The word "paraplexus" is spelled with two syllables: /ˌpærəˈplɛksəs/. The first syllable is pronounced with a short "a" sound and the stress falls on the second syllable. The "x" in the spelling represents the sound /ks/, and the "e" between "p" and "l" is pronounced like "eh". Overall, the pronunciation of "paraplexus" is quite straightforward if you are familiar with the International Phonetic Alphabet. However, the word itself is relatively uncommon in English and may not be familiar to everyone.
The choroid plexus of the lateral ventricles.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.