British Journal of Oral Surgery
BONE
14 (1976) 120-127
CAVITIES
IN FIBRO-OSSEOUS
A. D. FISHER, B.D.S.,
LESIONS
F.D.S.R.C.S.
Dental Department, Ro)lal Cornwall Hospital (City), Truro, Cornwall Summary. Two cases are described of intra-bony cavities occurring in areas of fibro-osseous abnormality. The criteria for the diagnosis of solitary bone cyst are stated and applied to each case. The possible aetiology of such cysts is discussed and a suggestion made about a possible pathogenesis.
Introduction Controversy surrounds the fibro-osseous group of lesions. Between fibroma and osteoma there exists an area of microscopic indecision from which terms like fibrous dysplasia and ossifying fibroma emerge. The confusion is made worse by the histological proximity of the giant cell group of lesions. Somewhere in this uncertainty is the solitary bone cyst. Traumatic bone cyst and haemorrhagic bone cyst are two other names for the solitary bone cyst. Of the jaws, only the mandible is affected and almost twice as often in males as in females (Stones, 1957). They are usually asymptomatic but often present with bony expansion. The associated teeth are usually vital and are not resorbed. The cavities may or may not be lined and may or may not be fluid filled. Any degree of surgical intervention or investigation of the cavity will usually result in spontaneous healing over the subsequent months. Their aetiology is uncertain and will be discussed later. Two cases are to be described both of which might be labelled solitary bone cyst, and which occurred in areas of fibro-osseous change.
Case 1 A 21-year-old white male was referred by his dentist with a bony swelling in the molar region on the right side of the mandible. He had previously been unaware of the swelling which was causing no pain, no limitation of mandibular movement and no mental anaesthesia. Examination showed moderate bony expansion of both buccal and lingual plates in the molar and second premolar region on the right side of the mandible. The overlying mucosa was not tender to palpation and although the first molar tooth had been lost several years previously the second and third molars were present and vital. Radiographically a fairly large, well-defined loculated radiolucency was seen in the first molar region extending from the second premolar to the third molar. There was scalloping of the cortex at the lower border of the mandible and although the apices of the second molar were involved in the lesion their lamina dura were intact (Figs 1 and 2). Laboratory investigations showed haematological and blood chemistry values to be within normal limits. Provisional diagnosis was of a benign neoplastic condition, probably fibro-osseous in nature. The patient was admitted to hospital and under a general anaesthetic a mucoperiosteal flap was raised to expose the buccal surface of the mandible from the right canine to the retro-molar pad. A small area of thin bluish bone was exposed through (Received
27 January
1976; accepted 25 May 1976)
BONE
CAVITIES
FIG. 1. Lateral oblique radiograph.
IN
FIBRO-OSSEOUS
FIG. 2.
LESIONS
121
Occlusal radiograph.
which several millilitres of bloodstained fluid were aspirated. A bony flap was cut and hinged back exposing a cavity devoid of lining. Specimens of bone from around the cavity were removed for investigation after which the flaps were replaced. The patient made an uneventful recovery. Electrophoresis of the aspirate showed it to contain 5.3 g per cent of protein, indicating a non-keratinising cyst-like condition. Histologically, the osseous tissue was found to have a fibrous but cellular stroma, very suggestive of it being osteogenic. Within this stroma were areas of calcification ranging from mature lamellar bone to extremely amorphous masses (Figs 3 and 4) and small cystic spaces the lumen of which contained necrotic and degenerating blood cells (Fig. 5). These small cysts appeared to have developed in areas of old haemorrhage but it was not clear whether or not they represented a smaller version of the larger cavity. The overall microscopic picture was of a fibro-osseous condition at the periphery of a solitary bone cyst, yet the cyst was within an area of bony abnormality which radiographically extended well beyond the biopsy site. Radiographs taken 4,7 and 14 months post-operatively, showed a gradual reduction in the size of the cavity with extensive new bone formation and marked reduction in the expansion of the cortical plates. However by 20 months post-operatively there appeared to be an increase in the size of the cavity compared with 6 months previously. In addition, there had been no new bone formation within that part of the lesion which was causing thinning and scalloping of the lower border of the mandible (Fig. 6). The reparative process seemed to have been reversed. Further surgical investigation was considered necessary. The patient was re-admitted and at a second operation under a general anaesthetic a flap was raised similar to that at the first operation. This revealed a bony swelling centred on the first molar region but smaller than that exposed on the first occasion. The outer surface of this bony prominence was removed with a chisel to reveal new bone filling the original defect. Removal of some of this bone exposed a small cavity near the lower border. Pieces of bone from around the edges of the cavity were removed and with specimens from other parts of the area sent for histological investigation. The flap was replaced and the patient made an uneventful recovery. The histological report on the bone reported it as being from a benign fibro-osseous lesion with the hard tissue component ranging from irregular calcifications to mature
122
BRITISH
JOURNAL
OF
ORAL
SURGERY
FIGS 3 and 4. Calcifications ranging from mature lamellar bone to amorphous deposits. (Haematoxylin x 200) & Eosin.
