British Journal of Radiology (2004) 77, 610-614
© 2004 British Institute of Radiology
doi: 10.1259/bjr/69860747
Aneurysmal bone cyst of the sternum: a case report of successful treatment with radiotherapy
A A Yavuz, MD
1
M 
ener, MD
2
M N Yavuz, MD
1
P Kosucu, MD
3 and
U Cobanoglu, MD
4
Departments of 1 Radiation Oncology, 2 Orthopaedic Surgery, 3 Radiology, and 4 Pathology, Karadeniz Technical University Hospital, Trabzon, 61080, Turkey
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Abstract
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An unusual case of a lytic, expanding lesion of the manubrium with histological diagnosis of aneurysmal bone cyst in a 13-year-old girl is presented. After a recurrence following primary surgery, the patient was treated successfully by external beam radiotherapy. A total dose of 25.2 Gy was delivered using conventional fractionation (1.8 Gy day–1) to the whole sternum. She remains recurrence- and symptom-free 46 months after the end of the treatment. This is the sixth patient with primary aneurysmal bone cyst in the sternal region, the first paediatric patient for this location, and the first case of its kind treated exclusively by radiotherapy ever reported in the literature. The histopathological, radiological and clinical findings of the patient are presented, relevant literature is reviewed, and radiotherapeutic management of such lesions is discussed.
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Introduction
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Primary tumours of the sternum are rare and 83–95% of them are malignant [1, 2]. Although aneurysmal bone cysts (ABC), which constitute of 1–2.5% of primary bone tumours, are benign, they are expanding, locally aggressive lesions [3–6]. Some authors believe that all ABCs are initially associated with a primary neoplasm, with the ABCs destroying all pathological evidence of that process [6, 7]. They occur most commonly between 10 and 20 years of age with a slight female predominance (1.5–2:1) and involve a long bone in 50–60% of cases and the spine in more than 30% of cases [3–8]. According to our knowledge, only 5 cases of ABCs in the sternum have been reported previously in the English literature. This report documents the clinical progress of a case with another such cyst. This is the first paediatric case for this entity and also the first one exclusively treated by radiotherapy for a post-operative recurrence in this location.
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Case report
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A 13-year-old girl was admitted to the hospital with a chief complaint of persistent, progressive pain and gradually increasing swelling in the sternal region for 6 months. There was no history of trauma. Local examination revealed a bony hard swelling measuring 2.5 cm x 4 cm situated over the manubrium. On palpation, the swelling was fixed, tender, appeared to be covered only by a thin shell of bone, and the local temperature over it was not raised. Laboratory studies were all within normal limits, including serum alkaline phosphatase. Lateral radiograph (Figure 1a
) and CT scan (Figure 1b) revealed a well-defined, markedly expanding, hypodense, cystic mass involving the manubrium. There was thinning at the anterior cortex without any destruction. No ossification or calcification was seen within the lesion. The lower part of the body appeared to be normal. A radiological bone survey showed no other lesion.
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Figure 1. (a) Lateral radiograph demonstrates an expanding, lytic lesion involving the manubrium sterni (arrows). (b) CT scan showing a well-defined, expansive cystic lesion in the manubrium. Note the anterior cortex is thin but not destroyed (arrow).
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An aspiration biopsy of the lesion was performed several days after admission. At the time of the aspiration biopsy, the needle easily punctured the thin anterior cortex and apparently fell into a cystic area. Two cubic centimetres of blood was easily obtained, after which aspiration became more difficult. Subsequent pathological studies demonstrated a small amount of fibrous tissue mixed with peripheral blood. No malignant cells were seen. The findings were interpreted as being compatible with an ABC.
