The thin bones that line the sphenoidal sinus allow the surgeon to penetrate the roof of the nasal cavity, go through the sphenoidal sinus and enter the hypophyseal fossa. A linear skull fracture can also occur that crosses a venous sinus, which typically causes significant bleeding that is difficult to control with simple digital pressure. The emissary veins, which traverse the cranium and enter the dural venous sinus system, are a pathway that infection can enter the brain.
This phenomenon is possible because the emissary veins have no valves. Emissary veins from the pterygoid plexus in the infratemporal fossa and ophthalmic veins from the orbit also pass through the cavernous sinus and can be a source of infection. In each case, infection is possible because the veins begin extracranially and become intracranial. Subdural hematomas typically result from injury to cerebral veins where they enter the superior sagittal sinus, which occurs because the cerebral veins are more mobile than the dura-encased sinuses.
This type of intracranial hemorrhage occurs between the dura mater and arachnoid mater, layers of the lining of the brain. A subdural hematoma can occur from the most trivial injury. Epilepsia open. Asia-Pacific journal of ophthalmology Philadelphia, Pa. Anatomical record Hoboken, N. Otolaryngologic clinics of North America. Clinical practice and cases in emergency medicine.
Acta neurochirurgica. International journal of pediatric otorhinolaryngology. Anatomy, Head and Neck, Nose Sinuses. Free Review Questions. Introduction A sinus is defined as: A channel that is not a blood or lymphatic vessel that allows for the passage of blood or lymph, such as found in the placenta, sinuses, or the cerebral meninges A cavity or hollow space in bone or other tissue A dilation in a blood vessel A fistula or tract that transforms into a cavity There are many types of sinuses, such as the paranasal sinuses of the skull or the dural sinuses of the cerebral meninges.
Structure and Function Paranasal Sinuses The total function of the paranasal sinuses is unclear. Dural Venous Sinuses The dural venous sinuses are in the brain. Embryology Paranasal Sinuses The ethmoidal and maxillary paranasal sinuses are very small in size but present at birth, while the sphenoid and frontal are both absent.
Dural Venous Sinuses The dural venous sinuses are present in a rudimentary form during infancy. This can be explained by the fact that the ethmoid air cells are developed and pneumatized earlier than the sphenoid sinus, so they have a room to extend posteriorly. The incidence of the sphenoethmoidal cell ranges from 3. The significance of this air cell is that it is closely related to the optic nerve on its superolateral wall, and the nerve can even be engulfed within the air cell as well Figure The pneumatization extends from the frontal sinuses.
Rarely can obstruct the frontal ostium [ 35 ]. A Endoscopic picture showing the left agger nasi air cell as a prominence just anterior to the neck of the middle turbinate asterisk. S, nasal septum; MT, middle turbinate. B Coronal CT scan at anterior level, showing bilateral agger nasi air cells asterisk. Parasagittal CT scan showing an ethmoid bulla EB that is not extending superiorly to the skull base, the gap created between it and the skull base is known as the suprabullar recess SBR.
Also, note that there is a gap between the posterior bullar wall and the basal lamella BL , which is referred to as the retrobullar recess RBR. PES, posterior ethoid sinus. A Parasagittal CT scan showing an extension of pneumatization over the orbit asterisks.
SS, sphenoid sinus. Anterior and posterior ethmoid sinuses receive blood supply by branches from the supraorbital, anterior, and posterior ethmoidal and sphenopalatine arteries. The venous drainage is via the accompanying veins to the superior ophthalmic vein or pterygopalatine plexus.
The innervation is by anterior and posterior ethmoidal nerves of the ophthalmic division V1 and the posterior nasal branch of the maxillary division V2 of the trigeminal nerve. The lymphatic drainage of the anterior ethmoid sinus is to the submandibular nodes, and the posterior ethmoid sinus drains to the retropharyngeal nodes.
