Association of cranial base suture/synchondrosis fusion with severity of increased intracranial pressure in Crouzon syndrome.

This study investigated how the fusion states of the cranial base is related to the degree of increased intracranial pressure (ICP) in patients with Crouzon syndrome. This retrospective cohort study enrolled patients who were diagnosed with Crouzon syndrome between May 2007 and April 2022. We categorized the patients into three groups: A, B, and C, according to the severity of increased ICP and the number of cranial vault remodeling procedures for corrective operation. The preoperative fusion states of the cranial base sutures/synchondroses were examined using facial bone computed tomography and compared between groups. Overall, 22 patients were included in Groups A, B, and C, including 8, 7, and 7 patients, respectively. The preoperative average grades of the total cranial base suture/synchondrosis fusion appeared to significantly increase with severity, except for the frontoethmoidal suture, which showed the opposite tendency. In the subgroup analysis, frontosphenoidal, sphenoparietal, sphenosquamosal, parietomastoid, and occipitomastoid suture and petro-occipital synchondrosis were associated with earlier fusion in the more severe group. Premature closure of the cranial base sutures/synchodroses seems to be associated with increased ICP severity in patients with Crouzon syndrome. Precise evaluation of minor sutures/synchondroses at the first visit might help build subsequent operative plans and predict disease prognosis.

Comparison of Internal and External Distraction in Frontofacial Monobloc Advancement: A Three-Dimensional Quantification.

BACKGROUND: Crouzon syndrome is characterized by complex craniosynostosis and midfacial hypoplasia. Where frontofacial monobloc advancement (FFMBA) is indicated, the method of distraction used to achieve advancement holds an element of equipoise. This two-center retrospective cohort study quantifies the movements produced by internal or external distraction methods used for FFMBA. Using shape analysis, this study evaluates whether the different distraction forces cause plastic deformity of the frontofacial segment, producing distinct morphologic outcomes. METHODS: Patients with Crouzon syndrome who underwent FFMBA with internal distraction [Hôpital Necker-Enfants Malades (Paris, France)] or external distraction [Great Ormond Street Hospital for Children (London, United Kingdom)] were compared. Digital Imaging and Communications in Medicine files of preoperative and postoperative computed tomographic scans were converted to three-dimensional bone meshes and skeletal movements were assessed using nonrigid iterative closest point registration. Displacements were visualized using color maps and statistical analysis of the vectors was undertaken. RESULTS: Fifty-one patients met the strict inclusion criteria. Twenty-five underwent FFMBA with external distraction and 26 with internal distraction. External distraction provides a preferential midfacial advancement, whereas internal distractors produce a more positive movement at the lateral orbital rim. This confers good orbital protection but does not advance the central midface to the same extent. Vector analysis confirmed this to be statistically significant ( P < 0.01). CONCLUSIONS: Morphologic changes resulting from monobloc surgery differ depending on the distraction technique used. Although the relative merits of internal and external distraction still stand, it may be that external distraction is more suited to addressing the midfacial biconcavity seen in syndromic craniosynostosis. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III.

Morphology of the Occipital Bones and Foramen Magnum Resulting From Premature Minor Suture Fusion in Crouzon Syndrome.

To identify skull-base growth patterns in Crouzon syndrome, we hypothesized premature minor suture fusion restricts occipital bone development, secondarily limiting foramen magnum expansion.Skull-base suture closure degree and cephalometric measurements were retrospectively studied using preoperative computed tomography (CT) scans and multiple linear regression analysis.Evaluation of multi-institutional CT images and 3D reconstructions from Wake Forest's Craniofacial Imaging Database (WFCID).Sixty preoperative patients with Crouzon syndrome under 12 years-old were selected from WFCID. The control group included 60 age- and sex-matched patients without craniosynostosis or prior craniofacial surgery.None.2D and 3D cephalometric measurements.3D volumetric evaluation of the basioccipital, exo-occipital, and supraoccipital bones revealed decreased growth in Crouzon syndrome, attributed solely to premature minor suture fusion. Spheno-occipital (ß = -398.75; P < .05) and petrous-occipital (ß = -727.5; P < .001) suture fusion reduced growth of the basioccipital bone; lambdoid suture (ß = -14 723.1; P < .001) and occipitomastoid synchondrosis (ß = -16 419.3; P < .001) fusion reduced growth of the supraoccipital bone; and petrous-occipital suture (ß = -673.3; P < .001), anterior intraoccipital synchondrosis (ß = -368.47; P < .05), and posterior intraoccipital synchondrosis (ß = -6261.42; P < .01) fusion reduced growth of the exo-occipital bone. Foramen magnum morphology is restricted in Crouzon syndrome but not directly caused by early suture fusion.Premature minor suture fusion restricts the volume of developing occipital bones providing a plausible mechanism for observed foramen magnum anomalies.

