The Spine

Spinal tumors

 

Apart from metastases spinal tumors are rare. The radiological evaluation of spinal tumors has undergone a dramatic change during the last decade after the introduction of MRI. This has led to a new approach to therapy at some hospitals because of the significantly improved information about the intrinsic architecture of the tumor that can be obtained preoperatively. Improved surgical technique and equipment has also in creased the demand for more information about the nature and spread of the tumor.

Modalities

Plain films

Every examination should start with plain films. In some patients this might even be sufficient, for instance if metastases are found, further evaluation may be unnecessary. In other patients plain films are needed for determination of the affected level before surgery. Although scalloping of a vertebral body or thinning of a pedicle, caused by pressure from the tumor, might be seen in some patients, plain films are normal in the majority of patients with intraspinal tumors.

Isotope studies

Isotope studies are valuable, especially for screening of metastases. However, it is important to be aware of that the method is unspecific, gives poor anatomical information and sometimes yields false negative results in patients with osteolytic metastasis, myeloma and lymphoma.

Myelography

Myelography has been used for many decades for the diagnosis of spinal tumors but has several significant limitations. In patients with spinal block only the lower tumor border is visualized if the contrast has been introduced in the lumbar region. Myelography gives information only about the contour of the cord but does not give information about its composition and the area beyond the root-sleeves is not visualized. In patients with cord compression, the lumbar puncture frequently worsens the patient's neurological deficits. Therefore, myelography should be avoided if MRI is available. However, in some situations myelography is valuable, i.e. in cases with subarachnoid spread of small tumor nodules, for instance from a medulloblastoma in the posterior fossa. The high spatial resolution sometimes allows diagnosis of such small tumor nodules on nerve-roots and on the surface of the cord, which are not always visualized on MRI. If a tumor has been found on myelography and there is a suspicion of spread outside the spinal canal, CT should also be performed. In cases with myelographic block, CT can sometimes visualize also the cord above the myelographic block. CT following myelography is also valuable in differentiating between a tumor and syringohydromyelia. In syringohydromyelia diffusion of contrast will visualize the cyst. CT examination in such cases should be performed approximately six hours after myelography to allow for this diffusion.

Computed tomography (CT)

CT without contrast in the subarachnoid space is a poor method for the diagnosis of spinal tumors, because the cord is not regularly visualized. As previously described, the method is, however, of great value in combination with myelography.

Magnetic resonance imaging (MRI)

MRI is the method of choice for spinal tumors. The advantage of this modality is that all components of the area are visualized, i.e. the cord and its content, the subarachnoid space, the epidural space, the paraspinal region, and the bone and bone-marrow. In patients with multiple tumors causing spinal block, MRI will succeed where myelography fails to show the area between tumors. MRI can separate cystic from solid tumor components. This is of great importance in the preoperative evaluation of intramedullary tumors. Contrast enhancement with a gadolinium-containing contrast medium facilitates the diagnostic work-up and should always be used in patients with intramedullary tumors and is often helpful in intradural extramedullary tumors. In patients with metastases to the vertebral bodies, contrast enhancement usually does not give any further information and can even obscure tumors.

Pathology

Anatomical considerations

The spinal cord, which usually ends at the Ll-L2 level in adults, has a fusiform cervical enlargement caused by the supply to the large spinal nerves, supplying the upper limbs, and a lumbar enlargement corresponding to the innervation of the lower limbs. These enlargements should not be misinterpreted as tumors. From the conus medullaris, the cord continues downwards in the filum terminale, reaching down to the sacrum. Parallel to the filum terminale, the peripheral nerves descend downwards in the cauda equina. It is important to be aware of that there is a considerable difference between vertebral level and segmental level in the spinal cord, which becomes more pronounced in the caudal direction. In a peripheral injury with compression of the cauda equina, the patient will develop a flaccid pares is, often combined with pain. When there is a compression of the spinal cord, there will be a spastic paresis since the upper motor neuron is affected, while the peripheral neuron is intact. In cord compression from outside, the long fibres to the legs will first be affected. When the compression is increased, the clinical level will ascend and eventually correlate with the level of compression. If a patient has signs of incomplete cord damage, the injury should thus be looked for at the clinical level or higher. This difference between central and peripheral injury is of great practical importance in determining the affected level. Paresis of the legs and bladder with spasticity can thus not be explained by a lumbar disk herniation, and the lesion must be looked for at the level of the cord. In a patient with such symptoms, it is not correct to perform CT of the lumbar spine to search for a disk herniation. Patients with signs of cord compression must be examined within 24 hours to avoid permanent damage to the cord.

