Year : 2002 | Volume
: 12 | Issue : 3 | Page : 383--390
Pictarial essay : MR appearances of osseous spine tumors
BN Lakhkar, M Aggarwal, J Jose
Dept of Radio Diagnosis & Imaging, Kasturba Medical College, Manipal 576119, Karnataka, India
B N Lakhkar
Dept of Radio Diagnosis & Imaging, Kasturba Medical College, Manipal 576119, Karnataka
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Lakhkar B N, Aggarwal M, Jose J. Pictarial essay : MR appearances of osseous spine tumors.Indian J Radiol Imaging 2002;12:383-390
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Lakhkar B N, Aggarwal M, Jose J. Pictarial essay : MR appearances of osseous spine tumors. Indian J Radiol Imaging [serial online] 2002 [cited 2020 Sep 22 ];12:383-390
Available from: http://www.ijri.org/text.asp?2002/12/3/383/28489
MRI is an ideal investigation for evaluating tumors of osseous spine as it provides comprehensive information on the extent of vertebral body involvement, presence/absence of cord compression, extent of cord compression, nature of the lesion and extent of paravertebral disease in one examination. It also detects early marrow changes in both symptomatic and asymptomatic patients. For the patient, it is a quick, well tolerated procedure which can be repeated frequently. Moreover the relative danger of rapid neurologic deterioration following lumbar puncture in patient with complete spinal block is avoided in MRI.
Normal MR Appearances of Osseous Spine
The MR appearances of marrow in any particular bone reflects a combined effect of the relative fractions of red marrow, yellow marrow and trabecular bone. On T1 weighted images, yellow marrow exhibits a signal intensity that is roughly similar to that of subcutaneous fat. Normal red marrow is hypointense compared with yellow marrow, although its signal intensity is still greater than that of muscle. On T2 weighted images, the signal intensity of marrow remains greater than that of muscle, while signal differences between red and yellow marrow become less apparent 
In the spine, where the red marrow fraction remains relatively large throughout life, marrow signal intensity will be lower than in locations where little red marrow remains (distal appendicular skeleton). As the fraction volume of vertebral haematopoietic marrow decreases with age (while the fat fraction increases). T1 relaxation times for vertebral bodies decline. This decrease is most pronounced in the first 4 decades of life. Later, reduction in the mineral content of vertebral bodies (by approximately 40% in men and 55% in women by age 75) probably contributes to alteration in relaxation time. T2 relaxation time show a similar decline with age.
As conversion of red to yellow marrow occurs in the spine, yellow marrow may replace red marrow in a more focal (rather than diffuse) pattern, resulting in a spotty appearance (bright spots in T2 images) of the bone marrow. These areas of focal conversion to fat are more evident in the posterior elements and at the periphery of vertebral bodies and end plates. This phenomenon is presumed to be a reflection of diminished vascularity in these regions prompting the red to yellow marrow conversion. Focal fatty infiltration increases with age and has an overall prevalence approaching 60%.
Tumors of Osseous Spine
Daffner et al reported that areas of abnormal bone marrow showed low signal intensity. Zimmer et al concluded that MR imaging has a high sensitivity but does not enable distinction to be made between benign and malignant tumors on the basis of signal intensity alone. The prolonged T1 in malignant tumors is well known to be caused by the higher ratio of free water to fixed water than in normal tissues . Tumors of osseous spine include .
Malignant tumors: metastasis, multiple myeloma, chordoma, chondrosarcoma, Ewing's sarcoma, lymphoma, leukemia, osteosarcoma
Benign tumors: Haemangioma, Aneurysmal bone cyst, Giant cell tumor, Osteochondroma, Osteoblastoma, Osteoid osteoma, Eosinophilic gralunoma
Metastasis: It is the most common malignant spine tumor in adults. In adults, spine metastases commonly arise from breast, lung or prostate cancer. Other frequent primary tumors are lymphoma, melanoma, renal cancer, sarcoma and multiple myeloma. Spine metastases in children are mostly caused by Ewing's sarcoma and neuroblastoma, followed by osteogenic sarcoma, rhabdomyosarcoma. Hodgkin's disease, soft tissue sarcoma and germ cell tumors . The lower thoracic and lumbar spine are the most frequently affected sites. In adults, the initial site is in the vertebral body, typically the posterior aspect. Loss of contours of pedicles occurs late in metastatic process and accompanies extensive destruction of trabecular bone in body. Bone marrow infiltration precedes osseous destruction and hence MRI is highly sensitive in detecting early marrow infiltration.
