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Home , Agger nasi, Nasal concha, Sphenoethmoidal recess, Vomeronasal organ

804 RESEARCH AND SCIENCE

Thomas von Arx1 Scott Lozanoff2 Extraoral in CBCT - Michael M. Bornstein3 a literature review 1 Department of Oral Surgery and Stomatology, School of Dental Medicine, University of Bern, Switzerland Part 1: Nasoethmoidal region 2 Department of Anatomy, Biochemistry and Physiology, John A. Burns School of Medi- cine, University of Hawaii, Honolulu, USA 3 Oral and Maxillofacial Radiol- ogy, Applied Oral Sciences, KEYWORDS Faculty of Dentistry, The Uni- Anatomy versity of Hong Kong, Prince CBCT Philip Dental Hospital, Hong Kong SAR, China Ethmoid

CORRESPONDENCE Prof. Dr. Thomas von Arx Klinik für Oralchirurgie und Stomatologie Zahnmedizinische Kliniken der Universität Bern SUMMARY Freiburgstrasse 7 CH-3010 Bern Cone beam computed tomography has become a Other structures of the septum include the Tel. +41 31 632 25 66 widely used imaging technique for dental indica- and the septal . The nasal meatuses sta- Fax +41 31 632 25 03 tions. Depending on the selected size of the field bilize the airflow and direct the inhaled air to the E-mail: of view, anatomical structures outside the den- nasopharynx via the choanae. The middle nasal [email protected] tomaxillary complex become visible. As a conse- meatus, which is also a part of the so called os- SWISS DENTAL JOURNAL SSO 129: quence, the clinician must be able to interpret tiomeatal complex, serves as the major drainage 804–815 (2019) also those anatomical regions. In this article, the area (semilunar hiatus) of the , Accepted for publication: anatomy of the nasoethmoidal region is present- i.e., , anterior ethmoid cells, and 10 December 2018 ed based on a literature review. The is char- . Posterior ethmoid cells empty into acterized by the and the superior, the superior meatus and the middle, and inferior conchae. The turbinates may drains into the , located be pneumatized (concha bullosa), mainly the above the superior concha. The nasolacrimal duct middle concha. The has a complex that is running along the middle portion of the morphology (ethmoid labyrinths) and contributes lateral nasal wall opens into the inferior nasal with its perpendicular plate to the nasal septum. meatus.

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Introduction Knowledge of anatomical structures and their spatial relation- ships is critical in medicine and dentistry for diagnosis and treatment planning (von Arx & Lozanoff 2017). Current medical and dental curricula teach anatomy at the very beginning of training in the undergraduate phase. As a consequence, ana- tomical knowledge may be gradually or selectively lost over the years of clinical work. Over the course of the last two decades, cone beam computed tomography (CBCT) has become the standard of three-dimen- sional imaging in dentistry. Main indications for using CBCT in the various disciplines of dental medicine have recently been established by the Swiss Association of Dentomaxillofacial Ra- diology (Dula et al. 2014, 2015). Maxillofacial surgery, ophthal- mology and otorhinolaryngology are other specialties with an increased interest in CBCT (Bremke et al. 2010; Tschopp et al. 2014; Lata et al. 2018). Nevertheless, CBCT has been reported to have also some shortcomings in comparison with advanced medical imaging procedures such as multi-slice computed tomography (msCT) or magnetic resonance imaging (MRI). This especially applies to the lack of a diagnostically distinct soft tissue contrast, narrow- ing down the diagnostic potential of CBCT imaging and limiting potential applications for soft tissue integration in presurgical Fig. 1 Graphic illustration of the skeletal framework of the nose and adjacent planning (Jacobs et al. 2018). Furthermore, Hounsfield units do structures not apply to CBCT images, which makes it impossible to com- 1 = upper lateral cartilage; 2 = superior margin of septal cartilage; 3 = lower lateral (alar) cartilage; 4 = ; 5 = frontal process of os maxillae; pare grey values among or within patients over time. This lack 6 = ; 7 = cavity for lacrimal sac; 8 = lamina orbitalis (papyracea) of standardized grey value distribution narrows down the use of ethmoid bone of CBCT for bone density analysis and follow-up of bone density changes (Pauwels et al. 2015). Compared to Hounsfield units for medical CT, the reliability of CBCT-based bone density as- sessment has been found unreliable over time and with signifi- cant variations influenced by CBCT devices, imaging parame- ters and head positioning. Currently, the vast majority of case-based CBCT imaging in- cludes dental and maxillofacial indications (de Vos et al. 2009). However, in larger fields of view (FOVs ≥10 × 10 cm), anatomical structures outside the oral cavity become visible (Bornstein et al. 2014). The clinician evaluating CBCT scans must assess and understand the relevant anatomy, but is also responsible for recognizing abnormalities within the complete image data set and beyond the region of interest (Carter et al. 2008; Horner et al. 2009). The objective of this series of publications entitled “Extraoral anatomy in CBCT” is to provide a literature update with detailed information about anatomical structures usually seen on larger FOVs that may be less easily identified by the dental practi- tioner. The clinician remains responsible for incidental findings in the CBCT image stack. This series of reviews is intended to refresh the dental practitioner’s anatomical knowledge base facilitating accurate assessment and ultimately improving the health of the patient. The first topic in this series addresses the nasoethmoidal region. Nose The nose includes the visible outer structures, such as the nasal wings and the nasal dorsum, and the nasal cavities internally. The skeletal framework of the nose is osseous (upper part) as well as cartilaginous (lower and lateral parts) (Fig. 1 and 2) (von Arx et al. 2018a). The two small and flat nasal form the central Fig. 2 Lateral view of dissected cadaveric nasal skeleton (right side) 1 = nasal bone; 2 = frontal process of os maxillae; 3 = upper lateral cartilage; part of the nasal root that is supplemented laterally by the frontal 4 = lower lateral (alar) cartilage; 5 = ; 6 = with processes of the os maxillae. Several contribute to the neurovascular bundle

