Tests and Scans

There are several tests that your specialist may want to perform to confirm your diagnosis. It is important to understand how these tests work, why your specialist orders them and what the terminology means in plain language.

What is a CT scan (CAT scan)?

Computed tomography or CT scans have been with us for many years and are performed for many different disease entities. A CT scan is made up of ordinary X-rays (tomograms) that are fed into a computer (computed). They can be performed with a contrast medium (dye) that is injected into the patient’s veins. This contrast medium is usually iodine-based and circulates in the vascular system of the body. It is taken up in areas where there is increased blood flow such as areas of inflammation, infection or cancer. It is also used to examine patients’ arteries and veins.

A CT scan is the best test to evaluate the integrity, alignment and pathology of the vertebrae of your spine. It is, however, not as effective when evaluating the softer tissues such as discs, ligaments and nerves. MRI scans are the best for evaluating softer tissues. 

When undergoing a CT scan, you are placed in a large machine that is shaped like a doughnut. The table you are lying on will move forward and backward as the scan is being performed. Older-generation CT scanners could do only one slice (exposure) at a time; modern scanners do many cuts at the same time and are much faster.

 

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This is a picture of a CT scan machine. The large square part in the back with the round opening is where the X-rays are generated around the patient. This is called the gantry and can be inclined at angles to allow for better visualisation of the tissues of the body.

Modern scanners are called spiral CT scan machines and can currently take many images at a time. The table moves with an electric motor and allows the X-rays to pass over different tissues of the body as the patient passes through the gantry. CT scan machines generate a large amount of radiation and a CT scan should therefore only be performed for specific clinical indications.

 

What is an MRI (magnetic resonance imaging) scan?

This scan is performed with magnetism. A very large magnet aligns and realigns the molecules of the body and a computer then interprets the signals that are received and turns them into images. These images are really very clear and all the tissues in the body can be seen in great detail. As with CT scans, contrast can be used to give greater detail to blood vessels and also to indicate inflammation and cancer.

Since this technology works with a large magnet, patients who have certain metal implants cannot undergo this test.

When you undergo this test you will be placed in a machine that has a narrow tunnel and claustrophobic patients frequently need some form of sedation for this procedure. The machine makes quite a lot of metallic banging and clattering noises and you will usually be offered earphones to block out the noise and in some institutions soft music is piped through these.

Several types of pictures are taken. The most frequently used images are T1-weighted and T2-weighted scans. This is a description of the different ways that the scan manipulates the magnetic field of the tissue that is being examined. It is not important to know anything about the difference between these different types of MRI pictures that are taken.
 
It is, however, useful to know that there are several cuts (planes in which the body is examined) that are done. The most frequently used cuts are the sagittal images. These are images that are taken of your body from a side-on view. They are very useful in giving an overview of the spine in its entirety.
 
The images that are more important for depicting the finer detail of the pathology are the axial cuts or planes that are taken straight through the spine and are like slices taken of a sausage. The nerves that are leaving through the foramina are seen side-on and look like little worms as they leave the spinal canal. This way your specialist can see a lot of detail about the nerves and any compression of the nerves.

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This is a picture of an MRI scan machine. The section that generates the magnetic field is a tubular structure and patients are moved into this cave-like tube on the table, which has an electric motor. The room is devoid of loose metallic objects, as these would become airborne when the machine is activated because of the magnetic field, which is extremely powerful. Objects such as the magnetic strips on bank cards are rendered useless by the machine, so make sure that you leave these outside the room.

These machines tend to be quite noisy on the inside with all manner of tapping and banging noises. These are perfectly normal and you should not be alarmed by them. Some institutions will have earphones with music available to reduce the noise.

 


There are other cuts as well, such as coronal cuts where the body is viewed from front to back. Both coronal cuts and sagittal cuts are useful for revealing the alignment of the spine. The coronal cuts demonstrate scoliosis well. Scoliosis is where the spine is bent (has an abnormal curve) when viewed from the front. The normal curve of the spine can be evaluated on the sagittal views.

