Extracranial head and neck

Extracranial head and neck

1)      Development of the face, lips and palate

a)      The ventral aspect of a fetal head showing the three processes:

i)        Fronto-nasal = face derived

(1)    Projected downwards from the cranium. Two olfactory pits

(2)    Nose, nasal septum, nostril and philtrum

ii)      Maxillary  = nose derived

(1)    Fuse with frontonasal process on each side – cheecks and upper lip (excl phitrum), upper jaw and palate

(2)    Groove between the frontonasal process and the maxillary process is called the nasolacrimal groove. During the 7^th week exctoderm invaginates this groove to form the nasolacrimal duct.

iii)    Mandibular = jaw derived

iv)    Abnormalities

(1)    Cleft palate

(a)    A bifid uvula

(b)   Partial cleft – soft palate and posterior part of the hard palate

(c)    Complete cleft –

(i)     Unilateral – full length of the maxilla

(ii)   Bilateral – the palate is cleft and the anterior V which seperates the premaxilla completely

(2)    External angular dermoid

(a)   

2)      The Tongue

a)      Development of the Tongue

i)        Develops from the I, III, IV pharyngeal arches

ii)       Anterior 2/3 Tongue

(1)    Tuberculum impar – fourth week

(2)    Lateral tongue swellings

iii)    Thyroid divertivulum

(1)    Foramen Caecum (thyroid diverticulum)

iv)    Posterior 1/3

(1)    Midline swelling

(a)     II pharyngeal Arch -  Copula

(b)   III pharyngeal Arch - hypobranchial eminence

(2)    Nerves

(a)    Muscles, CN XII except Mm palatoglossus (X)

(b)   Sensory,

(i)     Anterior 2/3,

1.       V3 – Mandibular branch – Arch I

2.       Taste buds – VII chorda tympani, Arch II

(ii)   Posterior 1/3

1.       Sensory and taste buds CN IX, Arch III

2.       Small part CN X, Arch IV

(3)    Entrance to larynx

3)      The Thyroid Gland

a)      Swelling in the 4^th week on the Apex of foramen cecum on the developing tongue.

b)      The decent of the thyroid, showing possible ectopic thyroid tissue or thyroglossal cysts, and also the course a thyroglossal fistula. Further decent of the thyroid may take place retrosternally into the superior mediastinum (remember the decent is anterior)

i)        Lingual thyroid

ii)      Suprahyoid thyroglossal fistula

iii)    Tract of thyroid decent and of thyroglossal fistula

iv)    Thyroglossal cyst or ectopic thyroid

v)      Pyramidal lobe

vi)    Retrosternal goitre

4)      Osseous Anatomy of the facial skeleton

a)      Synchondrosis or immovable sutures

b)      3 groups of bony struts

i)        Coronal Strut

(1)    Anterior: Frontal, nasal, alveolar process

(2)    Posterior: posterior wall of the maxillary antra, pterygoid process

ii)      Sagittal Strut

(1)    Medial and lateral walls of the maxillary antra, orbits and the nasal septum

iii)    Horizontal struts

(1)    Orbital floor and roof, cribiform plate, the zygomatic process, hard palate

c)       Skull frontal view

i)        Frontal bone, Maxilla, Zygoma

ii)      Supraorbital ridge, Supraorbtal foramen, Infraorbital foramen, Mental Foramen

iii)    Greater wing of the sphenoid           

d)      Lateral view

i)        Bregma

ii)      Pterion

iii)    Frontal bone, Glabella, Nasion

iv)     Temporal Fossa, TM Joint, Infratemporal fossa

v)      Pterygoid Process

e)      Plain radiographs

i)        OM: Occipito-mental radiograph (Water’s view). The petrous ridges should be projected just below the  maxillary  antra. Best view for the maxillary antra. Look for the lucency of the canal for the posterior superior alveolar nerve in the lateral maxillary antral wall.

(a)    Sinus - Frontal, Ethmoid, Maxillary

(b)   Lines – Innominate line and Upper Anterior Rim of the middle cranial fossa / greater wing of the sphenoid

(c)    Nasal septum and Zygomatic arch

(2)    671, 826, 827 Grants

ii)       OF: Occipito-frontal radiograph, Caldwell View. The Petrous Ridges should be projected over the lower third of the orbit. This is the best frontal view for the Ethmoid and frontal sinuses. Note the foramen rotundum, which always lies immediately below the supraorbital fissure.

