When conducting a PubMed search with the term “cone-beam computed tomography” at the time of this annotation (April 2, 2020), 13,976 results appeared. When filtering the search by date, the vast majority follow the year 2011, with a further significant increment after 2014. Five thousand ninety-four results are listed in the restricted period from 2017 onward. These numbers bring clear testimony to the enormous interest that the topic elicits. When the suffix “rhinoplasty” is added to the same search, the results are cut to a total of 13 articles. It is impressive that so little interest has been granted to cone-beam computed tomography in rhinoplasty, especially because cone-beam computed tomography is an imaging technique specific to the maxillofacial area. The experience of a single center by the senior author (E.R.) over the past 5 years and over 700 patients is detailed in this article as an argument for widespread adoption of cone-beam computed tomography technique in rhinoplasty practice.
WHAT IS CONE-BEAM COMPUTED TOMOGRAPHY AND HOW DOES IT COMPARE TO CONVENTIONAL COMPUTED TOMOGRAPHY?
Simply stated, cone-beam computed tomography is an imaging technique that uses a cone or pyramid-shaped x-ray beam, as compared to the narrow fan-shaped beam used in multidetector computed tomography (Fig 1). Among the plethora of articles, excellent reviews are to be found by Scarfe et al.1 and Nasseh and Al-Rawi.2 With the patient standing or seated, the cone-beam computed tomography unit makes a single rotation around the patient’s head to acquire two-dimensional “basis” images after a scout view is surveyed. This acquisition phase is followed by image reconstruction, creating both multiplanar and three-dimensional images. Multiplanar images are reformatted images in all three orientations, axial, coronal, and sagittal, usually simply read by a viewer. The anatomical area included in a cone-beam computed tomographic study, and thus subject to radiation exposure, is designated as field-of-view, varying from small (approximately 5 cm in height), to medium (5 to 10 cm), to large (>10 cm) when the whole craniofacial skeleton is to be studied.1–7 Since its introduction in Europe in the late 1990s3 and its approval by the U.S. Food and Drug Administration for use in the United States in 2001, cone-beam computed tomography models by different manufacturers have multiplied. Cone-beam computed tomography thus found a plethora of increasing applications prevalently in dental practice,8,9 also because of an increasingly diffuse and affordable in-office availability.
Its applications have so far prevalently concerned general dentistry, orthodontics, endodontics, periodontics, and Implantology.1,2,8–11 The American Academy of Oral and Maxillofacial Radiology suggests the use of cone-beam computed tomography as the preferred method for presurgical assessment of dental implant sites.12 More recent applications have extended to sinus imaging, endoscopic sinus surgery, temporomandibular joint, temporal bone, middle and inner ear assessment, airway volume imaging, and evaluation of lacrimal and salivary glands. Also, cone-beam computed tomography has been used in diagnostic and interventional neuroradiology, maxillofacial deformity, fibro-osseous lesions, and trauma.13–21 Thus, its use has been extended to spheres, where the gold standard previously consisted of magnetic resonance and computed tomographic imaging, raising interest in the study of extraoral anatomy by cone-beam computed tomography.22
Obviously, a cone-beam computed tomography study comes at the cost of exposure to radiation. Many studies and reviews discuss this delicate topic,23–31 including an excellent editorial by Scarfe23 and recommendations by the World Health Organization on pediatric patients.31 It is usually stated that a cone-beam computed tomography examination emits an average of seven to 10 times less radiation than a computed tomographic scan, equivalent to approximately nine or 10 panoramic radiographs, although these are generic statements. Using, alternatively, as a comparison the radiation dose of a chest x-ray, a cone-beam computed tomography examination will generically provide less than one-fiftieth the radiation provided by a single posteroanterior chest radiograph.31 However, in a vast meta-analysis, the mean effective dose delivered by cone-beam computed tomography with a wide field of view was found to be 212 μSv (i.e., equivalent to approximately 10 chest radiographs).26 The radiation dose produced by cone-beam computed tomography is also dependent on several parameters regarding both the machine and how it is operated (e.g., field of view, peak voltage, continuous or pulsed beam, scan time). When translated from dental to maxillofacial applications, a wide field of view is needed, which increases radiation. However, all studies concur that cone-beam computed tomography provides considerably reduced doses as compared with conventional computed tomography.8,9,11,23–31 “How much” reduced is difficult to determine because of the wide variability between units and imaging protocols used. A common statement is that a cone-beam computed tomography examination with a large field of view will determine dosage ranges of far less than 1 mSv, with a mean of 212 μSv in Ludlow’s meta-analysis26 as compared to an average of 2 mSv for computed tomography (1 mSv = 1000 μSv). Although “deterministic” effects of radiation are only possible above 100 mSv, a “stochastic” effect (tumor risk because of mutation of reproductive cells) remains real but so low as to be speculative and practically infinitesimal. Flawed assumptions would risk limiting the clinical benefit of cone-beam computed tomography diagnostic imaging, beyond the fact that the problem of specific risk in children does not exist for adults.
