Intracranial arachnoid cysts are rare cystic-appearing intracranial masses. In rarer cases, the arachnoid cysts originate from brain parenchyma, which is defined as intracerebral arachnoid cyst. Here, we present a patient younger than 2 years with massive intracranial arachnoid cysts (one of which was intracerebral arachnoid cyst), whose clinical symptoms included megacephaly and limb weakness. Ommaya reservoir implantation and repeated aspiration of the intracerebral cyst fluid were performed. The symptoms gradually improved, and the intracerebral arachnoid cyst gradually disappeared during 13 months of follow-up. The case highlights the potential of Ommaya reservoir implantation in the treatment of intracerebral arachnoid cyst, especially for young patients. We also reviewed the published literatures concerning the rare condition, including the mechanisms for its pathogenesis and enlargement.