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Duplication of mental nerve in a patient with cleft lip-palate and rubella syndrome
Duplication of mental nerve in a patient with cleft lip-palate and rubella syndrome R. H. B. Goodday, B. Corn., D.D.S., * and D. S. Precious, D.D.S.. M.Sc., F.R.C.D.(C)** Halifax, Nova Scotia, Canada DALHOUSIE
UNIVERSITY
AND
VICTORIA
GENERAL
HOSPITAL
A case of duplication of the mental nerve in a patient with presented. The most vunerable period of fetal infection by of development of the maxilla, mandible, and corresponding duplication of the mental nerve is discussed in relation to the growth and development of the mandible. The concept reviewed. (ORAL SURG olw. MED ORAL PATHOL 1988;65:157-60)
cleft lip, cleft palate, and rubella syndrome is rubella virus corresponds with the critical period orofacial structures. The significance of the influence that this anatomic structure has on of ativisms to explain such anomalies is
R
ubella, also known as German measles, is a disease caused, by an RNA togavirus. The diagnosis is suggested by a rash that begins on the face and neck and quickly spreads to the trunk and extremities within a few hours. This rash lasts only 2 to 3 days and may be accompanied by lymphadenopathy in the head and neck region. Oral manifestations are erythema of both the tonsils and soft palate. The buccal mucosa usually is clear and pale.’ Neither children nor adults who have contracted rubella feel ill, but in the case of the pregnant woman the consequences of the infection on the fetus can be disastrous. Rubella virus can cause serious damage to the fetus, the defects arising from a combination of the rapid death of some cells and the persistent viral infection in others. This damage often results in many of the following clinical manifestations: central nervous system defects, hearing loss, cardiac defects, visual defects, urogenital defects, growth retardation, and cleft lip and cleft palate.2 A definite correlation has been established between the gestational age of the fetus at the time of maternal infection and the type and severity of *Resident, Oral and Maxillofacial Surgery, Dalhousie University. **Head, Department of Oral and Maxillofacial Surgery, Victoria General Hospital/Dalhousie University.
Fig. 1. Two mental foramina, ent neurovascular bundle.
each with its own appar-
157
158
Goodday and Precious
Oral Surg February 1988
Fig. 3. Architectural and structural craniofacial analysisof Delaire demonstratingmandibularvertical excess.
2. Section through mental foramen of human embryoat 7 weeks.MC, Meckel’scartilage; M, developing bony mandible;black arrow, mental nerve. (Courtesy Dr. M. Goret-Nicaise,Brussels,Belgium.)
Fig.
resulting anomaly in the child. The fetus is most vulnerable during the first 8 weeks of gestation. Of interest to oral and maxillofacial surgeons is that this most vulnerable period coincides with the critical period of development of the maxilla, mandible, and corresponding orofacial structures. CASE REPORT
A 19-year-oldwhite man was referred to the Department of Oral and Maxillofacial Surgery at Victoria General Hospital for the surgicalcorrection of his dentofacial deformity. Past medicalhistory revealedexposureto rubella virus in utero, previoussurgeryfor repair of cleft lip and palate, myringotomies,and repair of an inguinal hernia. Physicalexamination revealedthe presenceof an oronasal fistula, maxillary anteroposteriordeficiency, mandibular vertical excess,hypertelorism,90%lossof vision in the right eye, and a II/VI systolicejection murmur. The patient was taken to the operating theater where, under endotracheal general anesthesia,he received an
anterior horizontal mandibular ostectomy concomitant with LeFort I maxillary osteotomywith advancementand repairof the oronasalfistula. During surgeryto correct the mandibulardeformity, two mental foramina,eachwith its own apparentneurovascularbundle,were observedon the patient’s right side. (Fig. 1). Becauseof the planned ostectomy cut it was necessaryto sacrifice the inferior division of the mental nerve. Subsequentexaminationof this bundle revealedneural tissueonly. The procedures were otherwisecompletedwithout event. DlSCUSSlON
In reviewing the current literature, we found only one published case of a bifid inferior alveolar canal that terminated in two separate mental foramina.3 Nortje and coworkers4 and Grover and associates5 conducted panoramic radiographic surveys and reported an incidence of bifurcation of the inferior alveolar canal of 0.9% and 0.08%, respectively. No observations were made of the number of mental foramina. An unpublished thesis, “An osteoradiographlc study of the mandibular canal,” by SermarP of South Africa points out that in man the mental foramen is usually single but may be multiple and that with multiple foramina the number is usually two. Records of fossil mad possessing little or no chin reveal that primitive man’s foramen was usually
Duplication
Volume 65 Number 2
Fig.
