Fisch's physiological bottleneck (narrowest pa) is present in which pa of the VIIth nerve

The labyrinthine segment is the narrowest pa of the facial nerve and is susceptible to compression by means of oedema. This is the only segment of the facial nerve that lacks anastomosing aerial cascades, making the area vulnerable to embolic phenomena, low-flow states, and vascular compression. Ref : Diseases of ENT by Dhingra 6th edition Pgno : 90