The patient had an operation 2 weeks later. Pre-operatively, curettage and cancellous autografting had been planned. During the operation, the tumour was explored through a longitudinal skin incision. In a small area, the anterior cortex of the manubrium sterni had been destroyed, possibly due to previous biopsy of the lesion. Just after starting the curettage, three units of blood had to be given in a short time due to instantaneous bleeding of the lesion, thus, grafting was not performed. Histopathological examination of the specimen revealed that the tumour consisted of large blood spaces separated by fibrous trabeculae containing histiocytes, multinucleated giant cells, inflammatory cells and foci of osteoid beside the blood-filled spaces (Figure 2). These findings were typical of an ABC. After the curettage, the patient's recovery was uneventful.
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Figure 2. (a) Histological examination revealed large, cavernous spaces filled with blood (haematoxylin and eosin x 40). (b) Fibrous septae containing histiocytes, multinucleated giant cells, inflammatory cells and foci of osteoid beside the blood-filled spaces (haematoxylin and eosin x 400).
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4 months later, the patient was re-admitted with a painful, recurrent mass measuring 2 cm x 3 cm at the same location. This time, the patient received external beam radiotherapy using a megavoltage photon beam on a cobalt 60 machine. In a continous course, the whole sternum was treated 5 days a week with standard daily fractions of 1.8 Gy up to a total dose of 25.2 Gy. The borders of the anterior field extended inferiorly to at least the caudal pole of the sternum, superiorly to the suprasternal notch, and the lateral margins extended 1.5 cm outside the bony margins of the sternum. Treatment portals were rectangular with a field size of 12 cm x 6.5 cm (length x width). She had complete relief from her symptoms within 2 weeks of completing radiotherapy. When last seen, 46 months after radiotherapy, she was symptom free. Radiograph and CT of the sternum taken at the last assessment is shown in Figure 3.
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Figure 3. 46 months after radiotherapy, (a) a lateral radiograph and (b) CT scan demonstrated a significant regression and sclerosis of the sternal mass. Note the thymus regressed due to irradiation.
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Discussion
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Primary tumours of the sternum are infrequent, as indicated in the study by Teitelbaum [9] in which over a 20 year period, a total of 750 primary bone tumours were reviewed. Of these 61 cases (8%) arose in the chest wall, 95% in the ribs and 5% intrinsically in the sternum. The vast majority of sternal tumours are primary and malignant [1, 2]. Dahlin [10] collected 6221 intrinsic bone tumours and found 32 of 34 sternal lesions to be malignant. In Ochsner's series of 134 chest wall tumours, 6 were in the sternum and 5 of them were malignant [1]. Pascuzzi et al [11] reported 18 neoplasms of the sternum, 17 of which were malignant and one of an equivocal nature. Benign sternal tumours are extremely rare. A few cases of benign tumours such as chondroma, giant cell tumour [12, 13], eosinophilic granuloma [1, 9], and chondromyxoid fibroma [9] have been reported in the sternum.
ABCs are benign lesions of bone, however, they have a propensity for local recurrence [3–8]. The lesion has been found in various parts of the skeleton but is most common in the metaphysis of long bones and in the vertebrae. Dabska and Buraczewski [14], while reviewing 193 cases of ABC, reported the first case of ABC of the sternum. Only four other cases of ABC in the sternum have been reported previously in the literature. The main characteristics and treatment results of these patients are summarized in Table 1.
ABCs are histologically characterized by cyst-like vascular spaces filled with free-flowing blood, with walls made of fibrous tissue and bone [3, 4]. On gross pathological studies of an ABC, an expanding lesion surrounded by a thin layer of subperiosteal bone is generally noted. Following removal or puncture of the bony shell, blood wells up from within the blood-filled spaces. The tissue, which is reddish or yellow, is generally soft, but if osteoid is present, may feel gritty. The vascular spaces are often separated by fibrous septa containing multinucleated giant cells, generally containing fewer nuclei than are observed in giant cell tumours. Strands of osteoid, stromal cells with spindle-shaped nuclei and macrophages containing haemosiderin may also be present [3, 4, 14–17].