The main practical advantage for cone-beam computed tomography is the specific ability to accurately view and analyze in three-dimensions the bony structures of the maxillofacial skeleton, while not allowing complete assessment of soft tissue. Accurate, submillimeter-resolution images can be provided of higher resolution than computed tomography, in formats that allow ideal three-dimensional visualization. This would be an ideal premise to the next logical step: extend on a broad basis the application of cone-beam computed tomography to preoperative assessment in rhinoplasty, regarding both diagnosis and guidance to the operation.
PATIENTS AND METHODS
The study population consisted of 586 patients, 335 primary and 251 secondary rhinoplasty patients, operated on by the senior author (E.R.) between September of 2014 and March of 2020. All patients were older than 18 years, except for six patients between the ages of 15 and 18 years. Cone-beam computed tomographic studies had been initially used by the senior author in 2008 on some secondary and posttraumatic cases because of the fortuitous circumstance of the availability of a cone-beam computed tomography device in the clinic. After a new cone-beam computed tomography model for maxillofacial use was acquired in September of 2014, this imaging was progressively extended to a larger patient population, including primary rhinoplasties. In these same years, new developments in nasal anatomy and instrumentation were taking place,32–35 with a profound effect on surgical techniques. Better imaging was called for in parallel to more refined bone work. Thus, the transition to general use of cone-beam computed tomography progressively occurred, with cone-beam computed tomography performed in all patients undergoing rhinoplasty over the past 3 years, save for those who already had a computed tomographic scan obtained elsewhere. All patients had one cone-beam computed tomographic scan before surgery and none subsequent to surgery.
The cone-beam computed tomography unit used is a NewTom VG scanner with a full maxillofacial 15 × 15-cm field of view covering most of the craniofacial skeleton from chin to above nasion (NewTom; Quantitative Radiology, Verona, Italy) (Fig. 2). The dose administered per examination per patient averages 100 μSv, within a range of variation depending on the dimensions of the patient’s head and the radiopacity of bone. This is approximately one-tenth of the dosage provided by a standard computed tomographic scan. Interpretation reports by a radiologist were obtained for every patient to alleviate diagnostic responsibility regarding the whole examined area. In every case, the cone-beam computed tomographic scan was used as a roadmap to surgery regarding varying indications as detailed below.
Questionnaire to Faculty of the Sixth Bergamo Open Rhinoplasty Course
On the suggestion of the second author (R.K.D.), a survey was conducted in the autumn of 2018, which polled by a specific questionnaire the Faculty of the Sixth Bergamo Open Rhinoplasty Course, numbering 39 internationally reputed rhinoplasty surgeons. (See Figure, Supplemental Digital Content 1, which shows the cone-beam computed tomography faculty poll. CT, computed tomographic; 3-D, three-dimensional; 2-D, two-dimensional; XRT, radiation therapy, http://links.lww.com/PRS/E411. See Figure, Supplemental Digital Content 2, which shows cone-beam computed tomography faculty poll graphs summarizing relevant percentage data. CT, computed tomographic; CBCT, cone-beam computed tomographic, http://links.lww.com/PRS/E412.) A short summary is given in Table 1.
