Neuroanatomy, Spinothalamic Tract

Structure and Function

The main function of the spinothalamic tract is to carry pain and temperature via the lateral part of the pathway and crude touch via the anterior part. The spinothalamic tract pathway is an imperative sensory pathway in human survival because it enables one to move away from noxious stimuli by carrying pain and temperature information from the skin to the thalamus where it is processed and transmitted to the primary sensory cortex. The primary sensory cortex communicates with the primary motor cortex, which lies close to it, to generate rapid movement in response to potentially harmful stimuli. Furthermore, the spinothalamic tract has a role in responding to pruritogens, causing us to itch. Interestingly, itching suppresses the spinothalamic tract neuron response to the histamine effect.

Clinical Significance

The spinothalamic tract is especially important when dealing with any kind of spinal cord injury. The spinothalamic tract is an anterolateral pathway. Since it is on the same side of the body, a lesion on this side of the body will cause a deficit of anything controlled below that point. Several spinal cord syndromes have spinothalamic tract involvement. Spinothalamic tract deficit leads to loss of pain and temperature sensations on one side of the body at about two levels below the lesion but on the contralateral side. An example of spinal cord syndrome with such findings is Brown-Sequard syndrome, also known as a hemicord syndrome, which compromises multiple tracts of the spinal cord, including the spinothalamic tract. However, bilateral loss of pain and temperature in a dermatomal fashion can be present in syringomyelia where the anterior white commissure becomes obliterated due to cavitation in the central spinal cord. Similar clinical presentations to syringomyelia also present in acute central cervical cord syndrome.[7][8][9]

In addition to trauma and cavitation, the spinothalamic tract can be compromised due to vascular issues as well. One example is anterior spinal artery syndrome, which is caused by infarction of the anterior spinal artery territory. Patients with anterior spinal artery syndrome present with pain and temperature loss bilaterally below the level of the lesion. However, vibratory and proprioceptive senses are preserved due to posterior column sparing. Lateral medullary syndrome caused by occlusion of posterior inferior cerebellar artery affects the spinothalamic tract as STT runs in the lateral aspect of the medulla, resulting in loss of pain and temperature sensations over the entire contralateral side of the body as well as on the ipsilateral face due to the spinal trigeminal tract involvement. Similarly, lateral pontine syndrome caused by the anterior inferior cerebellar artery can impact the spinothalamic tract giving a clinical picture that resembles that of lateral medullary syndrome. In lateral medullary and pontine syndrome, however, cranial nerve deficits and cerebellar findings coexist with STT deficit findings as well as Horner syndrome.  

A lesion localized to a ventral posterolateral in the thalamus will lead to an initial loss of all sensations from the contralateral side of the body, including pain. Over time, the patient may experience pain in all, or part, of the contralateral side of the body; this is referred to as thalamic pain syndrome (Déjérine-Roussy syndrome). This phenomenon of sensing the pain on the opposite side of the body can be detrimental to both the patient and practitioner. If the lesion is not obvious, the sensation and location described by patients can lead physicians to think that the pain is more psychological rather than physical. Practitioners need to keep this phenomenon in mind when evaluating patients for pain management.