BACKGROUND: The aneurysmal bone cyst (ABC) is a benign, but locally aggressive cystic lesion of the bone. It usually occurs in the metaphysis of long bones of adolescents and young adults but can also affect the pelvis.
METHODS: This single-center study is a retrospective review of 17 patients with primary ABCs of the pelvis. It examines the importance of polidocanol instillations as minimally invasive treatment option for ABCs of the pelvis compared to intralesional curettage or marginal resection.
RESULTS: Seventeen patients with the diagnosis of a primary ABC of the pelvis were included in the study. Six patients were male (35%) and 11 patients female (65%); the mean age was 18 (9-49) years. The mean follow-up time was 50 months (12-136 months). The most common location of manifestation was the pubis (6; 35%), followed by the ilium (6; 35%), the sacrum (3; 18%) and the ischium (2; 12%). Eight patients were treated by intralesional curettage with the use of adjuvants, one patient by marginal resection, seven by sequential instillation of polidocanol and one patient by simple observation. Five patients received an additional transarterial embolization. After intralesional curettage local recurrence was detected in 4/8 cases (50%). After instillation therapy six patients (86%) had a stable disease without recurrence, only one patient (14%) had a persistent disease with need of additional treatment and was therefore converted to intralesional curettage without local recurrence in the follow-up.
CONCLUSIONS: Sequential instillations of polidocanol are a promising, minimally invasive treatment method for ABCs of the pelvis and can be well combined with transarterial embolization.

(1) Background: An aneurysmal bone cyst (ABC) is a benign, locally aggressive tumor. Different treatment modalities are described in the literature i.e., en bloc resection, intralesional curettage and percutaneous sclerotherapy. (2) Methods: This single-center study is a review of 74 patients with primary ABCs who underwent a surgical treatment or polidocanol instillation. Cyst volume measurements using MRI and conventional radiographs are compared. (3) Results: The mean pre-interventional MRI-based cyst volume was 44.07 cm3 and the mean radiographic volume was 27.27 cm3. The recurrence rate after intralesional curettage with the need for further treatment was 38.2% (13/34). The instillation of polidocanol showed a significant reduction of the initial cyst volume (p < 0.001) but a persistent disease occurred in 29/32 cases (90.6%). In 10 of these 29 cases (34.5%) further treatment was necessary. After en bloc resection (eight cases) a local recurrence occurred in two cases (25%), in one case with the need for further treatment. (4) Conclusions: MRI scans are superior to biplanar radiographs in the examination of ABCs. Sequential percutaneous instillations of polidocanol are equally effective in the therapy of primary ABCs compared to intralesional curettage. However, several instillations have to be expected. In a considerable number of cases, a conversion to intralesional curettage or en bloc resection may be necessary.