Table 1. -
Summary of Replies to Faculty Poll
|Do you ever use a CT scan in your preoperative rhinoplasty assessment?
|If you do, do you use a conventional CT or a cone-beam CT scan?
| Conventional CT scan
| Cone-beam CT scan
|If you do, in which percentage of cases do you use a CT scan? (one choice)
| All cases
| 75–100% of cases
| 50–75% of cases
| 25–50% of cases
| <25% of cases
CT, computed tomographic.
Although 79 percent stated they used a computed tomographic scan for some indications, only 26 percent of those used a cone-beam computed tomographic scan instead of a conventional computed tomographic scan. Among those who used either conventional computed tomography or cone-beam computed tomography, 45 percent did so less than 25 percent of the time, whereas only 9.7 percent used it in all cases. The main reason for using computed tomography was studying septum, turbinates, sinuses, and nasal and neighboring bones. The primary rationale for not using it was cost, radiation exposure, insufficient relevance, reliance on physical examination, and use of endoscopy. In essence, although the majority of surgeons use computed tomography in some instances before rhinoplasty, the percentage using cone-beam computed tomography is less than one-quarter, and very few use it as a routine tool.
Role of Cone-Beam Computed Tomography in Preoperative Analysis for the Rhinoplasty Patient
It would be advantageous for any rhinoplasty surgeon to have a single, readily available examination that could work as a map to rhinoplasty by reuniting all anatomical parameters useful in operating on a primary or secondary nose: bony, functional, and surface anatomy, as related to clinical analysis. By “experimenting” with the tool, one will soon find where it is essential, where it is useful, and where it is redundant, in a way like when a new app is first used on a mobile device.
When opening a cone-beam computed tomography diskette for the first time on a personal computer, one notices that a vast number of visualization options and cross-sections are possible. What is most useful in rhinoplasty practice is, however, multiplanar two-dimensional reformatting (multiplanar) and three-dimensional reconstruction.
The first (multiplanar mode) incorporates axial, coronal, and sagittal section views on the same screen page, running all three in parallel and highlighting, with the use of tracking lines, any specific issue in all views at once. [See Figure, Supplemental Digital Content 3, which shows (above) the multiplanar rendering of reformatted images in the same screen of all three axial, coronal, and sagittal views. Each can be scrolled individually. A typical septal spur is shown, tracked by intersecting color lines in all three views. (Below) On this other multiplanar view, a septal deviation close to the vomer is highlighted, http://links.lww.com/PRS/E413.] Analyzing, for instance, a septal deviation with a bony spur in all three views will help develop within a short time the ability of “spatially viewing” the position of the item.
The second (three-dimensional reconstruction) has an outstanding imaging quality, which provides different modes and setups to highlight, progressively, bone versus soft tissue. This is not, however, only a pretty picture. It serves well to detail the intricacies of the shape of bone and will also provide a soft-tissue full “surface view,” eliminating unneeded peripheral items such as skin and eye color, which are distracting issues. Attention is thus drawn to clinically relevant details of surface morphology not equally immediately noted on a photograph. [See Figure, Supplemental Digital Content 4, which shows (above) on these three-dimensional frontal views, the bony anatomy in a primary rhinoplasty patient, with prominent, mildly asymmetric, short nasal bones. The surface contour highlights the component of dorsal deviation and tip shape, with some left alar retraction. (Below) On these three-dimensional frontal views, the bony anatomy is shown in a secondary rhinoplasty patient. The surface contour highlights the open roof, bony and septal deviation, inappropriate dorsal lines, saddling, and pinching of the tip caused by alar overresection, http://links.lww.com/PRS/E414.]
The 10 most pertinent applications of cone-beam computed tomography to rhinoplasty are listed below. Videos 1 and 2 illustrate applications in two patients, in the same way as when a cone-beam computed tomography diskette is directly run on a personal computer. [See Video 1 (online), which shows direct viewing of the related cone-beam computed tomographic scan demonstrated in this primary rhinoplasty case. See Video 2 (online), which shows direct viewing of the related cone-beam computed tomographic scan demonstrated in this posttraumatic case.]
