Thalamus - The gateway to cerebral cortex

Abstract

Introduction: Thalamus is an oval mass of gray matter between the third ventricle and the internal capsule. The medial, spinal, and trigeminal lemnisci are the great ascending sensory projections from the periphery. The lateral and medial geniculate bodies transmit the visual and auditory information to the cortex. The thalamus also contains motor projections from the basal ganglia, on their way to the motor cortex and supplementary motor area. Materials and Methods: Over 2-year period from November 2015 onward, 83 patients with magnetic resonance imaging confirmed nontraumatic thalamic lesions were identified, and followed up. The patient population consisted of adults above 18 years of age. They were investigated as to the cause of the lesion and treated. Results: There were 58 male patients, 25 female patients. Stroke was the major cause while less common diseases causing thalamic lesions were demyelination, tumor, calcification, and gliosis. The lesions were more common on the left side. The extent of thalamic involvement was global (50.6%) most commonly. The next common was posteromedial affection (18.1%) and dorsal thalamus (14.5%). Corresponding motor weakness (57.8%) was the most common symptom, though other symptoms such as sensory loss (30.1%), ataxia (27.7%), memory loss (12%), and gaze paresis (30.1%) were also present. Headache (31.3%) and giddiness (24%) were less common than motor weakness. Speech disturbance was seen in 49.4% of patients. Discussion: Stroke is unilateral disease, while venous thrombosis, demyelination, tumor, metabolic diseases and infection can affect thalami bilaterally. While stroke can explain the sudden onset of sensory and motor disturbances, some features like cognitive dysfunction were difficult to explain. A transient disorientation to time can follow acute anterior thalamic lesions. Some patients had language disturbances suggesting that the language dominance can extend down up to thalamus. Chronic pain can also be due to a gliotic lesion in the thalamus. Upward gaze palsy seen in a third of our patients could be due to global thalamic or due to medial longitudinal fasciculus involvement. Two patients had visual hemineglect. Sleep disturbances could also be observed in thalamic disease. Asterixis and hemifacial spasm were not seen in our patients. Three patients with strokes had brachial onset seizures, and one patient had generalized seizures. Different types of gait disturbances were observed in thalamic disease including ataxia, astasia-abasia, and hemiparetic gait. Conclusion: The most common thalamic lesion was an ischemic stroke, followed by bleed. Global thalamic involvement was more common than other partial lesions, though posteromedial and dorsal lesions are also commonly seen. Sensorimotor dysfunction is the most common clinical presentation and less frequent presentations include aphasia, memory disturbances, behavioral, and cognitive dysfunction. Movement disorders, ataxic gait, sleep disturbances, and infrequently, seizures were seen in our series.