Cerebrospinal fluid - main abnormalities

Cerebrospinal Fluid (CSF) or Cerebrospinal Liquid (CSL) is secreted by the choroid plexuses, circulates in the ventricular system and subarachnoid spaces, and is drained through venous resorption via the flap valves of Pacchioni's granulations.

It serves mechanical (shock absorption), immune, pressure regulation, and transport functions.

A sample can be obtained through a lumbar puncture, more rarely through a surgical device, or exceptionally, directly through a dural breach. Its analysis is a central step in the diagnostic, prognostic, or therapeutic evaluation of many neurological clinical situations.

Contraindications, Complications, and Indications... of a Lumbar Puncture (LP)

Contraindications (relative depending on the severity and clinical probability of the presumed diagnosis):

• Presence of a central nervous system lesion with a significant mass effect or obstructive hydrocephalus
• Proximity of the possible puncture points to a skin infection
• Major hemostasis disorders (always perform a complete blood count and coagulation test in cases of suspected hepatic insufficiency or hematopathy), thrombocytopenia (platelets < 30000/ mm3 or rapidly developing thrombocytopenia), effective anticoagulation. If sampling is essential, seek hematological advice beforehand to correct the disorders as best as possible (platelet transfusions, etc.).

Complications

Cerebral Herniation

• Rare, risk exists in the presence of a lesion with mass effect
• Risk of temporal herniation in cases of supra-tentorial lesion, cerebellar herniation in cases of infra-tentorial lesion. Rapid fatality is the norm.
• Upon suspicion: cerebral CT scan, notify a neurosurgeon (or any senior surgeon in the absence of a readily available neurosurgeon) to consider decompression without waiting for imaging results.

Extradural or Subdural Hematomas

• Exceptional, complications mainly occur in cases of coagulopathy or therapeutic anticoagulation at effective doses
• Risk of cauda equina and terminal cone (medullary) distress. Dark functional prognosis.
• Upon suspicion: spinal cord CT scan (MRI in case of negative CT if Hb < 10 g/dl, as blood may then appear isodense on the scan) → pain relief, correct coagulation disorders, neurosurgical consultation without waiting for imaging results.

Abscesses, Meningitis, and Septic Cerebral Venous Thromboses (CVT)

• Exceptional, by catheter contamination
• Prevention: equipment sterility, disinfection, ensure absence of local infection

Disc Herniation

• Exceptional, on ligamentous lesions

"Post-LP" Headaches

• Frequent, likely due to intracranial hypotension on occult dural breaches
• There are no Evidence-Based Medicine (EBM) on this matter, but certain measures are recommended by consensus to minimize the risk of their occurrence: thin catheter, strict 6-hour post-LP decubitus rest with oral hyperhydration
• Intracranial hypotension clinic (see intracranial hypotension syndrome): dominated by orthostatic headaches with +/- paresthesias, exceptionally observed cranial nerve involvement (traction), nonspecific visual disturbances
• Diagnosis is clinical. An MRI of the neuraxis with gadolinium - often not contributive - is only indicated in cases of atypical clinical presentation and diagnostic doubt.
• No therapeutic EBM, but suggest blood-patch + decubitus rest + pain relievers + hyperhydration. Spontaneous resolution of the syndrome in the following days is the norm.
• Suspect complications of intracranial hypotension (exceptional) in cases of disappearance of orthostatic character or worsening of symptoms:
  • Subdural Hematomas
  • Cerebral Venous Thromboses

Dermoid Implants

• Rare, with most cases described following the introduction of a catheter without a trocar. Their treatment consists of surgical excision.

Formal Indications for Emergency Lumbar Puncture

• For diagnostic purposes:
  • Suspicion of meningitis or meningoencephalitis: lumbar puncture within 30 minutes of admission.
    • Performing a lumbar puncture in no way justifies delaying the administration of antibiotics in cases of suspected bacterial meningitis and/or acyclovir in cases of suspected herpetic encephalitis. The analysis of cerebrospinal fluid, including cultures, is not altered in the first 24 hours following the initial administration of antibiotics.
    • Systematically perform a cerebral CT scan pre-puncture in cases of presence of focal neurological deficits or signs of intracranial hypertension
  • Strong suspicion of subarachnoid hemorrhage (SAH) with normal CT scan
  • Suspicion of intracranial hypertension (ICH) with normal cerebral imaging
  • Suspicion of acute inflammatory pathology of the nervous system (acute disseminated encephalomyelitis, myelitis, acute polyradiculoneuritis, ...)
• For therapeutic purposes:
  • Lumbar punctures for discharges of 30 to 40 cc in cases of intracranial hypertension in the absence of mass effect (cerebral venous thromboses, idiopathic intracranial hypertension, ...) with visual disturbances or significant headaches or papillary edema resistant to acetazolamide (diamox)

In cases of contraindication to performing a lumbar puncture, surgical sampling of cerebrospinal fluid can be exceptionally considered with a neurosurgeon depending on clinical imperatives.