Sphenoid sinus and optic nerve

Sphenoid sinus and optic nerve ;O.N DEHISCENCE;O.N PROTRUSION.
SLIDES COURTESY : DR SOMSHEKHAR REDDY

1. SPHENOID SINUS AND OPTIC NERVE Presented by : Dr.Soma S ekhar Reddy Moderated by : Dr.Neeta Sharma DEPARTMENT OF ENT , JLNH & RC , BHILAI

2. OPTIC NERVE: THE ANATOMY Four segments Intraocular segment Intraorbital segment Intracanalicular segment Intracranial segment

3. POSTERIOR PARANASAL SINUSES Posterior Ethmoid Sinuses Number ( 1 – 7 ) Onodi ( Sphenoethmoidal cell) lateral or superior to sphenoid sinus. Behind Basal lamella of Middle Turbinate. Drain into Superior/ Supreme meatus. Sphenoid sinus Number - 2 Right and Left. Divided by Intersphenoid septum. Located in Body of Sphenoid. Sphenoethmoidal recess via sphenoid ostium Anatomic relationships of the posterior ethmoid cells, sphenoid sinus, optic nerve, and internal carotid artery are critical when performing endoscopic sinus surgery

4. POSTERIOR ETHMOIDAL AIR CELLS ONODI CELL First described by Adolf Onodi (1857–1920) Definition “ Onodi cell as the most posterior ethmoid cell which pneumatises laterally and superiorly to the sphenoid and is intimately associated with the optic nerve.” Incidence : (3.4% -11.7%). Prevalence : ( 7% - 65%) . Importance : Close relationship with the optic nerve (ON), SS, ICA and Pituitary fossa. Failure to identify – during Posterior ethmoidectomy – risk to ON, ICA. Identification : Multiplanar CT scanning. (axial, coronal, and sagittal )

5. the most posterior ethmoidal air cell extending superolaterally to the sphenoid sinus (SS) . ONODI CELL

6. SPHENOID SINUS Dimensions : 20mm (height) x 23mm (width) x 17mm (depth) Volume : 3-10 ml Embryology : “ Pneumatisation” At birth - Erythropoietic marrow 2 years - HRCT 7 years - Reaches sella 14 years - Adult size Sphenoid Ostium (4mm) landmarks Posterior Choana 10.9 mm ( 5.7 - 21.5 mm) Anterior nasal spine 7 cms Anterior end of superior turbinate 2.2 cms Intersphenoid septum ( Single / Multiple/ Absent)

7. INTER SPHENOID SEPTUM VARIATIONS

8. DORSAL VIEW POSTERIOR CLINOID PROCESS

9. ANTERIOR VIEW

10. RELATIONS OF SPHENOID SINUS Optic Nerve Superolaterally , ICA Posterolaterally Maxillary And Vidian Nerve Inferiorly ANTERIOR CRANIAL FOSSA PITUITARY GLAND - FOSSA MIDDLE CRANIAL FOSSA CHOANA ROOF OF NASOPHARYNX CAVERNOUS SINUS & ITS CONTENTS POSTERIOR CRANIAL FOSSA CLIVUS BRAINSTEM POSTERIOR ETHMOIDS CAVERNOUS SINUS & ITS CONTENTS

11. ANATOMICAL VARIABILITY PNEUMATISATION OF SPHENOID SINUS PROTRUSION OF OPTIC NERVE & ICA DEHISCENCE OF OPTIC NERVE & ICA

12. SPHENOID PNEUMATIZATION HAMMER & RADBERG CLASSIFICATION ( SAGGITAL ) 1.Conchal 2.Presellar 3.Sellar Agenesis Primary ciliary dyskinesia Craniofacial syndromes

13. Sellar type further classified into six types based on the pneumatization direction . ( Wang J classification ) Sphenoid body Lesser Wing Anterior Lateral V. Clival VI. Combined Greater wing Pterygoid Full lateral Subdorsal Dorsal Occipital Combined Dorsal & Occipital

14. SPHENOID BODY LESSER WING ANTERIOR

15. GREATER WING PTERYGOID FULL LATERAL LATERAL TYPES

16. CLIVAL TYPES SUBDORSAL DORSAL COMBINED

17. CORONAL TYPE I Previdian pneumatization extends from the midline to the medial edge of VC. CORONAL TYPE II , Prerotundum / Intercanal Extends to the lateral edge of FR; CORONAL TYPE III Postrotundum the pneumatization extends lateral to the FR NEW CLASSIFICATION SPHENOID PNEUMATISATION

