804 RESEARCH AND SCIENCE Thomas von Arx1 Scott Lozanoff2 Extraoral anatomy 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 Nasal cavity Kong SAR, China Ethmoid bone 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 vomer Tel. +41 31 632 25 66 widely used imaging technique for dental indica- and the septal cartilage. 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 paranasal sinuses, Accepted for publication: anatomy of the nasoethmoidal region is present- i.e., maxillary sinus, anterior ethmoid cells, and 10 December 2018 ed based on a literature review. The nose is char- frontal sinus. Posterior ethmoid cells empty into acterized by the nasal septum and the superior, the superior meatus and the sphenoid sinus middle, and inferior conchae. The turbinates may drains into the sphenoethmoidal recess, located be pneumatized (concha bullosa), mainly the above the superior concha. The nasolacrimal duct middle concha. The ethmoid bone 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. SWISS DENTAL JOURNAL SSO VOL 129 10 P 2019 804-815_T1-1_vonarx_EDF.indd 804 01.10.19 11:09 RESEARCH AND SCIENCE 805 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 = nasal bone; 5 = frontal process of os maxillae; pare grey values among or within patients over time. This lack 6 = lacrimal bone; 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 jaw 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 bones 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 = nostril; 6 = infraorbital foramen with processes of the os maxillae. Several cartilages contribute to the neurovascular bundle SWISS DENTAL JOURNAL SSO VOL 129 10 P 2019 804-815_T1-1_vonarx_EDF.indd 805 01.10.19 11:09 806 RESEARCH AND SCIENCE 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 nostrils, 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 hard palate while the roof of the nasal cavity is formed by the cribriform plate 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- pharynx. 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 (ethmoid sinus); 3 = sphenoid sinus; Hairs (vibrissae) located in the vestibule have a cleaning func- 4 = sphenoethmoidal recess with opening of sphenoid sinus; 5 = upper nasal meatus with opening of posterior ethmoid cells; 6 = location of underlying tion, whereas the nasal mucosa warms and humidifies the sphenopalatine foramen; 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.