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It is also known as spinal tap. It's a procedure for collecting CSF (cerebrospinal fluid) performed in lower back at the level of L2 to L3, L4 to L5 or L5 to S1 vertebrae.


Anatomical Positioning

The subject is preferably positioned on left side with chin brought close to chest and knees placed close towards chest and back is hunched (the subject approximates foetal position). Sitting position is preferred in obese patients as it also prevents scoliosis. In this position, patient is invited to bend forward in order to enlarge the interlaminal space.
In children the procedure is done at the level of L4 to L5 level because the spine of children is different from adults.


Local anaesthesia is given to the subject and a spinal needle is inserted at the target point. Needle is inserted until two GIVES are felt.

  • The first give shows the needle has passed the ligamentum flavum;
  • The second give shows the needle has passed the dura mater. As the arachnoid membrane is pushed towards dura mater in living person due to pressure of CSF, second give indicates that the needle has entered the arachnoid as well.

After the insertion of needle, the stylet is removed and CSF starts dripping from the opening in the needle. The pressure of CSF may also be measured by using manometer.


It is used for obtaining CSF which is used for diagnosis of:

  • Meningitis
  • Reye’s Syndrome
  • Cancer of CNS
  • Polio
  • Guillan-Barrè syndrome
  • Lyme’s disease
  • Neurosyphilis.

Also used to measure raised pressure of CSF due to congestive heart failure, cerebral edema and many other causes. Decreased CSF pressure indicates leaking of the fluid, severe dehydration or circulatory collapse and spinal blockage.



  • Intracranial hypertension (due to intracranial tumor, high risk of brainstem herniation)
  • Skin infection at puncture site
  • Age more than 65 years
  • Recent history of seizure
  • Focal neurological signs
  • Abnormal respiratory pattern
  • Hypertension with bradycardia and deteriorating consciousness
  • Decreased platelets count
  • Vertebral deformities


Effects on subject

  • Nausea
  • Vomiting
  • Headache
  • Serious complications may include epidural bleeding, trauma to spinal cord and arachnoiditis 



Atlas of Human Anatomy, Frank H. Netter, 6th edition 

Clinical Anatomy by Regions , Richard S. Snell, 8th edition

Clinical Neuroanatomy, Richard S. Snell

Moore Clinically Oriented Anatomy, 7th Edition




Shah Dais, MS

Medical Student
Bakhtawar Amin Medical and Dental College
Multan (Pakistan)