Simple bone cyst

Kal F o r . e l l , Hell F o r . e l i , RlstoPekka Happonen and Marnl Neva Institute of Dentistry, Universityof Turku, Finland

Simple bonecyst Review of the literature and analysis of 23 cases K. Forssell, H. ForsselI, R.-P. Happonen and M. Neva: Simple bone c y s t - Review of the literature and analysis of 23 cases. Int. J. Oral Maxillofac. Surg. 1988; 17: 21-24. Abstract. A retrospective study of 23 simple bone cysts including analysis of clinical, radiographical, histopathological features and follow-up information was made. The age of the patients varied from 8 to 59 years (mean 21.4 years). All lesions were found in the mandible, and 2 of them were radiologicalty multilocular. A loose connective tissue lining was found histologically in 8 out of 17 cysts with the biopsy specimens available. At follow-up, 2 failures of the primary surgical treatment were noted. The results emphasize that a proper follow-up is required after the treatment of simple bone cyst.

The simple bone cyst of the jaws, first described by LtrCAS" in 1929, has attracted a great deal of interest in the dental literature. RUSHTON~3 has proposed the criteria for a lesion to be accepted as simple bone cyst. These criteria were further modified by H~SLrr~ etal. 13and they include: (1) The lesion is essentially an empty cavity, oecasionally

containing some fluid and/or small amounts of tissue. (2) Other findings (clinical, radiographic, anamnestic, histopathologic, etc.) do not exclude the diagnosis of simple bone cyst. The histogenesis and origin of the lesion remains unresolved which is also reflected by the variety of names used (i.e., traumatic bone cyst, hemorrhagic bone cyst, ex-

Table I. Histopathological findings in 17 simple bone cysts Specimen Bone 2 BB lamellar compact bone 3 BB lamellar compact bone lamellar compact bone with prominent resting lines 4 BB lamellar compact bone 5 BB no bone tissue 6 CM poorly mineralized woven bone 8 CM

Case no.

11

CM

woven bone with prominent osteoblasts

12

BB

t3

BB

15

BB

16

BB

lameliar compact bone with resting linesand disturbed architecture; prominent osteoblast rim lamellar compact bone with prominent resting lines and areas with giant cells lamellar compact bone with areas of newly formed bone disturbed in architecture, prominent osteoblast rim lameUar compact bone with resting lines, slightly dear-

Key words: law cysts; simple bonecysts; traumaticbone cysts. Accepted for publication 20 April 1987

travasationcyst,solitarybone cyst,progressive bone cavity and unicameral bone cyst).The name simple bone cyst, proposed by BERba~. & JOHNSON 2 and also used by S m V m U N K 3s seems to be most applicable. Through accumulation of numerous case reports and a few larger seriesof simple bone cysts1.6:3~2s,the clinical,

Lining no lining no lining no lining no lining no lining, lots of red blood cells loosemyxoid connectivetissuewith marked hemorrhage and some fat very loose connective tissue with capillaries and hemorrhage loose connective tissue with capillaries and lots of hemorrhage loose connective tissue with dilated capillaries looseconnective tissue with capillariesand hemorrhage no lining

ranged 17 18

BB

CM

normal lamellar compact bone chips of bone with osteoid and osteoblast rim

lamellar compact bone with resting fines hard tissue chips 22/i cM cancellous bone with resting lines and pYominent osteoblast rim 22/2 BB lamellar compact bone with prominent areas of hasophilia around Haversian canals 23 BB lameliar compact bone BB=buccal cortical bone plate. CM =curettaged material. 20

BB

21

CM

no lining loose connective tissue with fatty bone marrow and hemorrhage myxoid connective tissue with capillaries and fat very loose connective tissue with capillaries and fat loose connective tissue with capillaries and hemorrhage no lining no lining

22 NO OF CYSTS 15

Forssell, Forssell, Happonen and Neva

-

10 5

n <10

10 -19

20 30 40 -29 -39 - ~

50 AGE -5~

Fig. 1. The distribution of 23 simple bone eys~ according toageofthe patients.

