Pontine Lesions
Pontine lesions may involve the facial nucleus or intrapontine facial nerve fascicles (Figure 181.1). They produce an ipsilateral facial musculature deficit that equally affects the corner of the mouth, the nasolabial fold, the lower eyelid, the upper eyelid, and the forehead. When crying, the mouth deviates toward the normal side and the eyelid remains open or closes less tightly on the affected side.

Figure 181.1.— Schematic representation of the intrapontine trajectory of the facial nerve. N: nucleus; CN: cranial nerve; C: location of intrapontine lesion.

The facial nerve motor nucleus may be involved in Moebious syndrome and autosomal dominant congenital facial palsy; and by cerebrovascular accidents and tumors. Moebious syndrome has been described with degeneration, agenesis, and hypoplasia of the nucleus of the sixth and seventh cranial nerves. Moebious syndrome is characterized by bilateral but asymmetrical facial weakness (Figure 181.2). More about...164 Autosomal dominant congenital facial palsy is characterized by facial motor nucleus hypocellularity, neighboring structures are not involved.
Intrapontine lesions of the facial nerve fascicle are strictly unilateral. The intrapontine fibers of the facial nerve may be affected by cerebrovascular accidents and tumors. In addition to facial musculature involvement, they produce: (1) ipsilateral sixth cranial nerve palsy; (2) ipsilateral Horner syndrome and hypohydrosis and vasodilatation of the ipsilateral body; (3) ipsilateral decreased tearing; and (4) contralateral upper motor neuron hemiparesis. Magnetic resonance imaging is the study of choice to evaluate the facial nucleus and intrapontine fibers.

Figure 181.2— Moebious syndrome. [A] At rest, no asymmetry is noted. [B] During crying, the facial asymmetry becomes obvious.