Life-threatening posterior fossa cyst induced by pseudomeningocele after operation for acoustic neuroma

BACKGROUND: Pseudomeningocele is the term used to describe fluid accumulation due to the leakage of cerebrospinal fluid into the surrounding soft tissue. It may cause complications such as cosmetic deformities, chronic meningitis, and/or impingement on vital structures resulting in neurological deficits; nevertheless, life-threatening posterior fossa cyst formation is a rare event. CASE DESCRIPTION: We report a case of posterior fossa cyst formation induced by pseudomeningocele with brain stem compression leading to coma with pupillary dilation. These symptoms occurred after an operation for left acoustic neuroma. After emergent decompression and dural repair, the patient recovered well without experiencing any further neurological deficits. CONCLUSION: We discuss the clinical features, possible pathophysiological mechanisms, and treatment options for pseudomeningocele. Although most cases of pseudomeningocele follow a benign course and need only conservative treatment, the potential attendant complications, such as an enlarged cyst, may still have fatal consequences. We believe that it is beneficial to take an aggressive attitude toward this condition and to consider the possibility of surgical interventions more seriously.