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lower portion of the nose. The central nasal ridge is formed by the superior margin of the septal cartilage. The nasal wings con- sist of the triangular-shaped lateral cartilages, also called upper lateral cartilages. These cartilages project superiorly below the nasal bones and attach through dense connective tissue (Ogle et al. 2012). The edges of the nasal orifices, or , and the colu- mella are formed by the scroll-shaped alar cartilages (also called lower lateral cartilages) that form the curved external openings of the nose (Hafezi et al. 2010). Each lower lateral cartilage has a medial and a lateral crus that shape the nasal tip and maintain the patency of the nostrils (Ogle et al. 2012). Additional small cartilages contribute variably to the nasal wings and include the minor alar cartilages or sesamoid cartilages. Nasal cavity The nasal cavity is a bilateral structure located in the midface (Fig. 3–12). Inferiorly it is bordered by the while the roof of the nasal cavity is formed by the of the ethmoid bone. A midline septum oriented in the sagittal plane divides the nasal cavity into two bilateral cavities. Anteriorly, the nasal vestibules positioned outside the osseous part of the nose serve as the communication from the nostrils to the proper nasal cavities. The nasal cavities have anterior (ventral) open- ings, i.e. the nostrils (or nares), and posterior (dorsal) openings, i.e. the choanae. The latter represent the gateway to the naso- . Fig. 3 Graphic illustration of the left nasal cavity and adjacent structures Major functions of the nose include respiration and olfaction. 1 = frontal sinus; 2 = ethmoid cells (); 3 = sphenoid sinus; Hairs (vibrissae) located in the vestibule have a cleaning func- 4 = sphenoethmoidal recess with opening of sphenoid sinus; 5 = upper with opening of posterior ethmoid cells; 6 = location of underlying tion, whereas the warms and humidifies the ; 7 = partially resected middle concha; 8 = bulla inhaled air. The nasal conchae enlarge the functional mucosa ethmoidalis; 9 = opening of frontal sinus in upper part of semilunar hiatus; of the nasal cavities. Olfactory cells are mainly located on the 10 = opening of anterior ethmoid cells in middle part of semilunar hiatus; upper conchae. 11 = opening of maxillary sinus (ostium maxillare) in lower part of semilunar hiatus; 12 = uncinate process of ethmoid bone; 13 = middle nasal meatus; The three nasal conchae, superior, middle, and inferior, also 14 = partially resected inferior concha; 15 = opening of nasolacrimal duct; termed nasal turbinates (“turbid” from Latin to disturb), exhibit 16 = inferior nasal meatus; 17 = nasal opening of nasopalatine canal a scrolled cross-section in the coronal plane with the free end directed laterally. Occasionally, a paradoxical curvature, mainly of the middle turbinate, is observed, i.e., the turbinate is scrolled in a medial direction (Sava et al. 2018). The inferior concha typi- cally is the largest while the superior is the smallest. Rarely, a fourth concha suprema (Santorini’s concha) is described that is located at the posterosuperior aspect of the lateral nasal wall close to the lateral margin of the ostium of the sphenoid sinus (Sava et al. 2018). The term “concha bullosa” generally refers to the pneumatization of the middle turbinate. However, pneu- matization may also occur of the superior and inferior turbinates (Ila et al. 2018). In fact, the presence of a “void” within the con- cha(e) is an optical illusion on 2D pictures, since the “pneuma- tized” cavity always presents with a connection to the corre- sponding nasal meatus. The three conchae divide the nasal cavities into four spaces, i.e. from top to bottom, sphenoethmoidal recess, superior nasal meatus, middle nasal meatus, and inferior nasal meatus. The middle meatus, is the most complex and serves as the major drainage area of the paranasal sinuses (Ogle et al. 2012). The four air channels on each side divide and compartmentalize airflow. Furthermore, they increase and stabilize airflow pres- sure and velocity while also directing the air to the nasopharynx via the choanae (Doorly et al. 2008). Fig. 4 Medial view of left nasal cavity (paramedian section of dry ) The ostiomeatal complex is the functional unit of the anterior 1 = frontal sinus; 2 = anterior cranial fossa; 3 = nasal bone; 4 = os maxillae; ethmoid including the maxillary ostium, the middle meatus, 5 = superior concha; 6 = middle concha; 7 = inferior concha; 8 = sphenoeth- moidal recess; 9 = maxillary ostium; 10 = sphenopalatine foramen; 11 = sphe- the hiatus semilunaris, the uncinate process, and the bulla eth- noid sinus; 12 = hypophyseal fossa; 13 = nasopalatine canal; *** = semilunar moidalis (Gibelli et al. 2018). The ostiomeatal complex is con- hiatus

