A nine year old male with no past medical history presents to the emergency department accompanied by his mother, describing a two day history of acute on chronic right hip pain. The patient states that while bathing two days ago, he slipped on a bar of soap onto his right side. Subsequent to the fall, the patient has been having difficulty walking secondary to right hip pain, and the mother reports that the patient has developed a noticeable right sided limp. Additionally, the mother states that the patient has had occasional right hip pain for the past year. He has been able to participate in all school physical activities, albeit with some difficulty.
What's the diagnosis?
Aneurysmal bone cysts (ABCs) are benign bone lesions that predominantly develop in the pediatric population and form to create blood-filled cavities lined with fibroblasts, giant cells and trabecular bone (Figure 1). They are commonly found in the first two decades of life, and can present in any skeletal location, although there is a propensity for their development in the metaphysis of long bones. Their origin is thought to arise as either a primary neoplasm from a gain-of-function translocation causing rapid growth and expansion of lesions, or secondarily from other benign bone tumors [i].
ABCs universally present with pain and swelling at the affected site. Plain film radiography is obtained to identify the localized destruction and dilation of affected bone. Plain films characteristically demonstrate a radiolucent lesion surrounded by a thin layer of bony cortex (Figure 2); because plain films do not fully demonstrate the extent of invasion into nearby structures, or tissue characteristics and adjacent edema, cross-sectional imaging is also obtained [i].
Computed tomography is less frequently used as an imaging adjunct in the pediatric population due to radiation exposure; however when compared to magnetic resonance imaging (MRI), it is better able to evaluate cortical changes and diagnose pathologic fractures [ii].
Combined with plain radiography, MRI provides the highest positive predictive value and interobserver agreement in diagnosing ABCs [iii]. Features characteristically apparent on MRI include trabecular loculations, adjacent soft tissue edema, and fluid-fluid levels comprised of cellular blood products layering under serous components (Figure 3). However, fluid-fluid levels may also be present in malignant neoplasms, namely telangiectatic osteosarcomas, thereby necessitating a histologic analysis to achieve a definitive diagnosis [iv].
The standard treatment of ABCs is surgical: curettage with or without bone grafting depending on the size and position of the resulting void. Adjuvant therapies developed to decrease recurrence include augmentation of curettage with a high speed burr, argon beam coagulation, addition of phenol, cryosurgery, cementing, radiotherapy, arterial embolization and sclerotherapy. An emerging technique is “curopsy,” a less aggressive surgical technique involving percutaneous biopsy to obtain lining for diagnostic evaluation that by itself is hypothesized to disrupt the internal lesion architecture and induce healing [i]. Curopsy may be combined with an experimental treatment, instillation of doxycycline, which has anti-neoplastic properties and has been shown to further reduce recurrence [v].
The patient was admitted for interventional radiology guided percutaneous biopsy of the lesion, with instillation of intra-lesional doxycycline. The biopsy specimen was reviewed by pathology, and deemed insufficient for definitive diagnosis although aneurysmal bone cyst was suspected. Post-procedure, the patient was monitored with no complications, and discharged with pain control and follow-up.
Resident Reviewer: Dr. Ross
Faculty Reviewer: Dr. Tubbs
[i] Park HY, Yang SK, Sheppard WL, et al. Current management of aneurysmal bone cysts. Curr Rev Musculoskelt Med. 2016;9:435-44.
[ii] Wyers MR. Evaluation of pediatric bone lesions. Pediatr Radiol. 2010;40:468-73.
[iii] Mahnken AH, Nolte-Ernsting CCA, Wildberger JE, et al. Aneurysmal bone cyst: value of MR imaging and conventional radiography. Eur Radiol. 2003;13:1118–24.
[iv] Biermann JS. Common benign lesions of bone in children and adolescents. J Pediatr Orthop. 2002;22:268-73.
[v] Shiels WE 2nd, Beebe AC, Mayerson JL. Percutaneous Doxycycline Treatment of Juxtaphyseal Aneurysmal Bone Cysts. J Pediatr Orthop. 2016;36(2):205-12.