Spinal tumors are divided into intramedullary, intradural extramedullary and extradural tumors. Most tumors are found in one of these compartments, but some tumors, such as for instance neurinomas, might be seen in several compartments.

lntramedullary tumors

Intramedullary tumors are uncommon with an incidence of less than 10 cases/million/year. Ependymomas and astrocytomas constitute more than 90 % of intramedullary tumors. On imaging it is often difficult to differentiate between the two types. Usually there is a fusiform enlargement of the cord and frequently a cystic component is found both in the cranial and caudal direction of the solid central tumor (Fig. 36). In rare cases, somewhat more often in astrocytomas, the tumor is completely cystic. In such cases the tumor might be difficult to separate from a syringohydromyelia. It is important to visualize cysts and solid components, because treatment with ultrasound should be directed towards the solid component. Ependymomas are more frequent than astrocytomas in the lower spine, especially in the filum terminale. Astrocytomas are more frequent in the cervical and thoracic cord. Another difference is that ependymomas are more frequent in elderly patients. Tumors other than ependymomas and astrocytomas, are unusual in the spinal cord. A few spinal tumors are hemangioblastomas. This tumor is most frequent in the cerebellum, but can occasionally be found in the spinal cord and is characterized by a small solid richly vascularized tumor nodule, usually surrounded by a cystic component.

Intramedullary metastases can occasionally be found, usually in association with a known primary tumor. Intracranial medulloblastomas, ependymoma, and germinomas frequently cause tumor spread in the subarachnoid space, which can cause tumor nodules on the surface of the

	Figure 36. T1-weighted MRl showing cervical astrocytoma with central solid tumor and surrounding cystic components.
	Figure 37. T1-weighted MRl following gadolinium-DTPA injection. Slightly enhancing tumor nodules are seen on the surface of the spinal cord (arrows). The patient has an intracranial medulloblastoma.

Figure 38. Myelography and T1-weighted MRl of patient with syringohydromyelia. Myelography only shows an expansion of the cord, while MRI shows the cyst.

spinal cord (Fig. 37), nerve roots and, in some rare cases, to the central canal of the cord. Embryonal tumors are most frequently seen in the conus region and are often accompanied by dysraphism. Syringohydromyelia is not a tumor but might be misinterpreted as a neoplastic lesion because it causes an enlargement of the spinal cord. The lesion consists of a cyst filled with CSF. Theoretically, hydromyelia is a cystic enlargement of the central canal, lined with endothelium, while syringomyelia is an eccentric or central cord cavity, lined by glial cells. However, in practice it is often difficult to separate them and therefore the term

a	b	c
Figure 39.MRI showing cervical ependymoma. a) T1-weighted image shows fusiform enlargement with central low signal. b) T2-weighted image shows high signal from tumor and also surrounding edema which cannot be separated. c) TI-weighted image following gadolinium-DTP A injection shows enhancement of the tumor but not of the surrounding edema.

"syringohydromyelia" is sometimes used (Fig. 38). Syringomyelia is frequently associated with congenital malformations, especially the Chiari 2-malformation.

Plain films are most often normal in intramedullary tumors, but occasionally increased distance between the pedicles, thinning of the pedicles or scalloping of the vertebral body are seen. At myelography a fusiform widening of the cord is found, sometimes in combination with myelographic block. For differentiation of tumor and syringohydromyelia, CT should be performed approximately six hours after myelography, as previously described.

MRI is superior to all other methods in the diagnosis of intramedullary tumors, and a minimum requirement is T1- and T2-weighted images in the sagittal projection, followed by T1-weighted images after intravenous contrast enhancement with a gadolinium-containing contrast medium. This is extremely important, because solid tumor components usually enhance. Occasionally these components are seen without contrast, but if they are surrounded by cysts containing protein, their differentiation may be very difficult. Edema is often difficult to separate from tumor components without contrast enhancement (Fig. 39). In hemangioblastoma contrast enhancement is essential for the visualization of the vascularized tumor nodule. Embryological tumors often have a characteristic appearance on MRI because of fat content and calcifications. Hemorrhage in intramedullary tumors, which is especially common in malignant melanoma metastases, is visualized as an area of increased signal on T1-weighted images.

lntradural extramedullary tumors

Intradural extramedullary tumors are more frequent than intramedullary tumors but are still relatively rare. The dominating tumors are meningioma and neurinoma with an approximately even distribution between the two types. The tumors are usually rounded and displace and compress the spinal cord. Meningiomas are almost always completely intradural and are more frequent in the thoracic spine. Meningiomas are more frequent in middle-aged and elderly and more common in women than in men. Neurinomas are evenly distributed in the spinal canal, are found at all ages, and have an even sex distribution. The tumor is usually found on the dorsal root, and therefore the spinal cord is displaced in the anterior and lateral direction. Sometimes there is an extradural component which can continue in the root-canal as a dumb-bell tumor (Fig. 40). In neurofibromatosis there are often multiple neurinomas at many levels in the spinal canal. These patients also have an increased incidence of spinal meningioma and in some patients bone dysplasia and meningoceles are found which should not be misinterpreted as tumors. Other tumors are uncommon in this compartment. Occasionally,

a	b	c	d
Figure 40.Cervical neurinoma. a) T1-weighted image before contrast shows tumor with signal isointense with cord, with central low signal area indicating necrosis. b, c d) T1-weighted images after contrast show marked enhancement, displacement of cord and growth in the neural foramen.

Figure 41. Enlarged neural foramen due to dumb-bell neurinoma.

 

Figure 42. Myelography shows lower border of neurinoma causing myelographic block.

