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1. Orbit and Ocular Adenexa
AOrbit
1: Sinuses
The paranasal sinuses are cavities in the interior of the maxilla, frontal, sphenoid and ethmoidal bones. They vary considerably in size and shape in different individuals and at different ages. They are lined with mucoperiosteum and filled with air, they communicate with the nasal cavity through relatively small apertures.
All sinuses are lined by pseudostratified columnar ciliated epithelium.
Maxillary sinuses
The largest of the paranasal sinuses. Located in the body of the maxilla. The cavity is pyramid shaped. Its base forms part of lateral wall of the nose. The maxilla, the uncinate process of the ethmoid, the inferior concha and the perpendicular plate of the palatine bone all contribute to the lateral wall of the nasal cavity, part of which is the medial wall (base) of the maxillary sinus. The apex extends laterally into the apex of the zygomatic bone. The roof of the sinus is formed by the orbital plate of the maxilla and contains the infraorbital nerve and blood vessels. The floor is formed by the alveolar process. Sometimes, the bone that is separating the teeth from the sinus is missing. The anterior wall is related to the face and contains the canals for the anterior and middle superior alveolar nerves and blood vessels. The posterior wall is related to the infratemporal fossa and contains the posterior superior alveolar nerves and blood vessels.
The maxillary sinus communicates with the nose through an opening, the ostium,in the superior part of its medial wall and discharge into the middle meatus of the nose.
It reaches full size after the eruption of all permanent teeth.
-Nerve supply: The mucous membrane is supplied by the infraorbital nerve,from the ophthalmic V1 and the anterior, middle and posterior superior alveolar nerves, from the maxillary V2.
-Blood supply: This is from the anterior and posterior superior alveolar branches of the infraorbital and maxillary arteries respectively. Also the facial artery and the greater palatine artery is involved.
The veins drain the ostium and join the venous plexuses in the nose.
-Lymphatic drainage: The vessels pass through the ostium and drain into the submandibular nodes
Frontal sinuses
The two frontal sinuses lie within the frontal bone, separated by a bony septum. Both of the sinuses are triangular in shape extending upward above the medial end of the eyebrow and backward into the medial part of the roof of the orbit. The frontal sinus is usually incompletely divided into a number of recesses by bony partitions.
The anterior wall of the sinus is related to the fore head skin and the supraorbital and supratrochlear nerves. The posterior wall is related to the Anterior Cranial fossa, meninges,and the frontal lobe of the brain. The floor is related to the orbit and nose.
There is a communication with the nose via the infundibulum or the frontonasal duct. It opens into the hiatus semilunaris in the middle meatus, close to the openings of the anterior ethmoidal sinuses and the maxillary sinus.
These sinuses are rudimentary or absent at birth and are generally well developed between 7th and 8th years, but reach full size only after puberty.
-Nerve supply: The mucous membrane is supplied by a branch from the supraorbital nerve, from the ophthamic V1, as it passes through the supraorbital foramen.
-Blood supply: The arterial supply is from the supraorbital and anterior ethmoidal arteries. The veins drain into the venous plexuses of the nose and into the supraorbital vein.
-Lymphatic drainage: The lymphatic vessels drain into the submandibular nodes
Sphenoidal sinuses
These two sinuses lie within the body of the sphenoidbone. Of all the sinuses these vary most in their extent and development. Extension can be found as far as into the pterygoid processes or the greater wing of the sphenoid. It can partly surround the optic canal in the lesser wing of the sphenoid.
Most of the time the two sinuses are separated by a median septum. However, this septum usually is deviated to one side and makes that one of the sinuses is larger than the other.
The anterior wall is related to the nasal cavity and the ethmoidal sinuses. The posterior wall is related to the posterior cranial fossa and the pons. The cavernous sinus is located laterally to the sinuses. This contains the internal carotid artery and the abducent nerve.In front of the cavernous sinus, the sphenoid sinus is related to the orbital cavity. Superiorly the sinus is related to the Turkish saddle,sella turcica, which contains the hypophysis cerebri or the pituitary gland. Superior to this are the optic nerve and the Optic Chiasma. Inferiorly the sinus is related to the nasopharynx and the pterygoid canal.