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Fig. 5 Medial view of left nasal cavity (paramedian cadaveric section) 1 = frontal sinus; 2 = infundibulum of frontal recess; 3 = nasal bone; 4 = nasal septum; 5 = anterior ethmoid cells; 6 = posterior ethmoid cells; 7 = sphenoid sinus; 8 = bulla ethmoidalis; 9 = middle concha; 10 = inferior concha; *** = semilunar hiatus

sidered a critical area for paranasal ventilation and drainage since it is located at the crossroads between the nasal cavities and the paranasal sinuses (Khojastepour et al. 2015). The paranasal sinuses, i.e., frontal sinus, sphenoid sinus, ethmoid cells, and maxillary sinus, drain into the meatuses via distinguished openings or ostia. The largest gateway is the maxillary ostium serving as the communication between the maxillary sinus and the middle meatus. The maxillary ostium is located in the lower part of the semilunar hiatus, a broad and curved opening within the lateral nasal wall located between the inferior and middle turbinates. Also the frontal sinus drains into the middle meatus with its ostium located in the upper part of the semilunar hiatus. Multiple small openings serve for drain- age of the ethmoid air cells (see below). A structure not related to the paranasal sinuses but still drain- ing into the nasal cavity is the nasolacrimal duct. It originates from the lacrimal sac at the anteroinferior corner of the orbital cavity. The nasolacrimal duct terminates in the anterior third of the inferior nasal meatus (Wilhelm et al. 2009; Tschopp et al. 2014; Bornstein et al. 2017a). The bony nasolacrimal canal is usu- ally inclined posteriorly and laterally toward the maxillary first molar (Ali et al. 2014). In a study with 15 cadaveric half heads, the mean length of the nasolacrimal duct was 21.9 mm and its intranasal orifice was located on average 13.7mm above the nasal floor (Tatlisumak et al. 2010). Fig. 6 CBCT of a 20-year-old male (original FOV 10 × 10 cm) with coronal (A), sagittal (B) and axial (C) views 1 = cell; 2 = frontal sinus; 3 = middle concha (pneumatized on left Nasal floor side); 4 = inferior concha; 5 = nasolacrimal duct; 6 = maxillary sinus; 7 = per- The nasal floor is formed by the same osseous structures that pendicular plate of ethmoid bone; 8 = anterior ethmoid cells; 9 = posterior ethmoid cells; 10 = sphenoid sinus; *** = semilunar hiatus contribute to the hard palate, i.e., the palatine processes of the ox maxillae (anteriorly) and the horizontal plates of the palatine bones (posteriorly). Ventral and dorsal midline bony projections at the level of the nasal floor include the anterior and posterior above the fusion zone of the palatal processes of the os maxillae nasal spines. In a study of 50 embalmed cadaver hemiheads, the and the os palatinum. Prominent, funnel-shaped bilateral open- mean distance from the anterior to the posterior nasal spines ings are located along the anterior nasal crest and serve as the was 5.6 ± 0.3 cm (Donmez et al. 2005). The nasal crest is located nasal openings of the nasopalatine canal.

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Fig. 7 CBCT of a 34-year-old female (original FOV 10 × 10 cm) with coro- Fig. 8 CBCT of a 66-year-old male (original FOV 10 × 10 cm) with coronal (A), nal (A), sagittal (B) and axial (C) views sagittal (B) and axial (C) views 1 = nasolacrimal duct; 2 = inferior meatus; 3 = inferior concha; 4 = maxillary 1 = inferior concha; 2 = inferior meatus; 3 = middle concha; 4 = middle sinus; 5 = septal cartilage; 6 = nasal crest; 7 = perpendicular plate of ethmoid meatus; 5 = superior concha; 6 = superior meatus; 7 = sphenoethmoidal bone; 8 = anterior ethmoid cells; 9 = posterior ethmoid cells; 10 = sphenoid recess; 8 = perpendicular plate of ethmoid bone; 9 = vomer; 10 = nasal crest; sinus; 11 = frontal process of os maxillae; 12 = middle concha 11 = maxillary sinus; 12 = posterior ethmoid cells (*Onodi cell); 13 = anterior ethmoid cells; 14 = inferior orbital fissure; 15 = optic canal; 16 = superior orbital fissure; 17 = sphenoid sinus. Note that both maxillary sinuses demonstrate spherical mucosal thickenings on the floor (Fig.A).

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Fig. 9 CBCT of a 20-year-old female (original FOV 10 × 10 cm) with coro- Fig. 10 CBCT of a 67-year-old female (original FOV 10 × 10 cm) with coro- nal (A), sagittal (B) and axial (C) views nal (A), sagittal (B) and axial (C) views 1 = “sinus septi nasi”; 2 = sphenoid sinus (*extension of sphenoid sinus into 1 = nasolacrimal duct; 2 = inferior orbital fissure; 3 = ; nasal septum); 3 = maxillary sinus; 4 = vomer; 5 = perpendicular plate of 4 = middle concha (extensively pneumatized); 5 = inferior concha; 6 = maxil- ethmoid bone; 6 = nasopalatine canal; 7 = superior concha; 8 = middle lary sinus; 7 = sphenoid sinus; 8 = hypophyseal fossa concha; 9 = inferior concha; 10 = nasolacrimal duct

