Paranasal Sinuses Anatomy & Variants-A Systematic Approach To Imaging Before FESS

Dr Priyanka Vishwakarma

Four Paired Sinuses

EthmoidMaxillaryFrontalSphenoid

The sinuses develop as outgrowths from the nasal cavity; hence they all drain directly or indirectly into the nose

Meatisuperior meatus drains the posterior ethmoid air cells and the sphenoid sinus via the sphenoethmoidal recess middle meatus drains the frontal sinus via the nasofrontal duct/frontal recess, the maxillary sinus via the maxillary ostium, and the anterior ethmoid air cells via the ethmoid cell ostia. The nasolacrimal duct drains into the inferior meatus spheno-ethmoidal recess, above and posterior to the superior concha, receives the opening of the sphenoidal sinus

Osteomeatal unitCommon Drainage Pathway Of The Ant. Group of Sinuses.-Coronal scanThe osteomeatal unit (OMU) includes the uncinate processEthmoid infundibulumEthmoid BullaMiddle MeatusHiatus SemilunarisMost common site of inflammatory disease

Nasal SeptumCommonest Variation-DNSPneumatization

Inferior Turbinate-Hypertrophy

Maxillary sinus Largest and most constant pns.Pyramidal in shape- base is usually medial, with its apex in the zygomatic process of the maxillaBase -lat nasal wall-ostiumPosterior wall/Temporal- pterygomaxillary fossaRoof-Formed by roof of the orbit- infra orbital foramen containing the infra orbital vessels and nervesAnt-maxilla facial surface

Variants Related To the maxillary Sinus

Concha bullosaParadoxical curvature of MTHaller CellSeptaeDehiscent floor-1st ,2nd Molar Infn

Concha Bullosa pneumatization of the bulbous portion of the middle turbinate An enlarged concha bullosa may impede drainage from the middle meatus

Haller cells

Ethmoidal air cells belonging to the anteriorethmoidal group.Also known as the infra orbital cellsAdhere to roof of maxillary sinus forming the lat wall of infundibulumEnlargement of these cells can impede the maxillary sinus drainage

Paradoxical curvature- can potentially narrow or obstruct the infundibulum or middle meatus.

bony septum in the maxillary sinuses (MS)

Ethmoidal sinus basal lamellae of the middle turbinate separates the ethmoid into anterior and posterior groups with different drainage patternsAnt cells form 1st followed by the posterior cells.They are not seen on radiographs until age oneLateral wall-Formed by the orbital plate of the ethmoid,known as the lamina papyracea.this wall could be dehiscent-route of spread of infection

. The transition of thick fovea to the thin portion of roof of ethmoid medially is very weak-injuries during surgery leading on to CSF leak.

Ethmoids-ant and post

vertical attachment of basal lamellae to anterior skull base

Related VariantsA cell above the orbit is called a supraorbital cell.found in 15% of ptInvasion of an ethmoid cell into the floor of the frontal sinus is called a frontal cell(type 1-4)

Agger Nasi Cell term Agger in Latin - Mound/Eminence.anterior to the antero superior attachment of the middle turbinate and borders the frontal recess.its size may directly influence the patency of the frontal recess. These agger nasi cells are commonly involved in the pathogenesis of the formation of frontalmucocele.It is the 1st prominent anatomical landmark encountered in FESS

ethmoid bullasuperior to uncinate processes.Ethmoid bulla air cells are part of the anterior ethmoid sinuses and make up the superior border of the hiatus semilunaris. variable pneumatization.

Onodi Cells posterior ethmoidal cells extending supero lateral to the sphenoid sinus & can either abut to or impinging upon the optic nerve. When these Onodi cells abut or surround the optic nerve, the nerve is at risk when surgical excision of these cells is performed. It is also a potential cause of incomplete sphenoidectomy.

