What is the treatment approach for a posterior fossa arachnoid cyst?

Treatment of Posterior Fossa Arachnoid Cysts

Symptomatic posterior fossa arachnoid cysts should be treated surgically, with the specific approach determined by cyst location: midline intra-fourth ventricular/retroclival cysts are best managed with cysto-peritoneal shunting or endoscopic fenestration, while all other locations (cerebellopontine angle, extra-fourth ventricular, intracerebellar) should undergo open surgical excision via suboccipital approach. 1

Indications for Surgery

Surgery is warranted in symptomatic patients presenting with:

• Increased intracranial pressure (headaches, nausea, vomiting) 2
• Gait disturbances and ataxia from cerebellar compression 3
• Hydrocephalus from fourth ventricle obstruction (present in 26% of cases) 2
• Cranial nerve deficits including hearing loss 4
• Progressive head enlargement in pediatric patients 2

Surgical Approach Based on Location

Cerebellopontine Angle and Extra-Fourth Ventricular Cysts

Suboccipital retrosigmoid craniotomy with radical cyst excision is the preferred approach for these locations 5, 1:

• Provides excellent exposure of neurovascular structures and cranial nerves 5
• Allows complete cyst wall resection, reducing recurrence risk 5
• Achieves success rates of 64% with marsupialization alone 2
• Long-term follow-up (mean 3.3 years) shows improvement in most preoperative symptoms 5

Midline Intra-Fourth Ventricular or Retroclival Cysts

Cysto-peritoneal shunting or endoscopic fenestration should be performed for these locations 1:

• These cysts cannot be safely excised due to anatomical constraints 1
• Endoscopic cisternostomy provides good results as first-line treatment 2
• Shunting should be considered second-line due to high malfunction rates (45% of procedures in one series) 2

Surgical Outcomes and Complications

Marsupialization without shunting achieves better long-term results than shunt-dependent procedures 2:

• Marsupialization alone successful in 64% of cases 2
• Marsupialization with shunt successful in only 20% of cases 2
• Shunt malfunction represents 45% of all surgical procedures over time 2

Major morbidity is rare but can occur from:

• Injury to brainstem and cranial nerves during dissection 5
• Air embolism in semi-sitting position 5
• Strong adherence of cyst wall to neurovascular structures 5

Mortality is essentially zero in modern series 2, 5, 3

Postoperative Monitoring

Following surgery, expect:

• Variable decrease in cyst size on imaging even with clinical improvement 1
• Cerebellar re-expansion and decreased ventricular size if hydrocephalus was present 3
• Long-term follow-up (mean 93 months) shows sustained symptom resolution 2
• No recurrence when radical excision is achieved 3

Key Clinical Pitfalls

Avoid shunting as first-line treatment except for intra-fourth ventricular cysts, as shunt-dependent procedures have high complication rates requiring multiple revisions 2, 1. The high incidence of shunt malfunction (45% of procedures) strongly supports marsupialization or endoscopic approaches as initial management 2.

Do not assume all posterior fossa cysts require the same approach—location dictates surgical strategy, with midline intra-fourth ventricular cysts being the exception that benefits from shunting rather than excision 1.