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Osteoma or chondroma of the tongue; a clinical and postmortem study
Int. J. Oral Maxillofac. Surg. 1987: 16:713-717 (Key words:
osteoma; ehondroma; tongue; pathology, oral," tumor, benign)
Osteoma or chondroma of the tongue; a clinical and postmortem study N. VAN DER WAL AND I. VAN DER WAAL
Department of Oral Pathology, Free University, Amsterdam, the Netherlands
ABSTRACT - - The occurrence of an osteoma or chondroma in the soft tissues of the oral cavity is rather uncommon. This anomaly occurs mainly on the tongue. Less than 60 cases have been published in the literature. In the first part of this treatise, 2 other patients are described, a 61-yearold female with a chondroma on the dorsum of the tongue and a 3l-yearold female with an osteoma in the foramen caecum area. In the second part, the result of a post mortem study of 130 adult human tongues is reported. Not a single case of bone or cartilage formation was encountered in the cadaver tongues. The possible development of an osteoma or ehondroma in embryonic life is discussed.
(Accepted for publication 25 February 1987)
A n osteoma or c h o n d r o m a of the oral mucosa is rather u n c o m m o n , though obviously the tongue predominates in these cases. A few cases of osteomas of the mucosa of the cheek a n d palate has been described. It has been generally accepted that this anomaly is due to a developmental disorder, being an example of a choristoma. The suggestion has been made that it involves ectopic remnants of the branchial arches 1°,14. Fewer than 40 cases of an osteoma and approximately 20 cases of a c h o n d r o m a of the tongue have been published prior to 1985. Osteomas are more prevalent in women than in m e n ~°, while a chondroma occurs equally in women a n d m e n 14. Both anomalies have been diagnosed in most cases in the 3rd decade of life.
A n osteoma of the tongue seems to occur predominantly posterior to the circumval-late papillae or close to the foramen caecum ~°, whereas a c o n d r o m a or an osteochondroma is f o u n d particularly on the lateral borders of the anterior two thirds of the tongue 4,~4. A few reports deal with the occurrence of a n osteochondroma at the base of the tongue 16. A n osteoma, chondroma or osteochondroma of the tongue may give rise to signs a n d symptoms such as dysphagia and nausea or be chance findings on routine oral examination. In a postmortem study of 130 tongues, the possible occurrence of bone or cartilage tissue in clinically normal tongues has been looked for, both in the foramen caecum area and in the lateral borders. The aim
714
VAN D E R WAL A N D VAN D E R WAAL
o f this study was to l o o k f o r the possible presence o f b o n e a n d cartilage t h a t c o u l d explain the d e v e l o p m e n t o f a b o n y o r cartilage lesion either as a d e v e l o p m e n t a l or reactive p h e n o m e n o n .
Case reports In the files of the Departments of Oral Pathology and Oral Surgery in Amsterdam, 2 patients with an osteoma and a chondroma of the tongue were recorded in the past 15 years. The second case has already been reported briefly elsewherelL
Fig. 2. Osteoma of the tongue in the foramen caecum area (reprinted with permission of the Netherlands Journal of Dentistry'5).
Case no. 1
A 61-year-old woman presented with a 2 cm diameter firm, bony hard swelling on the left side of the dorsum of the tongue. The patient noted an increase in size of the lesion over the past 15
years. A provisional diagnosis of osteoma was made. The nodule was excised and healing was uneventful. Gross examination showed a grey-white glassy, well-encapsulated tumor of hard consistency. Microscopically, the nodule consisted of lobulated, mature cartilage and was surrounded by a rim of condensed fibrous connective tissue (Fig. 1). A diagnosis of primary chondroma was made. During the 2V~ years follow-up period, there were no signs of recurrence. Case no. 2
A M-year-old healthy dentate woman was referred by her dentist, who noted a symptomless swelling on the base of her tongue. In the foramen
Fig. 1. (a) Low-power view of chondroma of¢the
tongue. Notice the separate nodule in the upper right corner (H.E., orig.magn, x 13); (b) High power view of chondroma (H.E., orig.magn. x 130).