Four patterns of vertebral metastases are seen on MRI - focal lytic, focal sclerotic, diffuse homogenous, diffuse inhomogenous . Lytic lesions are most common. They are hypointense on T1 and hyperintense on T2W images [Figure 1]. Sclerotic lesions are hypointense on T1 and T2WI. [Figure 2]. Diffuse homogenous pattern involve multiple vertebrae which are hypointense on T1 and hyperintense / heterogenous on T2W images [Figure 3]. Diffuse heterogenous pattern involve multiple vertebrae which show mixed signal intensities on T1 and T2W images [Figure 4].
In suspected metastatic spinal cord compression, conventional myelography has the disadvantage of providing indirect evidence of cord compression. In the presence of a complete block, the extent of disease can only be demonstrated by a second intrathecal injection above presumed upper extent of disease. The main disadvantage in CT myelography is that only axial images can be obtained and full examination of spinal cords is impractical. MRI is the method of choice for investigation of patients with suspected metastatic spinal cord compression  [Figure 5]. On post contrast, some lesions enhance avidly. Sclerotic metastasis may not enhance at all [Figure 6]. Contrast enhancement increases specificity of MRI for extradural masses and aids in directing needle biopsy  [Figure 5]. Metastatic vertebral collapse show hypointensity on T1W1 and hyperintensity on T2W1 [Figure 7]. Benign vertebral collapse show marrow signal intensity which is isointense with normal vertebrae on all sequences ,. STIR sequences offer an advantage as pathologic collapse produces an increase in signal intensity on T1 and T2W1 and the additive effect of these two parameters results in high lesion contrast .
Multiple myeloma: It is a monoclonal proliferation of malignant plasma cells that affects the bone marrow. The peak incidence is in 6th decade. The spine is the most common site and epidural involvement is frequent. Spinal MR imaging in patients with early myeloma may reveal marrow involvement in both symptomatic and asymptomatic patient .
Moulopoulos LA, Varma DG et al performed spinal MRI in 29 patients with newly diagnosed, untreated multiple myeloma . They found three MRI patterns-focal, diffuse involvement [Figure 8] and homogeneous pattern of tiny lesions on a background of normal marrow [Figure 9]. Short Tau inversion recovery (STIR) pulse sequence helps in highlighting these lesions well  [Figure 10]. On T2 weighted gradient echo images, vertebral bone marrow has lower signal intensity ensuring good contrast between the myelomatous deposits and the uninvolved bone marrow .
Chordoma: They originate from intra osseous notochordal remnants. They account for only 1% to 2% of primary malignant bone tumors; although chordoma is the most common primary sacral neoplasm. Peak incidence is in the 6th decade. Typically it arises in the midline of spinal column at any location from clivus to coccyx . Over 85% are found in the skull base/sacrum. Less than 15% occur in vertebral bodies. More than 1 vertebral segment is involved. .
On MRI, chordomas have inhomogeneous predominantly low signal intensity on T1W1 and equal / exceed CSF signal intensity on PD and T2W images. Enhancement following contrast varies from little to striking [Figure 11]. With MRI, the exact extent of tumor and necessary depth of biopsy can be predicted. In addition, knowledge of the position of tumor with respect to vasculature is helpful in choosing the proper surgical approach. MR images were also useful in establishing portals for radiation therapy. MRI may also prove useful in predicting prognosis. Chondroid chordomas have a significantly better prognosis for the patient than do typical chordomas. MRI may prove helpful in distinguishing between chondroid chordomas and typical chordomas especially in cases with a substantial cartilaginous component .
Chondrosarcoma: These are malignant tumors arising from cartilage. Two thirds are males. Peak is between 30-60 years of age. Chondrosarcomas can arise as primary tumors or as secondary tumors from a pre-existing cartilaginous lesion, especially osteochondromas or enchondromas.
