It results from an absent or dysplastic abducens motor neurons with aberrant innervations of the lateral rectus muscle by the oculomotor nerve, from failure of normal development of the pontine abducens nucleus
or nerve resulting in failure of the normal innervation of the lateral rectus muscle on the affected side.
As facial nerve fibres encircle abducens nucleus
before leaving the pons, these fibres lie in close proximity to structures described above, they are also more prone to injury in this region causing additional seventh nerve involvement termed as "eight and a half" syndrome.
Co-activation of these 2-neuron groups within one abducens nucleus
is thus associated with horizontal movements of both eyes towards the same side.
They bend around the abducens nucleus
to form the first genu of the facial nerve.
Developmental differences also exist for Abd motoneurons, as the abducens nucleus originates from embryonic rhombomeres (Rhs) 5 and 6 for most vertebrates, including lampreys, teleosts, birds, and reptiles (1), and exclusively from Rhs 5 in frogs (16) and mammals (1).
In particular, a distinct subgroup of neurons largely ventrolateral to the abducens nucleus (Fig.
The abducens nucleus, located in the pons, is of central importance in the control of horizontal gaze as it governs conjugate movements of both the ipsilateral lateral rectus and contralateral medial rectus muscles (Fig 3).
The abducens nucleus receives input from several sources.
A similar case was reported by Sans Beom Han (10) where a metastatic mass in the facial colliculus of lower pons involving abducens nucleus resulting in Gaze palsy.
Presumed Metastasis of Breast Cancer to the Abducens Nucleus Presenting as Gaze Palsy.