18. CLASSIFICATION OF LATERAL PTERYGOID RECESS PNEUMATIZATION

19. STERNBERG CANAL Also called Lateral craniopharyngeal canal Incomplete fusion of greater wing of sphenoid with basipshenoid bone. Weak spot of skullbase . Lead to temporal lobe encephalocele into lateral recess of sphenoid sinus

20. OPTIC NERVE & POSTERIOR PARANASAL SINUSES The optic nerve (ON) has an intimate relationship to the posterior ethmoid cells(PEC) and sphenoid sinus (SS). The position of ON may be changed due to various degrees of pneumatization of the sinuses. A surgically dangerous area is pneumatization of PEC behind the annulus tendineus communis where the optic nerve is unprotected by surrounding extraocular muscles, fatty tissue and periorbita . Anatomical variations of the posterior paranasal sinuses greatly affect : - the choice of surgical approaches . the character of postoperative complications .

21. DIVIDED O.N INTO 4 TYPES DEPENDING ON ITS RELATIONSHIP WITH SPHENOID SINUS TYPE I – The ON is immediately adjacent to lateral or superior wall of the SS without contact or impinging on the sinus wall, TYPE II – The ON indents the SS on the lateral wall without contacting the PEC TYPE III – The ON courses through the SS rather than simply run adjacent to it, and is surrounded by the pneumatized sinus for at least 50% TYPE IV –The ON runs immediately lateral to both the SS and PEC with the contact to the ethmoidal sinus usually located at the sphenoethmoidal junction. DE LANO et al. CLASSIFICATION (1996).

22. TYPE I – The ON is immediately adjacent to lateral / superior wall of the SS without contact or impinging on the sinus wall, TYPE-I

23. TYPE II – The ON indents the SS on the lateral wall without contacting the PEC TYPE-II

24. TYPE III – The ON courses through the SS rather than simply run adjacent to it, and is surrounded by the pneumatized sinus for at least 50% TYPE-III

25. TYPE-IV TYPE IV – The ON runs immediately lateral to both the SS and PEC with contact to the ethmoidal sinus usually located at the sphenoethmoidal junction.

26. O.N DEHISCENCE Dehiscence is defined as : absence of visible bone density located between the sinus and the optic nerve. Optic Nerve Dehiscence was defined as absence of the bony wall overlying the optic nerve although some studies mention in terms of thickness of the separating bony wall.

27. O.N PROTRUSION Protrusion of the O.N into the S.S is defined as optic nerve surrounded by pneumatised space. Protrusion of the O.N in most studies was defined as a bulging of the optic canal into the sphenoid sinus cavity so as to cause exposure of more than half of the circumference of the nerve, with or without defects in the bony margins. Protrusion of ON may coexist with Ipsilateral pneumatization of anterior clinoid process or migration of the posterior ethmoid air cells posteriorly into the upper sphenoid – sphenoethmoidal or Onodi cells. A surgically dangerous area is pneumatization of PEC behind the “annulus tendineus communis ” where the optic nerve is unprotected by surrounding extraocular muscles, fatty tissue and periorbita

28. Coronal CT scans were preferred for the detection of protrusion of the ON into sphenoid sinus.

29. Axial scans are better for details of the complete course of the optic nerve to sphenoid and ethmoid sinuses.

30. Pre-intervention assessment of sphenoid sinus pneumatization is mandatory in approaching the sella and skull base structures. The sphenoid sinus is a natural route for access to sellar , parasellar , suprasellar , and clival regions in surgery of the ventral skull base, Meckel’s cave and Middle cranial fossa . SURGICAL APPROACHES

31. Multiple approaches to the sphenoid sinus. transseptal , transantral , transpterygoid , transethmoidal , transpalatal endonasal endoscopic approach endoscopic transnasal transsphenoidal method

32. Conclusion The variations in the extensions of pneumatization of the sphenoid sinus may facilitate entry into areas bordering the sphenoid sinus and play a role in the selection of a surgical approach to lesions bordering the sinus. Pre-intervention assessment of sphenoid sinus pneumatization is mandatory in approaching the sella and skull base structures either via the nose or open skull base surgery to avoid injury of the nearby structures and reduce the possibility of CSF leakage. A surgically dangerous area is pneumatization of posterior ethmoid cells behind the annulus tendineus communis where the optic nerve is unprotected by surrounding extraocular muscles, fatty tissue and periorbita . Uncomplicated sphenoid sinus – CT scan Complicated sphenoid sinus – MRI scan