Millard-Gubler syndrome is a rare lesion of the brainstem affecting the abducens (VI) and the facial (VII) cranial nerves, as well as the pyramidal tract. Unilateral palsy of these nerves accompanied by contralateral motor weakness of the limbs is the typical clinical presentation. The diagnosis is made on clinical grounds, and the underlying cause often requires a thorough imaging workup.
Millard-Gubler syndrome, initially described more than 150 years ago, is a lesion of the brainstem that develops in the ventral pons, and the term "ventral pontine syndrome" is often used as a synonym   . More specifically, it belongs to a group of "crossed paralysis syndrome", as it is responsible for causing facial lesions on one side and limb deficits on the other  . Scarce reports exist regarding its etiology, but vascular insults, tumors, and infectious diseases (neurocysticercosis and tuberculosis) have been described    . The clinical presentation is distinguished by unilateral palsy of the cranial nerves VI and VII (abducens and facial nerves, respectively), together with contralateral hemiparesis, as the corticospinal tract is affected before its decussation   . Hence, weakness of the lateral rectus muscle will lead to diplopia and medial deviation of the affected eye, whereas lesions of the facial nerve (responsible for innervating the muscles of facial expression, including the platysma, orbicularis oculi, mentalis, orbicularis oris, and several other), will present with deviation of the mouth angle and a variable degree of facial paralysis   . Millard-Gubler syndrome is distinguished from other similar brainstem disorders by the absence of sensory deficits, as both the medial lemniscus and the spinothalamic tracts are not damaged .
The diagnosis of Millard-Gubler syndrome rests on the ability of the physician to recognize this rare brainstem syndrome, which can be done only by performing a detailed physical examination. Lesions of both abducens and facial nerve, as well as hemiplegia, must be confirmed by a properly conducted neurological exam. Because of the fact that different etiologies might induce Millard-Gubler syndrome, a complete patient history should be taken as well, in order to identify whether additional symptoms could possibly point toward an infection (fever, for example) or a vascular insult (presence of additional neurological deficits). Regardless, the use of imaging studies should be advised, and computed tomography (CT), but more commonly magnetic resonance imaging (MRI), are effective methods for visualizing the ventral aspect of the pons   . More importantly, the associated lesions (tuberculomas, tumors, or cysticercus granulomas) can be readily identified using these methods  .