Neurosurgery Hydrocephalus Pneumocephalus

  1. Classification of hydrocephalus?
    1. obstructive (non-communicating): block proximal to the arachnoid granulations (AG). On CT or MRI: enlargement of ventricles proximal to block (e.g. obstruction of aqueduct of Sylvius -+ lateral and 3rd ventricular enlargement out of proportion to the 4th ventricle, sometimes referred to as triventricular hydrocephalus)

    2. communicating (non-obstructive): CSF circulation blocked at level of AG
  2. Etiology of HCP?
    • 1. Congenital
    • a. Chiari malformation
    • b. Aqueductal stenosis
    • c. Dandy Walker malformation

    • 2. Acquired
    • a. Infectious - post meningitis (TB, cryptococcus),
    • b. Post-SAH
    • c. Secondary to mass
  3. Signs and symptoms of HCP?
    Active HCP

    • In young children
    • 1. cranium enlarges at a rate > facial growth
    • 2. irritability, poor head control, NN
    • 3. fontanelle full and bulging
    • 4. enlargement and engorgement of scalp veins: due to reversal of flow from intracerebral
    • sinuses due to increased intracranial pressure23
    • 5. Macewen's sign: cracked pot sound on percussing over dilated ventricles
    • 6. 6th nerve (abducens) palsy: the long intracranial course is postulated to render
    • this nerve very sensitive to pressure
    • 7. "setting sun sign" (upward gaze palsy): Parinaud's syndrome from pressure on region of supra pineal recess
    • 8. hyperactive reflexes
    • 9. irregular respirations with apneic spells
    • In older children/adults with rigid cranial vault
    • Symptoms of increased ICP, including: papilledema, HI A, NN, gait changes, upgaze and/or abducens palsy

    • Chronic HCP
    • 1. beaten copper cranium  on plain skull xray
    • 2 . 3rd ventricle herniating into sella (seen on CT or MRI)
    • 3 . erosion of sella turcica  which sometimes produces an empty sella, and erosion of the dorsum sella
  4. CT/MRI criteria of hydrocephalus?
    • A. the size of both temporal horns (TH) is ≥2 mm in width (in the absence of HCP, the temporal horns should be barely visible). 
    • B. both TH are ≥2 mm, and the ratio.FH/ID > 0.5 (where FH is the largest width of the frontal horns, and ID is the internal diameter from inner-table to inner-table at this level). 
    • C. Other features 
    • 1. ballooning of frontal horns of lateral ventricles ("Mickey Mouse" ventricles) and/or 3rd ventricle (the 3rd ventricle should normally be slit-like)
    • 2. periventricular low density on CT, or periventricular high intensity signal on T2WI on MRI suggesting transependymal absorption of CSF
    • 3. Evans ratio : ratio of FH to maximal biparietal diameter (BPD) measured in the same CT slice: > 0.3
    • Image Upload 1
  5. Treatment of HCP?
    • A. Medical
    • 1. Diuretic therapy - acetazolamide, furosemide
    • 2. Spinal taps - HCP after intraventricular hemorrhage may be only transient Serial taps, may temporize until resorption resumes but LPs can only be
    • performed for communicating HCP.

    • B. Surgical
    • 1. choroid plexectomy
    • 2. eliminating the obstruction: e.g. opening a stenosed sylvian aqueduct.
    • 3. third ventriculostomy
    • 4. shunting
    • a. ventriculoperitoneal (VP) shunt
    • b. ventriculo-atrial (VA) shunt
    • c. ventriculopleural shunt
    • d. lumboperitoneal (LP) shunt
  6. Complications of shunt
    • A. obstruction:
    • B. disconnection at a junction, or break at any point
    • C. infection
    • D. hardware erosion through skin
    • E. Seizures
  7. Short note on Tension Pneumocephalus. [TU 2073, 72/6]
    Pneumocephalus is defined as the presence of intracranial gas. Tension pneumocephalus is defined as intracranial gas under pressure.

    • Mechanism:-
    • 1. When nitrous oxide anesthesia is not discontinued prior to closure of the dura
    • 2. "ball-valve" effect due to an opening to the intracranial compartment with soft tissue (e.g. brain) that may permit air to enter but prevent exit of air or CSF
    • 3. When trapped room temperature air expands with warming to body temperature: a modest increase of only - 4% results from this effect
    • 4. in the presence of continued production by gas-producing organisms

    • Causes of Pneumocephalus -
    • Trauma
    • Previous surgery
    • Tumours of the paranasal sinuses
    • Infections.
    • Nitrous oxide

    • Clinical features -
    • Severe restlessness
    • Deteriorating consciousness
    • Focal neurological deficits
    • Cardiac arrest
  8. Mechanism of Nitrous oxide to cause pneumocephalus?
    Nitrous oxide dissolves into the blood and enters the closed subdural space at a rate that is faster than the rate at which nitrogen is vented, thus increasing the amount of postsurgical pneumocephalus.
  9. Diagnosis of pneumocephalus?
    • CT scan - can detect air as low as 0.5 ml.
    • Air appears dark black (darker than CSF) and has a Hounsfield coefficient of -1000.

    'Mount Fuji’ sign - in tension pneumocephalus when the presence of subdural free air causes the compression and separation of the frontal lobes.
  10. Treatment of Pneumocephalus?
    • Breathing 100% 02 via a nonrebreather mask increases the rate of resorption (100% Fi02 can be tolerated for 24-48 hours without serious pulmonary toxicity).
    • Tension pneumocephalus producing significant symptoms must be evacuated.
    • The urgency is similar to that of an intracranial hematoma.
    • Dramatic and rapid improvement may occur with the release of gas under pressure.
    • Options include placement of new twist drill or burr holes, or insertion of a spinal needle through a pre-existing burr hole
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Neurosurgery Hydrocephalus Pneumocephalus