Cranial Morphology Associated With Syndromic Craniosynostosis: A Potential Detection of Abnormality in Patient's Cranial Growth Using Angular Statistics.

INTRODUCTION: Apert, Crouzon, and Pfeiffer syndromes are common genetic syndromes related to syndromic craniosynostosis (SC), whereby it is a congenital defect that occurs when the cranial growth is distorted. Identifying cranial angles associated with these 3 syndromes may assist the surgical team to focus on a specific cranial part during the intervention planning, thus optimizing surgical outcomes and reducing potential morbidity. OBJECTIVE: The aim of this study is to identify the cranial angles, which are associated with Apert, Crouzon, and Pfeiffer syndromes. METHODS: The cranial computed tomography scan images of 17 patients with SC and 22 control groups aged 0 to 12 years who were treated in the University Malaya Medical Centre were obtained, while 12 angular measurements were attained using the Mimics software. The angular data were then divided into 2 groups (patients aged 0 to 24 months and >24 months). This work proposes a 95% confidence interval (CI) for angular mean to detect the abnormality in patient's cranial growth for the SC syndromes. RESULTS: The 95% CI of angular mean for the control group was calculated and used as an indicator to confirm the abnormality in patient's cranial growth that is associated with the 3 syndromes. The results showed that there are different cranial angles associated with these 3 syndromes. CONCLUSIONS: All cranial angles of the patients with these syndromes lie outside the 95% CI of angular mean of control group, indicating the reliability of the proposed CI in the identification of abnormality in the patient's cranial growth.

The foramen magnum in scaphocephaly.

PURPOSE: The foramen magnum (FM) presents various alterations in craniosynostoses, such as brachycephaly or Crouzon syndrome. However, to date, no study has been devoted to its morphology and morphometry in scaphocephaly, which is the most common of cranial deformities resulting from premature fusion of cranial sutures. METHODS: We assessed the morphology and morphometry of FM using preoperative thin-cut CT scans of 107 children with non-syndromic sagittal craniosynostosis aged 1-12 months (mean age 5.38 months). A series of sagittal and transverse dimensions were taken and the FM area was calculated in each case. Obtained data were compared to the age-matched control group of 101 normocephalic children. RESULTS: Dolichotrematous type of FM was dominant in the scaphocephaly group and observed in 63/107 cases (58.9%). The mean FM area in the scaphocephaly group was 519.64 mm2 and was significantly smaller compared to the control group (p = 0.0011). The transverse diameter and anterior sagittal diameter were also significantly smaller (p = 0.0112 and p = 0.0003, respectively). CONCLUSION: The area of FM in scaphocephaly is smaller compared to normal individuals. This is associated with a significant reduction of the width of FM in children with sagittal craniosynostosis. FM in scaphocephaly is larger than in other reported series of children with brachycephaly or Crouzon syndrome.

Three-dimensional analysis of the palatal morphology in growing patients with Apert syndrome and Crouzon syndrome.

Patients with Apert syndrome or Crouzon syndrome present with severe defects in oral-maxillofacial growth and development. In this study, we conducted a quantitative three-dimensional (3D) analysis of the palatal morphology of patients with Apert syndrome and Crouzon syndrome. Four patients with Apert syndrome (average age, 11.0 ± 0.8 years) and five with Crouzon syndrome (average age, 10.1 ± 1.6 years) were investigated. The participants' maxillary dental casts were scanned and analyzed using 3D imaging. Palatal width, depth, cross-sectional area, and palatal angle (PW, PD, PCA, and PA, respectively) were measured, and standard scores were calculated based on sex- and age-matched Japanese standard values; the actual palatal surface areas (PSA) and palatal volumes (PV) were also measured. Our results show that patients with Apert syndrome and Crouzon syndrome had a very narrow PW (standard score: -3.79 and - 0.47, respectively). 3D analysis revealed that patients with Apert syndrome had a significantly shallower PD (standard score: -1.35) than those with Crouzon syndrome (standard score: 2.47), resulting in a smaller PCA (standard score: -5.13), PSA (5.49 cm2 ), and PV (1.11 cm3 ) and larger PA (standard score: -0.12) than those in patients with Crouzon syndrome. This might be due to the former having a narrower and shallower palate caused by the predominant swelling of the palatal mucosa. These findings improve our understanding of the differences in palatal morphology between Apert syndrome and Crouzon syndrome patients.