radiographic and histopathologic features of this lesion have become more dear. The lesion is mainly diagnosed in young patients, most frequently during the second decade of the life t3.js. The age of the patients varies from 23~ to 75 years 13. According to H t m n ~ R & TURLINGTON 19, the mean age is 19.7 years. The sex distribution is reported to be quite even ~3 or men are affected somewhat more frequently a,~8,~9,35. The majority of the lesions are asymptomatie, being detected in routine radiographic examinations ~8.~9.25. Pain is the presenting symptom in. 10% to 30% of patients '3,~a'~9 and swelling has been reported in up to about a fourth of the patients '9. Other symptoms including tooth sensitivity, parestbesia, fistula and even pathologic fracture of the jaw bone have been reported ~,",~8.~9.r~,35. The simple bone cyst is usually located in the mandible, especially in the dentulous area ~,6.~3.js~35. One third of the lesions are found in the maxilla, predominantly in the anterior part ~3. Very unusual locations reported include the condylar process '° and the zygomarie arch 3. Rarely, more than one cyst have been found in the same patient '~,24~7.28,30. The size of the lesion varies from 1 cm to those occupying almost one half of the mandible 8~3°~5. Expansion o f the cortical bone, usually the buceal cortex, has been reported in about half o f the casesZL Displacement of the teeth in the cyst area is unusual 'a.~9, and the cyst has no influence on the vitality of the adjacent teeth 35. Radiographically, the simple bone cyst manifests itself as a radiolucent area with an irregular but usually welldefined outline is. Charaeterisric for the simple bone cyst is the seaUoped outline found not only between the roots o f the teeth but also in edentulous areas ~.~. Most lesions are uniloeular ~J~, but also multilocular cysts have been

Fig. 2. Schematic presentation of 23 simple bone cysts by location, shape and size. Cases 9 and 10 w@rebilateral cysts in the same patient.

found 1.9.~zt6,2~-~. Opinions concerning the intactness o f the lamina dura of adjacent teeth vary. MoRRIs et aL 25 found the absence of lamina dura in 16%, whereas HOWE18 reported absence in 62% of eases. Apical resorption o f the teeth is very uncommon ~s,24. At operation, the simple bone cyst is found to be empty in about one third to one half of the cases. In the remaining cases, the contents vary from straw-coloured fluid to bright blood or fibrous tissue t3.1~. It has been proposed that the content reflects the age o f the lesion ~,1s,2~. Only about 10% of the lesions are lined by thin connective tissue lining 18,19.The

neurovascular bundle o f the inferior alveolar nerve may be exposed and crossing the cyst cavity freely in about one third to two thirds of the cysts Is'19. The present report is based on the evaluation o f records and surgical specimens of 23 cases o f simple bone cysts from the files of the Department of Oral Surgery and Department of Oral Pathology, Institute of Dentistry, University of Turku. Findings

The cysts were found in 22 patients. 9 of the patients were women, 13 men.

Simple bone cyst ' ~J$1f

Radiographic findings

Fig. 3. Case 9. A simple bone cyst with a scalloped contour. The lamina dura of the roots of the teeth 35 and 36 is mostly destroyed by the cyst.

The age of the patients varied from 8 to 59 years, with a mean age o f 21.4 years. The grouped distribution of cysts according to age of the patients is presented in Fig. 1.

Clinical findings The only symptoms caused by the cysts were pain in 5 cases, swelling in 1, and fistula in 1 case. In another case, no reaction with an electrical pulp tester was obtained from the teeth adjacent to a cyst, but the teeth turned to be vital at follow-up. A history of facial trauma was elicited in 4 patients.

All cysts were located in the mandible, 6 in the anterior part, 13 in the premolarmolar area, and 4 in the angulus-ramus area (Fig. 2). The radiographic appearance was unilocular with a scalloped contour (Fig. 3) in 16 cases, and with wavy or even contour (Fig. 4) in 5 cases. 2 cysts were multilocular (Figs. 5, 6). The largest diameter of the lesions varied from 12 to 70 ram, mean 31 mm. The borderline of the cyst was distinct (Fig. 4) in 10, and partly distinct and partly diffuse in 11 cases (Fig. 5). All cases with a distinct border were lined by a narrow radio-opaque zone. Thinning o f the cortical bone was caused by 11 cysts, but bone expansion only by 1 cyst. Scalloping o f the cyst between the roots of the teeth (Fig. 5) was observed in 10 cases. Divergence of the adjacent teeth was noticed in 5 cases. Lamina dura of the teeth was totally or partly destroyed (Fig. 3) by 12 cysts, and in 2 cases root resorption was noticed.