of mental nerve 159
4. Area of anestheticskin: A, 1 weekpostoperatively;B, 3 monthspostoperatively.
double or multiple. Serman interprets the presence of more than one foramen as evidence of primitiveness.6 Our interest in the number of mental nerves and foramina stems from the influence that these anatomic structures have on the growth and development of the mandible. As discussed by others,‘-” there seems to be general agreement that at 7 weeks, ossification of the mandible starts from a single center in the region of the angle formed by the incisive and mental nerves (that is, in the region of the future mental foramen) and that Meckel’s cartilage has a close positional relationship to the developing mandible but makes no direct contribution to it. Fig. 2 shows a human embryo at 7 weeks, with Meckel’s cartilage as an ovoid structure separated from the developing bony mandible by connective tissue. This tissue section intercepts the mental foramen through which passes the mental nerve, designated by a black arrow. The clinical finding of two mental foramina, each of which houses its own mental nerve, raises these questions: Are there two primary sites of ossification? Are there two Meckel’s cartilages? The implications of two Meckel’s cartilages are important, as shown by Diewert12 and Seegmiller and FraseP through separate studies that both demonstrate a strong correlation between induction of cleft palate and the presence of structural alterations in rodent Meckel’s cartilage. These studies support the concept that normal growth of Meckel’s cartilage is necessary for normal palate formation.
One could theorize that these two primary sites of mandibular ossification could cause excessive vertical growth of the mandible. This indeed was the case with our patient, as graphically portrayed by the architectural and structural craniofacial analysis of Delaire” (Fig. 3). It is interesting to note that our patient’s anomaly was unilateral, but the mandible showed symmetric vertical growth. The next question to be asked is “How does the body regulate growth if two sites of ossification are present?” The clinician who discovers an anomaly similar to the case we have discussed, should consider the possibility that it is an atavism. Atavisms are the reappearance of lost characteristics that are typical of remote ancestors (such as fossil man) but that are not seen in recent ancestors of the organism.ls The essential features of an atavistic characteristic are persistence into adult life, absence in the parents or other recent ancestors, presence in only one or a few individuals within a population, and close resemblance to the same characteristic possessed by all members of an ancestral population. Atavisms illustrate the hidden potential for morphologic change that all organisms possess. Atavisms arise because genes evidently can be conserved, unaltered but quiescent, for a very long time. Of direct clinical interest is the fact that our patient did not have duplication of the mental nerve, but division of this nerve, with each branch innervating a specific area of soft tissue. Postoperatively, using two-point discrimination testing, we localized
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Goodday and Precious
the area of innervation of the sacrificed branch by mapping the region that was anesthetic. The patient was examined on a regular basis. Sensation returned to the area within 8 months (Fig. 4). In conclusion, we have reported this case (1) to review rubella syndrome, of which our patient had multiple clinical manifestations, and to demonstrate that oral and maxillofacial surgeons have a role to play in the surgical correction of associated dentofacial deformities; (2) to urge the clinician not to consider trite observations of deviations from normal that on first glance appear to be insignificant; and (3) to put forth the principles of atavisms that might explain some anomalies surgeons encounter in clinical practice.
Oral Surg February 1988
6. I. 8. 9. 10. 11. 12. 13.
REFERENCES 1. Nolte WA. Oral microbiology with basic microbiology and immunology. 5th ed. St. Louis: the CV Mosby Co, 1977: 398-9. 2. Community Task Force on Maternal and Child Health. An immunization strategy for Manitoba: the prevention of congenital rubella and fetal damage. Winnipeg: Department of Health, Government of Manitoba, 1982:1-21. 3. Patterson JE. Funke FW. Bifid inferior alveolar canal. Oral Surg 1973;36:287-9. 4. Nortje CJ, Farman AG, Grotepass, FW. Variations in the normal anatomy of the inferior dental (mandibular) canal: a retrospective study of panoramic radiographs from 3612 routine dental patients. Br J Oral Surg 1977;15:55-63. 5. Grover PS, Lorton R. Bifid mandibular nerve as a possible
14.
