216 RESEARCH AND SCIENCE Thomas von Arx1 Scott Lozanoff2 Extraoral anatomy in CBCT - Michael M. Bornstein3,4 a literature review 1 Department of Oral Surgery and Stomatology, School of Dental Medicine, University of Bern, Switzerland Part 3: Retromaxillary 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 and Community Dental Care, Anatomy Faculty of Dentistry, The Uni- CBCT versity of Hong Kong, Prince Retromaxillary region Philip Dental Hospital, Hong Sphenoid bone Kong SAR, China Sphenoid sinus 4 Department of Oral Health Pterygopalatine fossa & Medicine, University Center for Dental Medicine Basel UZB, University of Basel, Basel, Switzerland CORRESPONDENCE Prof. Dr. Thomas von Arx SUMMARY Klinik für Oralchirurgie und Stomatologie In this review about extraoral anatomy as depict- lesser wings, and pterygoid processes. Important Zahnmedizinische Kliniken ed by cone beam computed tomography, the ret- neurovascular structures pass through the sphe- der Universität Bern romaxillary region is discussed. A medium-sized noid bone: the optic nerve and the ophthalmic Freiburgstrasse 7 (6 × 6 cm) or large (≥ 8 × 8 cm) field of view of the artery via the optic canal, the maxillary nerve CH-3010 Bern maxilla will inevitably depict the retromaxillary via the foramen rotundum, and the pterygoid Tel. +41 31 632 25 66 Fax +41 31 632 25 03 region that can be considered a “transition” zone nerve via the Vidian canal. The central body of E-mail: between the viscerocranium and the neurocrani- the sphenoid bone also contains the highly vari- [email protected] um. Major structures of the region include the able sphenoid sinus that is the most posteriorly sphenoid bone and the pterygopalatine fossae. located paranasal sinus. The bilateral pterygopal- SWISS DENTAL JOURNAL SSO 130: 216–228 (2020) The sphenoid bone is a single but complex bone atine fossae behind the maxillary sinuses contain Accepted for publication: located between the maxilla and the brain. It is several important neurovascular structures that 16 September 2019 composed of a central body, bilateral greater and supply the maxilla and the midface. SWISS DENTAL JOURNAL SSO VOL 130 3 P 2020 216-228_T1-1_vonarx_EDF.indd 216 27.02.20 07:22 RESEARCH AND SCIENCE 217 Introduction This third literature review about extraoral anatomy as depicted and seen in cone beam computed tomography (CBCT) scans ad- dresses the retromaxillary region. The latter can be defined as the zone immediately posterior to the maxillary bones on both sides. The region includes the sphenoid bone and the pterygo- palatine fossae. Both anatomical structures are usually depicted on CBCT scans of the posterior maxilla and/or the maxillary sinus performed, for example, for treatment planning prior to dental implant placement including sinus floor elevation proce- dures or periapical surgery of molars. The single sphenoid bone presents a complex morphology and it can be regarded as a “transition” bone between the viscerocranium and the neuro- cranium (Fig. 1). The sphenoid bone contributes to the orbital apex, to the anterior and middle cranial fossae, and to the later- al wall of the skull (Budu et al. 2013). The sphenoid bone also contains the highly variable sphenoid sinus that may have clini- cally perilous anatomical relations with the optic nerves and the internal carotid arteries. The bilateral pterygopalatine fossae are located behind the posterior aspect of the maxillary bones. The fossae are consid- ered the “control center” of the maxilla since they contain the maxillary nerve, the maxillary artery, and the pterygopalatine ganglion, all supplying the maxilla as well as the entire midface. Due to its inherent complex location, the pterygopalatine fossa Fig. 1 The sphenoid bone (highlighted in blue) is a viscerocranial component can potentially act as a natural conduit for the spread of inflam- of the craniofacial skeleton that forms a transition zone articulating with matory and neoplastic diseases across the various deep spaces contiguous neurocranial elements. of the head and neck (Tashi et al. 2016). Sphenoid bone extends laterally as the posterior clinoid processes (Chong et al. The anatomy of the sphenoid bone (“sphen” in Greek means 1998). The sphenoid body also contributes to the clivus that ex- wedge-shaped) is complicated since it is not a compact struc- pands posteriorly from the dorsum sellae and slopes downwards ture but rather presents with multiple wings and processes to the foramen magnum (Fig. 3). The inferior face of the clivus originating from a central body (Chong et al. 1998; Jaquesson represents the roof of the nasopharynx (Chong et al. 1998). et al. 2017) (Fig. 2). Furthermore, the sphenoid bone contains Three bony canals run through the lateral aspects of the sphe- several fissures, canals and foramina that convey neurovascular noid body: superiorly the optic canal, midway the foramen ro- structures from the middle cranial fossa to the maxillofacial re- tundum, and