Frontofacial Monobloc Advancement With Internal Distraction: Surgical Technique and Osteotomy Guide.

BACKGROUND: Craniosynostosis are cranial deformities resulting from the early closure of 1 or more sutures. Concomitant facial changes are complex and usually result from the involvement of multiple sutures, which may lead to restriction of cranial growth and brain expansion, ocular compression, and breathing difficulties. Surgical techniques to correct syndromic craniosynostosis have improved over time, considerably reducing the rate of complications of this procedure. OBJECTIVE: To describe in detail (step-by-step) and with pertinent anatomic considerations the technique of monobloc frontofacial advancement using internal distractors. METHODS: We describe the monobloc frontofacial advancement technique with the use of internal distractors, which we use in patients with primary syndromic craniosynostosis (Apert, Crouzon, and Pfeiffer) who have major facial hypoplasia and secondary respiratory repercussions. To illustrate this technique, the procedure was performed in 2 cranial models: an adult artificial acrylic skull of normal morphology for better evidence of anatomic repairs and a 3-dimensional printed infant skull from a tomography file obtained from a child diagnosed with Apert syndrome. RESULTS: The benefits of osteogenic distraction and better surgical timing for each procedure are presented. We presented the changes and details of osteotomies performed during the procedure, as well as anatomic details and care regarding the pterygomaxillary dysjunction. CONCLUSION: Monobloc frontofacial distraction is a procedure with widely demonstrated aesthetic and functional results, and this detailed step-by-step description may improve familiarity with the anatomic landmarks of the procedure and provide a better dynamic understanding of the distraction process.

Crouzon's Syndrome with a Dominant Sinus Pericranii Draining Transverse Sinus: Report of a Rare Association and Review of Literature.

INTRODUCTION: Crouzon's syndrome and sinus pericranii (SP) are rare entities. Only few cases having both the features are reported. SP most commonly drains in relation to superior sagittal sinus and their communication to major posterior dural sinuses is rare. CASE REPORT: We report a rare case of Crouzon's syndrome with SP at a suboccipital location with termination of left transverse sinus into the SP draining further through the extracranial suboccipital and extravertebral cervical venous plexi into external jugular veins. Distal transverse sinus and sigmoid sinus on the left side were absent. CONCLUSION: Crouzon's syndrome with SP is an extremely rare entity. SP with communication to major posterior dural venous sinuses is also rare and mostly associated with multi-suture craniosynostosis. Management depends on the volume of venous blood they are draining. Most of them are dominant type and their occlusion is not feasible. Preoperative diagnosis of a dominant SP is essential for proper surgical planning as it needs to be preserved mandatorily to prevent cerebral venous infarction.

Influence of Nonsyndromic Bicoronal Synostosis and Syndromic Influences on Orbit and Periorbital Malformation.