lamellar bone. Both osteoblastic and osteoclastic activity were clearly evident and the matrix showed a prominent mosaic pattern. The final diagnosis was equivocal. In the light of the clinical behaviour, this microscopic appearance was not inconsistent with a diagnosis of fibrous dysplasia and yet within this area was a cavity initially
BONE
CAVITIES
FIG. 5. Small cystic space containing
IN
FIBRO-OSSEOUS
necrotic and degenerating Eosin. x 200)
FIG. 6. Lateral oblique radiograph
LESIONS
blood cells. (Haematoxylin
123
&
20 months after first operation.
thought to be a solitary bone cyst. Another possible explanation was that the abnormal bone represented an attempt at healing of a solitary bone cyst, the osseous tissue being similar to bony repair tissue often found in the jaws. Case 2 A 27-year-old Libyan male was referred by his doctor with a bony swelling in the upper part of the left mandibular ramus. He complained of no pain, no limitation
124
BRITISH
JOURNAL
FIG. 7. Lateral
OF
ORAL
SURGERY
oblique radiograph.
of mandibular movement and no lingual or mental anaesthesia. He had been aware of the swelling for about two years. Examination showed a healthy young adult with a non-tender, bony swelling in the upper part of the ramus in front of the left ear. It was not attached to the overlying skin which was of normal appearance. Radiographically a large clearly defined mainly radiolucent lesion was seen in the vertical ramus on the left side of the mandible with expansion of the condylar neck laterally and an egg-shaped diffusely sclerotic enlargement projecting into the infra-temporal fossa from the inner aspect. &erupted upper and lower third molars were present (Figs 7 and 8). The provisional diagnosis was of a fibro-osseous lesion. The patient was admitted to hospital and under a general anaesthetic the outer aspect of the left ramus, coronoid process and the neck of the condylar process were exposed via a submandibular approach. A bony swelling was found centred just below the root of the condylar neck. A circular window of bone which was found to be unexpectedly thick was removed from the outer aspect of the swelling with burs and chisels. A well-defined bony cavity was exposed which extended medially into the infra-temporal fossa. The cavity had no fluid content but an intact lining was present not unlike that of a dental cyst. The lining was removed and the bony wall of the cavity was found to be complete except for a small area on its medial surface. The lining and the window of bone were sent for histological examination. The soft tissues were replaced and the patient made an uneventful recovery. Histologically, the bone was found to be mature lamellar cortex in which there were to be seen small immature foci of hypomineralised tissue. This was thought to represent a reaction to the underlying lesion. The lining consisted of a band of fibrous connective tissue. There were no epithelial elements. The collagenous tissue adjacent to the lumen was condensed and hyalinised and the outer part showed a chronic inflammatory infiltrate. Necrotic debris was to be seen within the lumen, the degenerative tissue being separated by clefts left by cholesterol crystals and, like necrotic debris elsewhere in the body, it contained dystrophic calcifications (Fig. 9). The clinical, histological and particularly the radiographical presentation of the
BONE
CAVITIES
IN FIBRO-OSSEOUS
FIG. 8. Anterior-posterior
LESIONS
125
view radiograph.
