**Question:** Dissociated sensory loss in a case of tumor of central Spinal cord is due to lesion of-

A. Cervical cord
B. Thoracic cord
C. Lumbar cord
D. Sacral cord

**Core Concept:** Dissociated sensory loss occurs when the sensory functions are preserved while motor functions are impaired in a spinal cord injury or tumor. This phenomenon is a result of the selective involvement of different segments of the spinal cord.

**Why the Correct Answer is Right:** In a tumor of the central spinal cord, the dissociated sensory loss is due to a lesion affecting the posterior columns of the spinal cord. The posterior columns are responsible for transmitting sensory information from the skin and deep tendon reflexes, while the anterior columns are responsible for motor functions. When the posterior columns are damaged, sensory functions remain intact, while motor functions are impaired.

**Why Each Wrong Option is Incorrect:**

A. The correct answer is not cervical cord; dissociated sensory loss does not occur when the lesion is only affecting the cervical cord.
B. Thoracic cord is incorrect as dissociated sensory loss is not specifically related to thoracic cord lesions.
C. Lumbar cord is incorrect as dissociated sensory loss is not specifically related to lumbar cord lesions.
D. Sacral cord is incorrect as dissociated sensory loss is not specifically related to sacral cord lesions.

**Clinical Pearl:** Understanding the anatomy of the spinal cord is crucial in assessing patients with spinal cord lesions or tumors. A thorough neurological examination, assessing sensory and motor functions, is essential for accurate diagnosis and management of spinal cord disorders.

**Correct Answer:** D. Sacral cord (S2-S3)

**Why the Correct Answer is Right:** In dissociated sensory loss, the lesion affecting the lower thoracic and lumbar segments of the spinal cord is less likely to result in dissociated sensory loss as these segments primarily involve motor functions. The dissociated sensory loss is most commonly seen when the lesion affects the sacral cord (S2-S3). The posterior columns in the sacral cord are responsible for sensory functions, while the anterior columns and motor neurons are present in lower thoracic and lumbar segments. Thus, when the lesions occur in sacral cord, sensory functions remain intact, while motor functions are impaired, resulting in dissociated sensory loss.

**Why Each Wrong Option is Incorrect:**

A. The correct answer is not cervical cord, as lesions in the cervical cord primarily affect motor functions, and dissociated sensory loss is less commonly observed.
B. Thoracic cord is incorrect because lesions affecting the thoracic cord primarily involve motor functions, making dissociated sensory loss less likely.
C. Lumbar cord is incorrect as lesions affecting the lumbar cord primarily involve motor functions, making dissociated sensory loss less likely.
D. Sacral cord is correct, as lesions in the sacral cord (S2-S3) result in dissociated sensory loss due to the involvement of sensory functions while motor functions remain intact.

**Clinical Pearls:**

1. Dissociated sensory loss is a key clinical sign that can help differentiate between