Teaching Case

Aneurysmal bone cyst is a benign, osteolytic, hyperplastic, hyperemic-hemorrhagic locally aggressive lesion mostly commune in children and young adults. Today’s therapy is selective arterial embolization or alternatively curettage and bone grafting. Embolization can have two aims: as preparation to surgery in order to decrease intraoperative bleeding risk or curative.

A 16-year-old Caucasian boy was referred to our department because of a pathologic fracture complicating an osteolytic lesion located on the proximal third of the right humerus discovered a month earlier during an X-ray performed for local pain and swelling.
There was no history of congenital or acquired bone pathology. There was no dysmetria of the upper limbs and no general symptoms such as fever, body weight and appetite lost. Pain increased through palpation; there were no ecchymosis or bruising. Systemic exams and laboratory studies were negative.
X-rays showed an eccentric osteolytic lesion with destruction of the lateral cortex at the proximal third of right humerus with local bump; a partially calcified hematoma was already present (fig.1); the aspect was highly suggestive of aneurysmal bone cyst (ABC). MRI showed a non-homogeneous lesion with internal septation (fig.2). Specific differential diagnosis was telangiectatic osteosarcoma. Bone scan indicated local uptake and absence of bone metastasis.
A needle biopsy was performed to exclude every malignancy and the clinical suspect was histologically confirmed.
A first embolization procedure was attempted and X-ray, performed after one month, showed a beginning of calcification process (fig.3); the last control, performed 10 months after the procedure, evidenced the healing of the ABC without the need of further procedures (fig. 4).

ABC in not a neoplasm but his aspect can be similar to other locally aggressive or malignant lesions. The most common sites are the methaphysis or meta-diaphysis of the long bones of the lower limb then of the upper limb, spine and pelvis but severalbones can be involved. Pain and swelling are principal symptoms; nevertheless the clinical presentation depends on ABC localization [1].
X-ray usually shows an osteolytic, usually eccentric lesion with the cortex thinned or destroyed. There is a periosteum reaction and a slight reactive bone sclerosis can demarcate the lesion. The aspect is confirmed by CT scan showing single or multiple fluid levels due to a blood-serum division[1].
MRI shows internal septation with “soap-bubble” features particularly evident in T2 weight images with an enhancement of the septa after gadolinium infusion. When present a fluid level is characteristic; on in T1 weight images ABC has intermediate or low signal.
Differential diagnosis includes telangiectatic osteosarcoma, simple bone cyst and giant cell tumor therefore biopsy is preferable for diagnosis.
Telangiectatic osteosarcoma rarely may present like an aggressive ABC and the fluid-fluid levels can be present; also histology can be not clear in rare cases of low-grade telangiectatic osteosarcoma.
Simple bone cyst sometime may mimic an aneurysmal central bone cyst. The puncture in simple bone cyst evidences a clear fluid instead of blood in ABC. CT and MRI show a unicameral lesion in simple bone cyst.
Usually Giant cell tumor arises in patient over 20-years old so that the most of giant-cell-tumor-like lesions near to an open growth plate is an ABC. Differential diagnosis can be difficult in the adults because of giant cells can be present in ABC as well [1].
The treatment approach varies depending on the location and aggressiveness of the lesion. In quiescent form follow-up is possible; in aggressive, surgery is the most used treatment consisting in curettage with effective adjuvant therapy and bone grafting but high recurrence rate was reported [2-4].
Nevertheless when surgical approach is difficult and very invasive such as in ABC located in spinal and pelvic bone, embolization may be the best option [5,6]. The results obtained by embolization encourage the use of this method as first choice also in “easy approached lesions” both therapeutic or as preparation to surgery [7]. Today embolization is principal approach to ABC; surgery is necessary when embolization gives no results and as first choice when there is a high risk of fracture. Although in most cases several embolizations are necessary to allow healing ABC, sometimes a single procedure can be enough. Radiologists and orthopedics have to follow the healing process in order to postdate a possible second procedure. As a matter of fact if a good evolution is evident at X-ray useless procedure should be avoided and to assure the least invasive and efficient treatment.