/
k
i $
‘e;
FIG. 9. Lining from cavity showing hyalinised connective tissue adjacent to the lumen which contains necrotic debris, cholesterol clefts, and calcification. (Haematoxylin & Eosin. x 200)
126
BRITISH
JOURNAL
OF
ORAL
SURGERY
case suggested it was a benign fibro-osseous lesion of some description, the major feature of which was a large bony cavity. It was thought to be a solitary bone cyst. Unfortunately, no follow-up information was available on this case as the patient unexpectedly returned to North Africa very soon after operation.
Discussion Two cases of intra-bony cavity have been described. The first occurred in an area of fibro-osseous abnormality but whether it appeared before or after the bony abnormality is unknown. The second case presented as a marked expansion of the upper part of the ascending ramus of the mandible. The evidence from histological examination of the overlying bone and cavity lining was not very revealing but the clinical presentation suggested that an expansile lesion had been present originally, the bony swelling being secondary to this. Rushton (1946) laid down four criteria a lesion must satisfy before being labelled solitary bone cyst. Firstly, that the cyst should be single, have no epithelial lining and show no evidence of acute or prolonged infection. Secondly, that it should contain principally fluid and not soft tissue. Thirdly, that the walls should be of bone which is hard though possibly thin in parts and fourthly, that the chemical and pathological findings do not exclude the diagnosis of solitary bone cyst. Howe (1965) adopted these criteria in a major review of the subject with the modification to the second that many writers have made that solitary bone cysts may be empty. The first case satisfied the first three criteria but there is room for doubt as to whether or not the pathological findings rule out the diagnosis. The fourth criteria was so worded as to exclude from the diagnosis those varieties of osteitis fibrosa, local or general, characterised by giant-cell tumours or large polycystic formation, or diffuse porosis and hyperostosis (Rushton, 1946). In fact this case is similar to the third of the cases Rushton himself described in which the bony cavity was found in conjunction with an area of osteitis fibrosa. What is not clear is whether the cyst developed in an area of pre-existing fibro-osseous abnormality or whether the fibro-osseous tissue was secondary to the cavity and represented a repair process aimed at healing the solitary bone cyst. The second case seems to satisfy all the criteria. It might be seen as evidence to support the belief that such cysts occur as a result of damage to an end-artery in the region of an epiphyseal cartilage leading to necrosis of an area of the bone, were it not for the fact that solitary bone cysts are rarely found in the region of the mandibular condyle. This brings into question the relationship between solitary bone cysts in the mandible and those elsewhere in the skeleton. Most of these occur near centres of endochondral ossification, the vast majority being found on the metaphyseal side of the epiphyseal plate in long bones. Although there are similarities between the two lesions there are also many discrepancies. Opinion in the literature is divided and the present state of knowledge prevents any conclusion being drawn on their relationship. Pommer (1919) carried out the work which formed the basis for the widely held belief that trauma is the cause of at least some solitary bone cysts. Trauma, it is postulated, that damages intra-bony blood vessels but does not fracture the bone or rupture its periosteum. This damage is thought to cause the formation of an intrabony haematoma which instead of undergoing the usual osteogenic organisation, undergoes cystic breakdown. Why it should do this is not clear. Howe (1965) found a history of trauma in just over half of the 60 cases he reviewed. Although clearly impressed by the theory suggesting the breakdown of an intramedullary haematoma, he will go only so far as to attribute trauma with their formation in a proportion
BONE
CAVITIES
IN
FIBRO-OSSEOUS
LESIONS
127
of cases. Some are doubtful about the importance of trauma in the aetiology of such cysts, notably Rushton (1946) who puts a strong case against it. He and Blum (1955) both suggest they bear a relationship to giant cell tumours occurring in endosteal tissue. Howe (1965) can find no evidence to support this theory. Many other suggestions have been propounded to explain these strange phenomena, all of which are discussed by Howe (1965). After weighing the volume of conflicting evidence the same writer states that ‘it is possible that these lesions do not have a single common aetiology and it is by no means certain that the formation of an haemorrhagic cyst is always preceded by the same sequence of events’. In view of this probability and in the light of the two cases here described the present author is impressed by another possible aetiology for some solitary bone cysts. Does attaching a label like fibrous dysplasia to a lesion prohibit that of solitary bone