anatomy_Modules/axialpages/Overview.html