Neuroscience 1A LC11: The Thalamus PDF

UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC11 The Thalamus COLLEGE OF MEDI...

UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC11 The Thalamus COLLEGE OF MEDICINE, BATCH 2026 Transcribers and Editors: Dr. Vida Margarette D. Andal | Nov. 2022 Samillano, Sanga, Santos, Segovia, Servito, Somera THE THALAMUS - Relay and integrative station for information going to the cerebral cortex, basal ganglia, hypothalamus and brainstem. Here comes the word afferent and efferent, afferent is body to brain and I. INTRODUCTION efferent is brain to body. Efferent = effect, the effect of the brain to the rest of the A. Neuroimaging body. Your thalamus is a part of your afferent relay process, think of it as a B. Gross Anatomy headquarters, everything that goes to your cerebrum and basal ganglia from the rest II. BOUNDARIES of the body must pass through your thalamus first. Before information can enter your A. Anterior End body, they must first go to the thalamus. B. Posterior End C. Inferior Surface - Pair of egg-shaped mass of gray matter connected by a band of gray D. Medial Surface matter called interthalamic connection. III. BLOOD SUPPLY When we say gray matter we talk about neurons, while white matter are axons. A. Thalamogeniculate Arteries They are called white matter due to myelination. Gray matter are full of cell bodies. B. Tuberothalamic Arteries The pair of thalami have a bridge called interthalamic connection, even the bridge- C. Thalamic-subthalamic Arteries connection is composed of gray matter. D. Posterior Choroidal Arteries a. Artery of Percheron - Found at the rostral end of the brainstem. IV. INTERNAL ORGANIZATION Rostral means top. Opposite of which is caudal which means bottom end. A. White Matter Thalamus sits on top of your brainstem. a. Stratum Zonale b. External Medullary Lamina - Found lateral to the third ventricle. c. Internal Medullary Lamina The third ventricle is in the inside surface of the thalamus. B. Subdivisions of the Thalamus a. Anterior Part b. Medial Part c. Lateral Part i. Dorsal Tier ii. Ventral Tier C. Other Nuclei of the Thalamus a. Intralaminar Nuclei b. Midline Nuclei c. Reticular Nucleus d. Medial Geniculate Body e. Lateral Geniculate Body v. CLINICAL APPLICATION (Thalamic Lesions) A. Infarctions a. Posterolateral Infarction b. Anterior Infarction c. Paramedian Infarction d. Dorsal Infarction B. Hemorrhage a. Fabry Disease Figure 2. The thalamus. b. Osmotic Demyelinating Syndrome (ODS) c. Acute Disseminated Encephalomyelitis (ADEn) d. Glioblastoma Multiforme e. Gliomatosis Cerebri f. Lymphoma I. INTRODUCTION - Forms the major part of the diencephalon Thalamus is a part of your brain and forms a major part of the diencephalon. The neural tube which gives rise to the forebrain (prosencephalon), which will develop into your cerebrum, thalamus, hypothalamus and epithalamus. But before the prosencephalon differentiate and develop into specific parts, it first divides into telencephalon and diencephalon. In some books, they would refer your thalamus as the diencephalon, but it is important to know that the diencephalon is not solely your thalamus. It is also composed of the hypothalamus and epithalamus. Figure 3. Pair of egg-shaped (oval) structure at the rostral end of the brainstem. It sits on top of your midbrain, pons and medulla. Figure 1. Shows the embryological development of the central nervous system. [NEUROSCIENCE1A]-01.11-The Thalamus– Dr. Vida Margarette D. Andal Figure 7. The thalamus found laterally to the third ventricle. A. NEUROIMAGING Figure 4. Posterior view of the thalamus. Figure 8. Magnetic Resonance Imaging (MRI). Axial and coronal view. Easy to identify thalamus due to gray matter appearance. Figure 5. Thalamus found lateral to the third ventricle. The diagram shows the ventricular system. Think of ventricles as a canal holding the cerebrospinal fluid (CSF). Figure 6. Coronal view of the thalamus. Figure 9. MRI. Sagittal view. Thalamus sits on the rostral end of the brainstem. Page 2 of 9 [NEUROSCIENCE1A]-01.11-The Thalamus– Dr. Vida Margarette D. Andal B. GROSS ANATOMY II. BOUNDARIES OF THE THALAMUS A. ANTERIOR END - Round and