Hydrocephalus in a 3-Month-Old: A Short Case Discussion
Case Presentation and Diagnosis
What was the presenting history of the 3-month-old female child?
The child was born at full term via normal vaginal delivery at home. She presented with a progressive increase in head size since 3 weeks of age. There was no history suggestive of any raised intracranial pressure (ICP) or congenital anomalies.
What were the key findings on general and local examination?
The child was playful and non-irritable. Weight was 3.65 kgs. The sunset sign (impaired upward gaze) was positive. Vitals were stable. Airway examination: both nares patent, mouth opening adequate, no facial asymmetry.
Local examination of the head revealed: uniform enlargement, head circumference of 60 cm, thin shiny scalp with distended scalp veins. The anterior fontanel was open, romboid in shape, bulging, and non-pulsatile. The posterior fontanel was also open.
What was the provisional diagnosis for this patient?
The provisional diagnosis was hydrocephalus in a 3-month-old female child with a progressive increase in head size over 3 weeks, a head circumference of 60 cm, and without any features of raised ICP. The patient was subsequently posted for a VP (ventriculoperitoneal) shunt surgery.
Understanding Hydrocephalus: Definition, Types, and Physiology
What is hydrocephalus and what are its different types?
Hydrocephalus is an abnormal increase in the amount of cerebrospinal fluid (CSF) resulting from a disturbance of formation, flow, or absorption of CSF, thus resulting in enlarged cerebral ventricles. The two main types are:
- Obstructive (Non-communicating): Caused by a blockage in the ventricular system.
- Communicating (Non-obstructive): Caused by impaired CSF absorption.
Surgical options include ventriculoperitoneal (VP) shunt, ventriculoatrial (VA) shunt, ventriculopleural (VPL) shunt, and intraventricular shunt.
What is the normal flow of CSF and how does this help differentiate types of hydrocephalus?
- CSF is produced by the ependymal cells in the choroid plexus of the lateral ventricles.
- From the lateral ventricles, it reaches the third ventricle via the interventricular foramen (foramen of Monro).
- From the third ventricle, it flows through the aqueduct of Sylvius to the fourth ventricle.
- From the fourth ventricle, it reaches the subarachnoid space through the lateral foramina of Luschka and the median foramen of Magendie.
- From the subarachnoid space, it is absorbed via the arachnoid granulations.
This pathway helps differentiate hydrocephalus types:
- Obstructive Hydrocephalus: Results from an obstruction at any point within the ventricular system, such as the aqueduct of Sylvius or the foramina.
- Communicating Hydrocephalus: Usually results from impaired CSF uptake at the level of the arachnoid granulations or, rarely, from increased production.
Why is cerebral perfusion pressure (CPP) important in managing a case of hydrocephalus?
Maintaining cerebral perfusion pressure (CPP) is crucial during the perioperative period to prevent brain ischemia. CPP is maintained by ensuring an adequate mean arterial pressure (MAP) and by taking measures to prevent an increase in intracranial pressure (ICP). Normal ICP varies by age: neonates and infants have 0-6 mmHg, toddlers and preschoolers 3-7 mmHg, and older children 5-15 mmHg. Normal CSF volume in children is 2-4 ml/kg.
What are the various etiological factors that cause hydrocephalus?
Etiological factors can be broadly divided into congenital and acquired conditions.
- Congenital: Obstruction at the aqueduct of Sylvius, myelomeningocele, Arnold-Chiari malformation, Dandy-Walker syndrome, benign intracranial cysts, vein of Galen aneurysm, congenital CNS infections, craniosynostosis, or X-linked inherited conditions.
- Acquired: Post-meningitis infection, tumors leading to CSF blockade, intraventricular hemorrhage, trauma, granulomatous conditions, subarachnoid hemorrhage, arachnoiditis, or post-surgical complications.
What are the common clinical features of hydrocephalus in children?
Children usually present with a large head, a bulging fontanel, and prominent scalp veins. If they present with features of raised ICP, symptoms can include headache, vomiting, and altered level of consciousness. They may also present with oculomotor nerve palsy, sluggish pupillary light reflex, bradycardia, and respiratory arrest.
If associated with congenital conditions like Arnold-Chiari malformation, they can present with vocal cord dysfunction and difficulty swallowing, putting them at high risk of aspiration.
Preoperative Assessment and Preparation
What are the objectives of a pre-anesthetic evaluation for a patient with hydrocephalus?
The objectives are to:
- Look for general features of raised ICP and complications due to hydrocephalus.
- Assess the general well-being of the patient.
- Identify coexisting congenital anomalies like congenital heart disease, Down syndrome, or spina bifida.
- Review medication history (e.g., anticonvulsants like barbiturates, narcotics, diuretics) for potential interactions with anesthetics.
- Formulate an airway management plan due to anticipated difficult airway from the large head and pediatric anatomy.
- Assess the risk of aspiration due to potential vocal cord dysfunction.
What investigations would you like to see and how would you prepare this patient for surgery?
