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Surg Radiol Anat DOI 10.1007/s00276-015-1468-x ANATOMIC VARIATIONS Infraorbital canal bilaterally replaced by a lateroantral canal M. C. Rusu1 • M. Săndulescu2 • O. C. Ilie3 Received: 21 October 2014 / Accepted: 23 March 2015 Ó Springer-Verlag France 2015 Abstract The infraorbital canal (IOC) normally courses above the maxillary sinus in the orbit floor. During a retrospective study of cone beam computed tomography (CBCT) scans, we found a previously unknown variant of the IOC. The IOCs were absent, being replaced by lateroantral canals coursing around and not above the maxillary sinus to open at infraorbital foramina which were located above the second upper premolar teeth. On coronal multiplanar reconstructions, the lateroantral canals were located anatomically at the outer limit of the zygomatic recess of each maxillary sinus, while the upper wall of the sinus was devoid of any canal. Such rare variant should be kept in mind by dental practitioners and surgeons, as it can determine modifications of common procedures. In this regard, the anatomy of maxilla, as well as mandible, should be evaluated in CBCT on a case-by-case basis. Keywords Maxillary sinus Orbit Cone beam computed tomography (CBCT) Maxillary nerve Infraorbital nerve All the authors have equally contributed to this study. & M. C. Rusu [email protected] 1 Division of Anatomy, Faculty of Dental Medicine, ‘‘Carol Davila’’ University of Medicine and Pharmacy, 8, Eroilor Sanitari Blvd., Sector 5, 050474 Bucharest, Romania 2 Division of Oral Implantology, Faculty of Dental Medicine, ‘‘Carol Davila’’ University of Medicine and Pharmacy, Bucharest, Romania 3 Department of Anatomy, ‘‘Victor Babeş’’ University of Medicine and Pharmacy, Timişoara, Romania Introduction The maxillary nerve exits the middle cranial fossa through the foramen rotundum in the greater wing of sphenoid bone [16]. It further traverses the pterygopalatine fossa and the pterygomaxillary fissure to continue, as infraorbital nerve (ION), in the infraorbital groove and canal located in the upper (orbital) wall of the maxillary sinus. The infraorbital vessels run in a mediosuperior position to the ION [10]. The ION exits through the infraorbital foramen (IOF) which is located below the infraorbital margin, on the anterior surface of maxilla [8]. During its course in the orbit floor, the ION distributes branches to the maxillary sinus and upper dentoalveolar arch and, after it emerges through the IOF, it ensures the sensory innervation of the midface, from the upper lip to the lower eyelid [8, 13]. Infraorbital nerve block is used in various maxillofacial and plastic surgical procedures, or to help diagnose neuralgia related to the maxillary nerve [13, 14]. The IOF is typically located by dropping a vertical line from the center of the pupil and palpating 4–5 mm medial to the line and 5–8 mm below the infraorbital margin [13]. There is, however, a disparity in literature regarding the distance between the IOF and the infraorbital margin [5]. The usually described anatomical variation of the infraorbital canal (IOC) refers to the number of IOF which lead passage for the terminal branches of the infraorbital nerve and infraorbital vessels. This number may vary from one to five [3, 4, 10, 13] but there are rarely found more than three foramina [13]. The IOF is usually single [4, 10] but additional IOF can convey, if present, separate branches of the infraorbital nerve to face and attention of surgeons is required when ION block is performed in such situations [20]. 123 Surg Radiol Anat The direction of the IOC is variable: the canal may run in antero-infero-medial, inferior, or medial directions [7]. The IOF is usually located above the upper premolar teeth [7]. The completeness of the IOC bony wall is also variable [7]. The morphology of the IOC can also be subject of variations which are related to the completeness of the bony canal [7]. Cone beam computed tomography (CBCT) has become an increasingly important source of three-dimensional (3D) volumetric data, since its introduction into dentistry in 1998 [9]. The large variation in the spatial relationships of the canalar structures mandates a case-by-case CBCT evaluation [2, 15]. During a retrospective CBCT study, a previously undescribed anatomic variation of the IOC was found and is reported here. Fig. 1 Antero-inferior view of a three-dimensional volume renderization (filter: transparent Skin, 98 % bone subtraction) in a 26-yearold female patient, presenting topographically normal infraorbital canals (arrows), as related to the maxillary sinuses pneumatizations. MS maxillary