imaging of the benign neoplasms of the vertebrae

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introduction
As compared with the rest of the skeleton, benign neoplasms of the axial skeleton particularly vertebrae are very rare. In the literature, several articles have been published under individual neoplasms, but as a group of benign neoplasms the publications are scarce, particularly with regards to imaging. This article is an attempt to describe the imaging findings of benign neoplasms of the vertebrae and to arrive at a correct diagnosis prior to therapeutic management.
Benign neoplasms of the vertebrae include hemangioma, giant cell tumor, osteoid osteoma, osteoblastoma and osteochondroma (Table 1). However, tumors like conditions are many which include fibrous dysplasia, Paget's, eosinophilic granuloma and aneurysmal bone cyst ( Table 2). It is quite essential to identify tumor like lesions as not infrequently, the patients are subjected to unnecessary costly investigations, biopsies and even surgery.   [8]. Radiologicpathologic correlation of primary tumours of spine have been described by Murphey et al., [9]. Fluid-fluid level: a nonspecific finding in tumors of bone and soft tissue have been described by Tsai et al., [10]. Imaging of osteochondroma, its variants and complications with radiologicpathologic correlation have been detailed by Murphey et al., [11]. Vertebral tumors and pseudotumors have been discussed by Laredo et al., [12]. Vertebral chondroblastomas have been described by Ilaslan and Vialle et al., [13,14]. Vertebral hemangiomata have been elaborately described by Baudre et al., [15][16][17]. Giant cell tumours have been described by Kwon et al., [18]. Aneurysmal bone cysts have been discussed by Papagelopoulos et al., [19,20]. Langerhans' cell histiocytosis of the spine has been described by Yeom et al., [21]. Fibrous dysplasia localized to spine: a diagnostic dilemma has been published by Gogia et al., [22]. Radiologic spectrum of Paget disease of bone and its complications with pathologic correlation have been described by Smith et al., [23]. However, no single paper has been published regarding benign tumors of vertebrae and discussed the differential diagnosis.
This paper consists of the spectrum of benign tumors of the vertebral column and the imaging findings, keeping in view of the previous literature.
Osteoid osteoma (OO): 10% occur in the vertebrae; Painful scoliosis, radicular pain; Size extend to 2-10mm in diameter; Incidence 3-20 yrs; Male to female ration 2:1; Most of them are located in posterior elements; Giant osteoid osteoma in the spine is rare.
Imaging findings: Round lucent lesion with a nidus (Figure 1a,b,c); Central calcifications are common; CT is the best imaging methods (Figure 1d,e,f,g); Scintigraphy is sensitive but not specific; MRI is rarely necessary which shows low signal in T1 and high in T2. Calcium low signal in all images.
In the differential diagnosis of a dense / ivory pedicle, metastasis (    present and where the contra lateral pedicle is absent ( Figure 2c).

cartilaginous tumors
Cartilaginous tumors are very rare in the vertebrae: Osteochondroma may be seen either isolated or part of multiple heriditary osteochondromata; Generally arises from posterior elements; Usually small in size; Produce neurological symptoms when they grow into the spinal canal.

Imaging methods & findings
Plain film findings are characteristic resembling a cauliflower like growth. The cortex extends from the host bone along the osteochodroma. Cartilaginous calcifications may be seen at the cap ( Figure  4a,b,c,d).
CT is the best examination to show calcifications (Figure 4e,f,g,h); MRI is rarely necessary (Figure 4i).
Malignant transformation is rare.

(g) (h)
Chondromyxoid fibroma and chodnroblastoma of the vertebrae have been described very rarely.

Vertebral hemangioma
Vertebral hemangioma is also known as hamartoma.
One of the commonest benign tumours of the vertebral column. The vast majority of these are asymptomatic. Infrequently, these can turn symptomatic and cause neurological deficit CT is ideal investigation to show the expansion and residual trabeculae with Polka dot appearance ( Figure 5c,d,e,f,g,h), Angiography is rarely necessary. However, it shows hypervascularity (Figure 5i), scintigraphy is not specific, MRI shows low signal in T1 and high signal in T2 (Figure 5j,k,l).

giant cell tumor (gcT)
GCT of the spine is very rare except in the sacrum. The radiological principles applied in long bone giant cell tumors may be applied in the spine.

Imaging findings
Plain film -(a) Well defined large lytic lesion without any mineralized matrix, (b) The transiltional zone is narrow, (c) The average age is 33 years, (d) Primary malignant GCT is very rare in the spine.
CT defines the margins much better than seen in plain films (Figure 6a,b,c), CT and MRI are helpful in showing the aggressive nature of the lesion. Fluid-fluid level may or may not be present except when ABC is associated with GCT (Figure 6d,e,f), Scintigraphy is non-specific.

Tumoral lesions of the spine (Benign) Aneurysmal bone cyst (ABc)
Primary & secondary: Enostosis -Bone island; Primary ABC; 80% occur between the ages of 5 and 30; Secondary ABC occur according the age of the primary lesion; Posterior elements are involved in the vertebrae; Invariably extend to the body of the vertebra.

Primary aneurysmal bone cyst (ABc)
It is encountered in first three decades of life. It occurs equally in both males and females. Over half of them occur in long bones mainly in metaphysic. Vertebral bodies and posterior elements are a common site.

Imaging findings
Plain film findings: (a) Expansile lytic lesion eccentrically located (Figure 8a,b,c,d), (b) Narrow zone of transition, (c) No periosteal reaction, unless there is a microfracture, (d) Residual trabeculae maybe noted in the matrix, (e) May extend from the vertebral body to posterior elements.
CT and MRI show multiple fluid-fluid levels ( Figure  8efg); Scintigraphy is non specific; Angiography may not be helpful.

eosinophilic granuloma (eg -langerhan's histiocytosis X)
Langerhan's histiocytosis X includes Litter Siwe's disorder in infants, Hand Schuller disease in young adults and eosinophilc granuloma at any age. EG often involves the vertebral body than its appendages.

Fibrous dysplasia (FD)
FD is a developmental disorder of the bone with fibrous replacement of the bone in a bizarre fashion.

Imaging findings
Plain film findings: The normal architecture of the vertebral body is disturbed by fibrous tissue and new bone formation. This may extend to vertebral appendages. The matrix is often shows ground glass appearance. The entire morphology is disturbed with mixed lysis and sclerosis (Figure 10a,b,c).
CT findings: CT and MRI do not manifest any additional findings than are described on plain films (Figure 10d).

Figure10a:
Fibrous dysplasia of L2 with compression and ground glass appearance.

Paget's disease
Paget's disease is very rare but involvement of the vertebra is not uncommon. This can be monostotic but often is polyostotic. Complications may include fractures, compression on the spinal cord and rarely malignant transformation.

Imaging findings
Plain film may show lysis with compression fracture.
In the mixed phase the findings include both lysis and sclerosis (Figure 11a). It may involve more than one vertebra (Figure 11b). In the sclerotic phase, the vertebral body is dense and is called ivory vertebra (Figure 11c).   conclusion Benign neoplasms of the vertebrae are quite rare. However, the conventional radiological findings are quite characteristic of each entity. Advanced imaging is rarely necessary for confirming the diagnosis. Of all the neoplasms, hemangioma of the vertebra is most common benign neoplasm. Tumoral lesions of the vertebrae such as bone island, aneurysmal bone cyst, eosinophilic granuloma etc., are discussed with differentiating points from imaging point of view.