Millard-Gubler syndrome (MGS) is a classic brainstem crossed syndrome caused by a unilateral lesion in the ventrocaudal pons. Its three main features are ipsilateral abducens nerve (CN VI) and facial nerve (CN VII) palsy, and contralateral pyramidal tract signs (hemiplegia or hemiparesis). It is also called facial-abducens crossed palsy syndrome or ventral pontine syndrome.
It was first reported in 1858 by French physicians Auguste Louis Jules Millard and Adolphe-Marie Gubler. It is one of the earliest brainstem crossed syndromes described in the 19th century and is considered a classic disease in neuro-ophthalmology.
A characteristic of this syndrome is that it involves the nerve fascicles rather than the cranial nerve nuclei themselves. The spinothalamic tract and medial lemniscus are located dorsal to the lesion and are not damaged, so somatosensory symptoms are usually absent.
It originates from the first report by French physicians Millard and Gubler in 1858. It is one of the earliest brainstem crossed syndromes described in the 19th century and is also called ventral pontine syndrome or crossed facial-abducens nerve palsy syndrome.
The following findings corresponding to the lesion location and affected nerves are observed.
The three affected structures and their corresponding findings are shown in the table below.
| Affected structure | Side | Main findings |
|---|---|---|
| Abducens nerve (CN VI) | Ipsilateral to lesion | Abduction limitation, esotropia, horizontal diplopia |
| Facial nerve (CN VII) | Ipsilateral to lesion | Peripheral facial nerve palsy, loss of corneal reflex efferent pathway |
| Corticospinal tract | Contralateral to lesion | Hemiplegia, hyperreflexia, Babinski sign |
In this syndrome, the fibers of the abducens nerve, facial nerve, and corticospinal tract are affected. The efferent pathway of the corneal reflex (CN VII) is lost, but the afferent pathway (trigeminal nerve CN V) is preserved, so corneal sensation is normal. Additionally, the spinothalamic tract and medial lemniscus are located dorsal to the lesion and are not damaged, so somatic sensory symptoms do not occur.
The anteromedial pons receives blood supply from the pontine perforating branches of the basilar artery. Ischemia, hemorrhage, tumor, or inflammation in this area can cause MGS. The distribution of causative diseases differs by age group.
Common causes in the elderly
Cerebrovascular disease (ischemia/hemorrhage): The most common cause. Associated with ischemia in the basilar artery territory. Risk factors include arteriosclerosis, hypertension, and diabetes.
Prepontine subarachnoid hematoma: Recognized as a form of space-occupying lesion.
Common causes in young adults
Space-occupying lesions (tumors, tuberculomas): A common cause in young people. In tuberculosis-endemic areas, brainstem tuberculomas are also important 1).
Infections: Tuberculosis, neurocysticercosis, rhombencephalitis.
Demyelinating diseases: Multiple sclerosis is a typical example. Differential diagnosis is needed in young patients with pontine lesions.
In young patients, common causes include space-occupying lesions (tumors, tuberculomas), infections (tuberculosis, neurocysticercosis), and demyelinating diseases (multiple sclerosis). In tuberculosis-endemic areas, isolated brainstem tuberculoma should also be considered in the differential diagnosis. In elderly patients, cerebrovascular disease is the main cause.
CT and MRI are performed in stages to confirm brainstem lesions and identify their causes.
It is important to differentiate MGS from similar pontine syndromes.
| Syndrome | Characteristic Deficits | Differences from MGS |
|---|---|---|
| Foville syndrome | CN VI + CN VII + PPRF + corticospinal tract | Associated with gaze palsy toward the lesion side and Horner syndrome |
| Raymond syndrome | CN VI + corticospinal tract | Without facial nerve palsy |
| Gelle syndrome | CN VII + CN VIII + pyramidal tract | Without abducens nerve palsy |
| Brissaud-Sicard syndrome | CN VII + pyramidal tract | Without abducens nerve palsy |
| Gasperini syndrome | CN V-VIII + spinothalamic tract | With sensory disturbance |
Foville syndrome involves PPRF impairment and presents with gaze palsy toward the lesion side. MGS does not involve the PPRF, so although there is abduction limitation due to abducens nerve palsy, gaze palsy does not occur.