Studying the Septum in Progression
When a computed tomographic scan is ordered before a rhinoplasty, this is most often for studying the septum.36–41 On a cone-beam computed tomographic scan, septum deformities and deviations are well highlighted in sagittal, axial, and coronal views22,42 (Figs. 3 through11). [See Figure, Supplemental Digital Content 5, which demonstrates coronal scan showing (above, left) septal deviation and previous subtotal left turbinate resection (above, center), septal fistula, and (above, right) measuring the inclination of the turbinate to the maxillary wall. (Center) Sagittal scans showing (center, left) modest portion of quadrangular plate versus ethmoid in a primary rhinoplasty case; (center, center) wide portion of residual available septum in a secondary rhinoplasty case; and (center, right) measuring the bone thickness at the radix, the thickness of skin at the most prominent point of the bony cap, and the length of the bony cap on top of the upper lateral cartilages. (Below) Axial scan showing (below, left) verticalized but symmetric orientation of the nasal bones and (below, center) collapsed L nasal bone following osteotomy in secondary rhinoplasty. No osteotomy was performed on the right side (below, right) measuring the inclination of the frontal process of the maxilla, http://links.lww.com/PRS/E415. See Figure, Supplemental Digital Content 6, which shows (left) mildly concave but pyramidal and symmetric orientation of the nasal bones; and (right) mildly convex but pyramidal and symmetric orientation of the nasal bones. Note the thinness of the bones, which would not allow osteoplasty maneuvers to address convexity, http://links.lww.com/PRS/E416.] By scrolling the images and relating views to each other in the multiplanar view, one can configure clearly the shape of the septum and plan septoplasty maneuvers. Interestingly, the sagittal view will also indicate the relative percentage between quadrangular cartilage and ethmoid bone (Figs. 5, 6, and 11). This allows estimating, obviously with some approximation, whether septal cartilage will be sufficient, for instance, in rebuilding the L-strut in secondary rhinoplasty or whether rib will be needed. With experience, the different areas in shades of gray that reflect deviations will be noted on sagittal cuts and discriminated from fistulas, the dimensions and position of which can also be determined. Interestingly, it will also be apparent from sagittal views when L-strut septoplasties have been previously attempted, and where the mucosal leaflets have become adherent to each other in areas devoid of cartilage.
Studying the Inferior and Middle Turbinates
Both (generically) the volume and (specifically) the percentage of bone versus mucosa in the inferior turbinates can be assessed by cone-beam computed tomography, as with any computed tomographic scan36–41 (Figs. 3 and 4). This element may guide the decision for turbinoplasty with or without resection and/or fracturing of uncinate bone. The senior author currently uses a long piezo insert, following transmucosal access, to fracture the uncinate bone, when noted to be large on a cone-beam computed tomographic scan.43 The presence of concha bullosa can also be readily seen. A large concha bullosa that impinges on the septum and has caused deviation congenitally by pushing it in the opposite direction can be assessed and surgical correction planned (Fig. 4). Smaller conchae that are not symptomatic and not causing deviation will also be seen, and a note that no surgery is needed is made. This will obviate the need for endoscopy, the same as regarding septal deviations.
Studying the Sinuses and Ostiomeatal Drainage
Like for the septum, this is one of the most frequent indications for computed tomography in functional nasal assessment.44 Cone-beam computed tomography offers similarly precise imaging in this regard.45,46
Studying the Internal Valve and Areas of Synechiae
The adequacy of the angle of opening of the internal valve can be evaluated while running in progression coronal sections in a multiplanar two-dimensional modality (multiplanar reconstruction). Likewise, areas of synechiae between the sidewall and septum and between the septum and inferior turbinates can be easily noted. This is obviously relevant in revision rhinoplasty.
