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Large sacral osteoblastoma: a case report and review of multi-disciplinary management strategies.

INTRODUCTION

Osteoblastomas are uncommon primary benign bone tumors characterized by active production of osteoid and primitive woven bone in a well-vascularized connective tissue stroma. (1) Some confusion of the terminology of the pathology remained until Jaffe (2) and Lichtenstein (3) proposed the term "benign osteoblastoma" in 1956. The sacrum remains a known, but uncommon, site of involvement. (4) Sacral osteoblastomas are generally slow growing, and due to their insidious nature, may reach imposing dimensions. (5) Treatment has remained challenging not only due to the frequent large sizes of these tumors, but also the risk of recurrence with incomplete resection. (6) We present a rare case of a large sacral osteoblastoma in a pediatric patient that was treated with a multidisciplinary team involving the departments of neurosurgery, neuroendovascular surgery, colorectal surgery, urological surgery, and various rehabilitation teams. At the time of the last follow-up at five-years post-procedure, the patient remains disease free. We discuss the importance of a multi-disciplinary approach for managing this rare and indolent disease.

CASE REPORT

A 15-year-old Hispanic male presented to our clinic in May 2006 with a two-month history of lower back pain. The pain was described as continuous in nature and moderate in intensity, with radiation down the left leg. He was also having difficulty walking. Computed Tomography angiography showed a hypervascular osteolytic sacral mass. MRI and CT revealed a hyperintense expansile and osteolytic mass destroying the S2 vertebral body, pedicles, and posterior arch with extension into the presacral space (Figures 2 and 3). In both CT and MRI images, the tumor showed intense enhancement with contrast administration.

An open biopsy was initially obtained to determine a definitive management. The biopsy was initially reported as a chordoma. For the next few months, the patient was lost to follow-up and presented in November of the same year with increasing pain and difficulty walking.

[FIGURE 1 OMITTED]

Repeat imaging showed a tumor that had increased in size and now involved the S1 nerve root. At this time, the pathology was revisited, and a diagnosis of an osteoblastoma was established. Definitive treatment of the lesion with surgical resection was discussed with the patient and the family. After informed consent, the patient underwent pre-operative embolization of the branches of the external and internal iliac arteries supplying the tumor to decrease the risk of massive hemorrhage during resection. The following day, the patient underwent anterior-posterior resection of the tumor with lumbosacral instrumentation for pelvic reconstruction.

The first stage (anterior approach) was carried out by the urology team and included a midline laparotomy and a trans-peritoneal approach to the right and left medial hypogastric arteries, which were then ligated. The colorectal team then mobilized the rectum and the sacrum. The superior, inferior, medial, and lateral tumor margins were defined using blunt and sharp dissection. Once the tumor was de-vascularized and isolated in the pre-sacral fascial plane, a silastic sheet was laid down to help identify the anterior margin of surgical resection in the next stage of surgery. The anterior abdominal wound was then closed in layers and preparations were made for the second stage (posterior approach) of the surgery.

For the second stage of the surgery, the patient was placed prone, and the sacrum was approached with a midline incision over the lower lumbar spine and the sacrum. A laminectomy at L5 and S1 levels was performed, and the thecal sac was ligated and mobilized superiorly. The S1 nerve roots were clearly seen entering the tumor and were sacrificed bilaterally. The amputated roots were mobilized with the amputated thecal sac superiorly. The tumor was then resected en-bloc, carefully using osteotomies and sharp dissection without damaging the internal iliac arteries anteriorly. Once the tumor was removed, the margins were examined for evidence of a gross resection. The specimen was then sent for pathological examination, and a Vicryl mesh was applied in the defect to prevent the rectum from herniating posteriorly. Lumbo-sacral-pelvic reconstruction was then carried out with lumbosacral instrumentation from L4 to the ileum and application of allograft and autograft (Figure 1). Pedicle screws were inserted bilaterally at L4, L5, and unilaterally in right S1 pedicle. Iliac screws were then inserted and connected to the lumbosacral pedicle screws with rod constructs.

The patient tolerated the procedure well, and no intra-operative complications were documented. The postoperative recovery period was uneventful, and the patient was slowly mobilized and discharged a month later to home with healthcare assistance. The S1 nerve roots bilaterally and the S1 pedicle on the left were resected due to tumor involvement. Due to resection of the sacral nerve roots, the patient developed postoperative are flexic bladder with intrinsic sphincter deficiency that required intermittent urinary self-catheterization. The patient also developed bowel incontinence that eventually required a colostomy. The patient has been followed up for more than five years postoperatively (Figure 1). At the latest follow-up, the patient's symptoms were stable. He reports no difficulty in ambulation and no pain in the surgical site. The patient has additionally undergone insertion of an artificial urinary sphincter obviating the need for self-catheterization. He reports no recent incidents of urinary tract infections. The urinary sphincter is incompatible with MRI; therefore, the patient has been followed with lumbo-sacral X-rays and CT. There is no evidence of erosive masses in the bone or new soft tissue masses. There is evidence of good bony fusion mass supporting the lumbo-sacral construct.