(1)    Foramen rotundum also lies above the canines.

(2)    Structures

(a)    Frontal sinus, Crista gali, Ethmoid sinus, planum sphenoidale, Floor of the pituitary fossa,

(b)    Lesser wing of the sphenoid, greater Wing of the Sphenoid, Superior orbital fissure, Pertrous Edge, Foramen rotundum, Lateral border of the lateral pterygoid process.  

iii)     Lateral radiograph of the facial bones. Note the V-shaped shadows of the Zygomatic recess of the maxillary antra and the shadows of the inferior and the middle conchae. The posterior walls of both antra are visible.

(1)    Structures

(a)    Lateral orbital roof, medial orbital roof, Sphenoid sinus, pituitary fossa

(b)   Posterior wall of the maxillary sinus, Middle Concha and Inferior Concha, Hard palate and Soft Palate , V-Shaped Zygomatic recess of the maxillary sinus.

(c)    Prevertebral soft tissue

iv)     Diagram of Dolan’s three lines of reference on the OM projection. Lines 2 and 3 form Dolans elephant. These lines are useful visual cues for facial symmetry in excluding fractures.

5)      The facial Musculature

a)      CN VII, Facial muscles of expression, and dilators and constrictors of orifices of eye, ear, nose and throat ( mouth)

b)      Muscles of mastication (Temporalis, Lateral Pterygoid, Medial Pterigoid, Masseter ) by CN V3 – trigeminal nerve

c)       MRI demonstrating the muscles of mastication. Axial and Coronal. The axial image follows intravenous gadolinium DTPA demonstrates normal enhancement of the pharyngeal mucosa.

i)        Axial

(1)    Temporalis, Lateral Pterygoid, Medial Pterigoid, Masseter, Submandibular gland

(2)    Nasopharynx and Sphenoid sinus

ii)       Coronal

(1)    Nasolacrimal duct, Maxillary sinus, Temporalis, Masseter, Lateral Pterygoid, Levator veli palatine, Longus Capitus

6)      The Infratemporal and the Pterygopalatine fossae

a)      CT images of the skull base demonstrating the Pterygopalatine and Infratemporal fossae and related anatomy.

i)        Lowest scan – shows the Pterygopalatine canal which communicates with the mouth

(1)    Grant 617, 624, 702

ii)       Spenopalatine foramen is seen in the opening to the nasal cavity posterior to the middle turbinate, Grant 695, 699, 700

iii)     The horizontal canals of the foramen Rotundum, and the perterygoid canal (Vidian )  link the pertyrigoid fossa to the foramen lacerum. The lateral opening of the petrygopalatine fossa into the Infratemporal fossa is called the pterygomaxillary fissure.

7)      The mandible and temporomandibular joint

a)      Diagram of the mandible. The masseter and the medial pterygoid muscles inset on the outer and inner aspacts of the angle of the mandible, respectively. The lateral pterygoid muscle inserts on the neck and the temporalis inserts on the coronoid process.

i)        Mandibular foramen, mental foramen, mental protuberance, alveolar process, mandibular notch

b)      Dental panoramic radiograph (or orthopantomogram) of the mandible and maxilla. This technique in which the x-ray tube and cassette rotate synchronously and reciprocally around the patients head, gives a good survey of the upper and lower jaws.

i)        Hard palate, Nasal septum, Zygomatic recess, Maxillary Sinus (Pull teeth may create a communication between the maxillary sinus and the oral cavity)

ii)       Coronoid process of the mandible, Temporomandibular joint, styloid process, mandibular canal,

iii)     Peridontal membrane, Lamina dura, Incisor medial and lateral, Canine, Premolar 1 and 2, Molar 1,2,3

c)       Schematic diagram of the Temporomandibular joint

i)        Structures

(1)    Bones

(a)    Articular tubercle, Roof of the mandibular fossa

(b)   Mandibular condyl

(2)    Compartments

(a)    Superior Joint compartment and Inferior Joint compartment function as separate joints that do not communicate.