The pathogenesis of ABC suggests a probable vascular anomaly [3, 18], e.g. a type of arteriovenous anastomosis. The haemodynamics of this anastomosis causes bone erosion and resorption, producing a labyrinth of vascular channels bounded by an expanded shell of periosteal new bone and accompanied by an osseous reparative process. Accompanying the reparative process are reactive giant cells and stromal cells lining vascular spaces surrounded by extensive fibroblastic and osteoblastic proliferation [3]. The differential diagnosis includes giant cell tumour, monostatic fibrous dysplasia, solitary bone cyst (most unlikely), haemangioma, chondromyxoid fibroma, metastatic disease and primary malignant neoplasm, e.g. chondrosarcoma, telangiectatic osteosarcoma, primary lymphoma of bone and Ewing tumour. Plasmacytoma would be a highly likely possibility in an older individual. In addition, ABCs are often accompanying or secondary to other intrinsic bone lesions including trauma, fibrous dysplasia, chondroblastoma, chondromyxoid fibroma, benign osteoblastoma, non-ossifying fibroma, telangiectatic osteosarcoma and, most commonly, giant cell tumour [3, 4, 7]. In this case, there was no previous history of sternal swelling or trauma. Incidentally, one of the pathologists who reviewed this case felt that it represented a benign giant cell tumour associated with an ABC. Since the possibility of an accompanying giant cell tumour was considered in this case, it should be noted that giant cell tumours seldom grow as rapidly as seen in this case, are less septated than ABC, and usually occur in the older age group (20 to 50 years). Similar to the current case, cavernous vascular spaces with little collagenous stroma and multinucleated giant cells might be seen histologically in giant cell tumours as well [13–17]. However, the presence of osteoid and bony trabeculae as seen in here may be taken as further evidence that the lesion was not a giant cell tumour.
It must be emphasized that the sternum is a difficult area to evaluate radiologically by standard radiographs. Normal anatomical variants, congenital anomalies, changes secondary to previous trauma or infection and other non-neoplastic conditions may mimic tumours. Often, special views for complete evaluation are required, including oblique radiographs and CT, which is an excellent adjunct in demonstrating a sternal lesion. The definitive diagnosis is, of course, made only by biopsy, but since the vast majority of these lesions are malignant, excisional biopsy or even more radical surgery is recommended whenever possible. After radiotherapy, as with other benign or malignant tumours of bone, the cystic cavity ossifies, does not change significantly in size, and generally does not return to its normal appearance [14, 19]. In this case, the soft tissue component of the tumour responded slowly to treatment with stabilization of the mass after 2 years or more, in contrast to the almost immediate relief of pain.
Treatment of ABCs is usually by primary surgical resection, which achieves very good control rates. In a summary of studies of different treatment methods, the following rates of recurrence were reported for ABCs of bones other than the sternum: marginal resection; 81 performed with 6 recurrences (7.4% recurrence rate), wide resection; 59 performed with 0 recurrences (0% recurrence rate), curettage and cryobiopsy; 78 performed with 10 recurrences (12.8% recurrence rate), curettage and bone graft; 484 performed with 149 recurrences (30.8% recurrence rate), irradiation and curettage; 35 performed with 5 recurrences (14.2% recurrence rate), irradiation; 34 performed with 4 recurrences (11.8% recurrence rate) [8]. When en bloc resection cannot be performed, curettage and bone graft [21] is the usual choice, however it is complicated by a high rate of recurrence (18% to 34%) [3, 4, 8, 22]. Generally, at sites where an adequate surgical procedure would result in significant morbidity and/or poor cosmetic results (such as vertebrae), radiotherapy can be used as an alternative [8, 16, 23, 24]. Thus, we elected to treat this recurrent sternal lesion by radiotherapy alone because of the thin bony shell of the cyst anteroposteriorly and the significant bleeding during the first curettage.