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Fig. 12 Anterolateral view of medial wall of left orbital cavity with trans- illuminated ethmoidal cells 1 = optic canal; 2 = superior orbital fissure; 3 = inferior orbital fissure; 4 = orbital floor; 5 = nasal boe; 6 = frontal process of os maxillae; *** = ethmoid cells

rior part), and the ethmoid bone (superior part). Furthermore, the small lacrimal bone also contributes to the lateral nasal wall roughly in the center portion. Larger openings in the lateral wall include the semilunar hia- tus and the sphenopalatine foramen. The sphenopalatine fora- men is either located at the posterior transition of the superior and middle meatus or posteriorly within the superior meatus (El-Shaarawy & Hassan 2018; Eördögh et al. 2018). The spheno- palatine foramen serves as the communication between the and the nasal cavity (von Arx & Lozanoff 2017). Two superior processes of the vertical plate of the contacting the sphenoid bone form the sphenopalatine foramen (Morton & Khan 1991). The mean diameter of the sphe- nopalatine foramen has been reported to be 5.3 mm (Hwang et al. 2011). According to a skull study by Prades et al. (2008), the sphenopalatine foramen is positioned on average 13 mm above the horizontal lamina of the inferior concha and 18.3 mm above the horizontal plate of the palatine bone. The semilunar hiatus is located approximately in the central area of the lateral nasal wall at the level of the middle nasal me- atus and laterally to the middle concha. The semilunar hiatus has a horizontal inferior (posterior) and a vertical superior (an- terior) component (Stammberger & Kennedy 1995), thus it shows an ascending crescent shape but may exhibit great morphologic variability (Dahlstrom & Olinger 2014). The latter authors quan- tified the width and length of the semilunar hiatus in 97 hemi- Fig. 11 CBCT of a 27-year-old female (original FOV 20 × 17 cm) with coro- sected embalmed human heads. The mean width at the supero- nal (A), sagittal (B) and axial (C) views 1 = infraorbital canal; 2 = maxillary sinus; 3 = middle concha (pneumatized); anterior border was 1.7 mm and at the inferoposterior border 4 = inferior concha; 5 = pterygopalatine fossa; 6 = uncinate process; 7 = os- 4.7 mm, whereas the mean length was 26 mm. The following tium maxillare; 8 = ethmoid cells; 9 = nasolacrimal duct; 10 = sphenoid sinus; structures drain into the semilunar hiatus: the frontal sinus into 11 = frontal sinus; * = large Haller cell. It appears that the patient has had maxillary sinus surgery on the right side (° Fig. A). the superior aspect, the anterior ethmoid cells into the middle aspect, and the maxillary sinus via the maxillary ostium into the inferior aspect of the semilunar hiatus. Lateral nasal wall Areas of the lateral nasal wall in which no bone exists are The lateral walls of the proper nasal cavities consist of the os called “nasal fontanelles” (Stammberger & Kennedy 1995). The maxillae (anterior as well as inferior parts), the vertical plate of mucosa of the maxillary sinus and of the middle nasal meatus the palatine bone (posterior part), the nasal bone (anterosupe- are only separated by a fibrous layer. The nasal fontanelles are