Foville syndrome involves damage to the PPRF (paramedian pontine reticular formation) and includes horizontal gaze palsy toward the lesion side, Horner syndrome, and loss of taste on the anterior two-thirds of the tongue. MGS does not involve the PPRF and is limited to abduction restriction due to abducens nerve palsy. If gaze palsy is added to CN VI + CN VII + pyramidal tract signs, suspect Foville syndrome.
For esotropia and diplopia due to abducens nerve palsy, the following steps are considered in a stepwise manner.
Peripheral facial nerve palsy accompanied by loss of corneal reflex and lagophthalmos increases the risk of corneal damage.
Strabismus surgery is considered when the deviation has been stable for at least 6 months. In mild to moderate cases, prisms or botulinum toxin injection are used first. Even after surgery, residual diplopia on lateral gaze is unavoidable, so thorough preoperative explanation is necessary.
MGS is a syndrome caused by damage to nerve fascicles, not to the nucleus. A unilateral lesion in the ventrocaudal basis pontis simultaneously affects three structures, resulting in a characteristic crossed syndrome.
Abducens nerve fascicle (CN VI)
Course: The nerve fascicle runs through the ventrocaudal pons.
Findings due to lesion: Ipsilateral abduction limitation, esotropia, and horizontal diplopia. Since the lesion is in the fascicle rather than the nucleus, gaze palsy is not present.
Correspondence with vascular supply: Damage occurs due to ischemia of the anteromedial pons (pontine perforating branches of the basilar artery).
Facial nerve bundle (CN VII)
Course: The nerve bundle at the “genu” that loops around the abducens nucleus.
Findings due to lesion: Ipsilateral peripheral (lower motor neuron) facial nerve palsy. Loss of forehead wrinkling, incomplete eye closure, and deviation of the mouth angle are observed. The efferent limb of the corneal reflex is lost (afferent limb CN V is preserved).
Corticospinal Tract Fibers
Course: Corticospinal tract fibers passing through the base of the pons. They travel along the pre-decussation pathway within the pons.
Findings due to lesion: Contralateral (opposite side of the lesion) hemiplegia, hyperreflexia of deep tendon reflexes, and positive Babinski sign.
Preserved structures: The spinothalamic tract and medial lemniscus are located dorsal to the lesion and are not affected.
The abducens nucleus consists of large-cell and small-cell groups and serves as the final common pathway for all horizontal eye movements. It is closely connected to the medial longitudinal fasciculus (MLF) and the paramedian pontine reticular formation (PPRF). In MGS, the nerve fascicles outside the nucleus are affected, so the MLF and PPRF are usually spared, and complete horizontal gaze palsy, which occurs with nuclear lesions, is not present.
The signal pathway for horizontal gaze consists of two routes: from the PPRF to the ipsilateral abducens nucleus to the lateral rectus muscle, and via the MLF to the contralateral oculomotor nucleus medial rectus subnucleus to the medial rectus muscle. When only the abducens nerve fascicle is affected in MGS, this conjugate pathway is preserved, resulting in isolated abducens palsy with only loss of lateral rectus contraction.
The vascular supply to the anteromedial pons comes from the paramedian pontine perforators of the basilar artery, and ischemia in this area is the most common cause of MGS. The anterolateral pons is supplied by the anterior inferior cerebellar artery (AICA), and the lateral pons by the lateral pontine perforators from the basilar artery, AICA, and superior cerebellar artery (SCA).
Vascular lesions are the most common cause of MGS, but MGS due to infectious lesions has also been reported.
Chakraborty et al. (2022) reported a case of MGS caused by a pontine tuberculoma in an adolescent female1). The patient presented with right abducens nerve palsy, right peripheral facial nerve palsy, left hemiparesis, and bilateral papilledema. MRI revealed a cluster of lesions with marginal enhancement on the anterior pons. Treatment with four-drug antitubercular therapy, an 8-week tapering course of dexamethasone, and levetiracetam resulted in marked reduction of the lesions on MRI at 6 months. Although residual paralysis remained, recovery was observed.
In tuberculosis-endemic regions, approximately 40% of intracranial space-occupying lesions are tuberculomas, of which isolated brainstem tuberculomas account for about 5%, making them rare1). Due to its near-orphan disease epidemiology, diagnosis is often delayed. It has been noted that the lipid/lactate peak on MRS is useful for differentiating tuberculomas1).