cyst also being applied to it? Rushton thought not, although he used the less specific label ‘osteitis fibrosa’ in his case. Microcysts are a not uncommon finding in fibrous dysplasia, Jaffe (1953) considers them to result from degeneration in areas of haemorrhage and localised oedema and describes how two or more might coalesce to form larger cysts. Obwegeser et al. (1973) refer to the presence of pseudocysts in one case they describe. In other words tissue breakdown and microcyst formation is well recognised in fibrous dysplasia. There are in addition the two cases described here and Rushton’s own third case, all of large bony cavities. This has several implications. Firstly, if macrocysts can and do occur in fibro-osseous lesions then the fact should be recognised to prevent errors of diagnosis. Secondly, could some solitary bone cysts be the result of cystic breakdown in areas of fibro-osseous disease? Finally, might some solitary bone cysts be attempts at healing occurring in pre-existing and undiagnosed fibro-osseous lesions ? If so then there will be a period of time during which both cyst and original lesion will be present before the cyst further encroaches upon and subsequently obliterates the original lesion. Acknowledgements I should like to thank Messrs P. F. Bradley and H. M. Alty, Consultant Oral Surgeons at Broadgreen Hospital, Liverpool, for allowing me to report their cases and for their help in the preparation of this paper, Mr J. H. Allan for advice on the pathology, and Mrs C. Taylor for her secretarial help. References Blum, T. (1955). Oral Surgery, Oral Surgery and Oral Pathology, 8, 917. Howe, G. L. (1965). British Journal of Oral Surgery, 3, 55. Jaffe, H. L. (1953). Oral Surgery, Oral Medicine and Oral Pathology, 6, 159. Obwegeser, H. L., Freihofer, H. P. M. & Horejs, J. (1973). Journal of Maxilla-Facial Surgery, 1, 161. Pommer, G. (1919). Hans Von Haberer’s Arch. Orthop. Unfallchir, 17,17. Rushton, M. A. (1946). British Dental Journal, 81. 37. Stones, H. H. (1957). Oral and Dental Diseases, 3rd Ed., p. 825. Edinburgh and London: Livingstone.
BONE
14 (1976) 120-127
CAVITIES
IN FIBRO-OSSEOUS
A. D. FISHER, B.D.S.,
LESIONS
F.D.S.R.C.S.
Dental Department, Ro)lal Cornwall Hospital (City), Truro, Cornwall Summary. Two cases are described of intra-bony cavities occurring in areas of fibro-osseous abnormality. The criteria for the diagnosis of solitary bone cyst are stated and applied to each case. The possible aetiology of such cysts is discussed and a suggestion made about a possible pathogenesis.
Introduction Controversy surrounds the fibro-osseous group of lesions. Between fibroma and osteoma there exists an area of microscopic indecision from which terms like fibrous dysplasia and ossifying fibroma emerge. The confusion is made worse by the histological proximity of the giant cell group of lesions. Somewhere in this uncertainty is the solitary bone cyst. Traumatic bone cyst and haemorrhagic bone cyst are two other names for the solitary bone cyst. Of the jaws, only the mandible is affected and almost twice as often in males as in females (Stones, 1957). They are usually asymptomatic but often present with bony expansion. The associated teeth are usually vital and are not resorbed. The cavities may or may not be lined and may or may not be fluid filled. Any degree of surgical intervention or investigation of the cavity will usually result in spontaneous healing over the subsequent months. Their aetiology is uncertain and will be discussed later. Two cases are to be described both of which might be labelled solitary bone cyst, and which occurred in areas of fibro-osseous change.
Case 1 A 21-year-old white male was referred by his dentist with a bony swelling in the molar region on the right side of the mandible. He had previously been unaware of the swelling which was causing no pain, no limitation of mandibular movement and no mental anaesthesia. Examination showed moderate bony expansion of both buccal and lingual plates in the molar and second premolar region on the right side of the mandible. The overlying mucosa was not tender to palpation and although the first molar tooth had been lost several years previously the second and third molars were present and vital. Radiographically a fairly large, well-defined loculated radiolucency was seen in the first molar region extending from the second premolar to the third molar. There was scalloping of the cortex at the lower border of the mandible and although the apices of the second molar were involved in the lesion their lamina dura were intact (Figs 1 and 2). Laboratory investigations showed haematological and blood chemistry values to be within normal limits. Provisional diagnosis was of a benign neoplastic condition, probably fibro-osseous in nature. The patient was admitted to hospital and under a general anaesthetic a mucoperiosteal flap was raised to expose the buccal surface of the mandible from the right canine to the retro-molar pad. A small area of thin bluish bone was exposed through (Received
27 January
1976; accepted 25 May 1976)
BONE
CAVITIES
FIG. 1. Lateral oblique radiograph.