There are two sinuses extending in the squamous part of the frontal bone. They are separated by bony septum because each sinus right and left develops independently; they are expected to be asymmetrically pneumatized. The larger sinus may pass across the midline and overlap the other. The inner table is a relative thin bony plate that separates frontal sinus from the anterior cranial fossa posteriorly.
On the other hand, the outer table is a considerable thick bony wall [ 36 ]. Also, these foramina act as sites of mucosal invagination within the bone, so failing to completely remove the mucosa in these sites during the sinus obliteration procedure may predispose to the development of mucocele.
The floor of each frontal sinus forms the anterior roof of the orbit. The floor consisted of a thin bone which can be eroded by the mucocele. Therefore, what lies superior to the frontal beak is frontal sinus, and what lies inferior to the beak is frontal recess [ 37 ].
The thickness of the frontal beak frontonasal process of the maxilla will determine the size and patency the frontal sinus ostium. Parasagittal CT scan images. Superior to the beak is the frontal sinus FS. Note that the large agger nasi cell causing a significant narrowing of the frontal recess dashed line.
As agger nasi cell forms the anterior wall of the recess, ethmoid bulla EB forms the posterior wall. So, any enlargement or pathology affecting either cells could compromise the patency of the frontal recess. Frontal recess is like an inverted funnel with its apex formed by the frontal sinus ostium. The frontal recess is not a structure by itself, rather it is formed by walls of the surrounding structures.
Boundaries of frontal recess are as follows: from the anterior and inferior side, the posterior wall of agger nasi cell; from the posterior side, the face of ethmoid bulla; lateral boundary is formed by the lamina papyracea; medial side formed by the lateral wall of olfactory fossa and the upper portion of middle turbinate; and superiorly, comes the fovea ethmoidalis. Depending on the superior attachment of the uncinate process, the frontal sinus drainage pathway drains into the middle meatus or the ethmoid infundibulum as mentioned in the uncinate process section [ 38 ].
When agger nasi cell is small, the frontal beak becomes prominent and narrows the ostium. In contrary, the large agger nasi cell results in a small frontal beak which means wider frontal sinus ostium. However, the large agger nasi cell might compromise the frontal sinus drainage pathway at the level of frontal recess, inferiorly Figure 18B [ 39 ].
Frontoethmoidal cells Frontal cells : Classification of frontal cells was first described by Kuhn [ 40 ]. However, later Wormald modified the frontal cells classification [ 41 ]. This chapter reviews the modified classification by Wormald. They were classified into four groups as follows:. Type 1 frontal cell : Single frontal recess cell above agger nasi cell and below the frontal ostium Figure 20A.
Type 2 frontal cells : Two or more cells in frontal recess above agger nasi cell and below the frontal ostium Figure 20B. Frontal bullar cell : Single cell extends from the suprabullar region along the posterior wall of frontal recess and extends into the frontal sinus, superiorly.
This differentiates it from the suprabullar cell, which does not extend into the frontal sinus. The posterior wall of the frontal bullar cell is related to anterior cranial fossa, and its anterior wall is related to frontal sinus Figure Caution must be taken during opening this cell not to cause unintentional trauma to anterior skull base.
Frontal intersinus septal cell: Occasionally, the intersinus septum is pneumatized forming an intersinus air cell, which might be communicating with either one of the frontal sinuses or could be completely an isolated air cell. It might compromise the frontal sinus ostium patency [ 42 ] Figure Coronal CT scan.
A Bilateral aplastic frontal sinuses. B Because each frontal sinus develops independently, a variant like unilateral aplastic frontal sinus can occur. Note that the posterior border of the cell is related to the anterior cranial fossa. And the frontal sinus FS is making the anterior border. The suprabullar cells SBC are limited to the frontal recess and are not extending to frontal sinus.
AN, Agger nasi; EB, ethmoid bulla. Coronal CT scan showing frontal intersinus septal air cell asterisk. Note the frontal cell type 3 on the right frontal sinus FC3. Frontal sinus ostium might be compromised because of the impact of either of these two cells. AN, Agger nasi cell. Parasagittal CT view of the frontal recess dashed line. Expanding of any of these air cells could have an impact on the patency of the frontal recess.