Olfactory fossaThe depth of the olfactory fossa is determined by the height of the lateral lamella of the cribriform plate, which is part of the ethmoid bone. In 1962, Keros had classified the depth of the olfactory fossa into three types, that is, Keros type I:

Keros type I-< 3 mm

Keros type II- 4 to 7 mm

Keros type III-6-18 mm

Frontal sinus different sizes, are separated by a bony septum that is usually deviated to one sideAsymmetry btw the two sinuses frequentIt may be absent in 5% of casesBest seen on Saggital imagesAmong the para nasal sinuses this sinus shows the maximum variations.

The post wall separates the frontal sinus from the anterior cranial fossa and is much thinner.Floor is formed by the upper part of the orbitsFrontal sinus appear very late in life. Infact they are not seen in skull films before the age of 6.Nasofrontal duct-misnomerFrontal Recess

the frontal recess can be conceptualized as an inverted funnel within the anterior ethmoid complex through which the frontal sinus drains.The tip or apex of the funnel lies at the frontal sinus ostium, -sagittal CT images as a waist located at the level of the nasofrontal process.The frontal recess typically flares out inferiorly and posteriorly to form the wider opening of the funnel. inferior portion of the frontal sinus (commonly referred to as the frontal infundibulum) + the frontal ostium + frontal recess = frontal sinus outflow tract

the right frontal recess (dotted red line), which is bounded anteriorly and laterally by an agger nasi cell (white arrow) and a type 1 frontal cell (black arrow), medially by the middle turbinate

posteriorly by the ethmoid bulla and bulla lamella. The nasofrontal process (arrowhead in b) forms the floor of the frontal sinus and demarcates the level of the frontal sinus ostium

superior compartment of the FSDP

Frontal outflow tract shows conglomeratization of air cells.Types of frontal sinus air cells include:I Type I frontal cell (a single air cell above agger nasi)II Type II frontal cell (a series of air cells above agger nasi but below the orbital roof)III Type III frontal cell (this cell extends into the frontal sinus but is contiguous with agger nasicell)IV Type IV frontal cell lies completely within the frontal sinus

Type 2 frontal cells

Type 3 frontal cell

Type 4 frontal cellsituated entirely within the right frontal sinus & bordered by the anterior frontal sinus wall. The type 4 cell does not abut the agger nasi cell.

Variants obstruct FSDPAgger nasiSupraorbital cells

Frontal recess is bounded anteriorly by agger nasi cell and posteriorly by suprabullar air cell- can compromise frontal sinus drainage pathway.

Supraorbital/suprabullar ethmoid cell

Pneumatized crista galli may communicate with the frontal recess and can potentially obstruct the frontal sinus ostium

Interfrontal sinus septal cell arises from the frontal sinus septum

Fess FailureFrontal sinusitis after FESS

The uncinate process may be attached to:Lamina papyracea or agger nasi (lamina terminalis). The frontal recess opens directly into middle meatus,medial to UP The lamina terminalis is the blind pouch between the UP and lamina papyracea Skull base or middle turbinate. The frontal recess drains into the ethmoid infundibulum lateral to UPOrbital floor or inferior aspect of the lamina papyracea (silent sinus syndrome, atelectatic uncinate process). This variant is associated with hypoplastic, ipsilateral maxillary sinus secondary to closure of the infundibulum.

Sphenoidal sinus They remain undeveloped until age three.By age seven the pneumatisation has reached the sell turcica.By age 18 the sinuses have reached full sizeOptic nerve and internal carotid arteries traverse its lateral wall.Pneumatisation can extend as far as the clivus,the sphenoid wings and the foramen magmum

sphenoid sinus (SpS) and the sphenoethmoidal recess marked by the (*).

(AE: anterior ethmoid, PE: posterior ethmoid, CC: carotid canal, NS: nasal septum)

(FR: foramen rotundum, VC: vidian canal, OC: optic canal, AC: anterior clinoid, PtP: pterygoid plate)

sphenoethmoidal recess

variations of intersinus septum

1.A single midline intersinus septum extending on to the anterior wall of sella.2. Multiple incomplete septae may be seen3. Accessory septa may be present. These could be seen terminating on to the carotid canal or optic

3 types

Concal-children-5%presellar-23%Sellar-67%

Pneumatized lateral recesses of sphenoid sinus (SpS) and foramen rotundum (FR) bulging into the sinus

pneumatized pterygoid plates

FESS-a roadmap to the otorhinolaryngologist prior to surgery. There are two main questions that the radiologist should address: 1. Are there anatomic features on the computed tomography (CT) scan that predispose the patient to impaired mucociliary clearance? 2. Are there anatomic features that pose a surgical hazard?