These are minute cavities at birth and main development is after puberty.
The sphenoid sinus opens into the nasal cavity in the sphenoethmoidal recess above the superior concha.
-Nerve supply: The mucous membrane is supplied by the posterior ethmoidal nerves and the orbital branches of the pterygopalatin ganglion.(all from V2)
-Blood supply: The arterial supply is from the posterior ethmoidal arteries. The veins drain into the posterior ethmoidal veins.
-Lymphatic drainage: The lymphatic vessels drain into the retropharyngeal nodes.
Ethmoidal sinuses
These aircells lie within the ethmoidal bone between the nose and orbital cavity. Sometimes there’s an extension into the maxillary, sphenoidal, lacrimal, frontal and palatine bones. These aircells are usually grouped together into an anterior, middle and posterior group.
Inferiorly they are related to the nose. Superiorly they are related to the anterior cranial fossa and the frontal lobe of the cerebrum. Laterally they are related to the orbital cavity and medially they are related to the nose. The anterior group communicates with the nose through one or more openings into the ethmoidal infundibulum or the frontonasal duct. The opening is into the middle meatus of the nose. The middle group of aircells opens by one ore more orifices on or above the ethmoidal bulla into the middle meatus of the nose. The posterior group of aircells, which lie close to the optic canal, open by one orifice into the superior meatus of the nose above the superior concha.
Grow rapidly between 6 and 8 years old and after puberty.
-Nerve supply: The mucous membrane of the ethmoidal airsinuses is supplied by the anterior and posterior ethmoidal nerves and by branches of the pterygopalatine ganglion.
-Blood supply: The arterial supply is from the anterior and posterior ethmoidal arteries and the sphenopalatine artery. The veins correspond the arteries.
-Lymphatic drainage: The lymphatic vessels of the anterior and middle group of aircells drain into the submandibular nodes. The lymphatic vessels of the posterior group of aircells drain into the retropharyngeal nodes.
2: Bones comprising the orbital walls
Fig 1
Orbit
7 individual bones form the orbit:
1: The maxilla
2: The palatine bone
3: The zygomatic bone
4: The sphenoid bone
5: The frontal bone
6: The ethmoidal bone
7: The lacrimal bone
The orbital margin (rim) has a quadrilateral shape with rounded corners. In the adult the orbital margin is less high (35mm) than it is wide (45mm).
Supraorbital margin
-is formed by the frontal bone.
-at the junction of the rounded medial third and the sharp lateral two thirds you can find the supraorbital notch or foramen. This transmits the supraorbital nerve and blood vessels.
Medial margin
-formed above by the maxillary process of the frontal bone and below by the frontal process of the maxilla.
-the frontal process of the maxilla forms the anterior lacrimal crest.
-lower part of this margin is easily felt, because it is sharp, whereas the upper part is indistinct
Infraorbital margin
- is formed medially by the maxilla and laterally by the zygomatic bone.
Lateral margin
-is formed by the process of the frontal bone above and the process of the zygomatic bone below.
-the suture between these bones, the frontozygomatic suture, can be easily felt in the living subject.
- this is the strongest part of the orbital margin.
The walls of the orbital cavity are lined with periosteum and consist of a roof, medial wall, floor, and lateral wall. The apex is formed by the optic canal, at the medial end of the superior orbital fissure.
Aid:
Roof, Floor, Lateral wall, Medial wall
RMF L
No. of bones2432
Roof
The concave roof or superior wall of the orbit is formed by 2 bones:
1: the orbital plate of the frontal bone
2: the lesser wing of the sphenoid bone
-the fossa for the orbital part of the lacrimal gland is located anterolaterally behind the zygomatic process of the frontal bone.
