ALDH1A1 and schwannoma: In cystic fluid from CS retinol-binding protein 4 (RBP4) was present and in the same specimens we also identified, at lower levels, aldehyde dehydrogenase 1 family member A1 (ALDH1A1), also known as retinal dehydrogenase, an enzyme that plays an important role in retinol metabolism and it is upregulated in schwannomas [67].