Disorders• 8 SECTIONMotor Ocular Brainstem

Dorsal Midbrain (Pretectal) Syndrome

Key Facts

•Impaired vertical gaze but intact horizontal gaze • Markedly impaired upgaze often with convergence–retraction movements of eyes • Dilated pupils that constrict poorly to light but briskly to a near target (see Tectal (Dorsal Midbrain) Pupils)

•Common causes:

• ischemic stroke • demyelination • hydrocephalus • pineal region tumor

Clinical Findings

•Markedly impaired upgaze • Lid retraction (Collier sign) • Convergence– retraction of eyes with attempted upgaze • Dilated pupils that constrict poorly to light but briskly to a near target

•With more ventral lesion, may also have:

• impaired pupil constriction to a near target • impaired downgaze • exotropia

• esotropia • skew deviation • torsional nystagmus

• Doll’s head maneuver may enhance vertical eye movement

Ancillary Testing

•MRI shows pertinent abnormalities in brainstem or diencephalic stroke and pineal region tumor, and sometimes in hydrocephalus and multiple sclerosis

Differential Diagnosis

Treatment

•Stroke: supportive care • Pineal region tumor: biopsy and radiation or chemotherapy • Demyelination: consider immunomodulatory agents

• Decompensated hydrocephalus: ventriculoperitoneal or third ventricular shunt

Prognosis

•Findings often disappear within weeks in mild stroke or demyelination but may be permanent in other conditions

A B

C D

Fig. 8.6 Pineal germinoma. (A) Axial FLAIR MRI shows high-signal round mass (arrow) in pineal region. (B) Image at midbrain level shows high signal in the dorsal midbrain (arrow), indicating infiltration or injury. Biopsy showed germinoma. Axial FLAIR MRI 1 year after systemic chemotherapy and whole brain radiation shows that pineal region tumor has vanished (C, arrow) and dorsal midbrain signal is now normal (D, arrow).

Syndrome (Pretectal) Midbrain Dorsal

Disorders• 8 SECTIONMotor Ocular Brainstem

Paramedian Thalamic or Midbrain Syndrome

Key Facts

•Upgaze and downgaze palsy with preserved horizontal gaze

•May have comitant esotropia, exotropia, or hypertropia

•May have unilateral or bilateral third cranial nerve palsy

•Common causes:

•occlusion of proximal branch of posterior cerebral artery (top of the basilar syndrome) • thalamic or midbrain hemorrhage • pineal region tumor • acute hydrocephalus • head trauma • demyelination • radiation

Clinical Findings

•Upgaze and downgaze palsies and sometimes third cranial nerve palsy

•Sometimes torsional nystagmus

•Esotropia, exotropia, or hypertropia

•Often hypersomnolence

•Often ataxia

Ancillary Testing

•Ischemic stroke: MRI may show restricted diffusion in one or both sides of paramedian thalamus and in paramedian midbrain

•Thalamic or midbrain hemorrhage: MRI and CT will show blood

•Hydrocephalus: MRI and CT show dilated lateral and third ventricles

•Thalamic, midbrain, or pineal tumor: MRI and CT show the mass

Differential Diagnosis

•Thalamic–midbrain ischemic stroke

•Thalamic–midbrain hemorrhage

•Head trauma

•Midbrain tumor

•Thalamic tumor

•Pineal tumor

•Hydrocephalus

•Demyelination

•Brain radiation

Treatment

•Cardiogenic embolism: warfarin anticoagulation

•Non-embolic ischemic stroke: supportive care

•Thalamic or midbrain hemorrhage: supportive care, control blood pressure

•Hydrocephalus: address need for shunt or repair of shunt malfunction

•Thalamic, midbrain, or pineal tumor: biopsy, chemotherapy, radiation

•Demyelination: evaluate for multiple sclerosis

•Radiation: supportive care

Prognosis

•Depends on underlying lesion

•In ischemic stroke and hemorrhage, hypersomnolence usually resolves within weeks

•Ocular motor manifestations improve more than ataxia

Fig. 8.7 Paramedian thalamic and midbrain (top of the basilar) syndrome. Eyes display the features of a dorsal midbrain (pretectal) syndrome. In addition, downgaze is absent or impaired. This is only one variant of the many ocular misalignment and motility manifestations caused by lesions in this region.

A B C

Fig. 8.8 Paramedian thalamic and midbrain infarction (top of the basilar syndrome). Axial diffusion-weighted MRI at (A) thalamic and (B) midbrain levels shows restricted diffusion (bright signal) in paramedian regions bilaterally (arrows). (C) Drawing shows how occlusion of proximal branches of the posterior cerebral artery produce these kinds of infarcts. (After Trobe JD. The Neurology of Vision. New York: Oxford University Press; 2001: 304, with permission.)

A B

Fig. 8.9 Paramedian thalamic infarction (top of the basilar syndrome). (A) Axial FLAIR MRI and (B) diffusion-weighted MRI show bilateral paramedian thalamic infarcts (arrows).

Syndrome Midbrain or Thalamic Paramedian