Fig. 3. Low-power view of osteoma after decalcification. Notice the rather sharp demarcation. There is mild cellular and nuclear polymorphism. No bloodforming elements present (H.E., orig. magn. x 20) (reprinted with permission of The Netherlands Journal of Dentistryl~).
OSTEOMA OF TONGUE caecum area, an exophytic, solid tumor with a maximum diameter of 1 cm was observed. The overlying mucosa was of normal color and aspect (Fig. 2). Scintigraphy showed a normally situated functioning thyroid and excluded lingual thyroid. A provisional diagnosis of osteoma was made. Under local anaesthesia, the lesion was removed by blunt dissection. Macroscopically, the tumor consisted of bony hard tissue, requiring decalcification before being processed into H-E stained slides. Histologic examination revealed a well-circumscribed bony lesion consisting of compact vital lamellar bone (Fig. 3). There were no chondroid changes. In the sparse marrow, no blood-forming elements were present. A definitive diagnosis of osteoma of the tongue was made.
Postmortem study Material and methods A series o f 130 consecutive tongues was studied histopathologically. The aim of this study was to look for the possible presence of bone and cartilage that could explain the development of a bony or cartilage lesion either as a developmental or reactive phenomenon. The age and sex of the 130 patients have been summarized in Table 1. The tongues were taken from patients who died in the Academic Hospital of the Free University in Amsterdam. Causes o f death included coronary artery disease, aneurysma rupture, aspiration pneumonion, congenital heart disease, car accidents and malignancy. From each tongue, 5 sites were studied, 3 from the dorsal surface near the foramen caecum and 2 from the right and left lateral borders of the anterior two-thirds of the
Table 1. Age and sex distribution of 130 postmortem examinations for bone and/or cartilage tissue Age (years) Male Female Total -40 7 2 9 40-60 18 5 23 60~80 50 28 78 8012 8 20 87 43 130
715
tongue. Sections from the foramen caecum were taken through the whole thickness of the tongue; sections from the lateral border were taken with a depth of approximately 2 cm. For the histopathologic examination, formalin-fixed, H-E stained slides were prepared.
Results In none of the 130 cadaver tongues could bone or cartilage tissue be demonstrated.
Discussion Formation of cartilage as well as of bone may be the result o f metaplasia from fibroblastic elements 7. This has been accepted since the occurrence of chondroid and osseous tissue in so-called epulis fissuratum 6 and in peripheral fibromas of the gingiva 2. The mode of formation of metaplastic bone is similar to the formation of developing membranous bone during intra- and extrauterine life. Metaplastic chondroid and osteoid tissue m a y occur in benign and malignant neoplasms, especially those that have been exposed to trauma, incised or treated by irradiation w,l~. Thus, a number of neoplasms or specific processes may induce secondary formation o f bone or cartilage. The results of experimental heterotopic bone induction indicate that the osteoinductor-reteasing cells are blood-borne monocytoid cells which enter the tissues by diapedesis and transform into histiocytes, macrophages, matrixclasts and osteoclasts. Their precursors are derived from bone marrow at sites remote from the area of bone induction. The cell populations responding to the osteoinductor released by this mechanism develop into osteoblasts and osteocytes and are the progeny of perivascular mesenchymal cells s. F r o m experimental research, it appeared that heterotopic ossification as a reaction
716
VAN D E R WAL A N D VAN D E R WAAL