Gross pathology examination revealed a firm tumor with tumor-free margins. The specimen was dissected to reveal a dark-red, hemorrhagic cut surface. Microscopic examination depicted an active production of osteoid and primitive woven bone in a well-vascularized connective tissue stroma. Mitotic activity was scattered and low. Given the characteristic appearance, a final diagnosis of osteoblastoma with clear margins was made.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

DISCUSSION

Demographics of Sacral Osteoblastomas

Osteoblastomas constitute 1% of primary bone tumors. In a series of 306 osteoblastoma cases, Lucas et al. found osteoblastomas in virtually every bone of the body. The vertebral column (sacrum included) accounted for 32% of their cases. (7) Within the spine, the sacrum is not a common location of involvement. Nemoto et al. reported that out of their 75 vertebral osteoblastomas, 13 involved the sacrum. (8)

Overall, osteoblastomas are more commonly encountered in males, and the mean age of incidence is approximately 20 years. (7) Incidence is similar in the vertebral column, with males twice as likely to present with the tumor as females, and the average age ranging from 14 to 20. (7,9)

Diagnostic findings

The most common symptom in patients with osteoblastoma is local pain that is relieved partially with analgesics. Other symptoms arise when there is involvement of the nerve roots with referred pain and weakness, as well as urinary and fecal incontinence. Other symptoms include a palpable mass, weight loss, and fever. (4) The non-specific nature of the presenting symptoms may lead to delays in diagnosis. An average patient in Nemoto et al.'s series with vertebral osteoblastoma experienced pain for 16 months before eventual diagnosis. This delay was even longer for patients with a sacral osteoblastoma averaging at 22 months. (8)

Imaging

Osteoblastomas do not always have specific radiological findings to refine the diagnosis. Often, however, radiographs are able to suggest the diagnosis by showing well-defined, expansile osteolytic lesions. These lesions also show partial or extensive calcification, with some depicting features similar to osteoid osteomas of a central nidus of sclerotic bone surrounded by a radiolucent halo. Spinal osteoblastomas mostly affect the posterior elements of the spine and rarely the vertebral body. Up to 25% of osteoblastomas can have features suggesting a malignant pathology, such as a large size and destructive growth. Scoliosis is another finding in sacral osteoblastomas, but is more commonly encountered in patients with lumbar or thoracic involvement. (7)

[FIGURE 4 OMITTED]

Computed tomography of the spine is the test of choice to anatomically define osteoblastomas. MRI scans are also used and are able to better detect the soft tissue involvement. However, peri-tumoral edema seen on MRI may be mistaken for a more malignant pathology, and so, findings should always be taken in context to the clinical and CT findings.

Technetium 99M bone scanning is used to assist in the diagnosis of osteoblastomas. Amacher and Eltomey, in their pediatric osteoid osteoma and osteoblastoma series, noted the importance of technetium 99M bone scanning in patients with back pain and a normal radiograph to diagnose osteoblastomas before the lesion grows enough to cause any scoliosis or cord compression. (10)

Pathologic findings

Grossly, the tumor appears red and gritty. The margins are usually well demarcated and occasionally scalloped. Reactive sclerosis is variable, and some tumors might show features of a central sclerotic nidus similar to a osteoid osteoma. Some tumors are highly vascular and may have cystic hemorrhagic areas. In contrast to long bone osteoblastomas that rarely extend into soft tissue, vertebral osteoblastomas extend into epidural and soft tissue relatively frequently. (7)

Microscopically, osteoblastomas show features similar to osteoid osteomas and are composed of inter-anastomosing trabeculae of woven bone within a loose fibrovascular stroma. A single layer of osteoblasts lines the trabeculae. Other features include primitive woven bone, numerous giant cells with Howship lacunae, and Pagetoid changes (depicting the continuous remodeling process). Cytological features of the osteoblasts are variable and mitotic activity is usually low. Areas resembling secondary aneurysmal bone cysts may be seen in up to 10% of cases. (7)

Differential diagnosis

The differential diagnosis for a sacral osteoblastoma includes osteoblastoma-like osteosarcoma, osteoid osteoma, giant cell tumor, aneurysmal bone cyst, and cartilaginous tumors. The size of the tumor has been used to differentiate between osteoid osteomas and osteoblastomas. Osteoid osteomas rarely exceed 1 cm in size. Osteoblastomas are typically larger at presentation, with a higher rate of growth and incidence of spinal cord extension. (11)

