Which procedure involves withdrawal of cerebrospinal fluid via a needle into the subarachnoid space?

• A. Lumbar puncture (spinal tap)
• B. Laparoscopy
• C. Laryngoscopy
• D. Hematocrit (Hct)

Answer: (A)

Accessing the cerebrospinal fluid requires inserting a needle into the subarachnoid space, and this is done with a lumbar puncture. In this procedure, a spinal needle is inserted in the lower back, typically between the lumbar vertebrae (below the end of the spinal cord, into the lumbar cistern), to withdraw CSF for analysis or to measure opening pressure. This is distinct from other procedures listed: laparoscopy explores the abdomen with a camera, laryngoscopy visualizes the larynx and airway, and hematocrit is a blood test measuring the proportion of red blood cells.