on a non-specific trauma is not to be regard- a synovial cavity below the epithelium ed a normal event at all. Besides, it became has been found which also supports the evident that in normal genesis heterotopic hypothesis of a developmental nature of this ossification does not have a cartilage fore- type oflesionL In our present cases, a develstage 17. opmental origin seems indeed to be the most In the case of a bony-like lesion in the likely explanation. A traumatic or infectious palatal mucosa, one may be dealing with a origin seems unlikely in view of the location true neoplastic process for which the term in the posterior part of the tongue. periosteal ossifying fibroma has been coiIn addition to an osteoma, chondroma ned 13. Likewise, a soft tissue chondroma or osteochondroma, the differential diagshould be distinguished from a periosteal nosis of a firm nodule in or close to the chondroma 8. A lingual osteoma or chon- foramen caecum area includes a fibroma, a droma on the posterior part of the tongue cyst, a salivary gland tumor and also ectopic is supposed to be a developmental dis- thyroid tissue. With regard to the latter order m4. possibility, it is advisable to perform a preDuring embryonic development, the operative scintigram. palatal shelves, from which most of the hard In histologic examination of an osteoma, palate and all of the soft palate will be chondroma or osteochondroma, more-orformed, grow downward beside the tongue. less normal tissue is encountered. In genAvailable evidence indicates that the shelves eral, the anomaly is well-demarcated. The are incapable of elevation until the tongue presence of blood-forming elements in maris first withdrawn from between them. At row has been described in a few cases. Reabout the end of the 8th gestational week, cently, a report has been published of 15 the shelves elevate, make contact, and fuse benign cartilaginous tumors arising in the with each other around the tongue 3. The soft tissues of the extremities 8. Despite the posterior one-third of the tongue develops presence of histological features suggestive from a subepithelial overgrowth of the third of low-grade chondrosarcoma, these lesions arch mesoderm over the second arch meso- were invariably benign. Occasionally osteoidderm. Besides, it is known that the anterior •appearing material can be found in spindle two thirds of the tongue is covered by ecto- cell or sarcomatoid squamous cell carciderm, whereas endoderm covers the pos- noma. Perhaps a case report of an osteogenterior one third. It is therefore, not inconic sarcoma of the tongue is an example of ceivable that some of the crest cells that such a phenomenon 12. Malignant changes later form the mesenchyme of the maxillary in osteomas, chondromas or osteochondroprocess, coming into contact with lingual mas of the tongue have never been reported. The negative finding in our postmortem endoderm, are induced by the endoderm to differentiate into bone tissue at the posterior study does not support a possible hypothesis that osteoma or chondroma of the one third of the tongue. It is known that inductive influences need only be present tongue may be the result of proliferation of commonly present bony or cartilaginous for a short time, after which the responding tissue is capable of independent develop- structures. Ectopic bone or cartilage formation in the tongue indeed seems rare. ment. It has also been hypothesized that a ctlondroma of the tongue is the result of embryologic displacement of Meckel's cartilage ~4. References In a rat's tongue, bone with articulation and 1. ALLARD, R. H. B., BLOK, P., VAN DER KWAST,
OSTEOMA OF T O N G U E W. A. M. & VAN DER WAAL, I.: Oral lipomas with osseous and chondrous metaplasia; report of 2 cases. J. Oral Pathol. 1982: 11: 18-25.
2. BALOGH, K. & RICHARDSON, J.: Chondrogenesis in peripheral fibromas of the gingiva. J. Oral PathoL 1986: 15: 169-171. 3. BHASKA~ S. N.: Development of face and oral cavity. In: Orban's oral histology and embryology, 10th edition. The C. V. Mosby Company, 1986, pp. 1-23. 4. BHAWAN,J. (~¢ RAJGOPALAN,M. R.: Osteochondroma of the tongue. Indian J. Pathol. MicrobioL 1976: 19: 135-137. 5. BORING, K.: On the origin of cells in heterotopic bone formation. Clin. Orthop. 1975: 110: 293-302. 6. CUTRIGHT, D. E.: Osseous and chondromatous metaplasia caused by dentures. Oral Surg. 1972: 34: 625-633. 7. HAJDU, S. [2 Extraskeletal bone tumors. In: Pathology of soft tissue tumors. Lea & Febiger, Philadelphia, 1979, pp. 483-486.
