|Year : 2014 | Volume
| Issue : 1 | Page : 65-68
Increased frontonasal angle and surface area of mandibular antegonial notch; reliable signs of Treacher Collins syndrome
Gyan P Singh1, Sneh Lata Verma2, Pradeep Tandon1, Divya Mehrotra3
1 Department of Orthodontics and Dentofacial Orthopedics, Faculty of Dental Sciences, King George's Medical University, Lucknow, Uttar Pradesh, India
2 Department of Orthodontics and Dentofacial Orthopedics, Babu Banarsi Das College of Dental Sciences, Lucknow, Uttar Pradesh, India
3 Department of Oral and Maxillofacial Surgery, Faculty of Dental Sciences, King George's Medical University, Lucknow, Uttar Pradesh, India
|Date of Web Publication||5-Feb-2014|
Gyan P Singh
D-1077, Indira Nagar, Lucknow - 226 016, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Background: Treacher Collin Syndrome is one of the most disfiguring congenital anomalies of the face, the visible part of the human body used for the identification of an individual. It is an inherited disorder in which there are bilateral symmetric anomalies of the structures within the first and second branchial arches. In general, there is complete penetrance and variable expressivity of the trait. Increased frontonasal angle and deep antegonial notch are syndrome specific characteristic distinguishing Treacher Collin Syndrome from other Syndromes. Main objectives of the presenting this case are to evaluate the validity of the aforementioned clinical signs for the diagnosis and to find out the significance of the surface area of antegonial notch in patient suffering from Treacher Collins syndrome. Methods: Persons of two generations of a family effected with Treacher Collins syndrome were examined for two cardinal signs traditionally associated with this disorder along with the normal siblings of the second generation for the above parameters. Conclusion: Significantly increased fronto nasal angle, frontal sinus area and deep antegonial notch was found in the father and son exhibiting characteristic signs of Treacher Collins-Franceschetti Syndrome in comparison to normal individuals of the family.
Keywords: Antegonial notch, frontonasal angle, Treacher Collins syndrome
|How to cite this article:|
Singh GP, Verma SL, Tandon P, Mehrotra D. Increased frontonasal angle and surface area of mandibular antegonial notch; reliable signs of Treacher Collins syndrome. J Cleft Lip Palate Craniofac Anomal 2014;1:65-8
|How to cite this URL:|
Singh GP, Verma SL, Tandon P, Mehrotra D. Increased frontonasal angle and surface area of mandibular antegonial notch; reliable signs of Treacher Collins syndrome. J Cleft Lip Palate Craniofac Anomal [serial online] 2014 [cited 2019 Mar 24];1:65-8. Available from: http://www.jclpca.org/text.asp?2014/1/1/65/126579
| Introduction|| |
Treacher Collins syndrome is an autosomal dominant condition with variable expressivity. ,,,, It is characterized by bilaterally symmetrical abnormalities of structures with in the first and second branchial arches. More than a dozen salient clinical features of this condition fall in the domain of opthalmologists, otolaryngologists, oral and maxillofacial surgeons, orthodontists, plastic, reconstructive and aesthetic surgeons.
The patient with fully expressed Treacher Collins syndrome has a convex facial profile with a prominent dorsum of the nose and a retrusive lower jaw and chin. An antimongoloid slant of palpebral fissure due to colobomata, hypoplasia of the lower lids and partial absence of the eyelid cilia are present in the eyes. The external ears are absent, malformed, or malposed. Hypoplasia of malar bones and hypoplastic zygomatic complex are the most cardinal signs of the syndrome. The maxilla and the mandible are characteristically hypoplastic with variable effects on the temporomandibular joint and muscles of the mastication. There is an Angle's class II malocclusion with anterior open bite and a steep occlusal plane angle.
Flattening of frontonasal angle was described as a clinical feature of Treacher Collins Syndrome for the first time by Rovin.  Gorlin et al. have emphasized that frontonasal angle is usually increased and the bridge of the nose raised in cases of Treacher Collins syndrome.  Garner and later Kolar et al. included open frontonasal angle among ten classical signs of Treacher Collins syndrome. ,
Deep antegonial notch, another recently recognized sign of Treacher Collins syndrome, is commonly present at the junction of ramus and corpus of mandible. It corresponds to the highest point of the notch or concavity of the lower border of the ramus where it joins the body of the mandible.
Roberts et al. attempted mathematically to characterize the concavity of the lower border of mandible in Treacher Collins syndrome by drawing a line tangent near the menton and gonion.  They measured height of nine perpendicular lines constructed along this line and expressed as a percentage of the length of the mandibular body. In contrast, Becker et al. in their study have reported that the ascending ramus is at a more obtuse angle to the body of mandible in subjects with Treacher Collins syndrome.  A study done by Grayson et al. suggested that the peculiarly broad concave downward curvature of the inferior border is a syndrome specific characteristic, distinguishing it from the other syndromes that involve the mandible. 
