Subarachnoid Space: Definition, Structure, Function and Related Pathologies

It is the space located between the arachnoid membrane and the pia mater.

It is formed by delicate trabeculae of the connective tissue and intercommunication channels.

The subarachnoid space contains cerebrospinal fluid which slowly seeps through the trabeculae.

At certain points, the pia mater and arachnoid membrane are separated by wide intervals that communicate freely with each other, known as subarachnoid cisternae, in which the subarachnoid tissue is less abundant.

Structure and function

In the central nervous system, the subarachnoid space, also called the subarachnoid cavity, is the center of three membranes that cover the surface of the brain.

The strengthening of the rod-like fibers, known as fibrous trabeculae, crosses the subarachnoid space to connect the arachnoid membrane with the pia mater, and cerebrospinal fluid fills the cavity to flow around the brain.

The subarachnoid space also contains the blood vessels that supply the brain and spinal cord with blood and oxygen.

This cavity helps cushion the brain to protect it from injury, and continues up the spinal column along with the arachnoid membrane.

As part of the blood-brain barrier, the subarachnoid space helps protect the brain from many blood-borne infections and some neurotoxins .

However, most viruses and some bacteria can cross this barrier, and treatment for these infections is difficult as antibodies and medications often cannot cross the barrier to fight infection.

Inflammation and hypertension , as well as radiation exposure, appear to make the blood-brain barrier more permeable, and this can sometimes be helpful in treating brain infections.

Nanotechnology may hold the key to treating brain infections and other brain diseases in the future, as drugs can be developed with particles small enough to break through the barrier.

Related pathologies

Arachnoid cyst

They are usually found within the subarachnoid space and contain cerebrospinal fluid .

In the images, they are characterized by being well-circumscribed cysts, with an imperceptible wall, which displaces the adjacent structures and follows the pattern of the encephalo-lobe fluid.

They can also have a remodeling effect on adjacent bone.

Arachnoid cysts represent approximately 1% of all intracranial masses.

Although the vast majority are sporadic, they are seen more frequently in mucopolysaccharidosis (as are perivascular spaces). Most arachnoid cysts are small and asymptomatic.

When symptoms do occur, they are usually the result of a gradual enlargement that produces a mass effect.

This results in either direct neurological dysfunction or distortion of the normal encephalo-lobe fluid pathways, resulting in obstructive hydrocephalus.

Arachnoid cysts are believed to arise due to the congenital division of the arachnoid layer with the accumulation of encephalorachial fluid within this potential space.

The cyst wall is made up of flattened arachnoid cells that form a thin translucent membrane.

There is no solid component and no epithelial lining.

Spinal arachnoid cyst

Spinal arachnoid cysts are relatively rare and can be intradural (meningeal cyst type III) or extradural (meningeal cyst type IA).

Spinal arachnoid cysts can present at any age and there is no gender predilection.

Most spinal arachnoid cysts are asymptomatic and are discovered accidentally.

Clinical symptoms, if present, may include pain, weakness, numbness, and / or incontinence of the bladder and bowel. They can be congenital or acquired.

Secondary arachnoid cysts are usually due to trauma, bleeding, inflammation, surgery, or lumbar puncture.

Subarachnoid hemorrhage

Subarachnoid hemorrhage is one of the types of extra-axial intracranial hemorrhage and denotes the presence of blood within the subarachnoid space.

Patients tend to be middle-aged, generally under the age of 60.

Subarachnoid hemorrhage accounts for 3% of strokes and 5% of deaths from stroke.

Patients generally present with a headache. It is often associated with photophobia and meningism.

In a considerable number of patients, it is associated with collapse and loss of consciousness.

Focal neurological deficits often present at the same time as a headache or shortly thereafter.