GAND classification and volumetric assessment of unilateral cleft lip and palate malformations using cone beam computed tomography

Abstract

The aim of this study was to propose a classification for unilateral cleft lip and palate (UCLP) malformations based on cone beam computed tomography (CBCT) images, as well as to estimate the amount of bone necessary for grafting, and to evaluate the relationship of this volume with scores obtained using the classification. CBCT images of 33 subjects with UCLP were evaluated according to gap, arch, nasal, and dental parameters (GAND classification). Additionally, these defects were segmented and the amount of graft needed for alveolar bone grafting was estimated. The reproducibility of GAND classification was analyzed by weighted kappa test. The association of volume assessment with the classification (gap and nasal parameters) was verified using analysis of variance, while the intra-observer agreement was analyzed using the intra-class correlation coefficient. The intra-observer reproducibility of the classification ranged from 0.29 to 0.92 and the inter-observer agreement ranged from 0.29 to 0.91. There were no statistically significant values when evaluating the association of the volume with the classification ( P > 0.05). The GAND classification is a novel system that allows the quick estimation of the extent and complexity of the cleft. It is not possible to estimate the amount of bone needed for alveolar bone grafting based on the classification; individualized surgical planning should be done for each patient specifically.

Orofacial clefts (OFC) are congenital malformations characterized by incomplete formation of structures involving the nasal and oral cavities: lip, alveolus, and hard and soft palate. OFC vary in size, from a defect limited to the soft tissue to a complete cleft that extends through the hard palate, alveolar process, nasal floor, and lip. OFC can affect one side (unilateral) or both sides (bilateral) of the patient. The pathogenesis of cleft lip and cleft palate is complex and the most widely accepted model to account for the development of OFC is multifactorial inheritance, according to which this pathology is connected to the interplay of genetic and environmental factors.

Non-syndromic OFC is the most common congenital malformation, affecting an average one in 600 live newborns worldwide. The treatment of cleft lip and palate deformities requires several staged surgical procedures and a multidisciplinary approach. Medical and non-medical providers count on the completeness and accuracy of medical records and images to develop comprehensive treatment plans. Several systems of classification have been used with the objective of facilitating communication among providers and describing the location and extent of the deformities. Most of the classifications available to date identify patterns of cleft phenotypes based on clinical records, photographs, intraoral models, and two-dimensional (2D) images.

There is an increasing need to move from 2D assessment and grading systems to three-dimensional (3D)-based systems. Cone beam computed tomography (CBCT), in particular, allows the assessment of craniofacial abnormalities, with exposure of the child to radiation doses lower than those of multi-slice CT, and has become increasingly important in the treatment planning and diagnosis of these conditions. CBCT imaging provides 3D volumetric data of the entire maxillofacial region with high resolution and accuracy. Moreover, a request for CBCT examinations in the treatment of patients with OFC is justified according to the guidelines of the SEDENTEXCT project (supported by The Seventh Framework Programme of the European Atomic Energy Community (Euratom)), allowing the incorporation of CBCT images in OFC management, especially for the assessment of alveolar bone grafting, dental implant installation, and orthodontic treatment of the cleft-adjacent teeth.

Regarding OFC, the most accepted classification was developed by Kernahan and Stark in 1958, and describes the cleft palate in relative terms by using the incisive foramen as a dividing point. The classification adequately describes the most common types of cleft: the complete unilateral cleft lip and palate and the isolated posterior cleft palate. Since then, several modifications and new classifications have been described in the literature. However, with the development of CBCT imaging, the assessment of the cleft in 3D is now feasible and allows medical and dental providers to exchange patient information and improve treatment plans, especially before secondary alveolar bone grafting (ABG).

There is a growing need for new methods for cleft assessment and classification based on CT images. A classification for unilateral alveolar and palatal clefts based on CBCT images, aimed at assisting providers in all aspects of treatment planning, is introduced herein. It consists of the evaluation of four parameters: gap, arch form, nasal floor, and dental features – establishing the GAND classification. This classification proposes a qualitative assessment using scores to evaluate each parameter, and is a method to aid clinicians to quickly estimate the extent and magnitude of the cleft. The higher the score, the higher is the complexity of the cleft.