8. HUMPHREYS,S., PAMBAKIAN,H., McKEE, R H. & FLETCHER,C. D. M.: Soft tissue chondroma - a study of 15 tumours. Histopathology 1986: 10: 147-159. 9. JAYARAJ,A. P.: Articulating bone formation in the rat tongue. J. Laryngol Otol. 1982: 96: 665-667. 10. MAIN, D. M. G.: Osseous polyp of the tongue: osteoma or choristoma? Br. Dent. J. 1984: 156: 285-286.
717
11. MAKEK,M. S. & SAILER,H. F.: Prothesenbedingte nodul/ire Chondrometaplasie des Obe'rkiefers. Sehweiz. Mschr. Zahnmed. 1985: 95: 551-559. 12. R~YES,J. M., VANGOI~, S. K., PUTONG, P. B., HARWICK, R., MILLER,A. S. & CrIEN, S. Y.: Osteogenic sarcoma of the tongue. J. Oral. Surg. 1981: 51: 421-425, 13. SAITO, 1., IDE, F., INOUE, M., TERATANI,K., SATOH, M., KIUCHI, K. & UMEMURA, S. J.: Periosteal ossifying fibroma of the palate. J. PeriodontoL 1984: 55: 704~707. 14. SEGAL, K., KATZAU, Y., SIDI, J. ~¢ ROTEM, A.: Chondroma of the tongue, report of two cases. Ann. OtoL RhinoL Laryngol. 1984: 93: 271-272. 15. VAN DER WAAL, I., BAART, J. A., KEUTER,G., HES, J. & VAN DER KWAST, W. A. M.: Het osteoom van de tong. Ned. Tijdschr. Tandheelkd. 1983: 90: 111-113. 16. WESLEY,R. K. & ZIELINSKI,R. J.: Osteocartilaginous choristoma of the tongue: clinical and histopathologic considerations. J. Oral Surg. 1978: 36: 59-61. 17. WOJTEK, E.: Experimentelle Untersuchungen zur Frage der heterotopen Knochenbildung. Zbl. Chit. 1964: 38: 1419-1437. Address: 1. van der Waal Vrije Universiteit Pathologisch Instituut Postbus 7057 1007 M B Amsterdam The Netherlands
osteoma; ehondroma; tongue; pathology, oral," tumor, benign)
Osteoma or chondroma of the tongue; a clinical and postmortem study N. VAN DER WAL AND I. VAN DER WAAL
Department of Oral Pathology, Free University, Amsterdam, the Netherlands
ABSTRACT - - The occurrence of an osteoma or chondroma in the soft tissues of the oral cavity is rather uncommon. This anomaly occurs mainly on the tongue. Less than 60 cases have been published in the literature. In the first part of this treatise, 2 other patients are described, a 61-yearold female with a chondroma on the dorsum of the tongue and a 3l-yearold female with an osteoma in the foramen caecum area. In the second part, the result of a post mortem study of 130 adult human tongues is reported. Not a single case of bone or cartilage formation was encountered in the cadaver tongues. The possible development of an osteoma or ehondroma in embryonic life is discussed.
(Accepted for publication 25 February 1987)
A n osteoma or c h o n d r o m a of the oral mucosa is rather u n c o m m o n , though obviously the tongue predominates in these cases. A few cases of osteomas of the mucosa of the cheek a n d palate has been described. It has been generally accepted that this anomaly is due to a developmental disorder, being an example of a choristoma. The suggestion has been made that it involves ectopic remnants of the branchial arches 1°,14. Fewer than 40 cases of an osteoma and approximately 20 cases of a c h o n d r o m a of the tongue have been published prior to 1985. Osteomas are more prevalent in women than in m e n ~°, while a chondroma occurs equally in women a n d m e n 14. Both anomalies have been diagnosed in most cases in the 3rd decade of life.
