Aneurysmal bone cysts constitute 1% to 2% of all primary bone tumors. They are rapidly growing benign bone tumors. Nearly 80% of aneurysmal bone cysts occur in the first 20 years of life, and most are primary tumors. Aneurysmal bone cysts are mostly benign, locally aggressive, and highly vascularized tumors. Generally, the period required for postoperative recovery and new bone formation is long. The relapse rate can be up to 50%. Although computed tomo-graphy and magnetic resonance imaging scans are the preferred diagnostic methods, biopsy is the most necessary prerequisite to confirm diagnosis, as aspects of these cysts can show similarity to many other bone lesions. Correct histopathologic diagnosis is important since malignancies may be seen in transplant recipients.

Key words : Biopsy, Bone lesions, Pathology, Transplantation

Introduction

The aneurysmal bone cyst was first described by Jaffe and Lichtenstein in 1942.¹ Aneurysmal bone cysts often originate from the metaphysis of long tubular bones and can typically be seen in vertebras or in flat bones.^2,3 Aneurysmal bone cysts constitute 1% to 2% of all primary bone tumors. They are rapidly growing benign bone tumors. Nearly 80% of aneurysmal bone cysts occur in the first 20 years of life, with most being primary tumors. However, 30% of these cysts are associated with another bone pathology and are called secondary aneurysmal bone cysts. In fact, these are not aneurysmal bone cysts but aneurysmatic changes. In some cases, aneurysmatic changes may completely obscure the underlying lesion. Lesions showing aneurysmatic changes include fibrous dysplasia, giant cell tumors, nonossifying fibromas, hemangiomas, osteoblastomas, simple bone cysts, chondroblastoma and chondromyxoid fibromas, and malignant osteosarcomas.⁴

Aneurysmal bone cysts were initially thought to be caused by vascular disorders in the bone, leading to an increase in intraosseous pressure causing local destruction and distention.⁵ Later studies showed that they have a genetic component. In particular, it was shown that the genetic component was translocation-dependent regulation of the ubiquitin-specific protease USP6 (Tre2) gene, which prefers a primary neoplastic process rather than a mechanical or vascular process.⁶

Case Report

In October 2017, an 18-year-old male patient underwent a successful renal transplant from his mother. Treatment with tacrolimus and prednisolone was initiated posttransplant. No pathologic findings were detected in the follow-up of the patient. In January 2019, the patient was examined in the neurosurgery outpatient clinic because of recent low back pain and increasing numbness in both legs. The neurologic examination was normal. Spinal com-puted tomography and magnetic resonance imaging revealed an expansive mass lesion with fluid levels having hemorrhagic areas in the posterior elements and corpus of the T11 vertebra (Figure 1).

A spinal angiography was performed by inter-ventional radiology to exclude vascular pathology and to determine the suitability of embolization treatment. However, no vascular structure to be embolized could be detected. Because the patient had complaints of increased numbness in both legs, surgical treatment was performed without planning any biopsy. The patient was operated in prone position and under neuromonitoring. The pathology was reached via a midline incision and bilateral subperiosteal dissection of muscles. Bilateral transpedicular screwing of T9-T10-T12-L1 vertebrae was performed with the control of C-arm. Following this, tumor tissue in the paravertebral area was excised and T11 total laminectomy and curettage of vertebral corpus from the defective pedicle were performed. There was no major bleeding during the surgical procedure. The patient was discharged on postoperative day 3 without any neurologic deficits.

Histopathologic examination revealed cavernous cavities, in which blood elements were found. Areas between these cavities were rich in fibroblasts; bone trabecular areas were also observed. The histo-pathologic diagnosis was aneurysmal bone cyst (Figure 2).

Discussion

Solid-organ transplant is a lifesaving treatment for certain end-stage diseases. Due to improvements in surgical techniques and postoperative immunosup-pressive treatments, there has been an increase in the survival of patients and consequently postoperative complications.⁷ Bone diseases after transplant are among complications that can be seen regardless of the organ type.⁸ They can be classified as quantitative disorders, such as osteoporosis, or qualitative disorders, such as hyperparathyroidism, adynamic bone disease, osteomalacia, and osteonecrosis. Bone diseases increase the risk of fracture and reduce the patient’s quality of life and survival. Although successful solid-organ transplant may lead to recovery of many metabolic abnormalities, bone disease may persist after transplant and may even worsen.

Aneurysmal bone cysts are mostly benign, locally aggressive, and highly vascularized tumors. Generally, the period required for postoperative recovery and new bone formation is long. The relapse rate can be up to 50%.9 Although computed tomography and magnetic resonance imaging scans are the preferred diagnostic methods, biopsy is the most necessary prerequisite to confirm the diagnosis, as aspects show similarity to many other bone lesions.¹⁰ Because immunosuppressive treatment used in the posttransplant process is intense, it is especially necessary to exclude malignant bone lesions and Brown tumors in patients with chronic renal failure.^11,12

There are 3 options in the treatment of ABCs. The choices are selective vascular embolization, total curettage by open surgery, and percutaneous insertion of doxycycline into the cavity.¹³ In our case, which is unique in the literature, surgical curettage and stabilization were performed to exclude malignant pathologies.

Conclusions

We suggest that the use of surgical curettage and stabilization is the most appropriate treatment option in such patients, which would allow correct histopathologic diagnosis and prevent possible instability and allow further adjuvant therapies to be planned, depending on the nature of the tumor.

References:

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