Narrow (like an egg) - Forms the posterior boundary of the interventricular foramen which connects the lateral ventricle with the third ventricle Figure 11. Axial View. Figure 14. Rostral end of brainstem (above), Anterior portion of Thalamus (below). B. POSTERIOR END - Expanded to form the pulvinar (butt of the thalamus/bumpy end) - Overhangs the superior colliculus Figure 12. Coronal View. Figure 15. Brain showing posterior end of Thalamus. Figure 13. Sagittal View. Page 3 of 9 [NEUROSCIENCE1A]-01.11-The Thalamus– Dr. Vida Margarette D. Andal - Supplies the posterior region of the thalamus, including the pulvinar (supplies anterior region also but mainly the pulvinar) Figure 16. Thalamus and quadrigeminal plate. C. INFERIOR SURFACE - Continuous with the tegmentum of the midbrain Figure 18. Blood Supply of Thalamus. a. ARTERY OF PERCHERON - Anatomic variant where a single unpaired artery arising from P1 portion of PCA supplies the bilateral paramedian thalami and sometimes the rostral Figure 17. The brainstem. midbrain too - In about 1/3 of the population, the tuberothalamic artery is missing and D. MEDIAL SURFACE its territory is supplied by the thalamic-subthalamic artery from the same - Forms part of the lateral wall of the third ventricle side. - Connected to the opposite thalamus by interthalamic - It is a normal anatomic variation connection/adhesion (Refer to Figure 14). - Occlusion results to bilateral paramedian thalamic infarction and may affect the midbrain III. BLOOD SUPPLY OF THE THALAMUS A. THALAMOGENICULATE ARTERIES - Arising from the P2 portion of the posterior cerebral artery (PCA) or from the basilar artery posteriorly (which runs through the back of the pons) - Supplies the ventrolateral region of the thalamus - They are as thin as hair. Very pliable vessels that cannot withstand high pressure and may rupture (eg. BP 200/140) - cerebral hemorrhages are common in this area B. TUBEROTHALAMIC ARTERIES - Also called the polar artery - Arising from the Posterior Communicating Artery - Supplies the anteromedial and anterolateral region of the thalamus C. THALAMIC-SUBTHALAMIC ARTERIES - Also called the paramedian thalamic arteries - Arising from the P1 portion of the PCA - Supplies the medial region of the thalamus D. POSTERIOR CHOROIDAL ARTERIES - Arising from the P2 portion of the PCA Figure 19. Normal Anatomy (L) and Artery of Percheron (R). Page 4 of 9 [NEUROSCIENCE1A]-01.11-The Thalamus– Dr. Vida Margarette D. Andal Figure 22. Subdivisions of the Thalamus. Figure 20. MRI showing occlusion that affected midbrain IV. INTERNAL ORGANIZATION OF THE THALAMUS A. WHITE MATTER a. STRATUM ZONALE - Thin layer of white matter that covers the superior surface of the thalamus difficult to identify in MRI because it is very thin b. EXTERNAL MEDULLARY LAMINA - Thin layer of white matter that covers the lateral surface of the thalamus c. INTERNAL MEDULLARY LAMINA - Vertical sheet of white matter that divides the thalamus into medial and lateral halves, Y-shaped Figure 23. Subdivisions of the Thalamus. Thalamic Subdivision Connections Function nuclei Receive the mammillothalamic tract from the Anterior mammillary nuclei Emotional tone Anterior nucleus Receive reciprocal Recent memory connections with the cingulate gyrus and hypothalamus Two-way connections Integration of a with the prefrontal large variety of cortex sensory Two-way connections information and Figure 21. White Matter- Thalamus. Dorsomedial Medial with the hypothalamic the relation of this nucleus nuclei information to B. SUBDIVISIONS OF THE THALAMUS Interconnected with one’s emotional a. ANTERIOR PART all other groups of feelings and - Anterior nucleus thalamic nuclei subjective states b. MEDIAL PART Lateral dorsal Not clear - Dorsomedial nucleus nucleus May have c. LATERAL PART Lateral interconnections with i. Dorsal Tier Lateral posterior other thalamic nuclei, Not clear - Lateral dorsal nucleus (Dorsal tier) nucleus cingulate gyrus, - Lateral posterior nucleus parietal, temporal and - Pulvinar Pulvinar occipital lobes ii. Ventral Tier Connected to the - Ventral anterior nucleus reticular formation, - Ventral lateral nucleus Ventral Influences Lateral substantia