On MRI, the signal intensity of chondrosarcoma is heterogeneous because of the mixture of soft tissue cartilage, calcification and haemorrhage. An associated soft tissue mass is defined well by MRI. Malignant lesions tend to have large soft tissue masses, irregular disorganised calcifications, destruction of bone and growth into adjacent soft tissues. The cortical margins may appear irregular and discontinuous with the parent bone. The thin cartilaginous cap typical of benign osteochondromas is not seen usually [Figure 12].
Ewing's sarcomas: Most of spinal Ewing's sarcoma represent metastatic tumor from another site of origin. Approximately 75% present before age 20 and 90% before age 30. Male predilection seen generally is not evident in vertebral column involvement. Most lesions are in the sacrum or less commonly in the lumbar spine. The extra-osseous component of the neoplasms may be quite extensive, especially in the sacrum. As local recurrences are common, MRI is the single best study for preoperative evaluation of tumor extent before both surgery and radiotherapy.
On MRI, an eroded vertebral body associated with a large para spinal soft tissue mass is typical. Ewing's sarcoma is hypo to isointense with muscle on T1 and hyperintense on T2W1 [Figure 13]. Hypointensity on T2WI after chemotherapy on follow up scans is a sign of tumor sterilization. Hyperintensity on contrast enhanced T1WI after chemotherapy on follow up scans is highly sensitive of viable tumor regions .
Lymphoma: Non-Hodgkin's lymphoma (NHL) accounts for more than 85% of cases of spine and epidural soft tissue involvement. It occurs in 40-60 years of age. There is a strong male predominance. NHL can cause bone destruction and hyperostosis. On MRI, Spinal lymphoma is typically hypointense on T1 and inhomogenously hyperintense on T2WI. Spinal cord compression occurs during the course of Non-Hodgkin's lymphoma in 0.1 to 6.5% of patients. Such involvement tends to develop late in the course of established disease when dissemination has occurred . Cord compression as the initial presenting feature of lymphoma is rare. Epidural extension is best delineated on MRI.
Leukaemia: It is the most common malignancy in children. It is also the 9th most common malignancy in adults . Acute lymphocytic leukaemia (ALL) represents 80% of all childhood leukaemia. Acute myeloid leukaemia (AML) accounts for 10% and remaining 10% is composed of less common histologic forms.
On MRI, there is homogenous decreased signal intensity on T1WI due to replacement of fatty marrow by leukemic cells. Compression deformities of vertebrae can also be seen. Foci of leukemic infiltration display increased signal intensity on T2WI. Gadolinium study may be useful because tumor infiltration enhances but marrow does not. MR relaxation time may be helpful in following progression of disease and in differentiating inactive disease from active disease . Other sarcomas like osteosarcoma and fibrosarcoma rarely invade spine.
Hemangioma: Vertebral hemangioma (VH) is the most common benign spinal neoplasm. Peak incidence is in fourth to sixth decades. Asymptomatic hemangiomas occur equally in both men and women but there is female predominance in symptomatic hemangiomas. About 60% of VHs are asymptomatic lesions which are discovered incidentally on imaging . Pain is the presenting complaint in 20% . VHs become symptomatic when pathologic compression fracture or epidural extension occurs. It involves part or all of vertebral body. Hemangiomas isolated to the neural arch is uncommon but 10-15% of vertebral body hemangiomas have concomitant involvement of the posterior elements. The lower thoracic and lumbar regions are the most common sites. Extradural hemangiomas occur secondarily as extensions of expanding intraosseous lesions.
On MRI, Vertebral haemangiomas are seen as round, well delineated vertebral body lesions which are high signal intensity on both T1 and T2 weighted sequences [Figure 14]. Some of them are predominantly low signal on T1 weighted images. These lesions often enhance following contrast administration. Histologically these lesions contain predominantly vascular rather than fatty stroma . It is often difficult to distinguish vertebral haemangiomas from focal fatty marrow replacement . VHs typically have high signal intensity on T1 and T2 WI, whereas fatty lesions become hypointense on standard T2 weighted images. However they are not of much importance as both are clinically indolent lesions in general.
Aneurysmal bone cyst (ABC): It is a benign non-neoplastic lesion of unknown etiology . Between 30% and 50% of ABCs are associated with a pre-existing osseous lesion such as chondroblastoma, giant cell tumor, osteoblastoma, non-ossifying fibroma or fibrous dysplasia.