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usually located above the insertion of the inferior concha with 33 cm2 in males and to 27 cm2 in females. In a similar study con- distinction of an anterior and a posterior fontanelle. ducted in 168 Koreans, the following mean surface areas were reported for males and females: vomer 964 mm2 and 822 mm2, Inferior concha perpendicular plate of ethmoid bone 1,084 mm2 and 975 mm2, The inferior nasal turbinate is considered an independent bone septal cartilage 768 mm2 and 713 mm2 (Kim et al. 2010b). The cal- that articulates with the , palatine, ethmoid and lacrimal culated mean total surface areas were 28 cm2 in males and 25 cm2 bones. It is the largest of all three conchae and extends along in females. the entire length of the nasal cavity (Ogle et al. 2012). The infe- According to Hur et al. (2016), the nasal crest contributes rior displays a complex morphology with long 5.6% to the surface area of the nasal septum. In contrast, the processes including the ethmoidal, lacrimal and maxillary ar- perpendicular plate of the ethmoid bone represents 43.0%, the ticulating with adjacent bones while also forming a portion of vomer 25.8% and the septal cartilage 25.6% of the septal sur- the medial wall of the maxillary sinus as well as the nasolacri- face area. The same authors also reported in 74.3% of the evalu- mal duct. Pneumatization of the inferior concha is a rare con- ated specimens the presence of an elevated premaxillary wing dition with a reported frequency of 1% (Shpilberg et al. 2015; that extended from the os maxillae upwards between the septal Koo et al. 2017). cartilage and the vomer. Nasal septal deviation is a common finding with frequencies Nasal septum ranging from 14 to 80% (Koo et al. 2017). Nasal septal deviation The nasal septum is a mixed osseous and cartilaginous structure is defined as any bending of the septal contour in the coronal or and it is composed of five parts (Fig. 13) (Ogle et al. 2012): axial planes (Shpilberg et al. 2015). The deviation of the septum – Perpendicular plate of ethmoid bone occurs usually at the union of the vomer either with the perpen- – Vomer dicular plate of the ethmoid bone or with the septal cartilage, – Septal cartilage respectively (Hur et al. 2016). The presence of a nasal septal de- – Nasal crest of maxillary bones viation is often associated with the occurrence of a unilateral – Nasal crest of palatine bones concha bullosa (middle turbinate), or a prominent bulging con- cha in the case of bilateral conchae bullosae (Stallman et al. The vomer and the ethmoid bone contribute to the osseous, 2004). As a result, the deformed septum shows a convexity to posterior part of the septum. The anterior part of the septum the opposite side with regard to the widened middle concha, comprises the septal cartilage that articulates with the nasal but the air channel between the deviated septum and the en- crest. larged concha is preserved. Surface area mapping of the nasal septum using CT in 100 Cau- casian patients revealed the following mean figures for males and Septal cartilage females, respectively: vomer 894 mm2 and 741 mm2, perpendic- The septal cartilage, quadrangular or triangular in shape, ular plate of ethmoid bone 1,244 mm2 and 1,066 mm2, septal car- extends anteriorly to the to which it is tilage 1,148 mm2 and 981 mm2 (Daultrey et al. 2018). In total, the attached via loose connective tissue fibers (chondrospinal junc- surface areas of the nasal septum amounted to approximately tion), thus allowing some mobility (Hafkamp et al. 1999). Some- times, the septal cartilage shows a posterior (sphenoidal) process projecting between the vomer and the perpendicular plate of the ethmoid bone (Hur et al. 2016). This sphenoidal process is con- sidered a remnant tail of the septal cartilage resulting from de- layed ossification of the nasal septum (Kim et al. 2012). The mean length of the posterior (sphenoidal) process in patients with a deviated nasal septum was 26.1 ± 5.3 mm versus 12.0 ± 2.4 mm in controls (Kim et al. 2010a). A long posterior (sphenoidal) process appears to contribute to exacerbation of septal deviation (Kim et al. 2012). Hwang et al. (2010) assessed the size and thickness of the sep- tal cartilage in 15 Korean cadavers. They reported a mean length and height of 3.31 ± 0.53 cm and 2.99 ± 0.47 cm. The thickness of the septal cartilage showed great variability (0.7–3.0 mm) depending on the site of measurement. Generally, the greatest thickness was observed along the septal base. The septal carti- lage may show a bulge in its central area, called the nasal septal body or septal turbinate (Elwany et al. 2009). The septal body is usually located superior to the inferior concha and anterior to the middle concha.

Fig. 13 Graphic illustration of the nasal septum (right side) and adjacent structures Vomer 1 = perpendicular plate of ethmoid bone; 1a = cribriform plate of ethmoid The vomer forms the inferior part of the bony septum, but ex- bone; 2 = septal cartilage; 2a = posterior (sphenoidal) process of septal carti- tends posteriorly up to the body of the sphenoid bone. Occa- lage; 3 = vomer; 3a = vomeronasal cavity; 4 = nasal crest of maxillary bone; sionally, bilateral cavities (“fetal remnants”) are observed en- 5 = nasal crest of palatine bone; 6 = anterior nasal spine; 7 = nasopalatine (incisive) canal; 8 = medial plate of pterygoid process of sphenoid bone; doscopically at the anterior bottom of the vomer close to the 9 = sphenoid sinus; 10 = frontal sinus; 11 = nasal bone nasal openings of the nasopalatine canal (Trotier 2011). The

