Benign osteoblastoma mimicking malignancy of the spine.V Maheshwari, VK Srivastava
Department of Pathology, Jawaharlal Nehru Medical College, Aligarh Muslim University.
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 0010740730
Source of Support: None, Conflict of Interest: None
A case of osteoblastoma of the spine in a sixty year old female is presented. These lesions usually get misdiagnosed as tuberculosis or malignancy of the spine. Salient diagnostic features have been discussed.
Keywords: Case Report, Diagnosis, Differential, Female, Human, Middle Age, Osteoblastoma, diagnosis,surgery,Spinal Neoplasms, diagnosis,surgery,Tomography, X-Ray Computed, Tuberculosis, Spinal, diagnosis,
Benign osteoblastoma or giant osteoid osteoma is a rare tumour and constitutes less than 1% of biopsied primary bone tumours,. The rarity of the lesion could easily be assessed as only 11 patients with osteoblastoma of the spine were treated at the Mayo Clinic from 1925 to 1983 and Mittal et al could not find a single case over 10 years study of spinal lesions. The involvement of spine is commonly seen ranging from 23% to 36%. Spinal involvement generally gives rise to root symptoms, dull aching pain and swelling. Such cases may be misdiagnosed as spinal tuberculosis in young adults or metastatic deposit in older age group both clinically and radiologically. The authors present here a case of benign osteoblastoma of spine occurring in a 60-year-old female and discuss the salient features of the case in relation to differential diagnosis.
A 60-year-old female patient presented to Neurosurgery Outpatient Department of JN Medical College, Aligarh with a history of progressive weakness of both lower limbs for two months. There was no history of trauma or tuberculosis. Objectively, the patient had grade O spastic paraplegia with a sensory level at L1.
Haemogram was within normal limits. ESR was 40 mm in the 1st hour (Wintrobe). X-ray chest was normal. Skiagram of the lumbosacral spine showed a wedge collapse at L1 vertebra and paravertebral shadows [Figure - 1] and [Figure - 2]. At CT scan, the image morphology showed a huge intra and extra spinal mass of mixed density. The mass had destroyed the vertebral bodies of D11 and D12. Spinal cord was seen compressed and pushed towards the left side [Figure - 3]. Radiological impression was that of a primary neoplasm. Serum calcium and alkaline phosphatase levels were normal.
A laminectomy at D12L1 was performed. After retracting the paravertebral muscles, the lamina was found to be eroded at D12 and L1 on the right side. A greyish pink mass was seen infiltrating the muscle plane. It had destroyed the lamina and was seen engulfing the dura from the right side. The mass was soft and rubbery. It could not be sucked and had to be excised. The wound was closed.
A squash smear was prepared from the tissue removed and stained with haemotoxylin and eosin. This showed presence of foreign body giant cells [Figure - 4] and other mononuclear cells with a light stained bluish background. The overall impression was that of a benign lesion in which giant cells (foreign body type) were the prominent feature and it ruled out the possibility of secondary metastatic deposits.
Histopathologic study revealed the presence of poorly mineralised irregular masses of osteoid tissue with multi-nucleated giant cells resembling osteoclasts encroaching the osteoid tissue [Figure - 5]. No evidence of any cellular atypia or mitotic figures was seen. The tumour was diagnosed as benign osteoblastoma involving the spine.
Osteoblastoma is a benign lesion, which is to be distinguished from osteoid osteoma by the large size of the nidus (> 1.5 cm), the absence of surrounding reactive new bone formation and lack of intense pain. Further the pattern of bone production may vary from field to field as compared to more uniform osteoid formation in osteoid osteoma as had been observed in the present case.
Involvement of the spine is fairly common as Marsh et al have reported that in a series of 197 osteoblastoma, 73 cases (41%) occurred in the spine. Pedicle, facet and lamina are generally involved. Younger age group is commonly affected as more than 80% of the cases are below 30 years. However, rarely osteoblastoma can occur over 40 years as was noticed in the present case. Myelogram is generally positive for an extradural mass in the patients with osteoblastoma as was also observed in this case. Scoliosis is one of the common manifestation of osteoblastoma,. Considering the age of the patient and the radiological picture, one would think in terms of neoplasia, either primary or secondary. The likelihood of malignant growth was ruled out to a great extent by examining the squash smear.
On histopathologic study the diagnosis of benign osteoblastoma was quite apparent. Seeing the sections under low power one could think of giant cell tumour but the intervening stromal cells were not spindle-shaped fibroblasts but plumper osteoblast like. Hence the possibility of giant cell tumour was ruled out. Moreover, there was no necrosis as well as the tumour was not much vascularised. Multiple sections were prepared to rule out the possibility of any aggressive activity of the tumour. Tumours with atypia and mitoses have been labelled as aggressive osteoblastoma or malignant osteoblastoma.
An osteoblastoma should be distinguished from an osteogenic sarcoma because at times it is difficult to differentiate the two both radiologically and histologically. Presence of epitheloid osteoblasts, trabecular osteoid, prominent osteoclastic activity, absence of cartilage, well demarcated woven bone-host bone interface, and low mitotic activity are some of the histological criteria to differentiate from osteosarcoma.
Prognosis is good though 10% recur following removal.
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5]