Arachnoid

Function of the arachnoid membrane

The arachnoid membrane has several important functions for your dog's spinal cord and brain:

• It forms a gap between the dura mater and the pia mater, in which the cerebrospinal fluid (CSF) is located. This fluid serves as a shock absorber, lubricant and means of transportation for waste products.
• It contains numerous fine fibers called arachnoid trabeculae. These fibers connect the arachnoid to the pia mater and hold the spinal cord and brain in place.
• It forms protrusions at certain points, which are known as arachnoid cysts. These cysts can fill with CSF and serve as a reservoir if the pressure in the spinal canal becomes too high.

Diseases of the arachnoid membrane

The arachnoid can be affected by various diseases that can affect your dog's spinal cord and brain. The most common diseases include

• Arachnoiditis: an inflammation of the arachnoid, which can be caused by infection, trauma or autoimmune disease. The inflammation can lead to scarring, adhesion and thickening of the membrane, which impedes the flow of CSF and leads to increased pressure in the spinal canal. Symptoms may include pain, weakness, paralysis or seizures.
• Arachnoid cysts: An abnormal accumulation of CSF in an outpouching of the arachnoid membrane. The cysts may be congenital or acquired and vary in size and location. Most cysts are asymptomatic, but some can press on the spinal cord or brain and cause neurologic problems. Treatment may include monitoring, puncture or surgical removal.
• Subarachnoid hemorrhage: A hemorrhage into the gap between the arachnoid and the pia mater. The hemorrhage may be caused by trauma, tumor, aneurysm rupture, or clotting disorder. The hemorrhage can lead to an increase in intracranial pressure, which can be life-threatening. Symptoms may include headache, neck stiffness, loss of consciousness or death. Treatment may require emergency care, hemostasis or surgery.