Management strategies

Treatment options for sacral osteoblastomas include en-bloc resection, curettage or intralesional excision, depending upon the site, size, and the extension of the tumor. These can be done through a posterior approach or through an anterior approach (trans-abdominal or retroperitoneal). The decision rests on the location of the lesion, as well as the extension beyond the bony sacral margins. (12) Complete removal cures the benign tumor, but in the proximity of normal sacral roots, curettage or intralesional excision is often a more viable option. Pre-operative bladder and bowel function documentation is important in making this decision. In our case, the osteoblastoma had grown large enough to involve the S1 root, and hence, the decision was made to sacrifice the nerve roots and perform an en-bloc resection. One of the major complications in resection of the tumor is a massive amount of blood loss. Cases have been reported where resection had to be abandoned due to this reason. With large multi-stage sacrectomies, pre-operative embolization can be valuable in decreasing the risk of massive hemorrhage. (13)

Radiotherapy is another option for sacral osteoblastomas and has traditionally been reserved for incomplete resections or palliative care. Despite a good response, the risk of radiation-induced malignancy in young patients prevents utilizing radiotherapy as a first-line treatment for sacral osteoblastomas. (14) There is scarce data on the efficacy of chemotherapy in osteoblastomas. There exist at least two case reports of recurrent cervical osteoblastomas managed with chemotherapy, resulting in tumor regression. No recurrence on follow-up was detected in either case. (15)

With complete excision of the osteoblastoma, the incidence rate for primary recurrence is low. With incomplete resection, however, the recurrence rate can reach up to 50%. (4)

CONCLUSION

The sacrum is a known, but rare, location for an osteoblastoma. We present a technically challenging case of a pediatric patient with a giant sacral osteoblastoma managed with a multidisciplinary approach, leading to a disease-free good functional outcome.

REFERENCES

(1.) Papagelopoulos PJ, Galanis EC, Sim FH, Unni KK. Clinicopathologic features, diagnosis, and treatment of osteoblastoma. Orthopedics 1999;22:244-247.

(2.) Jaffe HL. Benign osteoblastoma. Bull Hosp Joint Dis. 1956;17:141-151.

(3.) Lichtenstein L. Benign osteoblastoma; a category of osteoid-and bone-forming tumors other than classical osteoid osteoma, which may be mistaken for giant-cell tumor or osteogenic sarcoma. Cancer 1956;9:1044-1052.

(4.) Biagini R, Orsini U, Demitri S, et al. Osteoid osteoma and osteoblastoma of the sacrum. Orthopedics 2001;24:1061-1064.

(5.) Sar C, Eralp L. Surgical treatment of primary tumors of the sacrum. Arch Orthop Trauma Surg 2002;122:148-155.

(6.) Bisset GS 3rd, Kaufman RA, Towbin R, Bove KE. Case report 452: Recurrent sacral osteoblastoma. Skeletal Radiol 1987;16:666-669.

(7.) Lucas DR, Unni KK, McLeod RA, O'Connor MI, Sim FH. Osteoblastoma: clinicopathologic study of 306 cases. Hum. Pathol 1994;25:117-134.

(8.) Nemoto O, Moser RP Jr, Van Dam BE, Aoki J, Gilkey FW. Osteoblastoma of the spine. A review of 75 cases. Spine 1990;15:1272-1280.

(9.) Zileli M, Cagli S, Basdemir G, Ersahin Y. Osteoid osteomas and osteoblastomas of the spine. Neurosurg Focus 2003;15:E5.

(10.) Amacher AL, Eltomey A. Spinal osteoblastoma in children and adolescents. Childs Nervous Syst 1985;1:29-32.

(11.) Janin Y, Epstein JA, Carras R, Khan A. Osteoid osteomas and osteoblastomas of the spine. Neurosurgery 1981;8:31-38.

(12.) Raque GH Jr, Vitaz TW, Shields CB. Treatment of neoplastic diseases of the sacrum. J Surg Oncol 2001;76:301-307.

(13.) Gottfried ON, Schmidt MH, Stevens EA. Embolization of sacral tumors. Neurosurg Focus 2003;15:E4.

(14.) Rajkumar A, Basu R, Datta NR, Dhingra S, Gupta RK. Radiation therapy for sacral osteoblastoma. Clin Oncol (R Coll Radiol) 2003;15:85-86.

(15.) Camitta B, Wells R, Segura A, et al. Osteoblastoma response to chemotherapy. Cancer 1991;68:999-1003.

Imad Saeed Khan, MD; Jai Deep Thakur, MD; Prashant Chittiboina, MD, MPH; Anil Nanda, MD, MPH, FACS

Drs. Khan, Thakur, Chittiboina, and Nanda are with the Department of Neurosurgery, Louisiana State University Health Sciences Center, Shreveport.
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Author:Khan, Imad Saeed; Thakur, Jai Deep; Chittiboina, Prashant; Nanda, Anil
Publication:The Journal of the Louisiana State Medical Society
Article Type:Case study
Date:Sep 1, 2012
Words:2289
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