Dissociated sensory loss in a case of tumor ofcentral spinal cord is due to lesion of:

Decussating fibres of lateral spinothalmic tract Dissociated sensory loss is a pattern of neurological damage which involves selective loss of pain and temperature with preservation of fine touch and proprioception. Pain and temperature are carried by lateral spinothalmic tracts, which cross the central pa of the cord sholy after entering the spinal cord and ascend in the contralateral side. Fine touch and proprioception are carried in dorsal column fibres which do not cross the cord until medulla. Since fibers conducting pain and temperature sensation cross the cord in the anterior commissure, a lesion in this location will characteristically abolish these modalities on one or both sides over several segments but will spare the tactile sensation (fine touch and proprioception). This is known as dissociated sensory loss and is a characteristic feature of the Central spinal cord syndrome (Syringomyelic Syndrome). The central spinal cord syndrome is best exemplified by syringomyclia, hydromyelia, hematomyelia, and intramedullary cord tumors.