Spinal malalignment - Scoliosis and Listhesis
Scoliosis refers to abnormal curvature of the spine. Scoliosis may result from various structural causes, although the most common form of scoliosis is called idiopathic scoliosis, which has no known cause. Scoliosis may also occur with congenital malformations of the spine or may be due to spinal degeneration.
Scoliosis can occur in the mediolateral or in the anteroposterior direction. In the mediolateral direction, the curvature is rightward or leftward and is named according to the direction of the convexity of the curve. In the anteroposterior direction, the curvature is referred to as kyphosis (increased posterior convexity of the spine) or lordosis (increased posterior concavity of the spine). Most scoliosis also has a rotational component.
Conventional radiographs (X-rays) are an excellent means for assessing scoliosis. Examinations at HSS are performed utilizing one long continuous image of the entire spine, usually obtained with the patient standing. Utilizing this technique, the angles of the spinal curvature can be measured and the grade of the deformity can be determined. These measurements can be used to predict the progression of scoliosis and to determine if the spinal alignment changes over time. These measurements are also critical in assessing the impact of therapeutic interventions to correct the scoliosis and aid in the assessment of the progression or resolution of the spinal curvature. These measurements can be performed in all age groups, including children with congenital anomalies. With the development of new imaging techniques the radiation dosage to the patient has been significantly reduced for the evaluation of scoliosis. Decreasing radiation dosage is extremely important due to the young age of many patients with scoliosis and the need for serial exams.
Many surgeons request stress or lateral bending views of the spine to provide additional prognostic information for preoperative planning. In post-surgical patients, conventional radiographs also serve as a means to reevaluate the spinal curvature and the integrity of spinal instrumentation.
CT (computed tomography) and MRI (magnetic resonance imaging) can provide additional information in patients with scoliosis. MRI may be indicated to assess the brain and spinal cord in patients with certain types of scoliosis or congenital anomalies. CT may be indicated to assess vertebral body shape, particularly in preoperative planning where the size of the vertebral pedicles must be determined. In rare cases, scoliosis may be the result of a syndrome such as neurofibromatosis or a tumor such as an osteoid osteoma. In these cases, cross sectional imaging (CT and MRI) is invaluable for the initial diagnosis and treatment of these conditions. Scoliosis produces abnormal forces on the spine that may lead to early degenerative changes of the spine. In addition, patients that have undergone a spinal fusion to correct their scoliosis may be prone to spinal degeneration at the level adjacent to where the spinal fusion ends. CT and MRI can assess these degenerative changes.
Listhesis refers to the alignment of two adjacent vertebral bodies in the spine. Anterior displacement of the cephalad vertebral body with respect to the caudad vertebral body is called anterolisthesis and posterior displacement of the cephalad vertebral body with respect to the caudad vertebral body is called retrolisthesis. A lateral displacement of the cephalad vertebral body with respect to the caudad vertebral body is called a right or left lateral listhesis. Abnormal spinal alignment may lead to asymmetric loads on the spine and spine degeneration. Erect radiographs of the spine are optimal to evaluate spinal alignment (also referred to as spinal balance).
CT and MRI can provide additional information as to the etiology and effects of the listhesis. An anterolisthesis is typically the result of facet arthritis or spondylolysis (stress fractures of the pars interarticularis). With CT and MRI, it is possible to assess the dimensions of the central canal and neural foramina and the effects of bony proliferation on the thecal sac and the nerve roots. If surgery is needed to stabilize the spine and to prevent progression of the spinal deformity, both CT and MRI examinations are utilized to plan appropriate treatment. In certain instances, CT myelography, which is a CT scan performed after iodinated contrast is administered into the spinal canal via a spinal needle, may be indicated to better visualize the spinal cord and spinal nerve roots within the thecal sac.
Osteoporosis is a structural weakening of bone, most commonly affecting postmenopausal females, and has important implications in the spine. Osteoporotic bone is more susceptible to a fracture, which may occur with even minor trauma. Fractured or collapsed vertebrae may be very painful and may lead to spinal stenosis and compression of the neural elements. Fractured vertebrae may also result in spinal malalignment which may exacerbate a patient's pain.
Most vertebral compression fractures involve the vertebral body and may result in an anterior wedge deformity. Occasionally, a fracture may involve the posterior cortex of the vertebral body. If the posterior cortex of the vertebral body is displaced into the central spinal canal, the bony deformity may result in spinal stenosis and compression of the neural elements. In the thoracic spine, a fractured vertebral body may result in spinal cord compression. The thoracic spine is the most common location for osteoporotic fractures, but lumbar fractures are not infrequent.