sinus pneumatization, INM inferior nasal meatus pneumatization Variant report During a CBCT study performed retrospectively on a lot of subjects scanned prior to various dental procedures, the Informed consent for using the scan data being obtained, the anatomic variation of the IOC was found in one of these patients. The subjects were scanned using a CBCT machine—iCat (Imaging Sciences International), and the CT data were analyzed using the iCat Vision software and the application 3DVR v5.0.0.3, for the 3D reconstructions, the specific protocol being previously described [17]. Bidimensional multiplanar reconstructions (MPRs) in the axial, coronal and sagittal planes, as well as oblique MPRs were used, as well as three-dimensional volume renderizations (3D VRs) which used the filter ‘‘Transparent Skin’’ with variable bone subtraction. In a 25-year-old female patient, the IOC was absent from its normal anatomical location, i.e., the upper wall of the maxillary sinus. The later was documented in ten different female patients of similar age, and a ‘‘control’’ 3D VR of a normal IOC indenting the infraorbital border of the maxillary sinus pneumatization is presented here (Fig. 1). In the case reported, the maxillary sinuses were bilaterally symmetrical, with an average height of 30 mm (documented at the level of the first upper molars). On each side were found impacted upper third molars and the roots of the second and first upper molars were curved distally. Surprisingly, the IOC was bilaterally missing from the bony wall separating the maxillary sinus and the orbit. Therefore, we performed an oblique/axial MPR (Figs. 2a, 3) to evaluate the location of the canal. We found that the canal was turning around the maxillary sinus in an anteroinferior plane. Thus, a bilaterally symmetrical variant lateroantral canal was replacing the anatomically normal infraorbital canal. On axial MPRs (Figs. 2b, 4) only 123 segments of the lateroantral canals were identified laterally to the maxillary sinus. On coronal MPRs (Fig. 2c) and 3D VRs (Fig. 5) the lateroantral canal was observed, bilaterally, in the postero-supero-medial angle of the maxillary bone, above the third upper molar, and was continuing downwards, at the limit between the maxillary and zygomatic bones, to reach the lowest level at its anterior end, above the second upper premolar (both upper second premolars were biradicular, presenting each vestibular and palatal roots), at 18.25 above the vestibular root of the right upper second premolar and at 16.57 mm above the vestibular root of the left upper second premolar. The lateroantral canals were documented also on oblique/coronal MPRs (Fig. 6). The terminal part of each lateroantral canal had a lateral-to-medial and slightly inferior direction. On 3D VRs, the ‘‘amprent’’ of the lateroantral canal was identified on the outer part of the maxillary sinus pneumatization, bilaterally, the right one presenting a straight course while the left one was, seemingly, angulated (Fig. 2d, e). Nevertheless, it was interesting to observe that in the case reported here, the foramen rotundum was, bilaterally, slightly above the midheight of the maxillary sinus, at 11.75/ 11.25 mm inferior to an anatomical plane tangent to the upper wall of the left (Fig. 7) and, respectively, right maxillary sinus. In the other ten patients of similar age who were used as controls the respective distance varied from 0.25 to 8.75 mm. Discussion During development, the first bone tissue which forms in the maxilla is located, at 8–9 weeks, caudal to the later infraorbital foramen; thus, it supports the infraorbital nerve Surg Radiol Anat Fig. 3 Diagram of the oblique/axial MPR in Fig. 2a indicating the anatomical landmarks. 1 Right infraorbital foramen, 2 right lateroantral canal, 3 zygomatic bone, 4 zygomatic arch, 5 posterior ethmoid air cell, 6 greater wing of the sphenoid bone, 7 temporal fossa, 8 sphenoid sinus, 9 posterior clinoid process, 10 antero-lateral wall of the maxillary sinus, 11 inferior nasal concha, 12 left lateroantral canal, 13 maxillary sinus, 14 middle nasal concha, 15 superior orbital fissure, 16 middle cranial fossa Fig. 2 CBCT multiplanar reconstructions (MPRs, a–c) and threedimensional volume renderizations (3D VRs, filter: transparent Skin, 98 % bone subtraction) of a 26-year-old female patient depicting the lateroantral canal bilaterally replacing the infraorbital canal. On all MPRs, the maxillary sinuses are indicated by asterisks. a An oblique/ axial MPR (inset the plane of section depicted on a sagittal MPR through the left maxillary sinus) on which the bilateral lateroantral canals are identified (arrowheads) coursing