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vomeronasal cavities contain the vomeronasal organs (VNO) the middle turbinate divides the ethmoid cells into anterior and during fetal development, but eventually, the VNO regress in posterior divisons (Ogle et al. 2012). Many authors traditionally the neonate (von Arx et al. 2018b). describe a middle ethmoid air cell creating the projection of the ethmoid bulla extending into the middle meatus (Perez-Pinaz Ethmoid bone 2000; Drake et al. 2015). However, currently accepted guide- The singular ethmoid bone, located between the orbital cavi- lines for terminology of the paranasal sinuses indicate that the ties, contributes to the upper half of the nasal skeleton. The expressions “middle ethmoid” and “middle ethmoid cells” ethmoid bone has a complex morphology with multiple bony should not be used, because in terms of anatomy, physiology, plates, air cells (ethmoid labyrinths) and perforations. The eth- or function, no structure represents the middle of the ethmoid moid bone consists of five distinct components (Ogle et al. complex (Stammberger & Kennedy 1995). 2012): The ethmoid sinus is highly variable in form and structure – Crista galli as well as in the quantity of air cells (Zhang et al. 2007; Liu et – Cribriform plate al. 2018). Typically, seven smaller anterior cells and four larger – Perpendicular plate posterior cells are present (Ogle et al. 2012). Anterior ethmoid – Bilateral ethmoid labyrinths air cells drain into the middle meatus whereas posterior eth- moid cells drain into the upper meatus and into the spheno- The crista galli is not a part of the nasal cavity but rather of the ethmoidal recess, respectively. Anatomical variants of the eth- anterior cranial fossa. The perforated cribriform plate of the moid air cells have been reported extensively (Wormald 2003; ethmoid bone forms the roof of the nasal cavities. The perfora- Stallman et al. 2004; Shpilberg et al. 2015; Cheng et al. 2017; tions within the cribriform plate serve for passage of the olfac- Chmielik & Chmielik 2017; Liu et al. 2018) and include: tory (cranial nerve II) from the olfactory cells to – Agger nasi cell (occurrence rate 3–100%) (agger in Latin the brain. The size of the cribriform plate is as follows: length means “mound”): defined as the most anteriorly placed 20 mm, width 5 mm, and thickness (height) 2 mm (Ogle et al. frontal ethmoid cell that is located anterolateral and inferior 2012). to the frontal recess (the latter refers to the tubular space The centrally located perpendicular plate of the ethmoid bone connecting the frontal sinus to the middle nasal meatus) (PPE) forms the upper portion of the nasal septum. Superiorly, (Fig. 6). According to Ogle et al. (2012), Agger nasi cells lay the perpendicular plate is continuous with the cribriform plate. below the lacrimal sac from which they are separated by Mladina et al. (2017) concluded that compact bone is not con- only a very thin layer of bone. stant since they found some degree of pneumatization in 34.4% – Haller’s cell (occurrence rate 2–45%) (named after Albrecht of the PPE examined. This feature is referred to as “sinus septi von Haller, Swiss physician and anatomist, 1708–1777): nasi”. Hypothetically, this cavity formation within the nasal infraorbital ethmoid cell located below the medial orbital septum could be associated with extensions from the frontal floor and above the maxillary ostium (Fig. 11). According to or sphenoid sinuses into the PPE (Mladina et al. 2017). Caversaccio et al. (2011), Haller’s cell should be defined as The middle and superior turbinates are components of the an anterior ethmoid cell, localized in the infraorbital region, ethmoid bone. The superior concha is located in the posterior hollowing out the maxillary bone and originating from the third of the nasal cavity, with its anterior and highest portion ethmoid labyrinth. It is the most inferior ethmoid cell that is opposite the medial canthal tendon (Ogle et al. 2012). The con- located infraorbitally nearest to the ostium of the maxillary cha bullosa, i.e., the pneumatized middle nasal turbinate, is sinus. considered a normal and asymptomatic variant with reported – Onodi cell (occurrence rate 3–51%) (named after Adolf Onodi, frequencies of 13 to 53% (Koo et al. (2017). Pneumatization of Hungarian rhinolaryngologist, 1857–1919): most posterior the superior turbinate has also often been described with prev- ethmoid cell extending superiorly and laterally towards the alences ranging from 26 to 57% (Shpilberg et al. 2015). Ila et sphenoid sinus (Fig. 8). Onodi cells may show an intimate al. (2018) evaluated CT scans of 1,000 patients and reported relationship to the optic canal. Onodi cells are also known pneumatization of the superior concha in 14.9%. Of those as sphenoethmoid air cells. patients, 60.4% also presented pneumatization of the middle – Ethmomaxillary sinus (occurrence rate 0.7–7%): posterior eth- concha. A study by Koo et al. (2017) of 594 CT scans reported moid cell expanding toward or even entering the maxillary a frequency of superior and middle turbinate pneumatization sinus with drainage to the superior nasal meatus. of 38.7% and 53.7%, respectively. The ethmoid bulla is a protuberance lateral to the middle Discussion meatus and transmits drainage accordingly. The uncinate pro- This literature review presents an update of the clinical and cess of the ethmoid bone projects inferolaterally, contributes to radiological anatomy of the nasoethmoidal region. The latter the lower border of the semilunar hiatus, and may contact the includes the nasal cavities and the ethmoid bone. The ethmoid inferior concha. Superiorly, the uncinate process may attach to bone is a cuboidal structure that is located medial to the orbits the lamina papyracea, the skull base, or the middle turbinate above the nasal cavities and immediately inferior to the ante- (Cheng et al. 2017). Occasionally, pneumatization of the unci- rior cranial fossa. The nasal cavities are separated by a midline nate process (uncinate bulla) has been reported (Bolger et al. septum and contain each three nasal conchae (turbinates). 1990; Koo et al. 2017). A critical component of the nasoethmoidal region is the ostio- Ethmoid labyrinths housing multiple air cells (ethmoid meatal complex. Disturbance of (para)nasal ventilation and sinus) are located immediately medial to the medial orbital drainage via the ostiomeatal complex may result in pansinus- walls (Fig. 12). The most lateral parts of the ethmoid bone are itis. the thin laminae orbitales (laminae papyraceae) that contribute The prescribing clinician, taking and/or viewing CBCT imag- to the medial walls of the orbital cavities. The basal lamina of es is challenged with interpreting the entire CBCT volume. The