Conventional radiographs should be the initial imaging exam for the evaluation of spinal fractures. Radiographs provide accurate information as to the number of vertebral bodies involved and the degree of the vertebral body compression. Radiographs also provide means to assess spinal alignment after a fracture has occurred. Asymptomatic compression fractures that are detected incidentally when imaging the spine for other medical conditions may be followed for progression in order to determine if a spinal deformity develops. Due to decreased bone density, the evaluation of osteoporotic bones may be difficult with standard radiographs; other imaging modalities may be useful to determine if a fracture is present.
CT is the optimal exam to determine the extent of a fracture and the position of all the fracture fragments. CT is also an excellent means to confirm that the facture is due to osteoporotic weakened bone and not to weakened bone from tumor infiltration. With its multiplanar capabilities (the ability to reconstruct images of the spine in alternative planes from the initially acquired axial images), CT is the optimal test to evaluate spinal alignment after a fracture and to detect subtle non-displaced fractures.
MRI is particularly useful in the assessment of the soft tissues which may be injured at the time of a fracture. MRI is the optimum means to detect a disc herniation that may have occurred at the time of a fracture. MRI also provides useful information as to whether a fracture is acute or chronic. This is determined by the presence of edema in the fractured vertebra. The age of a fracture may determine whether a vertebroplasty or a kyphoplasty is performed to alleviate a patient's symptoms. Vertebroplasty and kyphoplasty are recent techniques for the treatment of compression fractures whereby a type of cement is percutaneously injected into the vertebral bodies to relieve symptoms, restore vertebral body strength and possibly increase vertebral body height. These procedures are most successful when the compression fracture is in the acute or subacute stage. MRI may also be of benefit to determine if a fracture is due to osteoporosis (called a benign fracture) or to a tumor (called a malignant fracture). PET (positron emission tomography) may also help distinguish between a benign and malignant fracture.
Fractures of the spine are more common in the cervical and thoracic spine than in the lumbar spine. Seatbelt injuries or Chance fractures typically occur in the upper lumbar spine. Conventional radiographs are used as a screening exam. With severe trauma, particularly when a patient is unconscious, a CT exam of the entire spine is typically performed to determine if a spine fracture is present. MRI is utilized to evaluate the integrity of the disc and spinal ligaments and the condition of the spinal cord and neural elements. MRI may detect unsuspected vertebral fractures by detecting edema in the fractured vertebral body. MRI is also the optimal exam to assess the ligaments and soft tissue which may affect spinal stability.
The elderly age group that is prone to osteoporotic compression fractures is also more likely to present with back pain due to the development of spinal tumors and vertebral body metastases (tumor that has originated from another site in the body and has spread to the spine). Metastases may replace healthy bone, weakening the vertebral bodies, and increasing the risk of fracture. MRI may help to distinguish a benign from a malignant fracture by detecting the replacement of normal marrow by abnormal tumor or by detecting a soft tissue mass that is associated with a bone tumor. Tumors of the spinal vertebrae may result in pain due to vertebral fractures or to the displacement or compression of the neural elements by tumor expansion. The most common primary benign bone tumor of the spine is a hemangioma which rarely causes symptoms. Other less common primary benign tumors, particularly seen in younger patients, include osteoid osteomas and osteoblastomas. Osteoid osteomas may cause a painful scoliosis. The most common primary malignant tumor of the spine is the chordoma. Chordomas are rare and are typically midline tumors that occur most commonly in the sacrum and clivus. The most common non-primary malignancies in the spine are metastatic disease and multiple myeloma.
Conventional radiographs are an insensitive means of detecting metastatic disease, particularly for lytic (destructive) lesions. MRI is the most sensitive exam to detect metastatic disease or multiple myeloma. Radionuclide bone scans are employed to determine if a tumor involves other regions of the skeleton. PET scans are used to determine if a bone lesion is due to a malignant process. If tissue diagnosis is required, biopsy can be performed utilizing imaging (usually CT) guidance.
Except for hemangiomas, which are benign, most spine tumors will require further evaluation with either CT or MRI. Additional imaging will be needed to determine the etiology and extent of a tumor, its effect on the neural elements, and to plan the optimal therapy to treat the tumor. After the beginning of the therapy for a tumor, follow-up MRI exams are utilized to determine the effects of the tumor treatment.
Primary tumors within the spinal canal are often neurogenic in origin and include neurofibromas and ependymomas. Other tumors, such as meningiomas, may arise from other structures in the spinal canal. The space-occupying effects of these tumors may be detected with conventional radiographs if the tumors cause deformities of the vertebrae, e.g., widening of a neural foramen, destruction of a pedicle or posterior scalloping of a vertebral body. In most cases, CT and MRI will be required to determine if a tumor is present.