A n osteoma of the tongue seems to occur predominantly posterior to the circumval-late papillae or close to the foramen caecum ~°, whereas a c o n d r o m a or an osteochondroma is f o u n d particularly on the lateral borders of the anterior two thirds of the tongue 4,~4. A few reports deal with the occurrence of a n osteochondroma at the base of the tongue 16. A n osteoma, chondroma or osteochondroma of the tongue may give rise to signs a n d symptoms such as dysphagia and nausea or be chance findings on routine oral examination. In a postmortem study of 130 tongues, the possible occurrence of bone or cartilage tissue in clinically normal tongues has been looked for, both in the foramen caecum area and in the lateral borders. The aim
714
VAN D E R WAL A N D VAN D E R WAAL
o f this study was to l o o k f o r the possible presence o f b o n e a n d cartilage t h a t c o u l d explain the d e v e l o p m e n t o f a b o n y o r cartilage lesion either as a d e v e l o p m e n t a l or reactive p h e n o m e n o n .
Case reports In the files of the Departments of Oral Pathology and Oral Surgery in Amsterdam, 2 patients with an osteoma and a chondroma of the tongue were recorded in the past 15 years. The second case has already been reported briefly elsewherelL
Fig. 2. Osteoma of the tongue in the foramen caecum area (reprinted with permission of the Netherlands Journal of Dentistry'5).
Case no. 1
A 61-year-old woman presented with a 2 cm diameter firm, bony hard swelling on the left side of the dorsum of the tongue. The patient noted an increase in size of the lesion over the past 15
years. A provisional diagnosis of osteoma was made. The nodule was excised and healing was uneventful. Gross examination showed a grey-white glassy, well-encapsulated tumor of hard consistency. Microscopically, the nodule consisted of lobulated, mature cartilage and was surrounded by a rim of condensed fibrous connective tissue (Fig. 1). A diagnosis of primary chondroma was made. During the 2V~ years follow-up period, there were no signs of recurrence. Case no. 2
A M-year-old healthy dentate woman was referred by her dentist, who noted a symptomless swelling on the base of her tongue. In the foramen
Fig. 1. (a) Low-power view of chondroma of¢the
tongue. Notice the separate nodule in the upper right corner (H.E., orig.magn, x 13); (b) High power view of chondroma (H.E., orig.magn. x 130).
Fig. 3. Low-power view of osteoma after decalcification. Notice the rather sharp demarcation. There is mild cellular and nuclear polymorphism. No bloodforming elements present (H.E., orig. magn. x 20) (reprinted with permission of The Netherlands Journal of Dentistryl~).
OSTEOMA OF TONGUE caecum area, an exophytic, solid tumor with a maximum diameter of 1 cm was observed. The overlying mucosa was of normal color and aspect (Fig. 2). Scintigraphy showed a normally situated functioning thyroid and excluded lingual thyroid. A provisional diagnosis of osteoma was made. Under local anaesthesia, the lesion was removed by blunt dissection. Macroscopically, the tumor consisted of bony hard tissue, requiring decalcification before being processed into H-E stained slides. Histologic examination revealed a well-circumscribed bony lesion consisting of compact vital lamellar bone (Fig. 3). There were no chondroid changes. In the sparse marrow, no blood-forming elements were present. A definitive diagnosis of osteoma of the tongue was made.
Postmortem study Material and methods A series o f 130 consecutive tongues was studied histopathologically. The aim of this study was to look for the possible presence of bone and cartilage that could explain the development of a bony or cartilage lesion either as a developmental or reactive phenomenon. The age and sex of the 130 patients have been summarized in Table 1. The tongues were taken from patients who died in the Academic Hospital of the Free University in Amsterdam. Causes o f death included coronary artery disease, aneurysma rupture, aspiration pneumonion, congenital heart disease, car accidents and malignancy. From each tongue, 5 sites were studied, 3 from the dorsal surface near the foramen caecum and 2 from the right and left lateral borders of the anterior two-thirds of the
Table 1. Age and sex distribution of 130 postmortem examinations for bone and/or cartilage tissue Age (years) Male Female Total -40 7 2 9 40-60 18 5 23 60~80 50 28 78 8012 8 20 87 43 130
715
tongue. Sections from the foramen caecum were taken through the whole thickness of the tongue; sections from the lateral border were taken with a depth of approximately 2 cm. For the histopathologic examination, formalin-fixed, H-E stained slides were prepared.