Investigations:
- Complete blood count: for baseline and to check for anemia.
- Renal function test and serum electrolytes: to correct dehydration or dyselektrolytemia from vomiting.
- Serum and urine osmolality: to rule out SIADH (Syndrome of Inappropriate Antidiuretic Hormone) due to pressure on the hypothalamus from increased ICP.
- Random blood sugar: to check for hypoglycemia.
- Chest X-ray and echocardiogram: if congenital heart disease is suspected.
- CT brain and MRA.
Preparation:
- Obtain informed and written consent from the parents.
- Explain NPO status: 6 hours for solids, 4 hours for breast milk, and 2 hours for clear fluids.
- Sedative medication is ideally avoided due to risk of respiratory depression. However, if the child is crying (which can raise ICP), the risk versus benefit must be calculated, and titrated doses of injection Midazolam may be given.
- Administer aspiration prophylaxis, such as a proton pump inhibitor or H2 blocker, and an anti-emetic due to delayed gastric emptying.
Intraoperative Anesthetic Management
What are the specific anesthetic concerns in a case of hydrocephalus?
Key concerns include:
- Difficult airway: Due to the large, wobbly head, which needs stabilization.
- Pediatric physiology: Anatomical and physiological variations of the pediatric age group must be considered.
- Maintaining CPP: By maintaining adequate MAP and taking measures to reduce ICP.
What is the preferred method of induction and what is the role of suxamethonium?
If an IV line is in place, IV induction is preferred to maintain CPP. Agents like propofol or thiopentone can be used; ketamine is best avoided as it can increase ICP. If no IV line exists, inhalation induction is used, especially if a difficult airway is anticipated. Once IV is secured, the case can proceed.
Suxamethonium causes a transient increase in ICP, but it allows for rapid airway securing. For a rapid sequence induction (RSI) with aspiration risk, suxamethonium can be used. If difficult airway is anticipated, inhalation induction is safer. Alternatives like rocuronium or atracurium can also be used.
How do you plan for intubation in a patient with a large head?
To align the airway axes, positioning is key. This can be achieved by:
- Placing rolled towels or support beneath the shoulders to align the ear with the chest.
- Lifting the child off the table, letting the head hang.
- Positioning the head hanging at the edge of the table. A flexometallic tube is used to prevent kinking, and intubation must be smooth to prevent rises in ICP or hemodynamic changes.
What are the specific intraoperative concerns and how are they managed?
Specific concerns include:
- Hemodynamic instability: Due to sudden release of CSF pressure or CSF loss, which can cause bradycardia.
- Positioning: Careful positioning is needed.
- Painful stimuli: Incision and tunneling are very painful and can cause hemodynamic changes. An extra bolus of fentanyl or alfentanil can be given.
- Hypothermia: Children are at high risk, so temperature monitoring is crucial.
- Ventilation strategy: Maintain normocapnia (EtCO2 35-45 mmHg) to avoid increased ICP (from hypercapnia) or brain ischemia (from hypocapnia).
- Maintenance: Use a mixture of air and oxygen. Avoid nitrous oxide as it is a potent vasodilator that can increase ICP. If using inhalation agents, keep them below 1 MAC to prevent increases in ICP.
How does the surgeon test the shunt and what is the anesthesiologist's role?
To assist the shunt, the anesthesiologist can perform a Valsalva maneuver. Increasing intrathoracic pressure facilitates the flow of CSF through the catheter and allows the surgeon to check for any CSF leak at the surgical site.
What are the specific concerns regarding fluid administration?
Assess for dehydration and ensure maintenance of circulatory volume with a balanced salt solution like Ringer's Lactate or Normal Saline. Due to poor feeding and a high risk of hypoglycemia, dextrose can be added to the solution. However, the mere use of 5% dextrose is avoided as it can increase ICP; instead, a 1% dextrose solution is preferred.
Postoperative Management and Complications
How do you extubate and manage the patient postoperatively?
The patient should be extubated only when fully awake to ensure a smooth emergence and prevent rises in ICP or hemodynamic changes. Postoperatively, the patient is shifted to a high-dependency unit with standard ASA monitors, including temperature monitoring.
Postoperative analgesia is multimodal:
- Injection bupivacaine 0.25% at the surgical site.
- Paracetamol infusion.
- Opioids are usually avoided due to the risk of respiratory depression; if used, close monitoring is required.
What is a 'ventricular slit event' and what is its significance?
A ventricular slit event can occur after a shunt placement, particularly with a ventriculopleural shunt. If the shunt valve malfunctions and drains CSF too fast, the ventricle can collapse over time, becoming a slit-like shape. This can lead to obstruction of the shunt catheter and subsequent shunt malfunction. This highlights the importance of checking valve function before leaving the shunt in place.
What is a possible thoracic complication of a ventriculopleural shunt?
During tunneling into the chest wall for a ventriculopleural shunt, there is a possibility of causing a pneumothorax. This is an important consideration in the postoperative period.