(3)    Bilaminar zone, Anterior band and posterior band.

d)      Arthrography of Temporomandibular Joint. Between 0.2 and 0.4 ml of contrast medium have been introduced into the lower joint compartment. Note the forward transition of the mandibular head and disc as the mouth opens and the posterior pooling of the contrast medium.

i)        Sagittal proton density (PD) MRI of the Temporomandibular Joint are better than T1W images in distinguishing the disc from surrounding tissues. T2W give and arthroscopic effect that may be useful for effusions and perforations.

8)      The Teeth

a)      Schematic Diagram of the tooth

b)      20 Deciduous teeth

c)       32 Permanent teeth, 8 in each quadrant. Eruption age:

i)        1^st molars; 6 years

ii)       Central Incisors; 7 years

iii)       Lateral incisors; 8 years

iv)     First premolars; 9 years

v)      Second premolars; 10 years

vi)     Canines; 11 years

vii)   Second molars; 12 years

viii)  Wisdom teeth; 18 years

d)      Abnormal lamina dura – look for hyperthyroidism

9)      Nasal cavity

a)      Deviation of the nasal septum is present on CT in 25% of the population

b)      Lateral radiograph of the nasal bones. The sutures and grooves for the branches of the nasocilliary nerves should not be mistaken for fractures.

c)       Diagram cartilaginous and bony components

d)      Diagrams of the lateral wall of the nasal cavity.

i)        Only the posterior ethmoid cells open into the superior meatus

ii)       Only the nasolacrimal duct opens into the inferior meatus

iii)     Frontal, Anterior and Middle Ethmoid ostia (posterior Ethmoid is in the superior meatus), Maxillary Sinus in the middle meatus

e)      Each of the paired sphenopalatine foramina lies immediately behind the superior meatus and transmits the nasopalatine nerve and vessels to the nasal cavity. The communicate with the pterygopalatine fossa and provide a conduit for infection or neoplasm to reach the orbit and cranial cavity.

f)       Mucosa is highly vascular with erectile cavernous tissue on the middle and inferior conchae and on the anterior nasal septum. Periodic swelling of alternative sides of nasal mucosa every 2 to 3 hours. Asymmetric congestion seen on MRI.

10)   The paranasal sinuses and ostiomeatal complex

a)      Coronal CT series on bone window settings demonstrating the anatomy of the paranasal sinuses and osteomeatal complex

b)      Look for a persistent metopic suture separating the frontal sinus.

c)       Maxillary sinus. 10% have hypoplasia of the maxillary sinus, and results in increased density on plain radiological films, don’t confuse this with inflammation.

d)      The roots of the molars or premolars may project into the sinus and is covered by a thin layer of bone and mucosa.

11)   The oral cavity, tongue and salivary glands

a)      T1W MRI of the head coronal

b)      T1W axial MRI of the floor of the mouth

12)   The salivary glands

a)      Intravenous contrast-enhanced axial CT through the parotid gland. Note the typical attenuation of the adult parotid gland

b)      Parotid sialogram. Note the long branching ductal pattern. The tip of the cannula is adjacent to the second upper molar tooth.

c)       Diagram of the submandibular and sublingual glands. The submandibular gland (grant 666,681,762,763,779,796,806,831) wraps around the posterior boarder of the mylohyoid muscle giving superficial and deep portions. Note the course of the diagastric muscle which takes origin from the mastoid notch of the temporal bone, passes through the sling of the hyoid bone (which divides it into anterior belly and posterior belly)  to insert into the inner aspect of the mandible.

d)      Submandibular sialogram. The duct branches are typically shorter than those within the parotid gland. Submandibular duct (Wharton Duct), is also 5 cm long, runs forward with the lingual nerve. Opens in the sublingual papilla on the floor of the buccal cavity.

13)   The pharynx

a)       

14)   The facial layers of the neck and the parapharyngeal space

15)   The Larynx

16)   Thyroid and parathyroid glands

17)   The craniocervical lymphatic system

18)   Cervical Arteries

19)   Duplex sonography of the cervical arteries

20)   Venous drainage of the head and neck

21)   Brachial plexus