BACKGROUND: Oculoorbital disproportion in patients with craniosynostosis has similarities and dissimilarities between syndromic and nonsyndromic cases. The authors hypothesized that these two conditions have specific individual influences as they relate to development of the orbital and periorbital skeletons. METHODS: A total of 133 preoperative computed tomography scans (nonsyndromic bicoronal synostosis, n = 38; Apert syndrome bicoronal synostosis subtype, n = 33; Crouzon syndrome bicoronal synostosis subtype, n = 10; controls, n = 52) were included. Craniometric and volumetric analyses related to the orbit and periorbital anatomy were performed. RESULTS: Orbital cavity volume was mildly restricted in nonsyndromic bicoronal synostosis (7 percent, p = 0.147), but more so in Apert and Crouzon syndromes [17 percent (p = 0.002) and 21 percent (p = 0.005), respectively]. The sphenoid side angle in Apert syndrome was wider than when compared to Crouzon syndrome (p = 0.043). The ethmoid side angle in Apert patients, however, was narrower (p = 0.066) than that in Crouzon patients. Maxilla anteroposterior length was more restricted in Apert syndrome than Crouzon syndrome (21 percent, p = 0.003) and nonsyndromic cases (26 percent, p < 0.001). The posterior nasal spine position was retruded in Crouzon syndrome (39 percent, p < 0.001), yet the anterior nasal spine position was similar in Apert and Crouzon syndromes. CONCLUSIONS: Orbit and periorbital malformation in syndromic craniosynostosis is likely the combined influence of syndromic influences and premature suture fusion. Apert syndrome expanded the anteriorly contoured lateral orbital wall associated with bicoronal synostosis, whereas Crouzon syndrome had more infraorbital rim retrusion, resulting in more severe exorbitism. Apert syndrome developed maxillary hypoplasia, in addition to the maxillary retrusion, observed in Crouzon syndrome and nonsyndromic bicoronal synostosis patients. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, II.

Crouzon Syndrome Anatomy, Usefulness of Vestibular Orientation.

ABSTRACT: Spatial resolution of computerized tomographic scanner has reached a level to which accurate anatomic measurements could be done in. Three-dimensional accurate measurements require a reliable referential system. In craniology landmarks are usually selected in the skull base. For craniofacial malformation the classical landmarks are of no help so the authors have used the vestibular orientation to study a series of 50 Crouzon syndrome computerized tomographic scan and compare the results (shape, position, linear mensuration, volumes…) with 122 controls in unaffected patients. The authors have confirmed Crouzon description of a high level of polymorphism in phenotypes, the authors propose an organigram to understand the abnormal growth patterns in crouzon syndrome, which lead to such consequences. This polymorphism implies that the planning of surgical treatment should be tailored for each case.

Robot-assisted frontofacial correction in very young children with craniofacial dysostosis syndromes: a technical note and early functional outcome.

OBJECTIVE: In this study, the authors aimed to 1) retrospectively analyze the early functional outcomes in a cohort of very young children with craniofacial dysostoses who underwent robot-assisted frontofacial advancement (RAFFA) or robot-assisted midface distraction (RAMD), and 2) analyze the utility of robotic assistance in improving the accuracy and safety of performing transfacial pin insertion for RAFFA or RAMD. METHODS: A retrospective analysis of a cohort of 18 children (age range 1-42 months at presentation), who underwent RAFFA or RAMD from February 2015 to February 2021 in the craniofacial unit at Amrita Institute of Medical Sciences and Research Centre in Kochi, India, was performed. Inclusion criteria were patients who had undergone RAFFA in a single stage or RAMD where the cranial vault had been addressed earlier, had been addressed on follow-up, or had not been addressed and had follow-up of at least 6 months. RESULTS: Overall, 18 children with syndromic craniosynostosis underwent LeFort level III midface distraction, with or without RAFFA, from February 2015 to February 2021 at a single center in India. The patients' ages ranged from 6 to 47 months at the time of the procedure. All patients had significant obstructive sleep apnea (OSA), significant ocular issues, and disturbed sleep as determined by the authors' preoperative protocol. Clinically significant intracranial pressure issues were present in 17 patients. None of the patients had injury due to the transfacial pin trajectory such as globe injury, damage to the tooth buds, or the loss of purchase during the active distraction phase. The mean distraction achieved was 23 mm (range 18-30 mm) (n = 16/18). Of the 18 patients, 10 (56%) had an excellent outcome and 6 (33%) had a satisfactory outcome. In all cases, the degree of OSA had significantly reduced after surgery. Eye closure improved in all patients, and complete closure was seen in 11 patients. On follow-up, the functional gain remained in 14 of 16 patients at the final follow-up visit. The distraction results were stable during the follow-up period (mean 36 months [range 6-72 months]). CONCLUSIONS: The early RAFFA and RAMD protocols investigated in this study gave a significant functional advantage in very young patients with craniofacial dysostoses. The results have demonstrated the accuracy and safety of robotic assistance in performing transfacial pin insertion for RAFFA or RAMD.

An Auxiliary Cranioparietal Anchorage System to Improve the Stability of the Rigid External Distraction Device in Children With Crouzon Syndrome.