-medially the fovea trochlearis, that is located approximately 4 mm from the orbital margin, forms the pulley of the superior oblique muscle
-the frontal lobe of the cerebral hemisphere and the anterior cranial fossa are separated from the orbit by the roof.
-the frontal sinus is located within the frontal bone.
Medial wall
The medial walls are almost parallel to each other.
The medial wall is the thinnest wall (lamina papyracea) and is formed by 4 bones, anterior to posterior:
1: the frontal process of the maxilla
2: the lacrimal bone
3: the orbital plate of the ethmoid bone
4: small part of the body of the sphenoid bone
Frontal Process of maxilla
-forms the anterior lacrimal crest
`forms the anterior part of the lacrimal fosa for the lacrimal sac.
Lacrimal bone
-lies posterior to the frontal process of the maxilla
-the anterior ½ contributes to the formation of the fossa for the lacrimal sac
Orbital plate of the ethmoid bone
-is largest bone, that forms the medial wall
-is a very thin and fragile bone,
-border the nasal cavity anteriorly and the ethmoid air cells and the sphenoid sinus posteriorly
Sphenoidal Bone
-a small portion is formed by the body of the sphenoid
-the sphenoidal sinus may reach this portion
On the anterior part of the medial wall is the lacrimal groove ( fossa) for the lacrimal sac.
-groove is formed by the lacrimal bone posteriorly and the frontal process of the maxilla anteriorly.
- groove is bounded in front and behind by the anterior and posterior lacrimal crests.
Floor
The thin floor of the orbit is formed by 3 bones:
1: the orbital plate of the maxilla
2: the orbital plate of the zygomatic bone
3: the orbital process of the palatine bone
The orbital plate of the maxilla separates the orbit from the maxillary sinus. The floor is continuous with the lateral wall anteriorly, but is separated from it by the inferior orbital fissure posteriorly. From this fissure the infraorbital grove is running forward and becomes the infraorbital canal about halfway the floor. This canal opens onto the face as the infraorbital foramen.
The floor slopes downward from posterior to anterior at approximately 20 degrees from the horizontal plane.
Lateral wall
The lateral wall is the thickest and strongest wall and is formed by 2 bones:
1: the zygomatic bone
2: the greater wing of the sphenoid bone
The lateral tubercle, (=Whitnall’s tubercle, marginal tubercle ), which is a small elevation of the orbital margin of the zygomatic bone, lies approximately 11mm below the frontozygomatic suture. This tubercle is the site of attachment , from before backwards, for:
- the aponeurosis of the levator muscle
- the lateral palpebral ligament
- the lateral check ligament and below it, the suspensory ligament of the eyeball
The zygomatic bone which forms the anterior third of the lateral wall, separates the orbit from the temporal fossa. The greater wing of the sphenoid bone which forms the posterior two thirds of the lateral wall, separates the orbit from the temporal lobe of the brain in the middle cranial fossa.
The superior orbital fissure separates the lateral wall from the roof posterior in the orbit.
3. Orbital foramina, ducts, canals and fissures
Foramina
The optic foramen
(optic nerve, the ophthalmic artery, sympathetic fibers from the carotid plexus)
The supraorbital foramen (blood vessels, supraorbital nerve)
The anterior ethmoidal foramen
-opens into the anterior cranial fossa at the lateral edge of the cribriform plate of the ethmoid bone
-transmits the anterior ethmoidal nerve and artery
- located in the frontoethmoidal suture.
The posterior ethmoidal foramen
-traverse the ethmoidal bone
-transmits the posterior ethmoidal artery and nerve, which supply the ethmoidal sinuses
-is located in the frontoethmoidal suture
The zygomatic foramina
-located in the zygomatic bone in its lateral aspect
-zygomaticfacial and zygomatictemporal nerve and artery
The nasolacrimal duct
-Travels inferiorly from the lacrimal fossa into the inferior meatus of the nose
-runs downward, backward and laterally
-is about 18mm long
The infraorbital canal
This is the anterior continuation of the infraorbital groove and exits 4mm below the inferior orbital margin.