nigra, - Ventral posterior nucleus anterior activities of the (Ventral tier) corpus striatum, - Ventral posteromedial nucleus nucleus motor cortex premotor cortex, - Ventral posterolateral nucleus other thalamic nuclei Page 5 of 9 [NEUROSCIENCE1A]-01.11-The Thalamus– Dr. Vida Margarette D. Andal Connected to the - Function is unknown, but obviously since it is involved with reticular reticular formation, formation it has something to do with consciousness substantia nigra, corpus striatum, premotor cortex, other thalamic nuclei Influences Ventral lateral PLUS activities of the nucleus Major input from motor cortex cerebellum and minor input from the red nucleus. Projects to the motor and premotor regions of the cerebral cortex Receives the ascending trigeminal Relays sensory Ventral which have both inputs to the posteromedial sensory and motor sensory cortex function and gustatory pathways Figure 25. Midline Nuclei. Receives tracts from medial and spinal c. RETICULAR NUCLEUS lemnisci then are - thin layer of nerve cells sandwiched between the external medullary Relays sensory Ventral transmitted to the lamina and posterior limb of the internal capsule inputs to the posterolateral postcentral gyrus - receive afferent fibers from the cerebral cortex and reticular formation sensory cortex which has something - send efferent to other thalamic nuclei to do with sensory - function is not fully understood; but may be concerned with a mechanism function by which the cerebral cortex regulates thalamic activity Table 1. Summarized subdivisions of the thalamus with corresponding connection and function. d. MEDIAL GENICULATE BODY - part of the auditory pathway C. OTHER NUCLEI OF THE THALAMUS - receive afferent fibers from the inferior colliculus (inferior brachium) - send efferent fibers to form the auditory radiation which terminates at the a. INTRALAMINAR NUCLEI auditory cortex of the superior temporal gyrus - small collections of nerve cells within the internal medullary lamina - receives auditory information from both ears but predominantly from the - receive afferent fibers from the spinothalamic and trigeminothalamic opposite ear. tracts - sends efferent fibers to other thalamic nuclei that project to the cerebral e. LATERAL GENICULATE BODY cortex - part of the visual pathway - sends fibers to the corpus striatum - receive afferent fibers from the optic tract - Influence the levels of consciousness and alertness - send of efferent fibers to form the visual radiation which terminates in the visual cortex of the occipital lobe One of the prominent symptoms of a thalamic dysfunction is an abnormal level of consciousness. Usually in patients with thalamic problems (e.g. thalamic stroke, V. CLINICAL APPLICATIONS (Thalamic Lesions) thalamic hemorrhage), they are drowsy. The intralaminar nuclei is small but they can influence the physical manifestation of a patient with thalamic problem because they Neurologic deficits depend on the thalamic nuclei that is/are affected: are easily compressed. Emotional tone Anterior nucleus Recent memory Integration of a large variety of sensory information and the relation of this Dorsomedial nucleus information to one’s emotional feelings and subjective states Lateral dorsa, lateral posterior, Not clear pulvinar Ventral anterior nucleus Influences activities of the motor cortex Ventral lateral nucleus Influences activities of the motor cortex Ventral posteromedial Relays sensory inputs to the sensory cortex Relays sensory inputs to the sensory Ventral posterolateral cortex Influence the levels of consciousness Intralaminar nuclei Figure 24. Intralaminar Nuclei. and alertness Receives auditory information from both b. MIDLINE NUCLEI Medial geniculate nuclei ears but predominantly from the - groups of nerve cells adjacent to the third ventricle and in the opposite ear interthalamic connection Lateral geniculate nuclei Receive visual information from the - Receive afferent fibers from the reticular formation opposite field of vision Table 2. The various thalamic nuclei and their functions. Page 6 of 9 [NEUROSCIENCE1A]-01.11-The Thalamus– Dr. Vida Margarette D. Andal A. INFARCTION side of the body contralateral to