ABSTRACT: Rigid external distraction (RED) device instability because of thin skulls in syndromic craniosynostosis patients remains challenging. The authors propose the use of an auxiliary cranioparietal anchorage system to improve RED device stability in patients with Crouzon syndrome. Five consecutive patients with Crouzon syndrome underwent Le Fort III osteotomy with midface advancement using a modified external device. Cephalometric analysis and three-dimensional computed tomography images were evaluated preoperatively and after device removal. Mechanical analyses of the RED device with and without the auxiliary cranioparietal anchorage system were performed. Both postoperative photographs and follow-up computed tomographs showed obvious midfacial advancement with no intracranial pin perforation or external frame migration. Mechanical analysis showed that the new system reduced the possibility of postoperative external frame migration. The auxiliary cranioparietal anchorage system might be considered an adjunct to the RED device in patients with Crouzon syndrome to avoid postoperative complications.

Orbitofacial morphology changes with different suture synostoses in Crouzon syndrome.

This study aims to investigate the influence of different cranial vault suture synostoses on orbital and periorbital morphological development in Crouzon syndrome. Computed tomography (CT) scans of Crouzon syndrome patients who had not undergone operation were subgrouped as follows: type I: bicoronal synostosis; type II: sagittal synostosis; type III: pansynostosis; type IV: perpendicular combinations of suture synostoses; and type V: bilateral squamosal synostosis. CT scans were measured using Materialise software. CT scans of 80 Crouzon syndrome patients and 72 normal controls were included. Orbital bony cavity volume was reduced in all subgroups (16-24%), including type V bilateral squamosal synostosis (16%, p = 0.003), although the reduction in type II sagittal synostosis Crouzon patients failed to reach statistical significance (p = 0.071). Globe volume was reduced only in type I bicoronal synostosis (9%, p = 0.018), while the retrobulbar soft tissue volume decreased in type III pansynostosis group by 11% (p = 0.005). Globe volume projection beyond the orbital rim was increased in all groups (p < 0.001), with the greatest increase in type IV perpendicular combination of sutures synostoses, by 100% (p < 0.001). The anteroposterior length of maxilla was significantly shortened in type I (10%, p = 0.028) and type III (9%, p = 0.022) but developed normally in other groups, although the maxilla was posteriorly displaced in all groups (all p ≤ 0.026). The influence of squamosal synostosis on craniofacial malformation is not equivalent to that of a major vault suture. Therefore, subtype suture fusion individualized surgical interventions, after initial occipital expansion, likely provide additional benefits in mitigating oculo-orbital disproportion.

Does the association between abnormal anatomy of the skull base and cerebellar tonsillar position also exist in syndromic craniosynostosis?

PURPOSE: Cerebellar tonsillar herniation (TH) occurs frequently in syndromic craniosynostosis; however, the exact pathogenesis is unknown. This study evaluates the association between skull base deformities and TH in syndromic craniosynostosis. METHODS: Retrospective study MRI study comparing syndromic craniosynostosis to controls. Measured parameters included clivus length, skull base angle, Boogard's angle, foramen magnum area, and cerebellar tonsillar position (TP). The association between skull base parameters and TP was evaluated with linear mixed models, correcting for age and risk factors for TH in craniosynostosis (hydrocephalus, intracranial hypertension, craniocerebral disproportion, and lambdoid synostosis). RESULTS: Two hundred and eighty-two scans in 145 patients were included, and 146 scans in 146 controls. The clivus was smaller at birth, and its growth was retarded in all syndromes. The skull base angle was smaller at birth in Apert and Crouzon syndromes, and the evolution through time was normal. Boogard's angle was smaller at birth in Apert syndrome, and its evolution was disturbed in Apert and Saethre-Chotzen syndromes. The foramen magnum was smaller at birth in Crouzon and Saethre-Chotzen syndromes, and its growth was disturbed in Apert, Crouzon, and Saethre-Chotzen syndromes. TP was higher at birth in Apert syndrome, but lowered faster. In Crouzon syndrome, TP was lower at birth and throughout life. A smaller clivus and larger foramen magnum were associated with a lower TP in controls (p<0.001, p=0.007), and in Crouzon syndrome, this applied to only foramen magnum size (p=0.004). CONCLUSION: The skull base and its growth are significantly different in syndromic craniosynostosis compared to controls. However, only foramen magnum area is associated with TP in Crouzon syndrome.