Checklist-Systematicthe extent of sinus opacification,patency of sinus drainage pathways, anatomic variants(obstruct drainage pathways &limit Surgical access), critical variants, (CP,LP,SphS dehiscence)and condition of soft tissues of the brain, neck, and orbits.-extrasinus extent of the disease

Referenceshttp://www.ajronline.org/doi/full/10.2214/AJR.09.3584http://dx.doi.org/10.1148/rg.291085118

*The maxillary sinus, the largest of the sinuses, is within the body of the maxilla. It is shaped like a pyramid; its base is usually medial, with its apex in the zygomatic process of the maxilla. Its roof is the floor of the orbit, and its floor is the alveolar process of the maxilla. The maxillary sinus drains into the middle meatus by means of the semilunar hiatus. The floor of the maxillary sinus is slightly below the level of the nasal cavity, and it is related to the upper teeth If present, a Haller cell can cause narrowing of the infundibulum and maxillary sinus ostuim potentially causing obstruction*Roof of ethmoid**olfactory fossae are deeper and the lateral lamellae are longer *olfactory fossae are very deep *Normal frontal recess anatomy. Coronal (a) and sagittal (b) CT images show the right frontal recess (dotted red line), which is bounded anteriorly and laterally by an agger nasi cell (white arrow) and a type 1 frontal cell (black arrow), medially by the middle turbinate, and posteriorly by the ethmoid bulla and bulla lamella. The nasofrontal process (arrowhead in b) forms the floor of the frontal sinus and demarcates the level of the frontal sinus ostium.Sagittal image shows frontal sinus ostium (*) and arrow pointing to the superior compartment of the FSDP. (FS: frontal sinus, AG: agger nasi, PE: posterior ethmoid, SpS: sphenoid sinus, MT: middle turbinate, IT: inferior turbinate)**Type 2 frontal cells. (a, b) Coronal (a) and parasagittal (b) drawings show a tier of type 2 frontal cells (blue areas) sitting atop an agger nasi cell. (c, d) Coronal (c) and sagittal (d) CT images show a tier of two type 2 frontal cells (arrows) sitting directly atop an agger nasi cell (*).

*Type 3 frontal cell. Coronal (a) and parasagittal (b) drawings show a type 3 frontal cell (blue area) sitting atop an agger nasi cell. The type 3 cell extends superiorly from the frontal recess through the frontal ostium and into the frontal sinus.

*Type 4 frontal cell. (a, b) Coronal (a) and parasagittal (b) drawings show a type 4 frontal cell (blue area) situated entirely within the right frontal sinus and bordered by the anterior frontal sinus wall. The type 4 cell does not abut the agger nasi cell. (c, d) Coronal (c) and sagittal (d) CT images show an opacified type 4 frontal cell (arrow) in the frontal sinus.

*Axial CT image shows the supraorbital ethmoid cell (arrow), which is clearly differentiated from the frontal sinus (*) by a discrete bony septum.

pneumatized crista galli. Pneumatized crista galli may communicate with the frontal recess and can potentially obstruct the frontal sinus ostium**which arises from the frontal sinus septum Axial image shows sphenoid sinus (SpS) and the sphenoethmoidal recess marked by the (*). (AE: anterior ethmoid, PE: posterior ethmoid, CC: carotid canal, NS: nasal septum)*Coronal image of the sphenoid sinus (SpS) and neighboring structures. (FR: foramen rotundum, VC: vidian canal, OC: optic canal, AC: anterior clinoid, PtP: pterygoid plate)

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