15.
cause of inadequate anesthesia in the mandible. J Oral Maxillofac Surg 1983;41:177-9. Serman NJ. An osteo-radiographic study of the mandibular canal. (Unpublished thesis.) Tyberberg, South Africa: University of Stellenbosch, 1982:39. Ten Cate AR. Oral histology development, structure and function. St. Louis: The CV Mosby Co, 1980:36-40. Scott JH, Dixon AD. Anatomy for students of dentistry. 4th cd. London: Churchill Livingstone, 1978:356-60. O’Rahilly R, Gardner E. The initial appearance of ossitication in staged human embryos. Am J Anat 1972;134:291308. Goore DH, Appleton J. Human dentofacial growth. Oxford, England: Pergamon Press Ltd, 1982:77-9. Goret-Nicaise M, Pilet 0. A few observations about Meckel’s cartilage in the human. Anat Embryo1 (Berl) 1983;167:36570. Diewert VM. Correlation between alterations in Meckel’s cartilage and induction of cleft palate with fl-amino-proprionitute in the rat. Teratology 1981;24:43-52. Seenmiller RE. Fraser FC. Mandibular growth retardation as a cause of cleft palate in mice homozy&us for the chondrodysplasia gene. J. Embryo1 Exp Morph01 1977;38:227-38. Delaire J. L’analyse architecturale et structurale craniofaciale (de profil). Principles theoriques. Queleques examples d’emploie enchirugie maxillo-faciale. Rev Stomatol Chir Maxillofac 1978;79:1-33. Hall BK. Developmental mechanisms underlying the formation of atavisms. Biol Rev 1984;59:89-124.
Reprint
requests
to:
Dr. D. S. Precious Department of Oral and Maxillofacial Surgery Dalhousie University Halifax, Nova Scotia B3H 355 Canada
UNIVERSITY
AND
VICTORIA
GENERAL
HOSPITAL
A case of duplication of the mental nerve in a patient with presented. The most vunerable period of fetal infection by of development of the maxilla, mandible, and corresponding duplication of the mental nerve is discussed in relation to the growth and development of the mandible. The concept reviewed. (ORAL SURG olw. MED ORAL PATHOL 1988;65:157-60)
cleft lip, cleft palate, and rubella syndrome is rubella virus corresponds with the critical period orofacial structures. The significance of the influence that this anatomic structure has on of ativisms to explain such anomalies is
R
ubella, also known as German measles, is a disease caused, by an RNA togavirus. The diagnosis is suggested by a rash that begins on the face and neck and quickly spreads to the trunk and extremities within a few hours. This rash lasts only 2 to 3 days and may be accompanied by lymphadenopathy in the head and neck region. Oral manifestations are erythema of both the tonsils and soft palate. The buccal mucosa usually is clear and pale.’ Neither children nor adults who have contracted rubella feel ill, but in the case of the pregnant woman the consequences of the infection on the fetus can be disastrous. Rubella virus can cause serious damage to the fetus, the defects arising from a combination of the rapid death of some cells and the persistent viral infection in others. This damage often results in many of the following clinical manifestations: central nervous system defects, hearing loss, cardiac defects, visual defects, urogenital defects, growth retardation, and cleft lip and cleft palate.2 A definite correlation has been established between the gestational age of the fetus at the time of maternal infection and the type and severity of *Resident, Oral and Maxillofacial Surgery, Dalhousie University. **Head, Department of Oral and Maxillofacial Surgery, Victoria General Hospital/Dalhousie University.
Fig. 1. Two mental foramina, ent neurovascular bundle.
each with its own appar-
157
158
Goodday and Precious
Oral Surg February 1988
Fig. 3. Architectural and structural craniofacial analysisof Delaire demonstratingmandibularvertical excess.