the thalamic stroke. The nature of the pain varies Blocking of vessels, normally arteries are blocked more than veins. It is considerably between patients, but is often moderate to severe in intensity, can be mainly blocked by cholesterol plaque, embolus plaque from the heart can travel to either persistent or episodic, can be either spontaneous or evoked (e.g. by cold brain, fat embolus, and plaque of tumor cell. If there is occlusion in the artery, blood stimuli), and may have other accompanying sensory deficits (including both will not be able to travel in artery so it would not nourish specific part of thalamus hyposensitivity and hypersensitivity). The location of the pain also varies considerably that supplies. There is also infarction of cholesterol plaques in the heart mainly on and can affect a large part of the contralateral body or a smaller portion depending coronary artery which cause myocardial infarction. on the exact size and location of the thalamic lesion. Additionally, the onset of the pain also is extremely variable, with some patients reporting onset immediately, while others years after the stroke. For example: Patient usually complaint of thalamic pain- they feel constant pain on the side of the body, needle sensation, this is because of sensory cortex misinterpreting a lot of signals because pathway is being destroyed. Thalamic pain syndrome or central post-stroke pain can occur when there are disruptions of one of the pathways of the brain that affects the sensation of temperature. There can be burning or tingling pain. Also, significant discomfort with temperature changes is a concern for thalamic pain syndrome following a stroke b. ANTERIOR INFARCTION Anterior nucleus deficiency. Thalamic nuclei artery and polar artery etc. are so small that you can’t even identify them in angiogram that is why they are prone in having infarction or hemorrhage. - Occlusion of the tuberothalamic or polar artery - Left side – thalamic aphasia- loss of reactivity, rarely seen. - Right side – hemineglect Hemineglect is an unawareness or unresponsiveness to objects, people, and other stimuli—sometimes patients even ignore or disown their own left limbs—in the left side of space. It is not that the patient can't see the stimuli, but rather that they have lost the will or motivation to attend to them or respond to them. Example: Patient close their eyes. You touch the right hand, patient can identify, you touch the left hand, patient can identify. When you asses one by one the patient can identify where did you touch her but if you touch her simultaneously or touch her on both side, patient only identify the right side, she Figure 26. Infarction. is neglecting the left side. Hemineglect can also see when you assess the vision, not only in touch but even in vision. - Alteration in consciousness, abulia, disorientation, personality changes. Abulia, also known as apathy, psychic akinesia, and athymia, refers to a lack of will, drive, or initiative for action, speech and thought, and is felt to be related to dysfunctions with the brain's dopamine-dependent circuitry. Emotional tone Anterior nucleus Recent memory Ventral anterior nucleus Influences activities of the motor cortex Ventral lateral nucleus Influences activities of the motor cortex Ventral posterolateral Relays sensory inputs to the sensory cortex Intralaminar nuclei Influence the levels of consciousness and alertness Figure 27. Neuroimaging: Infarction Medial geniculate nuclei Receives auditory information from both ears but predominantly from the opposite ear a. POSTEROLATERAL INFARCTION Lateral geniculate nuclei Receive visual information from the opposite field - Occlusion of the thalamogeniculate artery. of vision Supply lateral portion of the thalamus, function is mainly on sensory Table 3. The various thalamic nuclei and their functions. relaying. In patient expect a pure sensory deficit. Example: Patient came in with complaint that it can’t feel one side of the c. PARAMEDIAN INFARCTION body, is it stroke? Common people think that stoke is just a motor weakness/paralysis - Occlusion of the thalamic-subthalamic artery of one side of the body, but if thalamic stroke, body