Heinrich Quincke introduced the spinal tap in 1891
Lumbar puncture, or spinal tap, threads a needle into the spinal canal—usually to draw cerebrospinal fluid for diagnosis, sometimes to deliver drugs. German physician Heinrich Quincke introduced the method in 1891. Local anaesthetic and sterile technique guide a hypodermic into the subarachnoid space.
Adults carry roughly 125 to 150 millilitres of cerebrospinal fluid, made mostly by the choroid plexus, which cushions the brain and spinal cord and ferries nutrients and waste before being reabsorbed. Analysing a sample can rule infection, inflammation or cancer in or out, and needles can also deliver spinal anaesthesia or chemotherapy directly into the fluid.
The site is chosen for safety. The spinal cord ends around the first or second lumbar vertebra, below which nerves hang in a loose bundle called the cauda equina that slides aside from a needle, so the lower lumbar cistern is the usual target. Patients typically lie curled on one side, chin to chest and knees drawn up, though sitting upright distorts the anatomy less and helps in obese patients. Ultrasound, where available, cuts down on repeated needle passes. In newborns the cord can end as low as the third lumbar vertebra.
Repeated taps can briefly relieve idiopathic intracranial hypertension, which threatens headaches and permanent sight loss, but medication remains the mainstay because relief is short and the procedure uncomfortable. Some people with normal pressure hydrocephalus, marked by walking trouble, incontinence and dementia, improve after fluid is drained. Raised intracranial pressure of unknown cause generally rules the tap out because it can force brain tissue to herniate, unless pressure is being lowered deliberately after a blockage has been excluded.
The commonest complication is a headache with nausea after the membrane is pierced. Lying flat for two hours afterwards, long recommended, has not helped in large studies; painkillers, fluids and intravenous caffeine often do, and a persistent leak can be sealed with an injection of the patient’s own blood. Atraumatic needles sharply cut that risk, yet only about 16 percent of practitioners used them around 2014. Serious harm, such as bleeding or nerve damage, is extremely rare.
Source: Lumbar puncture