IN
FIBRO-OSSEOUS
FIG. 2.
LESIONS
121
Occlusal radiograph.
which several millilitres of bloodstained fluid were aspirated. A bony flap was cut and hinged back exposing a cavity devoid of lining. Specimens of bone from around the cavity were removed for investigation after which the flaps were replaced. The patient made an uneventful recovery. Electrophoresis of the aspirate showed it to contain 5.3 g per cent of protein, indicating a non-keratinising cyst-like condition. Histologically, the osseous tissue was found to have a fibrous but cellular stroma, very suggestive of it being osteogenic. Within this stroma were areas of calcification ranging from mature lamellar bone to extremely amorphous masses (Figs 3 and 4) and small cystic spaces the lumen of which contained necrotic and degenerating blood cells (Fig. 5). These small cysts appeared to have developed in areas of old haemorrhage but it was not clear whether or not they represented a smaller version of the larger cavity. The overall microscopic picture was of a fibro-osseous condition at the periphery of a solitary bone cyst, yet the cyst was within an area of bony abnormality which radiographically extended well beyond the biopsy site. Radiographs taken 4,7 and 14 months post-operatively, showed a gradual reduction in the size of the cavity with extensive new bone formation and marked reduction in the expansion of the cortical plates. However by 20 months post-operatively there appeared to be an increase in the size of the cavity compared with 6 months previously. In addition, there had been no new bone formation within that part of the lesion which was causing thinning and scalloping of the lower border of the mandible (Fig. 6). The reparative process seemed to have been reversed. Further surgical investigation was considered necessary. The patient was re-admitted and at a second operation under a general anaesthetic a flap was raised similar to that at the first operation. This revealed a bony swelling centred on the first molar region but smaller than that exposed on the first occasion. The outer surface of this bony prominence was removed with a chisel to reveal new bone filling the original defect. Removal of some of this bone exposed a small cavity near the lower border. Pieces of bone from around the edges of the cavity were removed and with specimens from other parts of the area sent for histological investigation. The flap was replaced and the patient made an uneventful recovery. The histological report on the bone reported it as being from a benign fibro-osseous lesion with the hard tissue component ranging from irregular calcifications to mature
122
BRITISH
JOURNAL
OF
ORAL
SURGERY
FIGS 3 and 4. Calcifications ranging from mature lamellar bone to amorphous deposits. (Haematoxylin x 200) & Eosin.
lamellar bone. Both osteoblastic and osteoclastic activity were clearly evident and the matrix showed a prominent mosaic pattern. The final diagnosis was equivocal. In the light of the clinical behaviour, this microscopic appearance was not inconsistent with a diagnosis of fibrous dysplasia and yet within this area was a cavity initially
BONE
CAVITIES
FIG. 5. Small cystic space containing
IN
FIBRO-OSSEOUS
necrotic and degenerating Eosin. x 200)
FIG. 6. Lateral oblique radiograph
LESIONS
blood cells. (Haematoxylin
123
&
20 months after first operation.
thought to be a solitary bone cyst. Another possible explanation was that the abnormal bone represented an attempt at healing of a solitary bone cyst, the osseous tissue being similar to bony repair tissue often found in the jaws. Case 2 A 27-year-old Libyan male was referred by his doctor with a bony swelling in the upper part of the left mandibular ramus. He complained of no pain, no limitation
124
BRITISH
JOURNAL
FIG. 7. Lateral
OF
ORAL
SURGERY
oblique radiograph.
