At the level of Sphenoid Sinus
- Scanogram, CT and Cadaver coronal section at the level of the Sphenoid sinus.
- Check list.
- Surgical Importance.
Anatomy:
- Sphenoid sinuses.
Fig. 126: Coronal section Scanogram at the Sphenoid sinus level.
Fig. 127: Coronal section in CT Scan at the Sphenoid sinus level.
Fig. 128: Coronal section in cadaver at the Sphenoid sinus level.
Fig.129: Representative line diagram of CT Scan at Coronal section at the Sphenoid sinus level.
Fig. 130: Correlation of CT Scan, Cadaver section and representative line diagram at the level of the Sphenoid sinus.
-Extent of sphenoid pneumatization.
-Presence ofOnodi cellsOptic nerve and Internal carotid artery prominence.
- Dehiscence of bone over optic nerve or carotid artery.
- Sulge and dehiscence of vidian nerve and maxillary branch of trigeminal nerve.
- Number, position and course of intersinus septa.
- Look for presence of horizontal septa, which indicates presence of Onodi cells.
- Intersinus septa attachments to Optic nerve or Internal carotid artery.
- Anterior clinoid process pneumatization andpresence of recess between optic nerve and Internal carotid artery. |
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Surgical importance
Instrumentation within the sphenoid could be dangerous when bone over the Optic neiie or Internal carotid artery is dehiscent . Care should be taken in cases where the intersinus septa is ending on Carotid artery or Optic nerve. Optic nerve injury will result in blindness and injury to Internal carotid artery will be catastrophic. When multiple septi are present in diseased sphenoid, all scpti needs to be resected in order to clear the disease from all chambers. Otherwise the disease may persist. When anterior clinoid process is pneumatizcd, there may be a recess between optic nerve and carotid artery. Disease clearance from this reccs» could be difficult and dangerous. |
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Sphenoid Sinuses:
Development:
Begins : In the 3rd fetal month.
At birth: May be Conchal.
Develops from : A mucosal invagination into the sphenoid bone from the posterosuperior (ecess of the nasopharynx.
Completion: Usually completes at the age of 14-15 years.
Pneumatization & Growth : Starts in the third year and generally ends in the fourteenth year.
Types of pneumatization: (Fig. 117-122)
Conchal (5%)
Presellar(28%)
Sellar(67%)
Fig. 131: Plain X-Ray of Skull, lateral showing Conchal type of Sphenoid.
Fig. 132: C-Arm image intensifier image showing Presellar type of Sphenoid.
Fig. 133: CT Scan Sigittal section showing Sellar type of Sphenoid.
Agenesis: Rare.
Visibility :At an early age.
Chambers : Usually two, one on each side. Almost always asymmetrical divided by thin bony intersinus septa, usually off the midline and occasionally dehiscent or absent. The septa can terminate on the carotid or the optic canal.
Adult size (Average):
Height: 19.5 (5-33) mm.
Width: 17.4 (2.5-34) mm.
Depth: 23.2 (4-44) mm.
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Variations : Congdon has aptly described the sphenoid sinus as "the most variable in form of any bilateral cavity or organ in the human body". Sphenoid sinus is a bilateral pneumatization of the sphenoid bone and
degree of pneumatization, size, shape and the number of septa vary even from side to side. Pneumatization may extend as far as the ciivus, foramen magnum, the lesser wing, the anterior clinoid process, root of the pterygoid process, the foramen lacerum and the occipital bone. Agenesis of the sinus occurs in about 1 % of cases.
The walls of the sphenoid sinus vary in thickness, depending on its pneumatization. The more extensive the pneumatization the thinner the walls. Generally the anterosuperior wall and the floor are thickest. Lateral wall and floor of the sphenoid sinuses have characteristic ridges and recesses formed due to the projection of vital neural and vascular structures.Vidian nerve and maxillary nerve may bulge into the floor and lateral wall respectively.
Most significant are the bulges formed by the optic nerve and carotid artery on the lateral wall. In cases with extensive pneumatization the optic nerve may be entirely surrounded by pneumatization.
If the anterior clinoid process is also pneumatized, there may be recess between the optic nerve and the internal carotid artery, pointing laterally and superiorly between the optic nerve and the internal carotid artery. The optic canal dehiscence is seen in 4%, and carotid artery dehiscence in 7% of the cases.
The number, position and direction of the intersinus septum may also vary. Asingle septum may be in midline, may lie in asymmetric position, dividing the sinus into asymmetric cavities. The posterior course of the septum may be median or may deviate laterally and superiorly and insert into the bony bulge over the optic nerve or the internal carotid artery.
Fig. 134: Coronal Section: Rostrum of the Sphenoid. SS: Rostrum of the Sphenoid sinus, PES: Posterior ethmoidal sinuses, MS: Maxillary sinus and F: Frontal sinus (Posteriory extensive frontal sinus pneumatization).
Fig. 135: Coronal Section: Showing extensive pneumatization of the Sphenoid. ACP:Anteior Clinoid process pneumatization, BS: Basal part of the Sphenoind pneumatization, and TP: Pterygoid process pneumatization.
Fig. 136: Coronal Section: Showing Horizontal septa in the spneoid. The cells above the horizontal septa are Sphenoiethmoid cells or Onodi cells and the one below are Sphenoid sinuses. HS: Horizontal Septa, ACP:Anteior Clinoid process pneumatization, and ICA: Intenral Carotid Artery.
Fig. 137: Coronal Section: Showing Sphenoid sinus with absent septa.
Fig. 138: Coronal Section: Showing Sphenoid sinusmutlitple septi (Arrows).
Fig. 139: Coronal Section: Showing Bilaterla dehiscent optic nerves within the sphenoid (Arrows).
Fig. 140: Coronal Section: Showing Sphenoid sinus with dehiscent Vidian canal (White arrows) and Foramen rotundum (Black arrow).
Fig. 141: Coronal Section: Showing Sphenoid sinus with dehiscent carotid canal on (L) side and an inter-sinus septa ending on the internal carotid artery on (R) side.
Fig. 142: Coronal Section: Showing Sphenoid sinus with inter-sinus septa ending on the Internal carotid aretery (Carotid canal).
Fig. 143: Coronal Section: Showing Sphenoid sinus with inter-sinus septa ending on the Optic nerve.
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