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anatomy of the nasal cavity is complex, in particular the eth- eigentlichen Nasenhöhle (Cavum nasi). Letztere wird durch das moid bone, and possess great variability with regard to form median und sagittal ausgerichtete Nasenseptum in zwei Kavi- and structure. Basically, the nose is one of two gateways for täten unterteilt. air to enter the body when (the other being the oral Das Septum nasi (Nasenscheidewand) ist aus fünf Teilen zu- cavity). Olfaction is another major function of the nose. The sammengesetzt: Lamina perpendicularis des Ethmoid, Vomer, cribriform plate of the ethmoid bone has multiple openings for Knorpelseptum, sowie Cresta nasalis des Os maxillae und des olfactory nerve axons to reach the olfactory bulbs in the ante- Os palatinum. In der Literatur wird über eine Gesamtfläche rior cranial fossa. des Septums von etwa 25 cm2 bis 33 cm2 berichtet, je nach Ge- With regard to CBCT imaging, the nasal floor, the inferior schlecht und Ethnie der Patienten. Das Knorpelseptum (Länge and middle conchae and the lower aspects of the nasal septum ca. 3 cm, Dicke 0,7 bis 3 mm) zeigt oft eine nach posterior gerich- are frequently observed on CBCT scans of the maxilla. Larger tete längliche Fortsetzung zwischen Vomer und Ethmoid. Der FOVs (≥ 10 × 10 cm), especially when used for diagnosis and Vomer bildet den unteren und hinteren Anteil der Nasenschei- treatment planning of implant placement in the posterior denwand und zieht bis zum Os sphenoidale hoch. maxilla or the use of sinus floor elevation procedures, will also Die Nasenhöhlen werden durch drei paarige Nasenmuscheln depict the complex ethmoid bone with its multiple air cells in vier Etagen unterteilt, sodass die einströmende Luft über and anatomical variants (Bornstein et al. 2017b; Jacobs et al. eine grosse Fläche erwärmt und befeuchtet wird. Eine mecha- 2018). nische Reinigung der Atemluft erfolgt zudem durch die Vibris- Understanding the complex anatomy and anatomical varia- sae im Nasenvestibulum. Die grösste Nasenmuschel ist die tions of the nasoethmoidal region is crucial for radiologic inter- Concha inferior, die als eigenständiger Knochen gilt. Diese pretation and diagnosis, especially from a clinical point of view Muschel erstreckt sich über die ganze Länge der Nasenhöhle (Gibelli et al. 2018). The precision and quality of current CBCT (ca. 6 cm). Die mittlere und die obere Nasenmuschel gehören imaging greatly support the clinician in the assessment of these zum Ethmoid (Siebbein) und sind kürzer und kleiner als die important anatomical structures, and to rule out (para)nasal untere Nasenmuschel. Alle Nasenmuscheln können radiolo- pathology. gisch eine Pneumatisierung zeigen, am häufigsten die mittlere Muschel (Concha bullosa). Acknowledgements Die vier Nasengänge (Meati nasales inferior, media et superior The authors thank Bernadette Rawyler, medical illustrator, sowie Recessus sphenoethmoidalis) pro Seite haben diverse Öff- and Ines Badertscher, media designer, School of Dental Medi- nungen, in die sich anatomische Nachbarstrukturen entleeren: cine, University of Bern, Switzerland, for the illustrations. The im unteren Gang der Tränenkanal (Ductus nasolacrimalis), im authors acknowledge the generous donation of the anatomical mittleren Gang die Kieferhöhle, die vorderen Siebbeinzellen materials by anonymous individuals in the Willed Body Pro- sowie die Stirnhöhle und im oberen Gang die hinteren Sieb- gram, University of Hawaii John A. Burns School of Medicine, beinzellen. In die oberste Etage (Recessus sphenoethmoidalis) Honolulu, USA. mündet die Keilbeinhöhle (Sinus sphenoidalis). Der mittlere We also acknowledge Dr. Andy Wai Kan Yeung, Oral and Nasengang wird auch als ostiomeataler Komplex bezeichnet Maxillofacial Radiology, Applied Oral Sciences, Faculty of Den- wegen seiner komplizierten Verbindungen zu den diversen tistry, The University of Hong Kong, Prince Philip Dental Hos- Nasen nebenhöhlen. pital, Hong Kong, China, for providing some of the CBCT imag- Der Nasenboden besteht aus den gleichen Strukturen, die es used in this study. Furthermore, we thank Dr. Odette Engel auch den harten Gaumen bilden: aus palatinalen Fortsätzen des Brügger, School of Dental Medicine, University of Bern, Swit- Os maxillae sowie aus horizontalen Fortsätzen des Os palatinum. zerland, for the French translation of the summary. Das Dach der Nase bilden die paarigen Nasenknochen sowie die Lamina cribriformis des Ethmoid. Die seitlichen Nasenwände Conflict of interest sind kompliziert aus mehreren Knochen zusammengesetzt: The authors declare that there are no conflicts of interest re- Os maxillae, Os frontale, Os lacrimale, Os palatinum sowie Os eth- lated to this review. moidale. Grössere Öffnungen in der lateralen Nasenwand sind der Hiatus semilunaris, u. a. mit dem Ostium maxillare, sowie das Zusammenfassung Foramen sphenopalatinum als Verbindung von der Nasenhöhle Die digitale Volumentomografie (DVT) wird heute in der zahn- zur Fossa pterygopalatina. medizinischen Diagnostik immer häufiger eingesetzt. Je nach Das Ethmoid (Os ethmoidale, Siebbein) ist ein sehr komplex Grösse des gewählten DVT-Fensters werden auch anatomische gebauter Knochen und umfasst hauptsächlich die Siebbeinzel- Strukturen ausserhalb des dentomaxillären Komplexes abgebil- len (Labyrinthe). Diese liegen medial zu den Augenhöhlen und det. Um auch diese Strukturen richtig interpretieren zu kön- drainieren zum mittleren und oberen Nasengang. Als anatomi- nen, muss der Kliniker entsprechende anatomische Kenntnisse sche Varianten gelten die Agger-nasi-Zelle (vorderste Siebbein- haben. In dieser ersten von vier Arbeiten wird die Anatomie der zelle), die Haller-Zelle (liegt infraorbital oberhalb des Ostium nasoethmoidalen Region dargestellt und anhand der aktuellen maxillare), sowie die Onodi-Zelle (hinterste Siebbeinzelle mit Literatur diskutiert. enger Beziehung zum Canalis opticus). Die Nase besteht grundsätzlich aus den äusseren, sichtbaren Strukturen wie Nasenflügeln und Nasenrücken wie auch aus Résumé inneren Strukturen, den Nasenhöhlen. Das Nasengerüst besteht Le Cone Beam ou « image volumétrique par faisceau conique » im oberen Teil aus Knochen (Os nasale sowie Processus frontalis est un outil de diagnostic de plus en plus commun dans la méde- des Os maxillae) und im unteren Teil aus mehreren Knorpeln cine dentaire moderne. Selon la taille choisie de la prise de vue, (Cartilagines laterales und Cartilagines alares). Das Vestibulum der on visualisera des structures dépassant le complexe dento-al- Nase verbindet die äusseren Öffnungen der Nase (Nares) mit der véolaire – structures dont l’anatomie doit être connue pour un