Also, other air cells like frontal bullar cell or frontal intersinus septal cell could compromise frontal sinus drainage pathway at the ostium level. Frontal sinuses are the only sinuses that are not present at birth. They start pneumatization by the age of two and reach the orbital roof by the age of 5—7. By age of 12, they reach the adult size [ 3 ]. The clinical application of the frontal sinus development process is that external trephination procedure is contraindicated before the developing sinus reaches the level of orbital roof because of the risk of intracranial penetration.
Frontal sinus receives blood supply from the supratrochlear and supraorbital arteries branching from ophthalmic artery. Venous drainage is by the superior ophthalmic and diploic veins. Lymph drainage is across the face to the submandibular nodes.
Frontal sinus receives innervation from the supratrochlear and supraorbital nerves. Sphenoid sinuses occupy the body of sphenoid bone. Typically, the ostium is located in the medial portion of sphenoidal face, about 10—12 mm superior to the upper border of the choana.
The posteroinferior end the tail of superior turbinate can be used to locate the ostium, which typically would be just superomedial to the tail of superior turbinate [ 43 ]. Inferior to sphenoid natural ostium, the posterior septal artery a branch of sphenopalatine artery crosses the sphenoid face from the lateral nasal wall to the posterior end of nasal septum.
Even if it bifurcates before crossing, both branches pass inferior to the ostium. The average distance between the sphenoid ostium and the posterior septal artery or its superior branch is about 5 mm. Because of that, during widening the ostium, it is safer to dissect and widen the sphenoid ostium horizontally and superiorly. Alternatively, to use the electrocautery if the ostium will be widening more than 5 mm inferiorly [ 44 ]. Vital structures such as pituitary gland, optic nerves, cavernous sinuses and carotid arteries, maxillary divisions V2 of the trigeminal nerves within the foramina rotundum, and vidian canals are closely related to the sphenoid body.
Roof of the sinus is related to the pituitary gland and middle cranial fossa. Posteriorly lie the pons and the posterior cranial fossa. The optic nerve canal crosses the corner formed by the roof and the lateral wall on the posterior portion of the sinus on each side. On the posterolateral walls, internal carotid artery canals cavernous segment will be seen as bony prominences. Within the lateral sphenoid walls, the maxillary division of trigeminal nerves pass through the foramina rotundum toward the pterygopalatine fossae in both sides.
Coronal CT scan at the level of sphenoid sinus showing the critical structures neighboring the sinuses. In hyperpneumatized sinus, when pneumatization extends laterally between foramen rotundum and vidian canal, creating a recess known as the lateral recess asterisk.
CP, anterior clinoid process. Sphenoid sinus pneumatization: Depending on the degree of pneumatization, sphenoid sinus is classified into three types [ 45 ]. Conchal type: The degree of pneumatization is limited to the anterior portion of the sphenoid body and not reaching the level of the anterior wall of sella turcica. Presellar type: Pneumatization extends up to the vertical level of the anterior wall of sella turcica but not beyond that.
Structure of the Paranasal Sinuses Skull Sinuses : This image shows the position of the sinuses in the human skull. The maxillary sinuses also called the maxillary antrechea, the largest of the paranasal sinuses are located under the orbits in the maxillary bones.
The frontal sinuses are superior to the orbits and are in the frontal bone. The ethmoid sinuses are formed from several discrete air cells within the ethmoid bone between the nose and the orbits. The sphenoid sinuses are in the sphenoid bone at the center of the skull base under the pituitary gland. The paranasal sinuses are lined with respiratory epithelium. The physicians, surgeons and nurses at the Cedars-Sinai Sinus Center are dedicated to providing the most advanced treatment for the full range of conditions affecting the nose, including sino-nasal trauma, sino-pulmonary syndrome, and complications and persistent disease after a previous surgery.
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