When the curve is more pronounced to the front, it is called kyphosis and when it is more curved towards the back, it is called lordosis. The coronal cuts are also useful for evaluating the nerve roots as they leave the spinal canal through the foramina and can demonstrate extraforaminal (outside of the foramen of the spinal canal) disc compression of the spinal nerves.

 

 What is a myelogram?

This test is performed with a contrast agent that is injected into the spinal canal with a technique called a lumbar puncture. The patient is placed on a table that can tilt and is tilted so that the contrast medium can run up and down the spinal canal. A CT scan of the spine is performed at the same time and images are then generated that can indicate whether there is an obstruction of the nerves of the spine. This procedure has mostly been replaced by MRI scans. It is still performed in cases where patients cannot undergo an MRI scan due to certain metal implants in the body and for other specific indications.

What is an electromyogram (EMG)?

This is a test of the electric conductivity of the nerves of the body. This can be done by measuring the transit time in nerves and measuring the response in the muscles that are supplied by these nerves. The measuring instrument is a small needle that is placed in the muscle and then connected to a machine that measures very small electric impulses. When your specialist receives a report that there is slowing in transit time in one of the nerves, this may indicate, among other things, that the nerve is being compressed by a lesion like a slipped disc.

 

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This is a picture of an EMG machine. It has several wires that are attached to electrodes inserted with small needles into the muscles of your arm or leg. It has a recording facility that measures the flow of electricity in your nerves to identify which of these nerves are being compromised.

What is a discogram?

In this test, contrast (dye) is injected with the help of fluoroscopy (mobile X-ray machine) directly into the intervertebral disc. The test has two elements. The first element is when your specialist attempts to mimic your pain by injecting fluid into your disc and therefore tries to place stress on the disc. This is a diagnostic test that can be very difficult to interpret. The other element is looking at the image on the fluoroscopy to see what the fibres of the disc look like and to see whether there is any damage.

What is a radio isotope scan?

In this test, radio isotopes are injected into a vein and allowed to circulate. A scan is then performed, which picks up radio isotope uptake. The radio isotopes are taken up in bony areas of the body where there is inflammation and will help your specialist decide where the main inflammation is located that causes your pain.

Terminology in the lumbar region for
CT scans and MRI scans

Spinal stenosis – This means that the spinal canal is narrowed. This is usually because the joints that are between the vertebrae, called the facet joints, have hypertrophied (become larger) secondarily to osteoarthrosis of these joints. At the same time the ligament that runs inside the spinal canal, the ligamentum flavum, has also hypertrophied and is pushing on the nerves. The third component that causes spinal stenosis is the pressure from discs that push into the spinal canal.

Facet joint hypertrophy – This is when the joints between the vertebrae become large and irregular. This is because the joints are damaged by arthritis (osteoarthritis).

Annular tear – This describes the condition where the intervertebral disc has early damage. The damage comprises of a tear in the annulus fibrosus (see the section Anatomy of the Spine). The tear causes different inflammatory substances to be released by the body and this can cause local back pain, referred pain and even radiculopathy (see the chapter Lumbar Slipped Disc).

Disc bulge – This describes the condition where the nucleus pulposus (see the section Anatomy of the Spine) starts to bulge through the damaged annular fibres.

Disc herniation/ disc extrusion – Both these terms mean that a portion of the nucleus pulposus has now extended outside of the confines of the annular fibres into the spinal canal (see the section Lumbar Slipped Disc).

Broad-based disc herniation – This is where the disc is damaged extensively and there is usually a decrease in the height of the disc and the disc looks a bit like a flat tyre with the whole or a large part of the nucleus projecting  beyond the confines of the annular fibres.

Foraminal disc herniation – In this case the disc herniation is on the side of the spinal canal where the nerve roots leave the spinal canal through the foramina. Even relatively small disc prolapses or hernias can cause a lot of pain or even weakness, as the space is very restricted in this area.