inferiorly the pterygoid (Vidian) canal. These ca- gion. The sphenoid bone contributes superiorly to the anterior nals transmit significant neurovascular structures to the orbits and middle cranial fossae, anterolaterally to the orbital walls, and pterygopalatine fossae (see below). laterally to the temporal fossae, and inferoanteriorly to the nasal cavities and to the pterygopalatine fossae. Sphenoid sinus The sphenoid bone has long been recognized as comprising The sphenoid sinus (SPS) is located within the central portion four parts (Fawcett 1910): of the sphenoid bone, i. e. the sphenoid body (Fig. 3–5). The SPS – central body shows great variability with regard to size, shape and compart- – greater wings mentalization. The SPS is the most posterior of the paranasal si- – lesser wings nuses. It drains into the sphenoethmoidal recess that is located – pterygoid processes superior or posterior to the superior nasal turbinate (Anusha et al. 2014; von Arx et al. 2019). Usually, the SPS is divided by an When viewed from anterior, the greater wings resemble the intervening septum into two compartments. Since the septum outstretched wings of a bird with the pterygoid processes ap- is rarely located in the midsagittal plane but rather deviated pearing as extended limbs (Chong et al. 1998). laterally, the SPS has asymmetric cavities. Often, there is a dominant cavity on one side (Tan & Ong 2007). Some SPS may Central body demonstrate subdivision into several recesses by accessory sep- The central body of the sphenoid bone has a cuboidal shape and ta. The average volume of the SPS ranges between 3 and 10 ml is actually hollowed by the sphenoid sinus. The body is the ori- (Anusha et al. 2014). gin for the paired greater and lesser wings as well as for the The extent of the SPS is commonly divided into three main pterygoid processes (Fig. 2). Superiorly, a bony depression (sella types (Budu et al. 2013; Anusha et al. 2014): (1) the conchal type turcica = Turkish saddle) serves as the hypophyseal or pituitary represents a very small sinus or pneumatization is completely fossa. Anterior (large) and posterior (small) clinoid processes absent and the “sinus” is filled with trabecular bone; (2) the represent the four corners of the sella turcica. Lateral to the sella presellar (or juvenile) type has pneumatization extending to the lies the paired cavernous sinus, a large venous cavity. The dor- sella turcica but not posterior to it; (3) the sellar (or adult) type sum sellae forms the posterior boundary of the sella turcica and demonstrates complete pneumatization of the sphenoid body. SWISS DENTAL JOURNAL SSO VOL 130 3 P 2020 216-228_T1-1_vonarx_EDF.indd 217 27.02.20 07:22 218 RESEARCH AND SCIENCE Fig. 2 Anterior view of the isolated sphenoid bone 1 = body of sphenoid bone; 2 = sphenoid crest; 3 = aperture of sphenoid sinus; 4 = lesser wing; 5 = orbital surface of greater wing; 6 = cranio-orbital foramen; 7 = superior orbital fissure; 8 = anterior opening of optic canal; 9 = foramen rotundum; 10 = pterygoid (Vidian) canal; 11 = vaginal process; 12 = palatovaginal (pharyngeal) canal; 13 = vomerovaginal canal; 14 = lateral plate of pterygoid process; 15 = medial plate of pterygoid process; 16 = sphenoid spine; 17 = dorsum sellae Furthermore, the SPS may expand into the greater and lesser Greater wings sphenoid wings, into the pterygoid processes, as well as into The paired greater wings originate from the lateral aspects of the the anterior clinoid processes (Unal et al. 2006; dal Secchi et al. central sphenoid body (Fig. 2). The greater wings have three sur- 2018). Pneumatization of the anterior clinoid process by the faces: (1) an anterior orbital surface contributing to the lateral sphenoid sinus has been reported in 6–29.3% (Anusha et al. orbital wall – the orbital surface is bounded by the superior and 2015). Generally, extensive pneumatization of the SPS can be inferior orbital fissures; (2) an external surface forming part of associated with irregularities in the sinus walls featuring pro- the lateral wall of the cranium; and (3) an internal posterior sur- trusions and recesses (dal Secchi et al. 2018). face that is oriented horizontally and contributes to the anterior Four vital structures run along the sphenoid sinus: the optic portion of the middle cranial fossa. The greater wings contain nerve in the superolateral wall, the internal carotid artery in the three important foramina, i. e. rotundum, ovale and spinosum. midlateral wall, the maxillary division of the trigeminal nerve in The foramen rotundum is located anteromedially while the fora- the inferolateral wall, and the Vidian nerve in the floor of the si- men ovale and foramen spinosum are positioned posterolaterally nus (Tan & Ong 2007). All of these neurovascular structures may (Chong et al. 1998). The sphenoid spine, a sharp bony projection indent the walls of the SPS or even show bulging into the sinus behind the foramen spinosum, also belongs to the greater wing.