2. ETHMOID BONE
• SINGLE DELICATE BONE
• NUMEROUS AIR CELLS – ETHMOID SINUSES
• HORIZONTAL PLATE – CRIBRIFORM PLATE
• VERTICAL PLATE – PERPENDICULAR PLATE – POSTERIOR
PART OF THE SEPTUM.
4. 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.
6. • 2 PARTS – Horizontal medial lamella and Vertical or Oblique
• 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 –
• Anterior ethmoidal artery piercing the dura medially – thinnest
area (0.05mm) in skull base.
8. • Ethmoid roof configuration differentiated based on the length of
the lateral lamella of cribriform plate – KEROS
• Type 1 – 1-3mm
• Type 2 – 4-7mm
• Type 3 – 8-17mm
9. • 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
• ETHMOID CELLS :
• Anterior and Posterior.
10. • Lateral to the perpendicular plate – two masses of air cells –
• 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
12. • Anterior cells – anterior to ground lamella – open in middle
• 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
13. • 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.
14. • 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
15. 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
17. • Medial end at cribriform plate – thinnest part of the anterior
• Oblique canal.
• Runs at a variable distance as much as 17mm below the roof of
• Attached to it by a Bony Mesentry.
• Lies 1-2mm behind the point where the anterior wall of bulla
meets skull base.
18. • If bulla does not extend to skull base, artery lies in suprabullar
• Endoscopic finding : artery is present where the vertical
posterior wall of the frontal sinus turns to form the horizontal
• On entering the cranial cavity – turns anteriorly along the
cribriform plate in a sulcus called the ETHMOIDAL SULCUS.
• Gives off a meningeal branch.
20. • 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.
21. 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
• Anteromedially – enter into cranial cavity – level of cribriform
• Traverses the cribriform plate in an anterior direction – passes in
one of its foramina to re enter the nasal cavity.