Results In none of the 130 cadaver tongues could bone or cartilage tissue be demonstrated.
Discussion Formation of cartilage as well as of bone may be the result o f metaplasia from fibroblastic elements 7. This has been accepted since the occurrence of chondroid and osseous tissue in so-called epulis fissuratum 6 and in peripheral fibromas of the gingiva 2. The mode of formation of metaplastic bone is similar to the formation of developing membranous bone during intra- and extrauterine life. Metaplastic chondroid and osteoid tissue m a y occur in benign and malignant neoplasms, especially those that have been exposed to trauma, incised or treated by irradiation w,l~. Thus, a number of neoplasms or specific processes may induce secondary formation o f bone or cartilage. The results of experimental heterotopic bone induction indicate that the osteoinductor-reteasing cells are blood-borne monocytoid cells which enter the tissues by diapedesis and transform into histiocytes, macrophages, matrixclasts and osteoclasts. Their precursors are derived from bone marrow at sites remote from the area of bone induction. The cell populations responding to the osteoinductor released by this mechanism develop into osteoblasts and osteocytes and are the progeny of perivascular mesenchymal cells s. F r o m experimental research, it appeared that heterotopic ossification as a reaction
716
VAN D E R WAL A N D VAN D E R WAAL
on a non-specific trauma is not to be regard- a synovial cavity below the epithelium ed a normal event at all. Besides, it became has been found which also supports the evident that in normal genesis heterotopic hypothesis of a developmental nature of this ossification does not have a cartilage fore- type oflesionL In our present cases, a develstage 17. opmental origin seems indeed to be the most In the case of a bony-like lesion in the likely explanation. A traumatic or infectious palatal mucosa, one may be dealing with a origin seems unlikely in view of the location true neoplastic process for which the term in the posterior part of the tongue. periosteal ossifying fibroma has been coiIn addition to an osteoma, chondroma ned 13. Likewise, a soft tissue chondroma or osteochondroma, the differential diagshould be distinguished from a periosteal nosis of a firm nodule in or close to the chondroma 8. A lingual osteoma or chon- foramen caecum area includes a fibroma, a droma on the posterior part of the tongue cyst, a salivary gland tumor and also ectopic is supposed to be a developmental dis- thyroid tissue. With regard to the latter order m4. possibility, it is advisable to perform a preDuring embryonic development, the operative scintigram. palatal shelves, from which most of the hard In histologic examination of an osteoma, palate and all of the soft palate will be chondroma or osteochondroma, more-orformed, grow downward beside the tongue. less normal tissue is encountered. In genAvailable evidence indicates that the shelves eral, the anomaly is well-demarcated. The are incapable of elevation until the tongue presence of blood-forming elements in maris first withdrawn from between them. At row has been described in a few cases. Reabout the end of the 8th gestational week, cently, a report has been published of 15 the shelves elevate, make contact, and fuse benign cartilaginous tumors arising in the with each other around the tongue 3. The soft tissues of the extremities 8. Despite the posterior one-third of the tongue develops presence of histological features suggestive from a subepithelial overgrowth of the third of low-grade chondrosarcoma, these lesions arch mesoderm over the second arch meso- were invariably benign. Occasionally osteoidderm. Besides, it is known that the anterior •appearing material can be found in spindle two thirds of the tongue is covered by ecto- cell or sarcomatoid squamous cell carciderm, whereas endoderm covers the pos- noma. Perhaps a case report of an osteogenterior one third. It is therefore, not inconic sarcoma of the tongue is an example of ceivable that some of the crest cells that such a phenomenon 12. Malignant changes later form the mesenchyme of the maxillary in osteomas, chondromas or osteochondroprocess, coming into contact with lingual mas of the tongue have never been reported. The negative finding in our postmortem endoderm, are induced by the endoderm to differentiate into bone tissue at the posterior study does not support a possible hypothesis that osteoma or chondroma of the one third of the tongue. It is known that inductive influences need only be present tongue may be the result of proliferation of commonly present bony or cartilaginous for a short time, after which the responding tissue is capable of independent develop- structures. Ectopic bone or cartilage formation in the tongue indeed seems rare. ment. It has also been hypothesized that a ctlondroma of the tongue is the result of embryologic displacement of Meckel's cartilage ~4. References In a rat's tongue, bone with articulation and 1. ALLARD, R. H. B., BLOK, P., VAN DER KWAST,
OSTEOMA OF T O N G U E W. A. M. & VAN DER WAAL, I.: Oral lipomas with osseous and chondrous metaplasia; report of 2 cases. J. Oral Pathol. 1982: 11: 18-25.