of mandibular movement and no lingual or mental anaesthesia. He had been aware of the swelling for about two years. Examination showed a healthy young adult with a non-tender, bony swelling in the upper part of the ramus in front of the left ear. It was not attached to the overlying skin which was of normal appearance. Radiographically a large clearly defined mainly radiolucent lesion was seen in the vertical ramus on the left side of the mandible with expansion of the condylar neck laterally and an egg-shaped diffusely sclerotic enlargement projecting into the infra-temporal fossa from the inner aspect. &erupted upper and lower third molars were present (Figs 7 and 8). The provisional diagnosis was of a fibro-osseous lesion. The patient was admitted to hospital and under a general anaesthetic the outer aspect of the left ramus, coronoid process and the neck of the condylar process were exposed via a submandibular approach. A bony swelling was found centred just below the root of the condylar neck. A circular window of bone which was found to be unexpectedly thick was removed from the outer aspect of the swelling with burs and chisels. A well-defined bony cavity was exposed which extended medially into the infra-temporal fossa. The cavity had no fluid content but an intact lining was present not unlike that of a dental cyst. The lining was removed and the bony wall of the cavity was found to be complete except for a small area on its medial surface. The lining and the window of bone were sent for histological examination. The soft tissues were replaced and the patient made an uneventful recovery. Histologically, the bone was found to be mature lamellar cortex in which there were to be seen small immature foci of hypomineralised tissue. This was thought to represent a reaction to the underlying lesion. The lining consisted of a band of fibrous connective tissue. There were no epithelial elements. The collagenous tissue adjacent to the lumen was condensed and hyalinised and the outer part showed a chronic inflammatory infiltrate. Necrotic debris was to be seen within the lumen, the degenerative tissue being separated by clefts left by cholesterol crystals and, like necrotic debris elsewhere in the body, it contained dystrophic calcifications (Fig. 9). The clinical, histological and particularly the radiographical presentation of the
BONE
CAVITIES
IN FIBRO-OSSEOUS
FIG. 8. Anterior-posterior
LESIONS
125
view radiograph.
/
k
i $
‘e;
FIG. 9. Lining from cavity showing hyalinised connective tissue adjacent to the lumen which contains necrotic debris, cholesterol clefts, and calcification. (Haematoxylin & Eosin. x 200)
126
BRITISH
JOURNAL
OF
ORAL
SURGERY
case suggested it was a benign fibro-osseous lesion of some description, the major feature of which was a large bony cavity. It was thought to be a solitary bone cyst. Unfortunately, no follow-up information was available on this case as the patient unexpectedly returned to North Africa very soon after operation.
Discussion Two cases of intra-bony cavity have been described. The first occurred in an area of fibro-osseous abnormality but whether it appeared before or after the bony abnormality is unknown. The second case presented as a marked expansion of the upper part of the ascending ramus of the mandible. The evidence from histological examination of the overlying bone and cavity lining was not very revealing but the clinical presentation suggested that an expansile lesion had been present originally, the bony swelling being secondary to this. Rushton (1946) laid down four criteria a lesion must satisfy before being labelled solitary bone cyst. Firstly, that the cyst should be single, have no epithelial lining and show no evidence of acute or prolonged infection. Secondly, that it should contain principally fluid and not soft tissue. Thirdly, that the walls should be of bone which is hard though possibly thin in parts and fourthly, that the chemical and pathological findings do not exclude the diagnosis of solitary bone cyst. Howe (1965) adopted these criteria in a major review of the subject with the modification to the second that many writers have made that solitary bone cysts may be empty. The first case satisfied the first three criteria but there is room for doubt as to whether or not the pathological findings rule out the diagnosis. The fourth criteria was so worded as to exclude from the diagnosis those varieties of osteitis fibrosa, local or general, characterised by giant-cell tumours or large polycystic formation, or diffuse porosis and hyperostosis (Rushton, 1946). In fact this case is similar to the third of the cases Rushton himself described in which the bony cavity was found in conjunction with an area of osteitis fibrosa. What is not clear is whether the cyst developed in an area of pre-existing fibro-osseous