2. Section through mental foramen of human embryoat 7 weeks.MC, Meckel’scartilage; M, developing bony mandible;black arrow, mental nerve. (Courtesy Dr. M. Goret-Nicaise,Brussels,Belgium.)
Fig.
resulting anomaly in the child. The fetus is most vulnerable during the first 8 weeks of gestation. Of interest to oral and maxillofacial surgeons is that this most vulnerable period coincides with the critical period of development of the maxilla, mandible, and corresponding orofacial structures. CASE REPORT
A 19-year-oldwhite man was referred to the Department of Oral and Maxillofacial Surgery at Victoria General Hospital for the surgicalcorrection of his dentofacial deformity. Past medicalhistory revealedexposureto rubella virus in utero, previoussurgeryfor repair of cleft lip and palate, myringotomies,and repair of an inguinal hernia. Physicalexamination revealedthe presenceof an oronasal fistula, maxillary anteroposteriordeficiency, mandibular vertical excess,hypertelorism,90%lossof vision in the right eye, and a II/VI systolicejection murmur. The patient was taken to the operating theater where, under endotracheal general anesthesia,he received an
anterior horizontal mandibular ostectomy concomitant with LeFort I maxillary osteotomywith advancementand repairof the oronasalfistula. During surgeryto correct the mandibulardeformity, two mental foramina,eachwith its own apparentneurovascularbundle,were observedon the patient’s right side. (Fig. 1). Becauseof the planned ostectomy cut it was necessaryto sacrifice the inferior division of the mental nerve. Subsequentexaminationof this bundle revealedneural tissueonly. The procedures were otherwisecompletedwithout event. DlSCUSSlON
In reviewing the current literature, we found only one published case of a bifid inferior alveolar canal that terminated in two separate mental foramina.3 Nortje and coworkers4 and Grover and associates5 conducted panoramic radiographic surveys and reported an incidence of bifurcation of the inferior alveolar canal of 0.9% and 0.08%, respectively. No observations were made of the number of mental foramina. An unpublished thesis, “An osteoradiographlc study of the mandibular canal,” by SermarP of South Africa points out that in man the mental foramen is usually single but may be multiple and that with multiple foramina the number is usually two. Records of fossil mad possessing little or no chin reveal that primitive man’s foramen was usually
Duplication
Volume 65 Number 2
Fig.
of mental nerve 159
4. Area of anestheticskin: A, 1 weekpostoperatively;B, 3 monthspostoperatively.
double or multiple. Serman interprets the presence of more than one foramen as evidence of primitiveness.6 Our interest in the number of mental nerves and foramina stems from the influence that these anatomic structures have on the growth and development of the mandible. As discussed by others,‘-” there seems to be general agreement that at 7 weeks, ossification of the mandible starts from a single center in the region of the angle formed by the incisive and mental nerves (that is, in the region of the future mental foramen) and that Meckel’s cartilage has a close positional relationship to the developing mandible but makes no direct contribution to it. Fig. 2 shows a human embryo at 7 weeks, with Meckel’s cartilage as an ovoid structure separated from the developing bony mandible by connective tissue. This tissue section intercepts the mental foramen through which passes the mental nerve, designated by a black arrow. The clinical finding of two mental foramina, each of which houses its own mental nerve, raises these questions: Are there two primary sites of ossification? Are there two Meckel’s cartilages? The implications of two Meckel’s cartilages are important, as shown by Diewert12 and Seegmiller and FraseP through separate studies that both demonstrate a strong correlation between induction of cleft palate and the presence of structural alterations in rodent Meckel’s cartilage. These studies support the concept that normal growth of Meckel’s cartilage is necessary for normal palate formation.
