Ethmoid bone anatomy

Anatomy of the ethmoid bone, Ethmoid bone anatomy, Anterior ethmoidal artery, posterior ethmoidal artery, Rule of six, Kero's classification, ethmoidal arteries

1. DR.SHILPA M J ANATOMY OF ETHMOID BONE AND ETHMOIDAL ARTERIES

2. ETHMOID BONE SINGLE DELICATE BONE NUMEROUS AIR CELLS – ETHMOID SINUSES HORIZONTAL PLATE – CRIBRIFORM PLATE VERTICAL PLATE – PERPENDICULAR PLATE – POSTERIOR PART OF THE SEPTUM.

3. CRIBRIFORM PLATE Fits into the notch in the frontal bone. Separates the nose from anterior cranial fossa Perforated by many foramina – transmits – olfactory nerves , anterior and posterior ethmoidal arteries. Upper surface – midline projection – CRISTA GALLI .

4. ANTERIOR VIEW

5. 2 PARTS – Horizontal medial lamella and Vertical or Oblique lateral lamella Lateral lamella articulates with the frontal bone . Skull base – Ethmoid Fovea – medially by lateral lamella (thin bone – 0.2mm) and laterally by frontal bone (thick bone – 0.5mm ). Anterior ethmoidal artery piercing the dura medially – thinnest area (0.05mm) in skull base .

6. POSTERIOR VIEW

7. Ethmoid roof configuration differentiated based on the length of the lateral lamella of cribriform plate – KEROS CLASSIFICATION Type 1 – 1-3mm Type 2 – 4-7mm Type 3 – 8-17mm

8. Posterior attachment – Horizontal plane – along lamina papyracea and perpendicular plate of the palatine bone up to the roof of the posterior choana . UNCINATE PROCESS : Articulates anteriorly - Lacrimal bone Posteriorly – Inferior turbinate and perpendicular plate of the palatine bone. ETHMOID CELLS : Anterior and Posterior.

9. Lateral to the perpendicular plate – two masses of air cells – ETHMOID SINUSES. Bounded – Medially – Middle and Superior Turbinate Laterally – Paper thin lamina papyracea . MIDDLE TURBINATE : Anterior attachment – saggital plane – frontonasal process of maxilla and cribriform plate. Turns laterally – coronal plane – attached to the lamina papyracea – BASAL OR GROUND LAMELLA

10. SUPERIOR VIEW

11. Anterior cells – anterior to ground lamella – open in middle meatus. Posterior cells – Posterior to ground lamella – Superior meatus or Spheno ethmoidal recess. The Ethmoidal Bulla – Large and Fairly constant anterior ethmoid air cell. The ethmoid cells – incomplete – superiorly and posteriorly – completed by superior by frontal bone and posteriorly by sphenoid bone.

12. PATHS OF PNEUMATIZATION : Anterosuperiorly : into frontal bone – FRONTAL SINUS Superiorly : above ethmoid bulla over the orbit and behind frontal sinus – SUPRAORBITAL CELL Inferolaterally : Roof of the maxillary sinus – HALLER CELL Posteriorly : Above sphenoid sinus – ONODI CELL .

13. Anteriorly : Lacrimal bone and frontonasal process of maxilla – AGGER NASI CELLS Superiorly : Frontal recess – different types of frontal cells Isolated cells – within ethmoidal infundibulum – INFUNDIBULAR CELLS .

14. ETHMOIDAL ARTERIES ANTERIOR ETHMOID ARTERY : Branch of ophthalmic artery – given off in orbit Enters nose, traverses across the roof of the ethmoidal sinus in an anteromedial direction and leaves the nose at lateral lamella of cribriform plate to enter cranial cavity. ORBITOCRANIAL CANAL – traverses through this canal. Lateral end – suture line of the frontal bone and the lamina papyracea

15. ANTERIOR AND POSTERIOR ETHMOIDAL ARTERIES

16. Medial end at cribriform plate – thinnest part of the anterior cranial fossa. Oblique canal. Runs at a variable distance as much as 17mm below the roof of the ethmoid . Attached to it by a Bony Mesentry . Lies 1-2mm behind the point where the anterior wall of bulla meets skull base.

17. If bulla does not extend to skull base, artery lies in suprabullar recess. Endoscopic finding : artery is present where the vertical posterior wall of the frontal sinus turns to form the horizontal base skull. On entering the cranial cavity – turns anteriorly along the cribriform plate in a sulcus called the ETHMOIDAL SULCUS . Gives off a meningeal branch.

18. Re-enters nasal cavity on either side of the crista galli . Passes in a groove along the inner surface of the nasal bone – supplying upper part of the septum and lateral nasal wall. Appears on the external surface of the nose through a nottch between the nasal bone and the upper lateral cartilage.

19. Posterior ethmoid artery Arises from ophthalmic artery in the orbit. Passes through the fissure between the frontal bone and the lamina papyracea 6mm in front of the optic foramen to enter nasal cavity. Anteromedially – enter into cranial cavity – level of cribriform plate. Traverses the cribriform plate in an anterior direction – passes in one of its foramina to re enter the nasal cavity.

20. Supplies the upper and posterior part of the septum .

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