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BENIGN BONE TUMOURS OF THE SPINE S. Pans, P. Brys, I. Van Breuseghem, E. Geusens1 A wide variety of primary bone tumours can involve the spine. The imaging features of these lesions are often characteristic. We present an overview of the primary benign bone tumours of the spine. The role of plain film, CT and MRI is discussed. Key-word: Spine neoplasms.

In this article we discuss briefly definition, prevalence, clinical symptoms and imaging features, and illustrate the most frequent benign vertebral tumours including osteoid osteoma, osteoblastoma, aneurysmal bone cyst, Langerhans cell hystiocytosis, giant cell tumour, haemangioma, fibrous dysplasia and osteochondroma (Table I).

Osteoid osteoma Osteoid osteoma is a benign osteoblastic lesion of limited growth, characterized by a nidus which consists of highly vascularized connective tissue, trabeculae of osteoid and calcified bone (1, 2). The majority (75%) of the spinal osteoid osteomas is located in the posterior elements (pedicles, laminae and articular facets) (3). It can be found at any age but most cases occur in the first three decades (5-25 years). A dull aching pain is the main clinical symptom, worse at night. In more than 70% of patients the pain is relieved by salicylates (4). A spinal osteoid osteoma is frequently associated with a painful scoliosis of rapid onset, concave to

the site of the tumour, due to muscle spasm. In spinal osteoid osteomas, the nidus is rarely visible on plain film and sometimes only the reactive osteosclerosis is seen on plain film. CT is regarded as the technique to study the extent, size and location of the osteoid osteoma in the spine. On CT, the nidus appears as a welldefined, low density area with smooth borders and a mineralized centre, often surrounded by reactive sclerosis (Fig. 1B). On MRI the majority of the spinal osteoid osteomas present with bone marrow oedema and/or soft tissue oedema (Fig. 1A). When bone marrow oedema is seen the posterior elements, an osteoid osteoma should be considered and a nidus may be present. The nidus is charac-

B

A

Fig. 1. — Osteoid osteoma in the right lamina of L5 in a 14 year old-patient. A. On sagittal T2 weighted image bone oedema is seen in de pedicle and posterior elements (white arrow). Note the extensive soft tissue oedema in the paravertebral soft tissue (arrow). B. Axial CT image shows a hypodense area surrounded by sclerosis at the right lamina (arrow). Note the calcified nidus (small arrow).

From: Department of Radiology, UZ Gasthuisberg, Leuven, Belgium. Address for correspondence: Dr S. Pans, M.D., Dpt of Radiology, UZ Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.

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terized by low signal intensity on T1, intermediate to high on T2. Post contrast MRI shows an enhancement of the lesion. In a few cases a spinal osteoid osteoma presents only with reactive bone marrow oedema and a differential diagnosis with a stress fracture can be difficult. Osteoblastoma

B

A

An osteoblastoma is a benign osteoblastic bone tumour of progressive growth with a potential for osteoid production, local bone destruction and aggressiveness. These tumours occur in the second and third decade with a peak incidence between 7 and 20 years. The majority of the osteoblastomas involves the posterior vertebral elements, although extension in the vertebral body is common. The osteoblastoma is equally distributed in the spine. Clinical symptoms are boring localized (nocturnal) pain lasting in duration for between a few weeks and 2 years. Scoliosis due to muscle spasm occurs in 30-50% of the cases. Neurological symptoms may be related to cord compression. The typical osteoblastoma is larger than 1.5 to 2 cm (5) in diameter. Plain films demonstrate a well circumscribed and expansile destructive radiolucent bone lesion with a thin shell of peripheral new bone. The tumour can be partially or extensively calcified. A secondary aneurysmal bone cyst which can be responsible for a rapid destructive growth has been found in 10-16% of the cases (6). Computer tomography is by far the best imaging procedure, delineating the location of the tumour and its size (Fig. 2A). MRI shows a low to intermediate signal on T1-weighted images (Fig. 2C) and a high signal on T2 in bone marrow and soft tissues (Fig. 2B) with a strong enhancement after intravenous contrast (Fig. 2D) (7). Aneurysmal bone cyst

C

D

Fig. 2. — Osteoblastoma of vertebra L2 in a 20-year-old patient. A.CT demonstrates an expansile hypodense lesion with sclerotic margin involving the processus spinosus (arrow). B. Axial T2-weighted image the lesion shows a high signal intensity of the processus spinsosus. C. Axial T1-weighted image a low signal intensity is seen in the processus spinosus. Note the hypointense linear area demarcating the tumour from the normal bone marrow (arrow). D. Axial post-contrast T1-weighted image shows intense enhancement of the lesion (arrow).

