Arachnoid Cyst

What is Arachnoid Cyst?

Arachnoid cysts are the most common type of brain cysts and are benign in nature. These cysts contain Cerebrospinal Fluid (CSF) and accumulate when it is not allowed to pass. The cyst arising in the skull is known as an intracranial arachnoid cyst and those seen in the spinal region is called spinal arachnoid cyst. If a child has the cyst, then it is considered to be congenital or present from birth and is known as a primary arachnoid cyst. Secondary arachnoid cysts develop in adults.


According to Galassi classification of middle cranial fossa arachnoid cyst, the cyst is divided into three categories-

Type 1

  • Free communication with CT cisternography
  • Small, spindle-shaped
  • Below the sphenoid ridge, limited to the anterior part of middle cranial fossa

Type 2

  • Temporal lobe displacement
  • Superior extent along Sylvian fissure
  • Slow communication with subarachnoid space

Type 3

  • Large in size, whole middle cranial fossa filled
  • Frontal & parietal lobe displacement
  • Very less communication with subarachnoid space
  • Resulting in midline shifting


The primary arachnoid cyst may be caused due to lack of development of the brain or spinal cord although its exact cause is unknown. Secondary arachnoid cyst can be present due to the following reasons-

  • Head or spinal injury
  • Complications during surgery
  • Tumor
  • Meningitis
  • Hemorrhage


Arachnoid cysts are asymptomatic and are identified by various signs and symptoms, but these symptoms depend entirely upon the location.

Around the head

  • Nausea
  • Headache
  • Vomiting
  • Hydrocephalus (excessive CSF) result in intracranial pressure

In spinal cord

  • Difficulty in controlling bowels or bladder
  • Pain in back
  • Weakness in muscles
  • Scoliosis
  • Tingling in arms or legs

Other parts of the body

  • Hearing disability
  • Seizures
  • Difficulty in walking and balancing
  • Dementia
  • Lethargy
  • Paralysis on one side (hemiparesis)


  • CT Scan
  • MRI


If the cyst does not show symptoms, then doctors recommend it to leave untreated. If the cyst causes irritation and problems, then surgical treatments include:


The doctors make a small incision near the cyst (craniotomy) and with the help of an endoscope allow the cerebrospinal fluid to drain to other parts of the body (a process known as fenestration).


Here, the doctors insert a shunt or a tube inside the cyst and allow the fluid to drain and absorb in any part of the body.


Some arachnoid cyst which shows symptoms and remains untreated can cause severe neurological damage. Bleeding from the cyst within the brain and spinal cord can dismantle the body system.



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