Algorithm to the treatment of Crouzon syndrome.

Clinical reports regarding the entire surgical sequence in Crouzon syndrome from the neonatal period to the adult age are rare. The purpose of this study is to trace an operative algorithm with a long term follow up in a homogenous group of patients affected by Crouzon syndrome. A retrospective review was conducted for all patients affected by Crouzon syndrome who completed the entire surgical sequence. 7 Crouzon patients (4 females, 3 males) completed the entire surgical sequence at different ages: fronto-orbital advancement (0.9 years), LF III distraction osteogenesis (11.5 years) and orthognathic surgery (18 years). The mean age at the last follow up was 19.3 years; normalization of the face was obtained in all cases with improvement of the respiratory problems. After orthognathic surgery, all patients had stable occlusion. A one-year postoperative CBCT scan revealed almost complete ossification of all osteotomy sites. Frontoorbital advancement and modified Le Fort III distraction osteogenesis are reliable surgical procedures. SARME and conventional orthognathic surgery with reductive genioplasty and fat grafting are performed at the end of the surgical sequence to enhance facial aesthetics.

Comprehensive management of Crouzon syndrome: A case report with three-year follow-up.

Crouzon syndrome is one of the most common craniosynostosis facial syndromes caused by a mutation in the fibroblast growth factor receptor 2 (FGFR2) gene. Less commonly, there is a mutation of the FGFR3 gene which results in Crouzon syndrome syndrome with acanthosis nigricans. It involves the premature fusion of sutures of the cranial vault, base, orbital and maxillary region. The clinical presentation of this congenital deformity depends on the pattern and timing of sutural fusion. The present report describes the features and management of this syndrome in an 18-year-old woman. The patient presented with a hypoplastic maxilla, deficient midface, exorbitism due to shallow orbits, severe crowding and bilateral crossbite. A multidisciplinary approach involving orthodontics and surgical intervention with distraction osteogenesis brought about marked improvement in the facial profile, occlusion and upper airway. The aesthetics and function were greatly enhanced, and the results were found to be stable at the end of three years.

Dental phenotype in Crouzon syndrome: A controlled radiographic study in 22 patients.

OBJECTIVE: This retrospective radiographic controlled study investigates the dental phenotype in patients with Crouzon syndrome to determine if differences are observed as suggested by the FGFR2C342Y/+ Crouzon mouse models, and whether these models could be of interest to study the role of this mutation in tooth development. DESIGN: We assessed dental phenotype using dedicated linear measurements in 22 children with Crouzon syndrome and compared tooth morphology in both primary and permanent dentitions to an age-matched control group. Descriptive statistics were performed with "Sex" and "Age" as covariates for the permanent tooth models and "Sex" only for the primary tooth models, to take into account potential confounding factors. RESULTS: We showed that permanent but not primary tooth dimensions were globally reduced in Crouzon syndrome, without microdontia. In permanent dentition, crown height, mesiodistal and faciolingual cervical diameters were reduced by 6.3%, 5.7% and 5.5% respectively (p < 0.05). CONCLUSION: Our results underline the implication of Fibroblast Growth Factor Receptor 2 (FGFR2) in dental development of humans and contribute to support FGFR2C342Y/+ Crouzon mouse models as partial replicas of this condition, including in the oral region.

Clinical application of "black bone" imaging in paediatric craniofacial disorders.

For decades, CT has been the primary imaging modality for the diagnosis and surveillance of paediatric craniofacial disorders. However, the deleterious effects of ionising radiation in the paediatric population are well established and remain an ongoing concern. This is especially so in the head and neck region, which has relatively poor soft tissue shielding with many radiosensitive organs. The development of "black bone" imaging utilising low flip angles and short echo time (TE) has shown considerable promise in alleviating the use of ionising radiation in many cases of craniofacial disorders. In this review article, we share our experience of utilising "black bone" sequence in children with craniofacial pathologies, ranging from traumatic injuries to craniosynostosis and focal osseous/fibro-osseous lesions such as fibrous dysplasia and Langerhans cell histiocytosis (LCH). A detailed discussion on the technical aspects of "black bone" sequence, including its potential pitfalls and limitations, will also be included.