An aneurysmal bone cyst (ABC) is a non neoplastic expansile and locally destructive highly vascular bone lesion characterized by channels or spaces filled with blood and separated by fibrous septa (8). Secondary ABC arises within other pre-existing bone tumours (GCT and osteoblastoma) (2). The tumour is most often diagnosed in the first two decades of life. The posterior elements are most affected. The clinical symptoms include pain and

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Table I. — Primary benign bone tumors of the spine : location of the tumor in the vertebra and distribution in the spine. Lesion Osteoid osteoma Osteoblastoma Osteochondroma

Location Posterior elements Posterior elements Posterior elements, processus spinosus

Aneurysmal bone cyst Vertebral body 40%

Posterior elements 60% Thoracic Lumbar

Haemangioma Giant cell tumour Langerhans cell hystiocytosis Fibrous dysplasia

Vertebral Vertebral Vertebral Vertebral

body body body body

Lumbar Cervical Thoracic Sacral Equally distributed Cervical Thoracic

Thoracic Lumbar Sacral Thoracic Lumbar

Fig. 3. — Aneurysmal bone cyst of L5 vertebra in a 15-yearold patient. A post-contrast computer tomography shows a lobulated multiseptated lesion involving the posterior elements, vertebral body extending in spinal canal. Note the fluid-fluid levels (arrows).

Fig. 4. — Aneurysmal bone cyst of L4 vertebra in a 13-yearold patient. An axial T2-weighted image shows a large multiseptated tumoral lesion with high signal intensity in the vertebral body and the right posterior elements extending in paraspinal muscles. Note also the fluid-fluid levels (arrows).

Fig. 5. — Langerhans cell histiocytosis of the vertebral body of L2 in a 9-year-old patient. Vertebra plana represents collapse of the vertebral body secondary to destruction of the bone by granulomatous lesion. Note the preservation of the intervertebral space.

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Fig. 6. — Fibrous dysplasia of vertebra L4 in a 62-year-old patient. Computer tomography shows a lesion in the vertebral body, partially lytic and ground glass appearance (arrow) with a thick sclerotic margin (arrow).

neurological symptoms due to pathological fractures and cord compression. Computer tomography shows an expansile lytic lesion in the posterior elements, often with extension to the vertebral body, soft tissue and adjacent vertebrae and ribs. Both CT and MRI show the cystic nature of the lesion with one or more fluid-fluid levels, due to haemorrhage and sedimentation (Fig. 3, 4). Langerhans cell histiocytosis A Langerhans cell granuloma (LGC) is a tumour-like lesion belonging to the group of the reticuloendothelioses. It is a rapidly growing lytic bone lesion leading to a variable collapse with preservation of the vertebral disc and it is often a self limited condition characterized by regeneration of the vertebral body. The thoracic spine is the most common site of this disease. A LCG occurs most often during childhood with a peak incidence between the ages of 5 and 10 years. The clinical manifestation includes local pain, tenderness, and soft tissue mass. Rarely, the patient may present neurological symptoms resulting from a vertebral collapse. A plain film remains an effective modality for the diagnosis and a typical vertebra

plana can be seen (Fig. 5). On CT, the lytic lesion and reactive sclerosis can be seen. Areas of marrow replacement with a low signal intensity on T1 and high signal intensity on T2 weighted images are seen on MRI (9). Sometimes an associated paravertebral mass or soft tissue oedema is shown on MRI. Giant cell tumor A giant cell tumour (GCT) is a locally aggressive neoplasm characterized by richly vascularized tissue containing stromal cells, osteoclastlike cells and multinucleated giant cells (10). The vast majority occurs in the sacrum. The GCT shows a predilection for the vertebral body (9). These tumours occur almost exclusively after skeletal maturity and patients are usually between the ages of 20 and 40 years. The symptoms most commonly reported include pain of increasing intensity with local swelling and tenderness sometimes resulting in a secondary kyphoscoliosis. The characteristic radiographic features of GCT on a plain film are those of a purely lytic destructive lesion. CT may outline the tumour extent and better delineate areas of cortical destruction and the welldefined margins. The lesion is radi-

Fig. 7. — Vertebral haemangioma of D6. Lateral plain radiograph demonstrates vertical striations of the haemangioma of D6.

olucent, frequently expansive without marginal sclerosis or mineralized matrix. On CT, the tumour has a soft tissue density. On MRI the tumour exhibits a low signal on T1 and a high signal on T2, sometimes with areas of necrosis and haemorrhage or cystic components or a het-

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A

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B

Fig. 8. — A. Vertebral haemangioma of D10. An axial CT image demonstrates a honeycomb pattern of the haemangioma of the vertebral body. B.Vertebral haemangioma of D5. Computer tomography shows the “polka dot” that indicates reinforced vertebral trabeculae (arrow) of the cancellous bone.

A Fig. 9. — Asymptomatic vertebral haemangioma of L4. A. CT scan shows predominantly fatty stroma within an osseous network. B. Sagittal T2-weighted MR image shows a low to intermediate signal intensity in the vertebral body of L4 (arrow). C. Sagittal T1-weighted image demonstrates a high signal in the vertebral body at the same level (arrow).