Regarding the gap or cleft size, this would be beneficial in preoperative planning as surgeons would be able to estimate the size of the defect and amount of bone necessary for grafting and whether an additional donor area would be needed. This parameter ranges from a notched alveolar process to large clefts, and these differences may change the type and amount of graft selected. The successful treatment of a notch in the alveolar process can be achieved with small amounts of bone graft, which could be obtained from allograft, alloplast, or xenograft material. However, for small clefts, autogenous bone from the chin, ramus, or iliac crest may be indicated; and for large clefts, the iliac crest or tibia would be the ideal donor area.

In relation to the arch form assessment, this allows the determination of the position of the lesser segment in relation to the greater segment. This can be aligned, or anteriorly and/or posteriorly constricted. This conformation is directly related to the need for expansion prior to bone grafting, since, ideally, the arch should be aligned before surgery, thereby avoiding orthodontic expansion of the recently placed bone graft.

The nasal parameter estimates the size of the defect present in the nasal base region/piriform margin and helps to determine the need for nasal floor augmentation during preoperative planning. The nasal floor augmentation may improve the position of the alar base on the cleft side and the overall nasal symmetry.

The assessment of dental features assists all dental professionals in the craniofacial team in making a decision regarding tooth extractions and space maintenance. It is important, prior to surgical interventions in the cleft region, to determine the presence of supernumerary or malformed teeth that may be extracted during the same procedure. In the case of teeth that will erupt in the graft area or patients with missing teeth in the cleft region, the space should be maintained for eruption or for future implant placement for an implant-supported dental prosthesis.

With the incorporation of segmentation and volumetric assessments when processing CBCT images, a quantitative evaluation of the gap and estimations for the surgical procedures are also possible. It is worth mentioning that an adequate volume of bone grafted during ABG is crucial for the success of the procedure, and also strongly related to donor site morbidity. This information is increasingly requested by craniofacial teams to improve preoperative planning and procedure predictability.

Previous studies have evaluated the bone volume necessary for secondary ABG in the alveolar cleft using surgical simulation software, and a significant correlation between the preoperative measurements and the actual volume of the bone graft used in the surgical procedure has been found. Consequently, the assessment of the amount of bone needed using CBCT images would be advantageous for cases of cleft repair.

The present study had three distinct purposes: (1) present a classification for unilateral alveolar and palatal clefts based on CBCT images (GAND classification) and evaluate its reliability, (2) estimate the amount of bone graft needed prior to ABG surgeries in these subjects, and (3) evaluate the relationship between the volumetric values and the gap and nasal parameter values obtained using the GAND classification.

Materials and methods

This study was approved by the institutional review board. Subjects with unilateral cleft lip and palate (UCLP) who underwent CBCT examination comprised the study sample. The CT scans were acquired for purposes unrelated to the study.

The inclusion criterion was the presence of a unilateral cleft. The exclusion criteria were patients with any diagnosed craniofacial syndrome, previous orthodontic expansion treatment, previous secondary ABG, and CBCT scans with excessive scattering and motion artefacts. A total of 50 CBCT scans were inspected for selection of the sample; 17 subjects were excluded from the sample due to orthodontic treatment ( n = 11), previous ABG ( n = 1), or inadequate image quality ( n = 5), thus the final sample comprised 33 subjects.

The enrolled subjects ranged in age from 6 to 11 years, with an average age of 8.03 years. The study population consisted of 15 females and 18 males, presenting with 11 right unilateral clefts and 22 left-side defects. Informed consent regarding the use of the CBCT data for this study was obtained from all patients.

For image acquisition, a CS 9300 CBCT unit (Carestream Health, Atlanta, GA, USA) operating at 60–90 kVp, 2–15 mA, 17 × 13.5 cm field of view, and 0.3-mm voxel size was used. All data were saved in DICOM files for subsequent evaluation in a secluded room with dim light. The study involved two different approaches for distinct purposes: GAND classification and volumetric assessment.

GAND classification

For the first assessment, the images were imported into Invivo software (Anatomage, San Jose, CA, USA) and scored according to the proposed GAND classification. The region of interest could be observed on multiplanar reconstruction (MPR) in the three planes (axial, sagittal, coronal), as well as using 3D reconstructions in maximum intensity projection (MIP). Each CBCT image was classified qualitatively according to the four parameters of the GAND classification based on the position of the lesser segment in relation to the greater segment: G (size of the gap), A (arch form), N (nasal base defect), and D (dental assessment). The classification was introduced to the examiners for calibration before image evaluation ( Fig. 1 ) and is outlined below.

Dec 15, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on GAND classification and volumetric assessment of unilateral cleft lip and palate malformations using cone beam computed tomography
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