Studying the Nasal Bones Regarding Shape, Symmetry, and Thickness
This is definitely one of the most important uses for cone-beam computed tomography (Figs. 7 through10). Imaging is vastly superior to computed tomography, first suggested in 1987 by Daniel regarding lateral wall anatomy and angulation.47 New concepts on how to manage bone in rhinoplasty have evolved considerably over the past few years.32–35 Cone-beam computed tomography gives a clear map—in multiplanar modality, by scrolling the images in all three views, and by means of three-dimensional reconstructions—of the shape, thickness, inclination, contour, and symmetry of each nasal bone–frontal process of the maxilla (Figs. 12 through17). This will help formulate a plan of individual bone manipulation regarding reshaping by osteoplasty or repositioning by osteotomies. It will be possible to determine preoperatively where the bone is thick enough to allow reduction by burr or piezo at its base, and where different orientation indicates different osteotomy solutions. For example, asymmetrically oriented nasal bones will indicate asymmetric osteotomies, “opening” on one side and “closing” on the other, or alternatively, an asymmetric push-down osteotomy. Localized bone convexities that call for intermediate osteotomies or criss-cross piezo osteotomies48 will be easily noted. Similarly, bony irregularities and stepoffs following previous rhinoplasty will be well visualized and the decision on whether to burr down the irregularity or remobilize the bone more easily taken. The array of situations being vast, understanding the bony anatomy preoperatively is highly advantageous. An especially useful view is the helicopter view from above, and indeed the three-dimensional image can be advantageously turned to any inclination in space. The senior author finds cone-beam computed tomography now to be an indispensable tool for planning osteotomies and osteoplasty in his practice.49 True, such practice now uniformly implies the use of power instruments and piezo devices, but the same would hold for using rasps and osteotomes.
Assessing the Thickness of the Skin
Skin thickness can be clearly appraised in cone-beam computed tomography, as previously studied with conventional computed tomography.50 Regarding the tip, this may help the surgeon in deciding on a more structural approach and planning direct debulking when the skin is thick or, if thin, in going directly to a subperichondrial approach, starting from the alar cartilages. Likewise, a very thin skin at the keystone may advocate a full subperiosteal-subperichondrial plane or anticipate the need for camouflage such as diced cartilage or temporalis fascia (Figs. 12 through14).
Assessing the Length and Shape of the Bony Cap and the Underlying Extension of the Upper Laterals
The preview of the length and shape of the bony cap is especially pertinent to the novel concepts of “decapping” the bony hump32 (Figs. 11 through14). Considerable anatomical variations exist regarding the location where the cartilaginous septum joins the perpendicular plate of ethmoid below the bony cap, although this distance is often considerable.32,33 Prior knowledge of the height of the bony cap may help in orienting toward the use of spreader flaps versus spreader grafts. Recognition of the length of the bony cap and of how much the upper lateral cartilages extend under it, together with other factors such as the S or V shape of the bony cap, may help in deciding on variations in surgery of the dorsum, especially whether to preserve it or reconstruct it.32,35,51 A short and low bony cap will frequently indicate the use of a cartilaginous dorsum pushdown “hybrid” technique, essentially linking component separation with midvault septal-T preservation.52 Choosing correctly among the current plethora of techniques for the dorsum is thus significantly facilitated by a preview of the bony-cartilaginous anatomy at the keystone on cone-beam computed tomography.
Three-Dimensionally Assessing the Whole Bony Anatomy of the Facial Skeleton
Assessing the bony anatomy of the facial skeleton beyond the nasal bones per se is clinically relevant in many situations. Facial asymmetry can be visualized and a true crooked nose differentiated from an asymmetric foundation of the nasal pyramid. An underdeveloped or dislocated nasal spine can be identified. The shape, length, and height of the chin can also be assessed in the context of appropriate facial proportions, regarding the potential need for implant augmentation or genioplasty.
Surface Contour Enhancement
The three-dimensional view of the cone-beam computed tomographic scan offers a bounty of immediate visual information regarding the nasal contour, of both bone and cartilage. In secondary cases, the direct influence of iatrogenic bony asymmetries onto surface anatomy is clearly elucidated. This dramatically facilitates analysis and planning (Figs. 16 and 17). It is interesting to note how contour enhancement is provided, albeit faithfully, in reticulum-like monochromatic imaging. This purifies the image from surrounding structures and color, thus highlighting deformities and specific depressions and prominences, such as bony irregularities, cephalic alar malposition, or alar asymmetries.