weakness/paralysis cannot be - Occlusion of Artery of Percheron - artery of Percheron is a rare anatomical expected all the time because the sensory input is affected here. Patient will variant of the posterior cerebral circulation, occlusion of which causes experience combination of pure sensory syndrome and motor syndrome. bilateral thalamic ischaemic strokes. This is characterized by the clinical Three common clinical syndromes: triad of vertical gaze palsy, memory impairment and coma. 1. Pure Sensory - Somnolence, memory loss, mood disturbances, vertical gaze 2. Sensorimotor abnormalities (VGA)- The vertical gaze abnormality in paramedian 3. Dejerine-Roussy thalamic infarctions is speculated to be due to interruption of - Contralateral sensory loss, thalamic pain, vasomotor disturbance, supranuclear fibers from the frontal eye fields traversing through the transient contralateral hemiparesis, mild hyperkinetic medial thalamus en route to the prerubral and pretectal areas. Some of disturbances the frontocortical fibers may decussate in the medial thalamus. Central post-stroke pain is a rare central neuropathic pain, thalamic pain VGA- patient can see on lateral side and downside but cannot be able to syndrome occurs after infarction of the ventroposterolateral thalamus. Déjerine- look up. Affect your midbrain, vertical gaze decreases gradually with age, but Roussy syndrome is characterized by chronic neuropathic pain that is present on the vertical gaze palsy is more severe than age-related changes. Usually, upward gaze Page 7 of 9 [NEUROSCIENCE1A]-01.11-The Thalamus– Dr. Vida Margarette D. Andal is affected. The most common cause of vertical gaze palsy is damage to the top part c. ACUTE DISSEMINATED ENCEPHALOMYELITIS (ADEN) of the brain stem (midbrain), usually by a stroke or tumor. In upward vertical gaze - Usually seen in kids palsies, the pupils may be dilated. When people with this palsy look up, they have - Monophasic postinfectious or postvaccination disorder that damages nystagmus. That is, their eye rapidly moves upward, then slowly drifts downward. myelin Seen during post infection or post vaccination (used to stimulate immune d. DORSAL INFARCTION system) due to overdrive (starts attacking the myelin) of the immune response of the - Occlusion of the posterior choroidal artery- can affect anterior nucleus, kid. It is considered as an autoimmune disease (the body inflate it upon itself). expect for vision problem. - T2/FLAIR hyperintensity - Homonymous quadrantinopia or hemianopia, variable sensory and - Frequently in thalamus, basal ganglia (and subcortical structures) hearing loss, memory impairment. - Dorsal hemorrhages or posterior choroidal artery infarcts present with minimal transient hemiparesis and hemihypesthesia; apraxia, aphasia, and amnesia have also been described. B. HEMORRHAGE As this happens, it does not respect territories, it crosses boundaries. It can extravasate anywhere. It can go inside the ventricles, and enter to the ventricular system and cause a lot of damage a. FABRY DISEASE - Seen in children - X-linked lysosomal storage disorder due to alpha-galactosidase A gene mutation - “Pulvinar sign” – T1 hyperintensity due to calcification Figure 28. Neuroimaging: Fabry Disease. b. OSMOTIC DEMYELINATING SYNDROME (ODS) - Formerly called central pontine myelinolysis or extrapontine myelinolysis - Loss of myelin due to uncontrolled osmotic gradient changes Figure 30. Neuroimaging: Acute Disseminated Encephalomyelitis. ODS is fault of the physician. When the patient is hyponatremic and you are trying to correct low sodium rapidly, as a result, the patient will have Osmotic d. GLIOBLASTOMA MULTIFORME Demyelinating Syndrome. - Primary Brain Tumor; frequently seen in the Thalamus - Common extrapontine locations: thalamus, basal ganglia, cerebral white - WHO Grade IV tumor matter, hippocampus, corpus callosum o With Glioblastoma Multiforme, at its onset, it’s already severe and Common location of ODS: at the Pons, that is why it was formerly called as aggressive. You must act quickly. central pontine myelinolysis, but can also be seen outside the pons, such as your o WHO Grade (severity) Tumor: I-mild; IV-severe