Tag Archives: hydrocephalus

Classification of Hydrocephalus

 

The first level of classification of hydrocephalus should be based on the point where flow of CSF is restricted.  These potential sites of restriction would include:

  • the foramen of Monro
  • the aqueduct of Sylvius
  • the basal cisterns
  • the arachnoid granulations
  • theoutflow of venous blood from dural venous sinuses

Hydrocephalus without a point of obstruction or increased resistance to flow would be communicating hydrocephalus.

After the point of obstruction has been determined, the classification should then include the etiology of the condition, chronicity and age of the person.

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[ABOVE] Illustration derived from applying engineering principles to the study of ventricular volume regulation.  The CSF system is illustrated using a compartmental model, with each compartment having its own pressure and volume related to CSF flow.  Circuit Diagram of the CSF pathway as a hydraulic analog of an electrical circuit.

[BELOW] Six compartment model of the CSF pathways.

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[BELOW] Artist rendering of the circuit diagram.

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Based on their studies, there were no pressure differential anywhere within the system.  Pulse wave was transmitted undiminished and instantaneously to all transducers intracranialy.  This means that the brain is a viscoelastic substance, acting as a fluid chamber where changes in pressure are transmitted instantaneously and fully to all areas.

Exception to the rule:  If one of the lateral ventricles was drained to subatmospheric pressure, a pressure differential of 12mm Hg can be measured.  This is seen in “post-shunt ventricular asymmetry” – in children who are shunted, septum pellucidum is drawn toward shunted ventricle and rests on head of caudate nucleus leading to a functional and reversible obstruction of flow.

NPH – likely obstruction between spinal and cortical subarachnoid spaces, dense arachnoidal thickening around brainstem in posterior fossa, blockage results from either SAH or infection, frequently involves area around brainstem selectively, amenable to endoscopic III ventriculostomy

Increased pressure in dural venous sinus results in pseudotumor cerebri and not HCP.  Drainage of CSF into venous sinuses requires a gradient between ICP and sagital sinus pressure of 5-7mm Hg.  If pressure in sagittal sinus is elevated, ICP must elevated in order for CSF to be absorbed.  ICP slowly goes up until CSF can be absorbed (if skull volume is fixed).  In cases of large craniectomies, ICP is in communication with atmospheric pressure.  ICP cannot go above atmospheric pressure and patient develops hydrocephalus.

Study done in rabbits where SSS was occluded.  Rabbits whose skull was intact developed intracranial hypertension without ventriculomegaly.  Craniectomized rabbits developed hydrocephalus.

Table below shows the treatment options for each point of obstruction in the CSF pathway.

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Reference

Rekate, Harold L. “A Consensus On The Classification Of Hydrocephalus: Its Utility In The Assessment Of Abnormalities Of Cerebrospinal Fluid Dynamics”. Child’s Nervous System 27.10 (2011): 1535-1541.

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Hydrocephalus CT Findings

KEY FINDINGS of HCP on neuroimaging:

  • expansion of the temporal horns
  • convexity of the third ventricular walls
  • rounding of the frontal horns
  • effacement of sulci
  • enlargement of ventricles out of proportion to sulcal dilatation

 

Reference:

Dupont, Stefan and Alejandro A Rabinstein. “CT Evaluation Of Lateral Ventricular Dilatation After Subarachnoid Hemorrhage: Baseline Bicaudate Index Balues”. Neurological Research 35.2 (2013): 103-106.

CHESS (Chronic Hydrocephalus Ensuing from SAH Score)

The European Journal of Neurology recently published a risk score that allows early estimation of the probability for shunt dependency after subarachnoid hemorrhage. CHESS stands for Chronic Hydrocephalus Ensuing from SAH Score.  This score can be helpful in deciding whether a permanent CSF diversion is needed in post-hemorrhage hydrocephalus (PHH).

Inclusion criteria for the study:

  1. admission and treatment of ruptured aneurysm within 48 hours post-ictus
  2. patient survives up to the time of decision-making for shunt placement

 

Baseline Characteristics:

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PHH was divided into 3 stages:

  1. acute (0-3 days post-SAH)
  2. subacute (4-13 days)
  3. chronic (>=14 days)

METHODOLOGY:

All patients with acute PHH underwent CSF diversion via EVD or lumbar drainage.  Continuous drianage was maintained for at least 7 days.  Patients who developed subacute PHH were treated with serial lumbar punctures.

The drain (EVD or lumbar drain) was challenged starting the second week of SAH in the absence of clinical contraindications (ICP issues or infection).  Drain was closed for 48 hours with CT scans performed before and after clamping.

Patients considered to fail EVD/LD challenge if:

  1. they deteriorate neurologically and/or they have increased headaches that improve with unclamping the drain
  2.  sustained ICP increase >20 cm H20
  3. radiographic evidence of increased ventricular size compared to baseline CT (CT prior to clamping)

Shunt placement was performed after two unsuccessful clamping trials.

 

RESULTS:

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The  following independent risk factors were identified and included in the CHESS:

  1. Hunt and Hess grade ≥IV (1 point, OR = 2.65)
  2. aneurysm in posterior circulation (1 point, OR = 2.37)
  3. (+) IVH on initial CT (1 point, OR = 2.41)
  4. (+) acute PHH (4 points, OR = 9.36)
  5. early cerebral infarction on follow-up CT scan (1 point, OR = 2.29)

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The ROC curve between the CHESS and shunt rates showed a significant cutoff at 6 points.

  1. CHESS score ≥6 = 6.74-fold higher risk for shunt dependency (P < 0.0001)
  2. CHESS score <6 points showed NPV of 84.9%.
  3. CHESS <2 points showed NPV of 98.5%

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UTIILITY:

  1. avoid unnecessary prolonged EVD/LD weaning (and reduce catheter-related meningitis)
  2. reduce readmission rates (for delayed shunt placement)

Based on this score, patients can be stratified into:

  1. high risk – score of 6-8
  2. moderate risk – 2-5
  3. low risk – 0-1

A shunt-restrictive policy as well as an early transfer to rehabilitation can be considered in SAH patients with low CHESS scores.

 

References

Jabbarli, R. et al. “The CHESS Score: A Simple Tool For Early Prediction Of Shunt Dependency After Aneurysmal Subarachnoid Hemorrhage”. Eur J Neurol (2016).