Interpeduncular arachnoid cysts in infants and children: insight into the entity based on a case series with long-term follow-up

Arachnoid cysts occupying the suprasellar region comprise 10-15% of intracranial distribution. Unlike large suprasellar cysts, pure interpeduncular cysts (IPCs) are rare, and their natural history is unknown. We describe a small series of children diagnosed with IPC and their long-term natural history. A retrospective review was conducted of interpeduncular arachnoid cysts diagnosed over the years 2000-2010 at our center. Patients with clearly suprasellar cysts were excluded. Serial magnetic resonance imaging and long-term follow-up examinations were analyzed. Additionally, we conducted an extensive literature review focusing on the differences between suprasellar cysts and IPCs. We identified three pediatric patients with "pure" IPC; all of these had a follow-up of more than 5 years, and none was operated. Only six additional cases were identified in the literature. In both our experience and in the literature review, IPCs proved stable over the course of time, both radiologically as well as clinically. The clinical and radiological features of IPCs are not well defined. Variations in the relationship of arachnoid cysts in this area to Liliequist's membrane may explain the different subgroups that have been identified as well as the confusing nomenclature. IPCs are usually diagnosed as incidental findings or present with mild endocrine disorders. Associated findings of hydrocephalus, mass effect, and compression of neighboring structures, such as the chiasm, are not as frequent as with suprasellar cysts. Given the high likelihood of continuing stability, a conservative strategy of follow-up is recommended for pure IPCs that demonstrate preservation of the third ventricle.