Foville Syndrome

Excerpt

Foville syndrome is a rare inferior medial pontine syndrome first characterized in 1858 by anatomist and psychiatrist Achille Louis Francois Foville. In his paper “Notes on a Little-known Paralysis of Eye Muscles and Its Relation to the Anatomy and Physiology of the Pons,” Foville posed a question: Does the analysis of paralytic symptoms provide a basis for the exact localization of cerebral disease? He included a description of a 43-year-old man who presented with unilateral conjugate horizontal gaze paralysis and facial nerve paralysis on the same side with crossed hemiparesis. Though several clinical variants have emerged, classic Foville syndrome presents with ipsilateral 6th nerve palsy, facial palsy, and contralateral hemiparesis. Reports exist of other features such as facial hypoesthesia, peripheral deafness, Horner syndrome, ataxia, pain, and thermal hypoesthesia.

Pontine Anatomy

The pons is a large tissue segment projecting superior to the medulla (see Image. Hindbrain, Superficial Dissection). Thick transverse fibers comprise the pons proper. The cerebral peduncles attach to the pons superoanteriorly, while the pyramids arise from the pons' inferior aspect. The paired abducens nerves (cranial nerve VI, CN VI, or 6th cranial nerve) emerge from the inferior pontine sulcus near the pyramids.

The transverse pontine fibers fuse laterally to form the middle cerebellar peduncles connecting the pons to the posteriorly located cerebellum. The cerebellopontine angle is the triangular space between the middle cerebellar peduncle's inferior edge, cerebellum, and superior medullary margin. The facial (CN VII or 7th cranial nerve) and vestibulocochlear (CN VIII or 8th cranial nerve) nerves arise from the cerebellopontine angle. The trigeminal nerves (CN V or 5th cranial nerve) pierce the middle cerebellar peduncles on the pons' superolateral side.

The posterior pontine margin serves as the superior surface of the fourth ventricle's floor. The pontomedullary junction and lateral recesses of the 4th ventricle lie in the widest area of this triangular region. The facial colliculus arises from the CN VI nucleus and CN VII fibers and lies superior to the lateral recesses. Completing the fourth ventricle boundaries are the superior cerebellar peduncles (walls), cerebellar vermis (roof), and anterior medullary velum (roof).

Histologically, the pons is structurally divided into the basilar portion (anterior) and tegmentum (posterior). The pons may also be divided functionally, with the inferior and superior pontine sections carrying different cranial nerve nuclei.

In the inferior (caudal) pons, the corticospinal tracts (CST) emerge at the basilar portion's center. These tracts control voluntary movement. Pontine nuclear fibers (transverse fibers) cross from one side to the other, giving rise to the contralateral middle cerebellar peduncle. The pontine fibers receive signals from the ipsilateral cerebral cortex, subsequently relayed to the cerebellum through the middle cerebellar peduncles.

The medial lemniscus passes from the medulla through the pontine tegmentum. This nerve tract transmits proprioceptive and tactile sensations from the body to the brain. The medial longitudinal fasciculus (MLF) crosses near the midline in the fourth ventricle's floor. The MLF consists of ascending fibers arising from the vestibular nuclei and projecting to the cranial nerve nuclei controlling the extraocular muscles.

The trapezoid body lies in the tegmentum's anterior aspect. Decussating fibers from this area are involved in audition. The superior olive is a small nucleus situated posterolaterally to the trapezoid body. This structure is also involved in auditory function.

The central tegmental tract is a pontine nerve collection that contributes to the ascending reticular formation, which sends thalamic and hypothalamic projections critical to wakefulness and attention. The paramedian pontine reticular formation (PPRF) also arises from the pontine tegmentum. The PPRF processes visual signals and sends projections to the abducens and oculomotor (CN III or 3rd cranial nerve) nerves, which control the eyes' horizontal movements. Ascending taste fibers also lie within the central tegmental tract and travel to the thalamus.

The facial nerve's motor nucleus lies medial to the trigeminal nerve's spinal tract and posterior to the superior olive. The internal genu is an internal loop formed by the facial nerve tracts, passing by the abducens nerve at this level (see Image. Pons Facial Colliculus Cross-Section). The abducens nerve arises from the abducens nucleus, passes through the pontine tegmentum, transits lateral to the pyramidal tract, and exits the brainstem to innervate the lateral rectus muscle. The vestibular nuclei are situated lateral to the fourth ventricle floor.

In the superior pons, the corticopontine fibers descend from the cerebral lobes to the pontine nuclei. These nerves are involved in controlling voluntary movement. The motor (medial) and principal sensory (lateral) trigeminal nerve nuclei are also found in this region. The mesencephalic trigeminal nerve tract passes in this region, carrying stretch receptor signals from the mastication muscles.

The basilar artery is the pons' main arterial source. This artery forms from the union of the vertebral arteries inferiorly and ascends through the ventral median sulcus (basal sulcus) to the superior pontine margin. Smaller paramedian perforating branches of the basilar artery supply each side of the paramedian caudal pons. The blood vessel bifurcates into the posterior cerebral arteries superior to the pons.