thalamus and other locations. o Different for Stage (how the tumor is spread in the body of the - T1, T2/FLAIR hyperintense patient) I-confined to the organ; IV-travels at distant parts of the Manifested as hyperintensities in the MRI T1 and T2, so this is an example body of involvement of thalamus (B) in ODS, as well as mainly in pons (C). This is very tragic, - Heterogenous iso- to hypointense on T1, hyperintense on T2/FLAIR the patient is ventilator dependent, with tracheostomy, with a lot of autonomic - Central necrosis, perilesional vasogenic edema, strong enhancement abnormalities but intact cerebrum, all this time, patient is awake, patient can hear (solid, nodular, patchy, “closed-ring”), occasional hemorrhage inside the you, patient is aware, but the patient is paralyzed neck down because of the resident tumor who is excited to correct the sodium level of the patient at the ER. Figure 29. Neuroimaging: Osmotic Demyelinating Syndrome. Figure 31. Neuroimaging: Glioblastoma Multiforme. Page 8 of 9 [NEUROSCIENCE1A]-01.11-The Thalamus– Dr. Vida Margarette D. Andal e. GLIOMATOSIS CEREBRI VI. TEST YOUR KNOWLEDGE - Diffuse white matter infiltration You don’t have a solid tumor. But in the Thalamus, even if it’s made up of 1. This surface of the thalamus is continuous with the tegmentum of the midbrain gray matter, it still has white matter around it and through it, so it can still involve the A. Inferior thalamus. B. Posterior - Homogenous T2/FLAIR hyperintense, T1 hypointense. Absent or minimal C. Medial enhancement D. Anterior - Involves two or more lobes (like parietal lobe, frontal lobe). Usually involves the thalamus, basal ganglia (both gray matter) and corpus 2. The thalamus developed from the _________. callosum (white matter). A. Telencephalon B. Myelencephalon C. Mesencephalon D. Diencephalon 3. This artery supplies the medial region of the thalamus A. Thalamogeniculate arteries B. Tuberothalamic arteries C. Thalamic-subthalamic arteries D. Posterior choroidal arteries 4. Small collections of nerve cells within the internal medullary lamina and influences the levels of consciousness and alertness. A. Reticular Nucleus B. Intralaminar Nuclei C. Midline Nuclei D. Medial Geniculate Body 5. Medial Geniculate Body is a part of the visual pathway that receives afferent fibers from the inferior colliculus (inferior brachium). A. TRUE B. FALSE 6. Results in contralateral homonymous hemianopia A. Result of MGN lesion B. Result of LGN lesion C. Result of anterior nucleus lesion D. Result of dorsothalamic lesion. Figure 32. Neuroimaging: Gliomatosis Cerebri. 7. It is a group of nerve cells adjacent to the third ventricle and in the interthalamic f. LYMPHOMA connection. You can have lymphoma from a different part of the body and entered the A. Reticular Nucleus blood brain barrier and went into the brain. Other evidence show that a person can B. Lateral Geniculate Body also have Primary CNS Lymphoma especially in patients who are C. Midline Nuclei immunocompromised (like that of HIV patients). Commonly seen in meninges and in D. Medial Geniculate Body the thalamus. - Periventricular white matter, thalamus, basal ganglia and corpus 8. What is hemineglect? callosum A. Patient does not attend to the side of space contralateral to the lesion. - Homogenous T2/FLAIR hyperintense, T1 hypointense. Homogenous B. Patient attend to the side of space contralateral to the lesion. contrast enhancement in absence of central necrosis. C. Patient does not attend to the side of ipsilateral to the lesion. - In contrast to GBM, less or absent peritumoral edema, necrosis and D. Patient attend to the side of ipsilateral to the lesion. hemorrhage (the most definitive way of determining it is through biopsies) 9. In about 1/3 of the population, the tuberothalamic artery is missing and its territory is supplied by the thalamic-subthalamic artery from the same side. A. True B. false 10. Thalamus is a relay and integrative station for information going to the basal ganglia, hypothalamus, brainstem, and cerebral cortex. A. True B. False ANSWER KEY Figure 33. Neuroimaging: Lymphoma. 1. A, 2. D, 3. C, 4. B, 5. B, 6. B, 7. C, 8. A, 9. A, 10. A Page 9 of 9