Which statement about the spinal cord and its surrounding meninges and nerves is correct?

Let's evaluate each statement to determine which one is correct.

• A. Pia mater of the spinal cord terminates prior to dura and arachinoid mater. The spinal cord proper ends as the conus medullaris, typically around the L1-L2 vertebral level. The pia mater continues as the filum terminale, which extends down to the coccyx. The dura mater and arachnoid mater form the dural sac, which typically extends down to the S2 vertebral level, enclosing the filum terminale and the cauda equina. Therefore, the pia mater (as the filum terminale) extends within the dural sac for a significant distance, and the dural sac itself terminates more caudally than the spinal cord. The statement is incorrect because the dura and arachnoid mater extend further caudally than the termination of the spinal cord itself, and the filum terminale (pia mater) is contained within this extended dural sac.

• B. Cauda equine contains spinal nerves extending from lumbar to coccygeal nerves. The cauda equina (Latin for "horse's tail") is a bundle of spinal nerves and nerve rootlets that extends from the conus medullaris. It includes the lumbar, sacral, and coccygeal spinal nerves, which descend within the vertebral canal before exiting at their respective intervertebral foramina. This statement is correct.

• C. Except the first cervical nerve, spinal nerves leave the vertebral column above the body of the corresponding vertebrae. There are 8 cervical spinal nerves (C1-C8) but only 7 cervical vertebrae (C1-C7).

  • C1-C7 nerves exit above their corresponding vertebrae.
  • The C8 nerve exits below the C7 vertebra (and above the T1 vertebra).
  • From the thoracic region downwards (T1-Co1), all spinal nerves exit below their corresponding vertebrae. Therefore, the statement is incorrect because only cervical nerves C1-C7 exit above their corresponding vertebrae, and all nerves from C8 downwards exit below.

• D. The size of grey matter of spinal cord progressively increased from cervical to sacral regions. The gray matter of the spinal cord is not progressively increased from cervical to sacral regions. It is largest in the cervical enlargement (C4-T1) and the lumbar enlargement (L2-S3) due to the innervation of the upper and lower limbs, respectively. The thoracic region has a relatively smaller amount of gray matter compared to the cervical and lumbar enlargements. Therefore, the statement is incorrect.

Based on the analysis, only statement B is correct.

The final answer is $\boxed{\text{B}}$