Hisfopathologlcal findings Biopsy specimens were available in 17 cases. In case 22, a biopsy had been taken at primary surgery and at reoperation. 12 biopsy specimens contained the buccal cortical bone plate and the remaining 6 specimens consisted of material curettaged from the walls of the bone cavities (Table 1). Various degrees of disturbances in the architecture of buccal bone were found in most cases. Prominent osteoblastic rimming was seen in 4 specimens, and giant cells of osteoclast type in 1 lesion. No soft tissue lining was present in 9 specimens. In others, the lining comprised loose vascular connective tissue with marked hemorrhage.

23

Fig. 5. Case 12. Multilocular appearance of a simple bone cyst with interradicular scalloping. The borderline is partly distinct and partly diffuse. The lamina dura of the roots in tooth 46 is intact.

a 2-year follow-up period, and a new operation has recently been performed. In another case (case 22, Fig. 6), a multilocular cyst in the left angulus-ramus region was found at operation to consist of 3 entirely separate compartments. After exposure through the buccal cortex, the bony wall between the lower compartments was removed. 4 months later, the radiograph revealed healing in the area of the 2 lower compartments of the cyst, but no healing in the uppermost part. A new operation was performed, where the buccal cortex o f the upper compartment o f the cyst was perforated. After 5 more months, total healing was achieved.

Discussion Because most simple bone cysts are asymptomatic and discovered on routine radiographs, the advent of panor-

Treatment and follow-up

Fig. 4. Case 18. A simple bone cyst with an oval radiographic shape. The borderline i s distinct with a thin radio-opaque zone.

All lesions were treated by exposure via the buccal cortex with additional curettage of the bone walls in 2 cases. 15 of the lesions were found to be empty. Serous fluid was found in 2, bloody fluid in 3 and loose tissue in 3 cysts. Capsular tissue was observed in none of the cysts. 17 6ut of 19 cysts that were followed-up healed primarily. The follow-up time varied from 5 months to 9 years (mean 3.5 years). In one case (case 17) a unilocular cyst in the right premolar-molar region failed to heal during

Fig. 6. Case 22. A large multilocular simple bone cyst with three separate compartments.

24

Forssell, Forssell, Happonen and Neva

amie radiography has been thought to increase the number o f simple bone cysts detected 4~. Simple bone cyst is, however, still considered uncommon 33. For example, in a survey o f oral biopsy material, only 15 simple bone cysts were found among 7427 cysts o f the jaws ~4. Information obtained from the present investigation basically agrees with most previously reported studies with regard to distribution o f patients according to age and sex, location, outline, content and histopathological findings. Expansion of the jaw bone was very unusual in the present series as were the symptoms caused by the cysts. The possibility that simple bone cyst can cause resorption of adjacent teeth was reinforced by the present findings. In most cases, a tentative diagnosis o f simple bone cyst can easily be made on the basis o f radiographical findings. In our series, there were 2 multilocular lesions causing difficulties in preoperative diagnosis. Case 22 (Fig. 6) was considered radiologically as ameloblastoma or keratocyst. The former diagnosis was thought to be more likely because o f medial and lateral bone expansion in the area o f the whole mandibular ramus. Radiographical diagnosis o f case 12 (Fig. 5) was also keratocyst. I patient had 2 simple bone cysts (Cases 9 and 10) bilaterally in the mandible, which is not a common finding. Thus, the clinical and radiographical features of simple bone cyst. may vary considerably, which should be kept in mind when diagnosing cystic lesions of the jaw bones. Although spontaneous healing of simple bone cyst has been reported 5.',3~, it is generally accepted that surgical intervention is necessary in order to confirm the diagnosis. Simple exploration o f the cyst is usually also curative. Some case reports have, however, shown that healing does not always take place primarily3~7 or it progresses very slowlytL A few recurrences have also been reported 7~. In the present material, 2 cysts failed to heal al'ter the first operation. It is thus clear that even simple bone cysts should be followed up after treatment, in order to confirm the healing o f the lesion.

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