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OSCE 456: Lumbar Puncture 2

Introduction

You are supervising a junior doctor perform a lumbar puncture for a patient with suspected meningitis. You suggest using a spinal needle with a pencil point tip…

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Question No. 2

Q: Give 2 advantages of using a needle with a pencil point tip? (2 marks)

Answer No. 2

  • Separates the longitudinal fibres of the dura without cutting them, causing less trauma 1
  • Reduces CSF leakage and hence PDPH rates 1
  • Generates a more convincing ‘click’ on breaching the dura 1

2

Question No. 3

Q: Which spinal needles have a pencil point tip? (2 marks)

Answer No. 3

  • Whitacre 1
  • Sprotte 1
  • Ballpen 1

2

Question No. 4

Q: What landmarks would you use for safe insertion of the needle to perform lumbar puncture? (3 marks)

Answer No. 4

  • Lumbar puncture should be performed below the L2/3 interspace 1:
    • In adults, the solid spinal cord ends at L1 (ranges from T11 to upper L3)
    • At this level the conus medullaris continues distally as the cauda equina
    • Puncture above this level risks damaging the cord
  • The L4/5 or L3/4 interspace is usually used
  • The L4 spinous process can be estimated using Tuffier's line:
    • An imaginary line drawn between the iliac crests 1
    • Significant anatomical variation exists between patients
  • Alternative anatomic landmarks include:
    • The tip of the scapula in line with T7 spinous process 1
    • The tip of the 10th rib in line with L1 spinous process 1
Surface landmarks for vertebrae

3

Question No. 5

Q: Which layers does a needle pass through during lumbar puncture? (5 marks)

Answer No. 5

  • Skin
  • Subcutaneous fat1
  • Supraspinous ligament1
  • Interspinous ligament1
  • Ligamentum flavum1
  • Epidural space1
  • Dura mater1
  • Arachnoid mater1
  • Subarachnoid space1
Layers passed through when performing lumbar puncture or spinal anaesthesia

5

Question No. 6

Q: Other than diagnosis of meningoencephalitis what are the indications for lumbar puncture? (5 marks)

Answer No. 6

Diagnostic
  • Investigate meningoencephalitis
  • Investigate neurological disorders max 1:
    • Multiple Sclerosis
    • Guillain Barre
    • Mitochondrial Disorders
    • Paraneoplastic Syndromes
  • Investigate subarachnoid haemorrhage 1
  • Investigate disorders of intracranial pressure 1
  • Administer diagnostic agents 1:
    • Contrast media in myelography
Therapeutic
  • Spinal anaesthesia1
  • Administer therapeutic agents max 1:
    • Intrathecal chemotherapy
    • Intrathecal antibiotics
    • Intrathecal baclofen
  • Manage specific disorders max 1:
    • Benign intracranial hypertension
    • Acute communicating hydrocephalus
    • Cryptococcal meningitis in HIV infection
    • CSF leak

5

Question No. 7

Q: What are the CSF features in keeping with a diagnosis of bacterial meningitis? (3 marks)

Answer No. 7

Normal
Bacterial Meningitis
Opening Pressure (cm/H2O)
5-20
>30 1
Appearance
Clear, colourless
Turbid
RBC
(per mm3)
<3
Normal
WCC
(per mm3)
<5
>500
(Up to 100,000) 1
Cell Differential
Usually lymphocytes and monocytes
Neutrophilic (polymorphonuclear) pleocytosis 1
Protein
(g/L)
0.2-0.4
>1
(High) 1
Glucose-Serum Ratio
0.5-0.66
(2.5-3.5 mmol/L)
<0.4 1
Lactate
(mmol/L)
<2.8–3.5
Elevated 1
Microscopy and Gram Stain
-
60-80% positive Gram Stain
Culture
-
Up to 80% positive
PCR
-
-
Other
-
-

3

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