Neurosurgery Hydrocephalus Pneumocephalus

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

• 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

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

• 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
• 

• 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

• A. obstruction:
• B. disconnection at a junction, or break at any point
• C. infection
• D. hardware erosion through skin
• E. Seizures

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

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.

• 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.

• 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