Spinal infections are relatively uncommon. In the past, one of the most common spinal infections was tuberculosis, which frequently led to spinal deformities. Cases of tuberculous spondylitis still occur, but with much lower frequency. Currently the most common organism causing spinal infection is Staphylococcus aureus. Spinal infections may occur in healthy patients or in patients who have undergone spinal surgery. Immunocompromised patients may present with spinal infections caused by more atypical organisms. Sources of spinal infection include heart valves, genitourinary infections and dental abscesses. Spinal infections may also result as a complication of spinal surgery.
Conventional radiographs are insensitive for detecting early infection. Radiographs become abnormal when an infection leads to significant bone or endplate destruction. A MRI exam is the best exam to evaluate a patient with a suspected spinal infection. MRI may detect changes within the disc, vertebral body or paraspinal soft tissues that indicate that an infection is present. Intravenous gadolinium may be administered in certain cases to more accurately evaluate the extent of infection. If the diagnosis of an infection is uncertain, or if the specific organism causing the infection is unknown, a biopsy of the vertebral body, disc or adjacent soft tissues can be performed utilizing CT guidance.
Sacroiliitis and the Seronegative Spondyloarthropathies
Sacroiliitis (arthritis of the sacroiliac joints) of various etiologies may result in low back pain. The sacroiliac (SI) joints may be involved with degenerative arthritis, an inflammatory arthritis or rarely by an infectious process. Certain types of inflammatory arthritides, including ankylosing spondylitis, psoriasis, reactive arthritis and arthritis associated with inflammatory bowel disease, have a predilection for involvement of the SI joints.
The SI joints can be evaluated on conventional radiographs, typically utilizing specialized angled and oblique views. In early stages of inflammatory disease, erosions and sclerosis may be detected. With some of the systemic inflammatory conditions, including ankylosing spondylitis, end-stage disease may result in fusion of the SI joints. In addition to involving the SI joints the inflammatory arthritides may affect the spine with the development of bony erosions or syndesmophytes which are thin bony excrescences that bridge the vertebral bodies. The Inflammatory arthritides may also affect the spine facet joints and the spinous processes.
MRI is more sensitive than radiographs for early sacroiliitis and to determine if the sacroiliitis is associated with acute clinical symptoms. A CT usually does not provide additional information over MRI, but CT-guidance can be used to access the SI joint with a needle, for either therapeutic cortisone injection or aspiration if infection is suspected.
The Postoperative Patient
MRI is the optimal exam to evaluate most patients presenting with back or leg pain after spinal surgery. In addition to the routine sequences, gadolinium may be administered to help differentiate a disc herniation from scar tissue. In some postoperative patients, imaging is more difficult due to the presence of surgical instrumentation (hardware) which generates scan artifacts. At HSS, MRI protocols have been optimized to minimize the scan artifacts from surgical hardware, improving the diagnostic quality of the MRI exam. With the advent of multi-detector CT scans, detailed imaging with reduction of metal artifact has also become possible. CT is the gold standard to assess the integrity of a spine fusion. As stated earlier, CT myelography, performed by injecting radiopaque contrast into the spinal canal, may provide additional information.
Imaging guided injection of an anesthetic agent, corticosteroid, or both can be performed for diagnostic and therapeutic purposes. These injections are made into the epidural space (the space which surrounds the thecal sac), into the neural foramen or lateral to a neural foramen around a nerve root. The purpose of the injection is to block the inflammation that may be associated with a disc herniation or spinal stenosis and which may be the cause of a patient's symptoms. A needle is positioned using fluoroscopic or CT guidance and the needle placement is confirmed with the injection of a small amount of radio-opaque contrast.
Imaging guided injection of an anesthetic agent, corticosteroid, or both can be performed into a painful facet joint for diagnostic and therapeutic purposes. The anti-inflammatory effects of corticosteroids can provide long-term relief with little systemic effects outside the site of injection. Synovial cysts arising from a degenerated facet joint, also called "facet joint cysts", may compress a neural structure and be a source of pain. The cysts can be aspirated and injected under fluoroscopy or CT guidance.
Discography, or injection of radio-opaque contrast into the nucleus of the intervertebral disc, provides diagnostic information about the integrity of the disc and whether it is the source of a patient's symptoms. Discography is performed under fluoroscopic-guidance, followed by a limited CT scan through that disc level to better characterize the morphology of the disc in question.
Reviewed by Yoshimi Endo, MD