Download Infraorbital canal bilaterally replaced by a lateroantral

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].
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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
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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.
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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
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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.
Undoubtfully, in such cases of lateroantral canal, a
CBCT evaluation of patients prior to any surgical procedures would be of great benefit. Puncture for anesthesia at
the IOF should not respect a common posterior–superior–
lateral direction but, instead, should be rather directed
posterior and lateral.
The CBCT evaluation of patients should be made on a
case-by-case basis, to identify rare anatomic variations,
such as this one in which the IOC was bilaterally replaced
by a lateroantral canal, previously undescribed in the
anatomic literature.
Conflict of interest
None.
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