SPG4 usually presents as pure HSP, but rarely, complex phenotypes are seen, including cerebellar ataxia, executive dysfunction, epilepsy, psychosis, WMHLs, arachnoid cyst of the posterior fossa, polyneuropathy, hand tremors, and amyotrophy of the hand muscles [10,15,18,19,20,21]. The gene discussed is SPAST; the disease is arachnoid cyst.