laterally to the maxillary sinuses and opened by infraorbital foramina (arrows). b The lateroantral canals (arrows) are partly identified on axial MPR. c On coronal MPR at the level of the interval between the second upper premolar and the first molar the lateroantral canals (arrows) are identified external to the zygomatic recesses of the maxillary sinuses. d 3D VR of the right maxillary sinus, laterally viewed; the lateroantral canal indents the sinus pneumatization beneath the zygomatic recess (the arrowheads indicate the origin and the arrows indicate the end of the lateroantral canal). e 3D VR of the left maxillary sinus (lateral view) depicting the left lateroantral canal (the arrowheads indicate the origin and the arrows indicate the end of the lateroantral canal) [11]. In this regard, a lateroantral canal, such as those reported here, could be speculated as being the result of an abnormal pattern of bone formation in which ossification of maxilla started internally to, and not beneath, the future Fig. 4 Diagram of the axial MPR in Fig. 2b indicating the anatomical landmarks. 1 Antero-lateral wall of the maxillary sinus, 2 right lateroantral canal, 3 zygomatic bone, 4 pterygopalatine fossa, 5 zygomatic arch, 6 tip of the coronoid process of mandible, 7 palatovaginal canal, 8 pterygoid (vidian) canal, 9 carotid groove, 10 body of sphenoid bone, 11 inferior nasal concha, 12 inferior nasal meatus, 13 left lateroantral canal, 14 maxillary sinus, 15 middle nasal concha, 16 pterygomaxillary fissure, 17 pterygoid recess of the left sphenoidal sinus, 18 articular eminence, 19 head of mandible infraorbital canal. A slowly growing nasal capsule could also play a role in this process. This altered chronology could have lead to a low position of the foramen rotundum, as found in this case, and, consequently, to a lateroantral course of the infraorbital nerve. However, further studies performed on relevant lots should establish whether the relative position of foramen rotundum relates to a certain anatomical pattern of the infraorbital nerve course. 123 Surg Radiol Anat Fig. 5 Three-dimensional VR (filter: transparent Skin, 20 % bone subtraction) of a thin coronal cut at the level of the upper second molars. 1 Crista galli, 2 superior wall of the maxillary sinus, 3 right lateroantral canal, 4 antero-lateral wall of the maxillary sinus, 5 alveolar process of maxilla, 6 ethmoidal labyrinth, 7 left orbit, 8 middle nasal concha, 9 zygomatic bone, 10 left lateroantral canal, 11 inferior nasal concha, 12 palatine process of maxilla Fig. 6 Oblique/coronal MPR of the maxillae (left the plane of section depicted on a sagittal MPR through the left maxillary sinus). 1 Superior wall of the maxillary sinus, 2 right lateroantral canal, 3 maxillary sinus, 4 hard palate, 5 second upper molar, 6 left lateroantral canal, 7 inferior nasal concha, 8 alveolar process of maxilla Although the morphology of the maxillary sinus depends on congenital or pathological modifications [12], there were not reported related changes of the IOC location, which keeps its infraorbital location no matter the degree of maxillary sinus pneumatization is. There are, however, morphometric differences between individuals in what regards the infraorbital groove, the IOC and the position of the IOF relative to various osseous or soft-tissue landmarks [8, 19]. Not only the number but also the shape of the IOF is variable [10]. It was also reported the anatomical possibility of a doubled IOC [13]. Gender should also be taken into account when the IOF is to be located, as the distances may be shorter in females than in males [5]. Although there were studies indicating that race, gender 123 Fig. 7 Sagittal MPR through the left foramen rotundum; it is measured the vertical distance (11.75 mm) between it and an anatomical plane tangent to the upper wall of the maxillary sinus. 1 Foramen rotundum, 2 pterygoid process, 3 maxillary sinus and side should be considered when referring anatomical variation data to an individual subject [1, 6], it was recently discussed that the mean distance from the infraorbital margin to the center of IOF does not show any significant differences regarding laterality in males and females, both between genera, regardless of the side and regardless of genus [18]. The large variations of the IOF anatomical characteristics could be due to the diversity of the used parameters as well as to the distinct investigated lots [18]. As referred to the three types of Le Fort fractures of the face, in a type II Le Fort Fracture a lateral antral canal seems lesser exposed than a common IOC. 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