One could theorize that these two primary sites of mandibular ossification could cause excessive vertical growth of the mandible. This indeed was the case with our patient, as graphically portrayed by the architectural and structural craniofacial analysis of Delaire” (Fig. 3). It is interesting to note that our patient’s anomaly was unilateral, but the mandible showed symmetric vertical growth. The next question to be asked is “How does the body regulate growth if two sites of ossification are present?” The clinician who discovers an anomaly similar to the case we have discussed, should consider the possibility that it is an atavism. Atavisms are the reappearance of lost characteristics that are typical of remote ancestors (such as fossil man) but that are not seen in recent ancestors of the organism.ls The essential features of an atavistic characteristic are persistence into adult life, absence in the parents or other recent ancestors, presence in only one or a few individuals within a population, and close resemblance to the same characteristic possessed by all members of an ancestral population. Atavisms illustrate the hidden potential for morphologic change that all organisms possess. Atavisms arise because genes evidently can be conserved, unaltered but quiescent, for a very long time. Of direct clinical interest is the fact that our patient did not have duplication of the mental nerve, but division of this nerve, with each branch innervating a specific area of soft tissue. Postoperatively, using two-point discrimination testing, we localized
160
Goodday and Precious
the area of innervation of the sacrificed branch by mapping the region that was anesthetic. The patient was examined on a regular basis. Sensation returned to the area within 8 months (Fig. 4). In conclusion, we have reported this case (1) to review rubella syndrome, of which our patient had multiple clinical manifestations, and to demonstrate that oral and maxillofacial surgeons have a role to play in the surgical correction of associated dentofacial deformities; (2) to urge the clinician not to consider trite observations of deviations from normal that on first glance appear to be insignificant; and (3) to put forth the principles of atavisms that might explain some anomalies surgeons encounter in clinical practice.
Oral Surg February 1988
6. I. 8. 9. 10. 11. 12. 13.
REFERENCES 1. Nolte WA. Oral microbiology with basic microbiology and immunology. 5th ed. St. Louis: the CV Mosby Co, 1977: 398-9. 2. Community Task Force on Maternal and Child Health. An immunization strategy for Manitoba: the prevention of congenital rubella and fetal damage. Winnipeg: Department of Health, Government of Manitoba, 1982:1-21. 3. Patterson JE. Funke FW. Bifid inferior alveolar canal. Oral Surg 1973;36:287-9. 4. Nortje CJ, Farman AG, Grotepass, FW. Variations in the normal anatomy of the inferior dental (mandibular) canal: a retrospective study of panoramic radiographs from 3612 routine dental patients. Br J Oral Surg 1977;15:55-63. 5. Grover PS, Lorton R. Bifid mandibular nerve as a possible
14.
15.
cause of inadequate anesthesia in the mandible. J Oral Maxillofac Surg 1983;41:177-9. Serman NJ. An osteo-radiographic study of the mandibular canal. (Unpublished thesis.) Tyberberg, South Africa: University of Stellenbosch, 1982:39. Ten Cate AR. Oral histology development, structure and function. St. Louis: The CV Mosby Co, 1980:36-40. Scott JH, Dixon AD. Anatomy for students of dentistry. 4th cd. London: Churchill Livingstone, 1978:356-60. O’Rahilly R, Gardner E. The initial appearance of ossitication in staged human embryos. Am J Anat 1972;134:291308. Goore DH, Appleton J. Human dentofacial growth. Oxford, England: Pergamon Press Ltd, 1982:77-9. Goret-Nicaise M, Pilet 0. A few observations about Meckel’s cartilage in the human. Anat Embryo1 (Berl) 1983;167:36570. Diewert VM. Correlation between alterations in Meckel’s cartilage and induction of cleft palate with fl-amino-proprionitute in the rat. Teratology 1981;24:43-52. Seenmiller RE. Fraser FC. Mandibular growth retardation as a cause of cleft palate in mice homozy&us for the chondrodysplasia gene. J. Embryo1 Exp Morph01 1977;38:227-38. Delaire J. L’analyse architecturale et structurale craniofaciale (de profil). Principles theoriques. Queleques examples d’emploie enchirugie maxillo-faciale. Rev Stomatol Chir Maxillofac 1978;79:1-33. Hall BK. Developmental mechanisms underlying the formation of atavisms. Biol Rev 1984;59:89-124.
Reprint
requests
to:
Dr. D. S. Precious Department of Oral and Maxillofacial Surgery Dalhousie University Halifax, Nova Scotia B3H 355 Canada