For sites other than the sternum, local control rates of ABCs after radiotherapy alone are reported to range from 75% to 92% (comparable with surgical results) [3, 8, 14, 19, 23, 24]. Historically, several investigators reported an incidence of radiation-induced malignancies as high as 12–25%, causing radiotherapy to fall out of favour. Interestingly, secondary cancers appear early [3, 25]. When we reviewed the literature, we found that all the patients who developed radiation-induced malignancies were treated suboptimally, using obsolete equipment and techniques. Orthovoltage or other low-energy photons are acceptable for treating superficial tumours (less than 2 cm deep). Unfortunately, for deeper tumours, the skin, or superficial, dose can be significantly higher [19] than the dose prescribed to the tumour. In addition, when treating with orthovoltage near the bone, the biologically effective dose is increased by the higher absorbed dose in bone and by increased scatter. When megavoltage radiation is used, both of these problems are eliminated, reducing the radiation dose to the overlying skin and the surrounding tissues, and making the distribution of dose more homogeneous. Marks et al [19] estimated that the average exposure of 2000 roentgens at midline using 250 kVp orthovoltage had an equivalent biological effect to 30 Gy in soft tissue and 35 Gy in bone with megavoltage. At higher doses of radiation, the likelihood of a radiation-induced malignancy also increases [20]; therefore, if the biological dose is decreased by using megavoltage machines, the incidence of radiation-induced cancer should also be reduced. Another potential factor in radiation-induced cancer is the volume of irradiated tissue. CT treatment planning can define the tumour volume more accurately, which allows the radiation oncologist to locate the tumour more accurately and smaller radiation fields can be used, thus sparing normal tissue. However it is important to note that secondary cancers have also been described after treatment of ABCs when radiotherapy was not used. Some investigators believe that all ABCs are components of a secondary process, either benign or malignant [3, 25]. They suggest that the ABC destroys the architecture of the primary tumour so it cannot be identified, and that would explain the cancers that occur soon after completion of radiotherapy. In addition, sometimes a malignant tumour is initially misdiagnosed as an ABC (most commonly a telangiectatic osteosarcoma) [4, 25].
Many studies have suggested that women under 30 years, particularly those younger than 20 years, who have received radiotherapy to the chest wall for conditions such as Hodgkin's disease are at an increased risk of breast cancer and heart disease, with the risk increasing dramatically more than 15 years after therapy [26]. However, these risks may relate to use of older techniques of radiotherapy employing higher doses (>30–40 Gy) and a lack of optimal shielding of critical organs. There may also be other risk factors for heart disease or breast cancer in patients included in such studies [27, 28]. According to the literature, ABCs were controlled with doses as low as 500 to 1500 roentgens using older treatment units [3, 23], but as described earlier [19, 24], the actual tumour dose was equivalent to a prescribed tumour dose of 26–30 Gy using standard fraction sizes and megavoltage energy, as we used. Due to the age of our patient, we feel that particular attention should be paid to breast screening and monitoring of cardiac function for the next decade, although the dose to the heart and breast tissue incidental to the treatment of the whole sternum was low.
In conclusion, we report an unusual case of a girl with an ABC in the sternum which was successfully treated by external beam radiotherapy (1.8 Gy day–1, total 25.2 Gy) using megavoltage radiation. She remains recurrence- and symptom-free 46 months after the end of the treatment. This is the sixth patient and the first paediatric patient with primary aneurysmal bone cyst of the sternal region, and the first case of recurrence treated by radiotherapy alone ever reported in the literature. We recommend radiotherapy for patients whose tumours are inoperable because surgical resection would lead to poor functional or cosmetic outcomes, such as sternal tumours, and for patients with recurrent ABCs.
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Acknowledgments
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We would like to thank Ms Emma Duncan for her editorial assistance.
Received for publication June 16, 2003.
Revision received September 29, 2003.
Accepted for publication October 20, 2003.
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Abstract
Introduction
