You are here

Arachnoid Cyst F090

Last amended 
6 April 2020
Current RMA Instruments
Changes from previous Instruments

SOP Bulletin 184

ICD coding
  • ICD-9-CM: Brain: 348.0; Spinal cord: 349.2
  • ICD-10-AM: Brain: Congenital Q04.60; Acquired G93.0; Spinal cord: G96.1.
Brief description

A cyst is a pathological fluid filled cavity surrounded by a membrane. An arachnoid cyst is located in the meningeal lining of the brain or spinal cord, between the pia mater and the arachnoid mater (layers of the meninges). The cyst may be asymptomatic, or manifesting with focal or general neurological signs and symptoms.

Confirming the diagnosis

The diagnosis is made based on high resolution MRI or CT scan of the brain/spinal cord. A cyst may also be noted on myelogram, but it would require further delineation with a CT or MRI scan.  Note that this is often an incidental finding, so the condition may not be symptomatic.

The relevant medical specialist is a neurologist.

Additional diagnoses covered by these SOPs
  • Arachnoid cyst of the brain
  • Arachnoid cyst of the spinal cord
  • Leptomeningeal cyst
Conditions not covered by these SOPs
  • intra-cerebral cysts#
  • cerebral meningioma*
  • acoustic neuroma*
  • malignant neoplasm of the brain*
  • soft tissue sarcoma*
  • spinal adhesive arachnoiditis* 

* another SOP applies

# non-SOP condition

Clinical onset

The clinical onset will be the earliest time when the symptoms were present and in the opinion of the specialist neurologist were attributable to the arachnoid cyst.  However many arachnoid cysts are asymptomatic, and hence the onset will be when the condition was first found to be present via imaging.  Some of the symptoms are non-specific, such as headache, and may be attributable to other conditions such as primary migraine or tension-type headache. This can complicate the issue of a clinical onset.

Clinical worsening

Most arachnoid cysts are asymptomatic, and do not require treatment.  Hence clinical worsening will generally not be an issue.  Cysts can expand in size and cause pressure effects and location specific symptoms.  Clinical worsening could be indicated by an increase in symptoms or signs that closely follows one of the events covered by the SOP worsening factors.  Inability to undergo surgical treament for a cyst that is expanding could result in clinical worsening.