	Figure 43.T1- weighted MRl shows meningioma in the anterior spinal canal with broad attachment to the dura. The cord is compressed and displaced posteriorly. The signal pattern is similar to the cord.
	Figure 44.Myelography and T1-weighted MRl of neurinoma in the dural sac at the level of sacrum. Myelography shows only the upper pole of the tumor, while MRI shows the complete tumor (arrows). The low signal in the centre of the tumor indicates necrosis, which is a frequent finding in large neurinomas.

metastatic spread is seen from intracranial medulloblastoma, ependymoma and germinoma, as previously described.
Plain films occasionally show enlargement of a neural foramen, indicating a dumb-bell neurinoma (Fig. 41). Otherwise, plain films are usually normal. Myelography easily visualizes both meningioma and neurinorna, but should always be combined with CT for visualization of possible extradural tumor component. The typical finding is a rounded contour, representing the border of a tumor (Fig. 42), an enlarged subarachnoid space, and displaced cord. In cases with myelographic block,

a	b	c
Figure 45. Intradural paraganglioma. This tumor is extremely rare in this location and has the appearance of a meningioma. a) TI-weighted image shows tumor which cannot be separated from cord. b) Following intravenous gadolinium-DTPA injection, tumor and cord can be separated. c) T2-weighted image.

CT frequently is capable of visualizing the upper border of a tumor, since some contrast usually passes the blocked area, even if it is not visualized on myelography. In cases with suspected spread of intracranial tumor with small tumor nodules, myelography is an excellent method because of the high spatial resolution. Otherwise, MRI is the main method for diagnosis. On T1-weighted images both meningioma and neurinoma have a signal pattern like the spinal cord but are usually easy to detect, since they have a high contrast relative to the low signal CSF (Fig. 43, 44). Neurinoma usually has a high signal on T2-weighted images - higher than meningioma, which has a more fibrous tissue, giving lower signal. Both types of tumor usually enhance, following injection of a gadolinium-containing contrast medium, which makes the tumors easy to detect and differentiate from the cord. Contrast enhancement is especially valuable when small tumors are looked for, as for instance in the subarachnoid spread of a medulloblastoma and also for differentiation of tumor from cord (Fig. 45).

a	Figure 46.MRI of paraspinal lymphoma. a) Sagittal T1-weighted image shows invasion of a tumor of the bone marrow and growth in the neural foramen at two levels (arrows). b) Axial T1-weighted view shows paraspinal tumor component (arrows) replacing the normal fat, and growth through the neural foramen.
b

Figure 47. T1-weighted image shows chordoma in the sacrum.

Extradural tumors

The most common spinal tumors are extradural, and among these vertebral metastases are the largest single group. The most frequent primary tumors are breast- and lung cancer and cancer of the prostatic gland. In some rare cases extradural tumors are found only in the extradural space without connection to the bone. This is especially common in lymphoma which has a tendency to spread from a paraspinal location through the neural foramen into the epidural space (Fig. 46). In the pediatric age group, neuroblastoma has a similar growth pattern. Primary bone tumors are unusual. Hemangiomas are usually asymptomatic and have a characteristic appearance on plain films with thickened bony trabeculae, leading to a palisade pattern. Chordomas are unusual and are most often found in the sacrum (Fig. 47). Tumors involving the bone-marrow, such as myeloma and lymphoma, are frequently localized to the spine and are sometimes associated with neurological symptoms caused by compression of nervous tissue. As previously mentioned, neurinoma sometimes has an extradural spread, which is indicated by a widening of the intervertebral foramen.

Plain films will usually reveal the malignant extradural tumors because of bone destruction. Plain films are, however, not sufficient when the

Figure 48. Metastasis from sarcoma in the thigh. The tumor displaces and compresses the cord. Note that there is also metastasis in the vertebral body further down.

patient has neurological symptoms, because it is important also to visualize the degree of involvement of nervous structures, paravertebral growth, etc. Bone scintigraphy is excellent for the screening of metastases in patients without neurological symptoms. Myelography has been used for many decades for the evaluation of cord compression in patients with metastasis. It is usually easy to visualize the level of compression, but when there is a block it is difficult to show the whole extent of a tumor and also whether there are multiple tumors or not. As for other spinal tumors, MRI, if available, is the method of choice. Usually T1-weighted images are sufficient because this sequence will visualize the level of compression and degree of paraspinal growth. It is also easy to visualize metastases at multiple levels (Fig. 48). Tumor growth in the bone marrow is easily visualized because the fat, normally giving a high signal on T1-weighted images, will be replaced by low signal caused by the invasion of malignant cells. T2-weighted images are usually not necessary and the metastases are often less well visualized on this sequence. Contrast enhancement is usually not necessary and will actually obscure the tumors growing in the fatty bone-marrow, because the enhancing tumor will then get a signal similar to fat on T1-weighted images, unless fat suppression techniques have been used. MRI is very sensitive for detecting the infiltration of bone-marrow, and this is particularly important in those tumors, such as lymphomas, which have a permeative growth pattern in bone. (They often escape detection on plain films and also when CT is used.) Isotope studies can also be negative in such cases.

 

Stig Holtås, Maximilian F. Reiser and Axel Stäbler