Interestingly, Behrents concluded that this basic mandibular form is established "in utero " and is maintained throughout the period of postnatal growth and development.  Moreover, how the antegonial notch develops, is still not fully understood. The current view is that a single field of surface resorption is present on the inferior border of the mandible at the ramus - corpus junction. This forms the antegonial notch by remodeling from the ramus just behind it as the ramus relocates posteriorly and antegonial notch depth, when extreme in magnitude, might be used to predict facial growth. ,,
| Case Report|| |
Persons of two generations of a family effected with Treacher Collins syndrome were examined for two cardinal signs traditionally associated with this disorder along with the normal siblings of the second generation for the same parameters. The father [Figure 1] and a son [Figure 2] exhibited signs of Treacher Collins syndrome , whereas the mother and the two siblings revealed no visible anomalies.
|Figure 1: Frontal and lateral profi le photographs of the father effected with Treacher Collins syndrome|
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|Figure 2: Frontal and lateral profi le photographs of the son effected with Treacher Collins syndrome|
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Significantly increased frontonasal angle was found in the father and son exhibiting characteristic signs of Treacher Collins-Franceschetti (TCOF) Syndrome. The depth of antegonial notch was determined by standard cephalometric techniques after Burstone and the surface area was calculated from projection on a graph paper [Figure 3]. Furthermore three dimensional computerized reconstructions of tomographic scans showed pronounced antegonial notches. Intrafamily comparison of these findings revealed significant increment in depth and surface area of antegonial notch in person suffering in the TCOF. In the adolescent age (13 years to 19 years) there is significant increase in depth and area of antegonial notch. The frontonasal angle showed no correlation with the size of frontal sinuses.
|Figure 3: Lateral Cephalogram shows method of measuring frontonasal angle, frontal sinus area, antegonial notch depth and its area|
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The values of the various parameters investigated in a TCOF Syndrome family are summarized in [Table 1].
|Table 1: Comparative values of variables in the family of Treacher Collins syndrome|
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Notably, occurrence of flat frontonasal angle enables one to differentiate Treacher Collins syndrome clearly from the other types of mandibullofacial dysostosis, Goldenhar syndrome and hemifacial microsomia [Figure 4] and [Figure 5].
|Figure 4: Increased frontonasal angle in a case of Treacher Collins — Franceschetti Syndrome|
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|Figure 5: Normal frontonasal angle (130°) in a case of hemifacial microsomia|
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Three dimensional reconstruction of tomographic scans showed that the mandible is hypolplastic in the ascending ramus, body and in the projection of the chin. There is a marked antegonial notch with an obtuse gonial angle and a tendency for chin to rotate inferiorly, which gives the mandible a bowed appearance [Figure 6] and [Figure 7].
|Figure 6: Deep and wide antegonial notch with obtuse gonial angle are clearly visualized from the left side|
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| Discussion|| |
To the best of our knowledge the present study for the first time evaluates the values of frontonasal angle, frontal sinus area, depth of antegonial notch and area of antegonial notch at an interval of 6 years in a family suffering from Treacher Collin syndrome.
The radix or root of the nose is the narrowest and back-sited point of the nose which differentiates the nose from the forehead and determines two important angles of the face viz. frontonasal and nasofacial angles. , Therefore, any change in the horizontal and vertical position of this region can induce prominent changes in the appearance of the face. Significantly higher value of frontonasal angle in the father and son suffering from Treacher Collins syndrome in comparison with the normal siblings supports the conclusion of Koppel and Moos and Gorlin et al. , The intrafamily comparisons may be of greater value for diagnostic confirmation of Treacher Collins syndrome than comparison with literature norms.  The flat frontonasal angle coupled with deep antegonial notch and the resultant downward and backward rotation of ventral segment of the mandible may explain the characteristically convex "bird like" physiognomy of Treacher Collins syndrome cases. Notably, the frontonasal angle of the son shows an increment of 7® at an interval of 6 years, which is consistent with the "adolescent period of growth" (13 years to 19 years in this case).
Three dimensional reconstruction of tomographic scans revealed that mandible is hypoplastic in the ascending ramus, body and the projection of chin. Our study has unmasked the craniofacial morphological features accompanying deep antegonial notch. Subjects with deep antegonial notch show retrognathic lower jaws. This can range from microgenia to true micrognathia in both the vertical and horizontal dimensions.
Whereas Singer et al. suggested that clinical presence of a deep mandibular antegonial notch was indicative of a diminished mandibular growth potential and a vertically directed mandibular growth pattern.  Kolodziej et al. concluded that antegonial notch depth fails to provide sufficient indications of future facial growth to warrant its application as a growth predictor in a non-extreme population.  The ultimate shape of fully grown mandible is the result of genetic determinants that express themselves under the influence of the functional environment.
| Acknowledgement|| |
I gratefully acknowledge Professor Dr. Mahdi Hasan for his valuable contribution.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]