Extraforaminal disc compression – In this instance the nerve is compressed outside of the spinal canal and outside of the foramen as it leaves on its way to the leg. This is usually caused by a broad-based disc herniation.

Central disc herniation – This is where the disc herniation is in the middle of the spinal canal. Since this is a fairly large space, the disc herniation needs to be fairly large compared with a foraminal disc prolapse before symptoms occur. In some cases the spinal canal is already partly occluded by facet joint hypertrophy and compression from the ligament inside the spinal canal – the ligamentum flavum – and even small disc herniations can cause symptoms in these cases.

Thecal sac – This is the name given for the elongated membraneous tube that extends from the brain to the end of the spine in which the spinal cord and nerve roots run. It is made up of – and is continuous with – the membrane that covers the brain.

Flattening of the thecal sac – This is a description of the situation that occurs when a herniated (slipped or prolapsed) disc has extended so far into the spinal canal that it is pushing on the thecal sac.

Nerve root – This is the nerve root that leaves the thecal sac and exit the spine through the intervertebral foramen. Most of the exiting nerve roots can be seen side-on in the axial planes as well as the coronal planes and are seen end-on in the sagittal plane.

Foraminal stenosis – This is a narrowing of the foramen and the exiting nerve root can become compressed in the foramen by either a disc herniation or a hypertrophied facet joint or a combination of both.

Spondylolisthesis – This is the term that describes a slip of one vertebra on the vertebra directly below and is secondary to a weakness in the bone that supports the facet joints that keep the spine stable.

Spondylolysis – This is frequently the cause for spondylolisthesis and is the process where the bone supporting the facet joints is weak and fractures.

Spondylosis – This is spinal degeneration and is characterised by bone spurs  (osteophytes) that develop on the vertebral bodies and are usually asymptomatic, except if they compress nerves.

Synovial cyst – The joint space of the facet joints are lined with a membrane – the synovial membrane – which allows for free and easy movement of the joint. Sometimes, as the joints become damaged, this synovial membrane can bulge out and form a cyst. The cyst is filled with synovial fluid that is usually found in the joint space for lubrication. These are completely benign (harmless) lesions and should not be confused with cancerous lesions. They can, however, cause nerve compression and foraminal stenosis.
 
Tarlov cyst – This cyst is filled with spinal fluid and develop in the membrane that covers the nerve roots. If it is large, it can cause nerve compression and pain. Surgery for this benign lesion can be difficult. The diagnosis is made based on the fact that the cyst is in direct contact with a nerve root.

Arachnoid cyst – This is also a benign lesion and is formed from the inner layer of the covering of the spinal cord. It is usually asymptomatic and will only require surgery if it is very large and is causing symptoms secondary to nerve compression.

Cauda Equina – This term is Latin for horse’s (Equina) tail (Cauda). It describes the nerve roots that dangle down from where the spinal cord ends and looks like a horse's tail. The spinal cord ends at approximately the level of the first lumbar vertebra. When these nerve roots become compressed the resulting syndrome of pain, weakness  and paraesthesia (pins and needles) in the legs with associated bladder and bowel dysfunction is called Cauda Equina syndrome. This is a spinal emergency and requires immediate surgery.

Conus Medullaris (Conus) – This is the name given to the end of the spinal cord. It has a tapered conical shape and the nerve roots of the Cauda Equina exit from here. It is usually at the level of the first lumbar vertebra.

Filum Terminale (Filum) – This is the continuation of the conus medullaris and is the thin cord-like structure that extends down to the end of the spinal canal.

 

 
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This website is a patient resource compiled from information from leading spinal surgeons practicing in South Africa and complements the My Spine – Lumbar and My Spine – Cervical information booklets that you can obtain directly from your spinal specialist. You will find information about spinal conditions and treatment on this website.

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