It transmits the infraorbital nerve.
The optic canal
-lies in the lesser wing of the sphenoid, medial to the body of the bone
-situated at the apex of the orbit
-measures 4 to 10 mm long ( for MCQ 5mm)
-connects the middle cranial fossa with the orbit
-transmits
1 the optic nerve
2 meningeal sheaths and extension of the subarachnoid space
3 ophthalmic artery
4 sympathetic plexus
-the sphenoidal sinus lies close to it
-sometimes the ethmoidal sinus also lies very close to it.
Fissures
The superior orbital fissure
- lies between the lesser and greater wings of the sphenoid.
-lies below and lateral to the optic foramen.
-connects the middle cranial fossa with the orbital cavity.
-lies between the roof and lateral wall of the orbit.
-the widest part is at the medial end.
-about halfway the fissure on the greater wing of the sphenoid is a small sharp spine for the lateral rectus muscle
-the common tendinous tendon is attached to this spine on the greater wing.
Passing through the superior orbital fissure, laterally, outside the common tendinous ring are, from lateral to medial
1 lacrimal nerve
2 frontal nerve
3 trochlear nerve
( remember this as LFT= Liver Function Test)
4 superior ophthalmic vein ( drains into the cavernous sinus)
Passing within the common tendinous ring
1 upper and lower divisions of the oculomotor nerve,
2 nasociliary nerve and
3 abducens nerve
Passing medial to the common tendinous ring
The inferior orbital fissure
-lies between the greater wing of the sphenoid and the orbital plate of the maxilla
-connects the pterygopalatine and infratemporal fossae with the orbit
-is closed in the living subject by the periorbita and the muscle of Muller
-transmits
1 maxillary nerve, which immediately changes its name to infraorbital nerve.
2 transmits the zygomatic nerve, branches of the pterygopalatine ganglion
3 inferior ophthalmic vein, which drains into the pterygoid venous plexus.
After you have studied this chapter,
1correct any mistake you see with ‘italics, size 14’
2add anything else that you think might be asked in MCQ
and return it to me
AOrbit
1: Sinuses
Paranasal sinuses
- are cavities in maxilla, frontal, sphenoid and ethmoidal bones.
-most sinuses are rudimentary or absent birth
-enlarge during the eruption of the permanent teeth.
- are lined with pseudostratified columnar ciliated epithelium mucoperiosteum.
Maxillary sinuses (Fig 2A & 2B)
-is the largest of the paranasal sinuses and is pyramid shaped, with the base forming part of lateral wall of the nose.
-the anterior wall is related to the face.
-its roof is formed by the orbital plate of the maxilla and it contains the infraorbital nerves and blood vessels.
-the inferior orbital canal usually ridges the sinus from the roof to the anterior wall.
-the apex of the root of the two premolar and three molar teeth may produce a conical projection on the sinus floor.
-the posterior wall is related to the infratemporal fossa and it contains the posterior superior alveolar nerves and blood vessels.
-opens at the posterior end of the hiatus semilunaris situated in the middle meatus
-a second opening may lie posteriorly.
-it reaches full size after the eruption of all permanent teeth.
Nerve supply
- the mucous membrane is supplied by the infraorbital nerve and the anterior, middle and posterior superior alveolar nerves.
Blood supply
-is from the anterior and posterior superior alveolar branches of the infraorbital and maxillary arteries respectively.
-is also from the facial artery and the greater palatine artery.
-the veins drain through the ostium and join the venous plexus in the nose.
Lymphatic drainage
- the vessels pass through the ostium and drain into the submandibular nodes
Frontal sinuses
-the two frontal sinuses lie within the frontal bone, separated by a bony septum.