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
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
Signs and symptoms of 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
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
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
Complications of shunt
- A. obstruction:
- B. disconnection at a junction, or break at any point
- C. infection
- D. hardware erosion through skin
- E. Seizures
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.
- 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 -
- Previous surgery
- Tumours of the paranasal sinuses
- Nitrous oxide
- Clinical features -
- Severe restlessness
- Deteriorating consciousness
- Focal neurological deficits
- Cardiac arrest
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.
Diagnosis of pneumocephalus?
'Mount Fuji’ sign
- 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.
- in tension pneumocephalus when the presence of subdural free air causes the compression and separation of the frontal lobes.
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