Arachidonitis Imaging - Diagnostic techniques

Introduction:

The central nervous system chiefly comprises the brain and the spinal cord. It is a complex network that processes and regulates the entire functioning of the body. This intricate network is crucial for carrying out breathing, talking, eating, and walking. The spinal cord is an extension of the brain that relays the message, which is then processed in the brain. Hence it is vital to protect these structures from any external damage. The brain is enclosed in the bony skull, and the spinal column is shielded by small bones known as vertebrae. In addition, they are also protected by three membrane-like coverings known as meninges. The meninges seal the brain and spinal cord completely, thus guarding them in an enclosed environment. The three meninges are described below:

1. Dura Mater: It is the outermost layer closest to the skull. It is extremely tough.

2. Arachnoid Mater: It is the middle layer. It resembles a web-like structure and is filled with fluid (cerebrospinal fluid) that gives a cushioning effect to the brain.

3. Pia Mater: It is the innermost layer adjacent to the brain and spinal cord. It is a delicate thin membrane. It wraps closely around the brain and spinal cord, thus maintaining their structure.

These meninges support and protect the brain and spinal cord from any fatal trauma or injury.

What Is Arachnoiditis?

The brain and spinal cord, despite being shielded exclusively, may suffer certain conditions that may damage the organ or its associated structures. Arachnoiditis is a painful, inflammatory condition affecting the arachnoid membrane. Any infection, injury resulting in cord compression, or trauma can result in swelling and inflammation of the arachnoid membrane. It is considered a progressive disorder as the inflammation could result in the formation of scar tissues, thereby causing the spinal nerves to adhere to each other resulting in various symptoms such as burning pain, numbness or weakness, or tingling sensation in the lower extremities. Severe cases could interfere with the proper functioning of the bladder and bowel, and sexual functions or even result in paralysis of the lower extremities.

What Are the Causes of Arachnoiditis?

Arachnoiditis is an acquired condition that rarely is hereditary. The causes are mentioned below:

• Trauma to the Spine: Any direct injury to the spinal cord damaging the arachnoid membrane.

• Chemical Irritation: The contrast dye used in the myelogram test (a diagnostic test used to view the spinal cord) can cause chemical irritation surrounding the spinal cord. The preservative used in epidural steroid injections may also result in arachnoiditis.

• Infection: Bacterial, viral, or fungal infections can contribute to arachnoiditis.

• Compression of Spinal Nerves: Chronic degenerative spinal cord diseases or narrowing of the spinal column may result in inflammation of the arachnoid membrane.

• Surgical Complications: Postoperative complications from spinal surgical procedures may damage the spinal cord and its adjacent structures.

What Are the Symptoms of Arachnoiditis?

There are no consistent symptoms of arachnoiditis. It may vary in individuals and may depend on the severity or extent of the damage. It primarily affects the lower extremities, and a burning or stinging pain is its characteristic feature. Hence most patients in the early stage consider it to be joint or muscle pain and seek over-the-counter help to relieve the pain. Other symptoms that may occur as the disease progress are mentioned below:

• Numbness or weakness in the lower extremities.

• Tingling sensation.

• Muscle cramps or spasms.

• Urine dysfunction.

• Sexual dysfunction.

• Change in bowel movement.

• Altered vision or hearing.

• Uncontrollable body movements.

• Fatigue.

What Are the Types of Arachnoiditis?

Arachnoiditis can be classified into six types. They are:

1. Adhesive Arachnoiditis: This type is considered the most severe and progressive type and happens when the inflammation of the arachnoid membrane results in the spinal nerves adhering to each other.

2. Arachnoiditis Ossificans: This condition occurs when the arachnoid membrane gets converted to bone.

3. Cerebral Arachnoiditis: Inflammation of the arachnoid membrane surrounding the brain. This causes intense and persistent headaches.

4. Hereditary Arachnoiditis: This type is rare and is usually a result of genetic conditions.

5. Neoplastic Arachnoiditis: Arachnoiditis occurs due to cancer.

6. Optochiasmatic Arachnoiditis: This form of arachnoiditis occurs behind the crossover of the optic nerve, which may result in complete loss of vision.

What Is the Role of Imaging Modalities in the Diagnosis of Arachnoiditis?

Arachnoiditis is a rare entity compounded with a lack of awareness and vague symptoms; diagnosis is a challenge. Though arachnoiditis cannot be cured, imaging tests will help in a treatment plan that will help relieve the pain and other associated symptoms before they worsen. The various imaging tests used in the diagnosis of arachnoiditis are given below:

• Radiography: Radiography is not the imaging modality of choice for arachnoiditis as the spinal cord and nerve roots being soft tissues, cannot be visualized in x-rays. They can more prominently image the vertebral bone and other bony structures. However, x-rays can be used along with myelography tests. It is an invasive procedure where a contrast dye is injected into the spinal column through a long thin needle. Subsequently, x-rays can be used to capture images of the spinal column. Any inflammation would appear as a clumping of nerve roots (which would adhere to each other). It can also depict any blockage in the cerebrospinal fluid.

• Computed Tomography (CT): Due to the poor image resolution, CT is not much preferred for any spinal abnormalities unless MRI is contraindicated in the patients. In such patients, CT myelography is preferred over conventional CT. Abnormal or negligible filling of the dye material is suggestive of matted nerve roots and narrow spaces between the meningeal layers.

• Magnetic Resonance Imaging (MRI): MRI is the preferred tool to diagnose arachnoiditis. It is non-invasive, has excellent image resolution, and can take images in multiple planes, thus improving diagnostic accuracy. MRI can precisely diagnose cord abnormalities, adherence of the nerve roots, or the presence of inflammation. Narrowing of the meningeal spaces and accumulation of the cerebrospinal fluid due to obstruction within the spinal canal can also be accurately detected. The contrast enhancement in MRI may show certain patterns specific to arachnoiditis. They may occur as a smooth, linear layer, in a nodular pattern, or rarely in a diffuse pattern filling the intradural space entirely. However, the gadolinium-based contrast agents used with MRI imaging are known to be nephrotoxic; hence, they are contraindicated in patients with end-stage renal diseases.

• Myelography: Myelogram is a diagnostic test used to detect any abnormalities in the spinal cord. It is most accurate in imaging the spinal canal, spinal cord, nerve roots, and meningeal spaces. It can be conducted using x-rays, CT or MRI. CT myelography is indicated in patients in whom MRI is contraindicated, such as in patients with cardiac pacemakers or any foreign body implants. A contrast dye is injected into the spinal column and imaged using any imaging modalities. It is the gold standard test that can be used to diagnose arachnoiditis.

Conclusion:

Arachnoiditis is a progressively debilitating disorder with treatment that cannot cure the condition but provide only symptomatic relief. Surgical interventions are controversial as the prognosis is poor and somewhat unpredictable. However, spinal imaging may help diagnose the condition early, and prompt intervention may prevent the progression of the disease.