Neuro-Ophthalmic Manifestations of Thalamic Disease
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Disease Entity
Disease
Thalamic lesions are associated with possible neuro-ophthalmologic deficits that are important to distinguish from those caused by lesions in the midbrain or other locations. Deficits can result from various etiologies and can result in ocular motility difficulties presenting most commonly as vertical gaze palsies, but can also include skew deviation, convergence problems, third cranial nerve palsy, nystagmus, pupil and lid abnormalities, or deficits in saccades or smooth pursuits[1].
Etiology
While vascular accidents, either hemorrhagic or ischemic, are the most common etiologies causing acute thalamic lesions, other reported etiologies include migraine, metabolic (e.g., thiamine deficiency), inflammatory (e.g., cerebral lupus), infectious (e.g., bacterial abscesses, cerebral syphilitic gumma), traumatic, neoplastic (e.g., tumors or cysts) and iatrogenic (e.g., deep brain stimulation)[1].
Risk Factors
Risk factors for acute thalamic lesions include the common vasculopathic risk factors, such as hypertension, diabetes, and a history of smoking[1].
Pathophysiology
The thalamus is one of the principal relay stations for pathways linking cortical regions to the brainstem. This includes the vestibulo-ocular pathway, connections to the frontal eye fields, and pathways to the posterior parietal cortex responsible for visual processing. Specific ocular motility issues that can be caused from damage to pathways located in various sections of the thalamus are summarized in Table 1[1].
| Location of Thalamic Lesion | Ocular Deficit |
|---|---|
| Paramedian area, medial rectus sub-nucleus | Convergence deficit |
| Mediodorsal nuclei | Loss of saccadic activity |
| Ventrolateral neurons, paralaminar regions of the mediodorsal and ventroanterior nuclei | Loss of smooth pursuit activity |
| Ventral lateral and ventral anterior nuclei | Loss of voluntary motor actions and arousal |
| Inhibitory descending pathways for convergence, caudal territory | Pseudo-abducens palsy (thalamic esotropia) |
| Inferolateral territory | Hypermetric saccades |
| Posterolateral territory | Ipsilateral Horner Syndrome |
| Dorsal territory | Horizontal or vertical diplopia |
Table 1. Locations of thalamic lesions and subsequent ocular motility deficit
Compromised vascular supply to any of these areas can cause important ocular deficits. The thalamus has vascular support provided by several arterial branches, such as the thalamotuberal artery supplying the posterior section of the hypothalamus, anterior thalamic nuclei, ventral section of the internal medullary lamina, ventral pole of the medial dorsal nucleus, and the rostral ventrolateral nucleus. These areas can alternatively be supplied by the paramedian artery in individuals lacking the thalamotuberal artery. The paramedian artery supplies the dorsomedial portion of the thalamus as well as the paramedian section of the midbrain. Furthermore, the thalamic inferolateral arteries and the pulvinarian inferolateral arteries supply most of the ventral lateral nucleus, the pulvinar, and the ventral posterior nucleus. Finally, the posterior choroidal arteries also supply the thalamus through the mesencephalon-posteriomedial system and the hippocampo-posterolateral system. These supply the dorsolateral thalamus, substantia nigra, pulvinar, and lateral and medial genicular bodies[1].
Primary prevention
Prevention of strokes is possible by minimizing vasculopathic risk factors.
Diagnosis
Thalamic lesions may occur with or without caudal extension to the midbrain. The common but variable vascular supply to both regions can result in a combination of thalamic and midbrain signs[1].
History
Vertical gaze palsy is a common manifestation of thalamic eye disease, but other symptoms and signs may be present (see Table 1).
Signs and Symptoms
Bilateral thalamic lesions commonly produce more severe ocular motility deficits when compared to unilateral lesions. While unilateral defects may cause upgaze palsy, bilateral damage can cause upgaze, downgaze, or combined vertical palsies as well as convergence abnormalities, bilateral internuclear ophthalmoplegia, and cranial nerve III involvement with caudal midbrain extension of the lesion (Jones). Other adjacent structures may also be involved including the internal capsule, subthalamic nucleus, basal ganglia, cerebellum, or cerebral hemispheres. Thalamic strokes extending to the brainstem can result in pupil abnormalities, ptosis, and cranial nerve III, IV, V, or VI palsies[2].
Imaging
Acute ischemic or hemorrhagic infarction can be seen on magnetic resonance imaging (MRI) or computerized tomography (CT) of the brain for strokes involving the anterior and posterior circulation[3]. It is important to first distinguish a hemorrhagic stroke from an ischemic stroke by using a non-contrast CT. In the appropriate clinical situation and if hemorrhagic stroke is excluded, patients with acute thalamic ischemia seen within the appropriate (e.g., 4.5-hour) therapeutic window may benefit from thrombolytic therapy. Diffusion-weighted imaging (DWI) may also be used to visualize acute thalamic ischemic strokes.
Management
Medical therapy
Intravenous tPA can be administered to patients with ischemic thalamic strokes that fall within the 4.5-hour tPA window from onset of symptoms. Medical therapy should be directed to the stroke etiologies. Treatment of other underlying etiologies are dependent on the individual cause.
Prognosis
The prognosis depends on the underlying etiology. Although thalamic lesions are uncommon and may sometimes be difficult to localize clinically, modern neuroimaging is typically the initial step in management and predicts both etiology and prognosis.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Jones E, Rowe FJ. Ocular motility consequences following lesions of the thalamus: a literature review. British and Irish Orthoptic Journal. 2009;6:40. doi:10.22599/bioj.7.
- ↑ Gupta N, Pandey S. Post-Thalamic Stroke Movement Disorders: A Systematic Review. European Neurology. 2018;79(5-6):303-314. doi:10.1159/000490070.
- ↑ Bewermeyer H, Dreesbach HA, Rackl A, Neveling M, Heiss W-D. Presentation of bilateral thalamic infarction on CT, MRI and PET. Neuroradiology. 1985;27(5):414-419. doi:10.1007/bf00327605.