Measurements of Thickness, Length, and Angles
A variety of measuring tools allow measurements of thicknesses and lengths of segments, angles, and volumes on cone-beam computed tomographic images, as has been done using computed tomography in several publications.20,53–57 This has limited immediate preoperative relevance for most surgeons, but is of importance in selected cases and patient studies (Fig. 11).
It is bizarre that the use of cone-beam computed tomography, currently so widespread that many dentists now have one in their offices, has interacted with rhinoplasty surgery only to a minimal degree. The current pertaining literature is indeed remarkably scarce.20,42,45,54,58,59 A plausible reason can be that cone-beam computed tomography is so powerfully pertinent to the dental and maxillofacial world as to be primarily identified with the same, although its characteristics and advantages well justify significant applications in rhinoplasty.
It is a fact that making a proper plan before a primary rhinoplasty, and especially a secondary rhinoplasty, is important toward achieving an ideal result. Although rhinoplasty is a dynamic operation in which cause-and-effect events constantly occur, it would stand to reason to make the game plan as predictable as possible by proper anatomical guidance.
Bone manipulation and septal work are essential in modern rhinoplasty, and cone-beam computed tomography will address the surgeon to do what and how. Surface imaging, in a fine monochromatic mesh-like reticulate manner, not dissimilar from three-dimensional imaging reported by Toriumi and Dixon,60 will also highlight the location of specific areas of contour change and the relationship of structural framework to skin cover.
Also, not all surgeons have access to or familiarity with endoscopy. In that sense, cone-beam computed tomography is a good substitute, and in fact, while running through all three sections in the multiplanar mode, one develops the feel for a three-dimensional view. Cone-beam computed tomography will provide adequate functional assessment and documentation for insurance and medicolegal purposes. Not least, showing the patient his or her cone-beam computed tomographic scan before surgery is highly educational and provides direct efficient visual communication.
A cone-beam computed tomographic scan takes only a few minutes to obtain, with the patient standing without any inconvenience, and once the diskette is edited, it is fast and easy to view. In the senior author’s practice, this evaluation usually takes less than 10 minutes.
Of course, the technique has drawbacks and limitations. Drawbacks are the cost to the patient and suboptimal soft-tissue contrast. However, the cost is very limited (approximately €100) but different from country to country.61 Technically, the suboptimal soft-tissue contrast prevents accurate soft-tissue assessment. However, this is seldom relevant in rhinoplasty. The concern about radiation dosage has been previously addressed. In essence, it stands to reason to define as scarcely significant as, for an adult patient, the dose of radiation is less than 100 μSv for the scanner used in the study (i.e., approximately one-tenth of the radiation delivered during conventional computed tomography). It obviously may still be questioned whether even this small amount of radiation is justified, with respect to the principle of “as low as reasonably achievable.”21,26,28 Thus, cone-beam computed tomography may be deemed unnecessary by experienced surgeons well accustomed to relying on expertise and clinical examination. The endpoint is, however, that contradictory messages exist in the literature; however, often the most alarming scientific publications are privileged by global media. The essence is whether skipping an examination that could be easily performed at a very low or no radiation risk may cause a less accurate diagnosis of specific items relevant to surgery and thus a poorer outcome than could otherwise be achieved.62
This article has the limitations of not providing any detailed statistics of which specific information from cone-beam computed tomographic scans was used on specific patients and for which specific reason. It is essentially a single-center experience and offers only a subjective assessment of the value of cone-beam computed tomography in rhinoplasty for aesthetic and functional purposes. It is, however, the authors’ opinion that, once tried and clinically applied, the advantages of cone-beam computed tomography will become so evident toward diagnosis and treatment planning as to make it an essential tool in rhinoplasty.
Cone-beam computed tomography is a user-friendly, easy, quick, and helpful technique that will work as a roadmap for the rhinoplasty surgeon in many instances, with significant clinical impact and cost-effectiveness. The reasons for its allure are multiple and its many advantages far outweigh its few disadvantages. The authors propose the use of cone-beam computed tomography before performing any rhinoseptoplasty.
The authors would like to acknowledge Paolo Tomà, M.D., head of the Department of Radiology and Bioimaging, Pediatric Hospital Bambino Gesù, Rome, for precious advice and support.
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