EMBRYOLOGY AND DEVELOPMENT SINUS ANATOMY AND FUNCTION -4 th week gestation: -frontonasal process identified, arises over developing forebrain -ectodermal -contributes to nasal capsule -9 th and 10 th week gestation: -nasoturbinals: -become Agger nasi cells -ethmoturbinals or basal lamellae -six ridges on lateral wall numbered anterior to posterior direction; separated by furrows -first becomes uncinate process -furrow between first and second becomes ethmoid infundibulum -second becomes anterior wall of bulla ethmoidalis -third forms attachment of middle turbinate to lateral nasal wall -fourth forms attachment of superior turbinate -fifth to sixth coalesce and disappear by birth -maxilloturbinal -becomes inferior turbinate -inferior turbinate not related to ethmoturbinals -chronologic sequence of development: -maxillary (65 th day) ethmoid (3 rd - 4 th month) frontal (4 th month) sphenoid (4 th month) -maxillary and ethmoid sinuses are the only sinuses at birth which are large enough to be of clinical significance Maxillary sinus: -first sinus to begin development (65 th day GA) -not evident on x-ray until 4-5 months of age fluid filled -biphasic growth: -first 3 years of life -second growth acceleration between 7-12 ya pneumatization laterally -slow expansion until 18 years -adult dimensions: 34x33x23 mm; 15 ml Ethmoid air cells: -begin development in 3 rd fetal month -anterior cells as evaginations in middle meatus, then posterior cells in superior meatus -3-4 cells at birth (most developed paranasal sinus at birth) -not evident on x-ray until 1 ya -reach adult dimension by 12 ya -dimensions: 20x20x10 mm; 15 ml Frontal sinus: -begins development during 4 th month -visible usually after 2 nd year on radiographs -sinus invades frontal bone by 5 ya, reaching adult size in late adolescence -dimensions: 17x28x27; 6-7ml -4-15% of population: developmental failure of one frontal sinuses present F.Ling - Sinus Anatomy and Function (1)
Sphenoid sinus: -pneumatization begins at 3 ya -growth to sella turcica by 7 ya -adult size by 18 ya -dimensions: 23x20x17 mm; 7.5 ml ANATOMY Ethmoidal Sinus -lateral wall: lamina papyracea -medial wall: functions as lateral wall of nose -midline vertical plate of ethmoid bone: -superior portion termed crista galli -inferior portion termed perpendicular plate of ethmoid bone -roof of ethmoid bone = horizontal plate: separates anterior cranial fossa from nasal cavity -thin medial portion: cribriform plate -thick lateral portion: fovea ethmoidalis -lateral lamella: extremely thin lateral part of cribriform plate -Keros classification: -Type I: cribriform plate 1-3 mm below fovea ethmoidalis -Type II: 4-7 mm below -Type III: 8-16 mm below -anterior vertical attachment of middle turbinate to horizontal plate separates cribriform plate from lateral lamella and fovea ethmoidalis -dissecting lateral to turbinate prevents entrance into horizontal part of cribriform plate -presence of Keros type II or III ethmoid roof risk of entering anterior cranial fossa through lateral lamella -dome of ethmoid bone in horizontal plate: -area where anterior ethmoidal artery traverses ethmoid roof -may cause orbital hematoma if injured -anterior cells: -drain into ethmoid infundibulum of middle meatus -frontal recess cells: -most anterior cells -0-4 cells -form frontal sinus, supraorbital air cells -infundibular cells: -next most anterior -1-7 cells -agger nasi cells extend outside ethmoid capsule -represent superior remnant of the first ethmoturbinal -in close proximity to frontal recess -often opened during FESS to get better view of nasofrontal duct -can obstruct outflow of frontal sinus -bullar cells -1-6 cells -consistent location in middle meatus F.Ling - Sinus Anatomy and Function (2)
-form bulla ethmoidalis -may form suprabullar recess if anterosuperior wall of bulla does not reach ethmoid roof -uncinate process: -thin semilunar piece of bone; part of ethmoid bone -remnant of first ethmoturbinal -middle turbinate: -concha bullosa: -pneumatization of middle turbinate; in 12% of population -may result in nasal obstruction -anterior end attaches to horizontal plate -posterior end inserts laterally on lamina papyracea -divides anterior from posterior ethmoid cells -sinus lateralis or retrobullar recess: occurs if posterior wall of bulla ethmoidalis does not contact third basal lamella -posterior cells: -drain into superior meatus -Onodi cell: -posterior ethmoid cell that can pneumatize an area of sphenoid bone superior and lateral to sphenoidal sinus in 9-12% of population -optic nerve and carotid artery can be exposed and injured during dissection in this area -vasculature: -anterior and posterior ethmoid arteries -maxillary and ethmoid veins (cavernous sinus) -innervation: -anterior and posterior ethmoidal nerves (from nasociliary nerve, V1) Maxillary