2. BALOGH, K. & RICHARDSON, J.: Chondrogenesis in peripheral fibromas of the gingiva. J. Oral PathoL 1986: 15: 169-171. 3. BHASKA~ S. N.: Development of face and oral cavity. In: Orban's oral histology and embryology, 10th edition. The C. V. Mosby Company, 1986, pp. 1-23. 4. BHAWAN,J. (~¢ RAJGOPALAN,M. R.: Osteochondroma of the tongue. Indian J. Pathol. MicrobioL 1976: 19: 135-137. 5. BORING, K.: On the origin of cells in heterotopic bone formation. Clin. Orthop. 1975: 110: 293-302. 6. CUTRIGHT, D. E.: Osseous and chondromatous metaplasia caused by dentures. Oral Surg. 1972: 34: 625-633. 7. HAJDU, S. [2 Extraskeletal bone tumors. In: Pathology of soft tissue tumors. Lea & Febiger, Philadelphia, 1979, pp. 483-486.
8. HUMPHREYS,S., PAMBAKIAN,H., McKEE, R H. & FLETCHER,C. D. M.: Soft tissue chondroma - a study of 15 tumours. Histopathology 1986: 10: 147-159. 9. JAYARAJ,A. P.: Articulating bone formation in the rat tongue. J. Laryngol Otol. 1982: 96: 665-667. 10. MAIN, D. M. G.: Osseous polyp of the tongue: osteoma or choristoma? Br. Dent. J. 1984: 156: 285-286.
717
11. MAKEK,M. S. & SAILER,H. F.: Prothesenbedingte nodul/ire Chondrometaplasie des Obe'rkiefers. Sehweiz. Mschr. Zahnmed. 1985: 95: 551-559. 12. R~YES,J. M., VANGOI~, S. K., PUTONG, P. B., HARWICK, R., MILLER,A. S. & CrIEN, S. Y.: Osteogenic sarcoma of the tongue. J. Oral. Surg. 1981: 51: 421-425, 13. SAITO, 1., IDE, F., INOUE, M., TERATANI,K., SATOH, M., KIUCHI, K. & UMEMURA, S. J.: Periosteal ossifying fibroma of the palate. J. PeriodontoL 1984: 55: 704~707. 14. SEGAL, K., KATZAU, Y., SIDI, J. ~¢ ROTEM, A.: Chondroma of the tongue, report of two cases. Ann. OtoL RhinoL Laryngol. 1984: 93: 271-272. 15. VAN DER WAAL, I., BAART, J. A., KEUTER,G., HES, J. & VAN DER KWAST, W. A. M.: Het osteoom van de tong. Ned. Tijdschr. Tandheelkd. 1983: 90: 111-113. 16. WESLEY,R. K. & ZIELINSKI,R. J.: Osteocartilaginous choristoma of the tongue: clinical and histopathologic considerations. J. Oral Surg. 1978: 36: 59-61. 17. WOJTEK, E.: Experimentelle Untersuchungen zur Frage der heterotopen Knochenbildung. Zbl. Chit. 1964: 38: 1419-1437. Address: 1. van der Waal Vrije Universiteit Pathologisch Instituut Postbus 7057 1007 M B Amsterdam The Netherlands