abnormality or whether the fibro-osseous tissue was secondary to the cavity and represented a repair process aimed at healing the solitary bone cyst. The second case seems to satisfy all the criteria. It might be seen as evidence to support the belief that such cysts occur as a result of damage to an end-artery in the region of an epiphyseal cartilage leading to necrosis of an area of the bone, were it not for the fact that solitary bone cysts are rarely found in the region of the mandibular condyle. This brings into question the relationship between solitary bone cysts in the mandible and those elsewhere in the skeleton. Most of these occur near centres of endochondral ossification, the vast majority being found on the metaphyseal side of the epiphyseal plate in long bones. Although there are similarities between the two lesions there are also many discrepancies. Opinion in the literature is divided and the present state of knowledge prevents any conclusion being drawn on their relationship. Pommer (1919) carried out the work which formed the basis for the widely held belief that trauma is the cause of at least some solitary bone cysts. Trauma, it is postulated, that damages intra-bony blood vessels but does not fracture the bone or rupture its periosteum. This damage is thought to cause the formation of an intrabony haematoma which instead of undergoing the usual osteogenic organisation, undergoes cystic breakdown. Why it should do this is not clear. Howe (1965) found a history of trauma in just over half of the 60 cases he reviewed. Although clearly impressed by the theory suggesting the breakdown of an intramedullary haematoma, he will go only so far as to attribute trauma with their formation in a proportion
BONE
CAVITIES
IN
FIBRO-OSSEOUS
LESIONS
127
of cases. Some are doubtful about the importance of trauma in the aetiology of such cysts, notably Rushton (1946) who puts a strong case against it. He and Blum (1955) both suggest they bear a relationship to giant cell tumours occurring in endosteal tissue. Howe (1965) can find no evidence to support this theory. Many other suggestions have been propounded to explain these strange phenomena, all of which are discussed by Howe (1965). After weighing the volume of conflicting evidence the same writer states that ‘it is possible that these lesions do not have a single common aetiology and it is by no means certain that the formation of an haemorrhagic cyst is always preceded by the same sequence of events’. In view of this probability and in the light of the two cases here described the present author is impressed by another possible aetiology for some solitary bone cysts. Does attaching a label like fibrous dysplasia to a lesion prohibit that of solitary bone cyst also being applied to it? Rushton thought not, although he used the less specific label ‘osteitis fibrosa’ in his case. Microcysts are a not uncommon finding in fibrous dysplasia, Jaffe (1953) considers them to result from degeneration in areas of haemorrhage and localised oedema and describes how two or more might coalesce to form larger cysts. Obwegeser et al. (1973) refer to the presence of pseudocysts in one case they describe. In other words tissue breakdown and microcyst formation is well recognised in fibrous dysplasia. There are in addition the two cases described here and Rushton’s own third case, all of large bony cavities. This has several implications. Firstly, if macrocysts can and do occur in fibro-osseous lesions then the fact should be recognised to prevent errors of diagnosis. Secondly, could some solitary bone cysts be the result of cystic breakdown in areas of fibro-osseous disease? Finally, might some solitary bone cysts be attempts at healing occurring in pre-existing and undiagnosed fibro-osseous lesions ? If so then there will be a period of time during which both cyst and original lesion will be present before the cyst further encroaches upon and subsequently obliterates the original lesion. Acknowledgements I should like to thank Messrs P. F. Bradley and H. M. Alty, Consultant Oral Surgeons at Broadgreen Hospital, Liverpool, for allowing me to report their cases and for their help in the preparation of this paper, Mr J. H. Allan for advice on the pathology, and Mrs C. Taylor for her secretarial help. References Blum, T. (1955). Oral Surgery, Oral Surgery and Oral Pathology, 8, 917. Howe, G. L. (1965). British Journal of Oral Surgery, 3, 55. Jaffe, H. L. (1953). Oral Surgery, Oral Medicine and Oral Pathology, 6, 159. Obwegeser, H. L., Freihofer, H. P. M. & Horejs, J. (1973). Journal of Maxilla-Facial Surgery, 1, 161. Pommer, G. (1919). Hans Von Haberer’s Arch. Orthop. Unfallchir, 17,17. Rushton, M. A. (1946). British Dental Journal, 81. 37. Stones, H. H. (1957). Oral and Dental Diseases, 3rd Ed., p. 825. Edinburgh and London: Livingstone.