MRI typically demonstrates a lobulated, multiseptated lesion with fluid-levels and blood degradation products [Figure 15]. Fluid levels are due to settling of degraded blood products within the cysts ,. On MRI, when fluid levels are present, dependent layer are of higher density than the supernatant. The dependent layer is hyperintense on T1WI due to T1 shortening by methemoglobin [Figure 16]. Fluid levels can also been in other lesions like telangiectatic osteosarcoma, giant cell tumor and chondroblastoma, but the thin, well-defined margins of an ABC should help to distinguish it from other lesions. Each cyst is surrounded by a thin, well-defined, low signal rim on both T1 and T2 weighted sequences.
The constellation of a) young patient b) an expansile lesion bordered by a thin low signal rim c) increasing signal with augmented T2 weighting and d) possibly a lobulated contour / fluid levels within it strongly suggests diagnosis of ABC.
Giant cell tumor: They are lytic, expansile locally aggressive primary benign bone tumors which extend to cortex but rarely transgress the periosteum. They account for only 3% to 7% of spine tumors. Most occur in sacrum. Pain and neurologic deficits are common presenting symptoms. Malignant transformation occur in approximately 10% of cases. Peak incidence is in third decade. Female predominance is seen in giant cell tumors involving vertebrae other than the sacrum.
On MRI, they are seen as a mixed signal, multi compartmental cystic mass that frequently contains blood degradation products. A hypo-intensive rim around the lesion on T2 WI suggests less aggressive nature of the tumour .
Osteochondroma: It is also known as osteocartilaginous exostosis. It arises through lateral displacement of epiphyseal growth cartilage. This results in formation of a bony excrescence with cartilage covered cortex and a medullary cavity contiguous with that of parent bone. Mean age for multiple spinal osteochondromas is 20 years. It most commonly involves spinous / transverse processes. These rarely cause neurologic symptoms .
On MRI, lesions show mixed signal intensity on both T1 and T2WI. However, it is very useful to delineate the cartilage cap. The thin cartilaginous cap less than 1 cm typical of benign osteochondromas is seen usually on MRI. Thus MRI helps to detect malignant transformation where the thin cartilaginous cap typical of benign osteochondromas is not seen usually [Figure 12]. Spinal cord compression, if any, is also well delineated on MRI .
Osteoblastoma: It is also known as giant osteoid osteoma. They are typically 2 cm or greater in size. Nearly 40% of osteoblastomas are located in spine.
Two thirds are confined to posterior elements. One third extend anteriorly to involve the vertebral body. These are nearly always solitary lesions. Pain is the most common presenting symptom seen in 80% of cases. Osteoblastomas often enlarge.
On MRI, they show intermediate signal intensity on T2WI with mixed high signal foci on T2WI and a wide band of reactive sclerosis.
Osteoid osteoma: It is a benign skeletal neoplasm which has a central nidus of interlacing osteoid and woven bone mixed with loose fibrovascular stroma. They are sharply demarcated from surrounding bone and are surrounded by varying degrees of osteosclerosis. The nidus rarely exceeds 1.5 to 2 cm in diameter. It occurs in patients between 10 and 20 years of age. Osteoid osteomas are rarely seen beyond 30 years of age. It occurs in the neural arch. Vertebral body lesions are unusual. The most commonly affected region is the lumbar spine. Approximately 10% of osteoid osteomas are found in the spine. Pain is the presenting symptom in over 95% of cases. This is relieved by salicylates in 75% of patients. Scoliosis is common in these patients.
On MRI, lesions show heterogenous signal intensity whereas nidus is low to intermediates in signal intensity on T1 and T2 weighted MR scans . Nidus of osteoid osteomas enhance following contrast administration.
Eosinophilic granuloma. It is a benign non-neoplastic disorder. Spine eosinophilic granuloma commonly occur between the age of 5 and 10 years. In the spine, it is seen as a lytic lesion without surrounding sclerosis. It is a classic cause of a single collapsed vertebral body the so-called vertebra plana. It is typically hyperintense on T2 weighted MR scans, although signal on T2WI is variable. Strong enhancement following contrast administration is seen 
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