Sinus -supraorbital nerve dehiscent in 14% of population -Haller cell: -pneumatization of ethmoid complex into the roof to the maxillary sinus -may occlude ostia -1 st and 2 nd molars: two most dehiscent teeth in maxillary sinus (2.2% and 2.0% of persons, respectively) -removal of teeth may result in oral-antral fistula -accessory ostia present in 15-40% of cases -Vasculature: -maxillary and facial artery -facial vein -Innervation: -infraorbital nerve (V2) Frontal Sinus -develops from anterosuperior ethmoidal cells -frontal recess: -medial wall: middle turbinate, uncinate process -lateral wall: lamina papyracea -posterior wall: anterior face of bulla ethmoidalis -anterior wall: agger nasi cells F.Ling - Sinus Anatomy and Function (3)
-drainage pattern: -A: UP LP (80%); drainage medial to uncinate process to middle meatus -B: UP base of skull; drainage lateral to uncinate process to infundibulum -C: UP middle turbinate; drainage lateral to uncinate process to infundibulum -vasculature: -supraorbital and supratrochlear arteries -ophthalmic (cavernous sinus) and supraorbital (anterior facial) veins -innervation: -supraorbital and supratrochlear nerves (V1) -structure of sinus variable -anterior wall is strongest, twice as thick as posterior wall -drainage ostium in posteromedial portion of sinus floor -Foramina of Breschet: small venules that drain the sinus mucosa into the dural veins Sphenoidal Sinus -anatomical relationships of sphenoid ostium: -face of sphenoid sinus lies 7 cm from nasal sill at 30 o angle with floor of nasal cavity -empties into sphenoethmoidal recess via small ostium -adjacent to posterior border of nasal septum -adjacent to posterior border of nasal septum -0.5-4 mm in diameter -located 10-15 mm above sinus floor or 30 degree above floor of nasal cavity -1/3 up from choana to base of skull -Congdon classification of pneumatization: -Conchal (5%): posterior extent of sinus well anterior to sella turcica -Presellar (24%): posterior wall of sphenoidal sinus reaches anterior face of sella turcica -Postsellar (67%): sinus extends past level of sella turcica to approach pons posteriorly and allows sell to make superior indentation in the sinus -cavernous sinus external and lateral to sinus -bony tubercle surrounding optic nerve dehiscent in 4% of population -dehiscent internal carotid artery in 7% -maxillary branch of trigeminal nerve and vidian nerve produce bulges in sphenoidal sinus in 30% population -vasculature: -sphenopalatine artery F.Ling - Sinus Anatomy and Function (4)
-maxillary vein (pterygoid plexus) -innervation: -sphenopalatine nerve (parasympathetic fibers and V2) Lymphatic Drainage of the nose and sinuses -anterior 1/3 of nose submandibular nodes -posterior 2/3 of nose and sinuses retropharyngeal nodes (Rouviere) and superior deep cervical nodes F.Ling - Sinus Anatomy and Function (5)
PHYSIOLOGY Functions of Sinuses (theories) -humidification of inspired air -lightening of skull -aids in resonance of speech -increased surface area for olfaction -absorption of shock to the face or skull -regulation of intranasal pressure -secretion of mucous to keep nasal chambers moist Sinus Epithelium -pseudostratified ciliated columnar epithelium -four basic cell types: -ciliated columnar epithelial cell: -50-200 cilia per cell; 9+2 microtubule doublets; 10-20 beats/s -nonciliated columnar cells: -contain microvilli that expand surface area to improve humidification and warming of air -basal cell: -may be primitive stem cell that can differentiate into other epithelial cells -goblet cell: -produce thick mucous after stimulation by irritating substance -higher amount in maxillary sinus than other sinuses F.Ling - Sinus Anatomy and Function (6)
-submucosal glands: serous and mucinous glands penetrate lamina propria -parasympathetics thick mucous -sympathetics thin mucous -density highest at ostia of maxillary, sphenoid, and anterior ethmoidal sinuses Mucous Blanket -two layers: -sol layer: -thin, periciliary fluid allowing cilia to be mobile -produced by microvilli -gel layer: -upper layer of thick mucous (mucoglycoproteins) that supplies insertion point for tips of the cilia -produced by goblet cells and submucosal glands -provides protection against low humidity and cold -traps foreign particles and bacteria -IgA inhibits adherence of bacteria to epithelial surface -causes agglutination then clearance by phagocytosis -IgG and interferon to provide antiviral role -lactoferrin -transports iron into bacteria antioxidant activity -lysozyme -secreted by serous cells -mucociliary clearance: -3-25 mm/min towards natural ostium -maxillary sinus: star-shaped drainage pattern from sinus floor superiorly to ostium -frontal sinus: medial wall of frontal recess roof lateral downward and medially toward sinus ostium F.Ling - Sinus Anatomy and Function (7)