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diagnostic adéquat. Ce travail – premier d’une série de quatre – Les cavités nasales subdivisées en quatre étages par les cor- présente l’anatomie de la zone nasoethmoïdale ainsi que les pu- nets communiquent avec d’autres structures anatomiques par blications actuelles en rapport avec ce sujet. différents canaux. Le conduit lacrymonasal débouche dans le Le nez se compose des structures externes, visibles – le dos méat inférieur. Le sinus maxillaire, les parties antérieures et et les ailes du nez – ainsi que des structures internes – les cavi- moyennes du labyrinthe ethmoïdal ainsi que le sinus frontal tés nasales. Le squelette du nez est composé d’une partie supé- s’ouvrent vers le méat moyen ; la partie postérieure du laby- rieure osseuse (Os nasale et Processus frontalis des Os maxillae) rinthe ethmoïdal vers le méat supérieur. Les sinus sphénoï- et d’une partie inférieure cartilagineuse (Cartilagines laterales daux quant à eux communiquent avec l’étage supérieur des et Cartilagines alares). Le vestibule du nez relie les ouvertures cavités nasales, les Recessus sphenoethmoidales. Au vu des externes – les narines – aux deux cavités nasales proprement nombreuses relations avec les différents sinus, on utilisera dites (Cavum nasi). Ces dernières sont situées de part et d’autre aussi le terme de complexe ostiomeatal pour évoquer le méat d’une cloison sagittale médiane, le septum nasal. Cette cloison moyen. ostéo-cartilagineuse se compose de cinq parties distinctes : la La paroi inférieure des cavités nasales est composée des lame perpendiculaire de l’ethmoïde, le vomer, le cartilage sep- mêmes éléments que le palais dur : le processus palatin du tal ainsi que la Cresta nasalis des maxillaires et du palatin. La lit- maxillaire ainsi que la lame horizontale du palatin. La paroi térature parle d’une surface totale de 25 à 33 cm2 selon le sexe supérieure est composée par les deux Os nasale ainsi que par et l’appartenance ethnique du patient. Le cartilage septal (3 cm la lame criblée de l’ethmoïde. La paroi latérale quant à elle de long, 0,7 à 3 mm d’épaisseur) présente souvent un prolonge- est complexe dans sa constitution : le maxillaire, le frontal, ment postérieur entre le vomer et l’ethmoïde. Le vomer cons- le lacrymal, le palatin et l’ethmoïde en font partie. Ses ouver- titue la partie inférieure et postérieure de la cloison nasale se tures les plus importantes sont le Hiatus semilunaris comprenant prolongeant vers le haut jusqu’au sphénoïde. entre autres l’Ostium maxillare ainsi que le Foramen sphenopala- Les cavités nasales sont subdivisées en quatre étages par trois tinum (ouverture vers la fosse pterygopalatine). paires de cornets nasaux augmentant ainsi la surface d’échange L’ethmoïde est une structure osseuse particulièrement com- permettant de réchauffer et d’humidifier l’air inspiré. Ce dernier plexe dont la composante principale est le labyrinthe ethmoï- sera de plus filtré mécaniquement par les vibrisses dans le vesti- dal. Situé en médial de l’orbite, ce dernier se déverse dans la bule du nez. Le cornet le plus grand – le cornet inférieur - est un cavité nasale à hauteur des méats moyen et supérieur. On évo- os à part entière s’étendant sur toute la longueur des cavités na- quera les variantes anatomiques suivantes : la cellule d’Agger sales (environ 6 cm). Les cornets moyens et supérieurs font par- nasi (pneumatisation excessive d’une cellule ethmoïdale anté- tie de l’ethmoïde. Ils sont plus courts et plus petits que le cornet rieure), la cellule de Haller (position infraorbitaire en dessus inférieur. Tous les cornets peuvent présenter une pneumatisa- de l’Ostium maxillare) ainsi que la cellule d’Onodi (cellule la plus tion, surtout le cornet moyen (Concha bullosa). postérieure au contact du canal optique).

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