B

C

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A

B

Fig. 10. — Symptomatic vertebral haemangioma of L1. A. Sagittal T2-weighted MR image shows a high signal intensity in the vertebral body of L1. B. Sagittal T1-weighted image demonstrates a low signal intensity in the vertebral body at the same level.

erogeneous signal intensity both on T1 and T2 weighted images due to the presence of hemosiderine and collagen (10). Fluid levels in the tumour are considered to be a secondary ABC and can be seen in a pre-existing GCT both on MRI and CT (11). Fibrous dysplasia Fibrous dysplasia is a developmental disorder in which bone is replaced by islands of metaplastic woven bone in a background of spindle cell stroma. This disorder is considered as a developmental anomaly of the bone forming mesenchyme with an arrest of maturation at the woven bone stage. The disease may involve one bone (monostotic form, 85% of cases) or multiple bones (polyostotic form, 15% of cases) (12). In the monostotic form, spinal involvement is unusual. In the polyostotic disease, the lumbar spine is most involved with a predilection for the vertebral body. Fibrous dysplasia is in 75 to

85% of the cases diagnosed before the age of 30 years (13, 14). This entity may cause complaints of pain or can be asymptomatic. CT shows a round to elongated or even an expansile bone lesion with sclerotic margins caused by a complete thin to thick shell of reactive host bone reaction similar to lesion in the appendicular skeleton (Fig. 6) (13). It may be completely radiolucent or have a ground glass or even cystic appearance or exhibit an increased density depending on the amount of bone formation and calcifications (Fig. 6). The lesion of fibrous dysplasia shows a variety of appearances on MRI. Some lesions show a decreased signal on both T1 and T2 sequences, and some low signal on T1 but either mixed or high on T2 images. The sclerotic rim is imaged as a band of low signal intensity on the T1 and T2 both sequences. Haemangioma Haemangioma is a benign lesion composed of newly formed blood

vessels in a substratum of fatty marrow. The majority of the vertebral haemangiomas (VH) are cavernous haemangiomas (15). This lesion is often discovered incidentally on imaging performed for other reasons. VH are diagnosed at any age with a peak incidence after the fourth decade. The vertebral body of the thoracic spine is most involved although it may extend into the lamina. The majority of the VH are asymptomatic. Symptoms occur when the haemangioma expands in the direction of the spinal cord and causes cord compression. This neurological complication is most seen in the midthoracical spine. On plain film the lesion is characterized by vertical striation (Fig. 7). On CT scan, VH characteristically exhibit a pattern of multiple dots (often referred to as the polka dot appearance) (Fig. 8b) or a honey comb appearance according to the reinforced trabeculae (Fig. 8A). On MRI, the T1and T2-weighted images reveal areas of high signal intensity corresponding to the vascular compo-

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nent. Laredo et al. found that the stroma could have either fat or soft tissue attenuation or both (15). They found that fat attenuation values on CT and a high signal intensity on T1 weighted images were associated with a normal to a slightly increased vascularisation (Fig. 9a, b and c) while predominant soft tissue density content on CT and low signal intensity on T1-weighted images were associated with moderate to increased hypervascularisation (Fig. 10 A,B). The first pattern (high signal on T1 and intermediate signal on T2weighted sequence) was predominantly found in the asymptomatic VH while the soft tissue density and a lower signal on T1-weighted images occur mostly in the symptomatic group. Osteochondroma An osteochondroma rarely occurs in the spine and arises most often in the posterior elements with a predilection for the cervical spine (16). This entity is usually diagnosed in the second and third decade. The clinical symptoms include a palpable mass, neurological deficit due to myelopathy and rarely dysphagy. CT and MRI are the most effective investigations which show the extent. The most characteristic feature is the cartilage cap and the continuity of cortex and bone marrow of the osteochondroma and the posterior vertebral elements (16).

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lesions of bone and joints. Churchill Livingstone, Edinburgh, 1988, p 531546. Drevelgas A., Chourmouzi D., Boulogianni G.: Imaging of primary bone tumours of the spine. Eur Radiol, 2003, 13: 1859-1871. Murphey M.D., Smith W.S., Al-Assir et al.: MR imaging of giant cell tumour of bone: signal intensity characteristics with radiologic-pathologic corelation. Radiology, 1995, 197-195. Greenspan A.: Miscellaneous tumours and tumour like lesions. In: Greenspan A., Remagen W. Differential diagnosis of tumours and tumour-like lesions of bones and joints. Lippincott Raven, Philadephia, New-York, 1998, Chapter 7, p 315. Forest M.: Fibrous dysplasia. In: Forest M., Tomeno B., Vanel D. Orthopedic surgical pathology: diagnosis of tumours and pseudotumoral lesions of bone and joints. Churchill Livingstone, Edinburgh, 1988, p 595609. Mirra J.M.: Osseous tumours of intramedullary origin. In: J.M. Mirra: Bone tumours, clinical, radiologic, and pathologic correlations. Philadephia, London, Lea & Febiger, 1989, 191-226. Kransdorf M.J., Moser R.P., Gilkey F.W.: Fibrous dysplasia. Radiographics, 1990, 10: 519-537. Laredo J.D., Assouline E., Gelbert F. et al.: Vertebral hemangiomas: Fat content as a sign of aggressiveness. Radiology, 1990, 177: 476-472. Giuidici M.A., Moser R.P., Kransdorf M.J.: Cartilaginous bone tumours. Radiol Clin North Am, 1993, 31: 237-259.