Hydrocephalus Associated with Myelomeningocele

Abstract

Hydrocephalus (HCP) is one of the most common associations of myelomeningocele, and it may be overt and present at birth or be latent and develop following the repair of myelomeningocele. In patients with myelomeningocele, aqueductal stenosis, fourth ventricular obstruction, subarachnoid obstruction at the tentorial hiatus, and the crowded posterior fossa, which are all related to Chiari II malformation, are the various causes of hydrocephalus. The clinical manifestations depend on the age at presentation, but most patients present with macrocephaly and craniofacial disproportion, increasing head size, bulging anterior fontanelle, calvaria sutural diastasis, distended scalp veins, poor feeding as well as signs of raised intracranial pressure such as vomiting, headache, and altered consciousness. Diagnosis is based on clinical features and supportive radiological investigations such as transcranial ultrasound, brain computerized tomographic scan, and brain magnetic resonance imaging. Prompt treatment is very important to obtain optimal clinical outcomes, and this may be by inserting a shunt or performing endoscopic third ventriculostomy with or without choroid plexus cauterization.

1. Introduction

Hydrocephalus may be defined as abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles of the brain, leading to ventricular expansion or enlargement and usually associated with raised intracranial pressure [1, 2]. Hydrocephalus (HCP) is one of the most common associations of myelomeningocele, and it may be overt and present at birth or be latent and develop following the repair of myelomeningocele. It complicates 35–91% of myelomeningocele [3, 4].

It has been reported that the rate of treated hydrocephalus in patients with myelomeningocele varies with the anatomic level of the lesion, 60.7% for sacral, 82.4% for lumbar, and 92.2% for thoracic [4].

Prenatal (fetal) myelomeningocele repair has been shown to significantly reduce the need for insertion of ventriculoperitoneal shunt at 1 year following fetal surgery (prenatal group: 40% vs. postnatal group: 82%) [5].

2. Pathogenesis of hydrocephalus in patients with myelomeningocele

Several obstructive and absorptive factors act together to cause hydrocephalus in patients with myelomeningocele.

The unified theory proposed by McLone and Knepper is the most popular postulation for the evolution of hydrocephalus in patients with myelomeningocele. It postulates that persistent CSF loss from the neural tube defect impairs brain and CSF pathways development, which results in the downward displacement of the brain stem and crowding of the posterior fossa that leads to hydrocephalus [6].

Type II Chiari malformation with an overcrowded posterior fossa causes obstruction of the fourth ventricular outlets and disturbance in the flow of cerebrospinal fluid at the craniocervical junction, and it is the major factor responsible for obstructive hydrocephalus in patients with myelomeningocele [7]. There may be associated stenosis or forking of the cerebral aqueduct, also causing obstruction to CSF flow. The crowded posterior fossa results in venous compression, which leads to increased venous pressure that impedes CSF absorption [7, 8]. Furthermore, there is a higher resistance to the flow of CSF across the tentorial hiatus and there may be associated underdevelopment of the arachnoid granulations, which results in impaired or inadequate CSF absorption [9].

These factors result in progressive ventriculomegaly and raised intracranial pressure if unchecked, which are responsible for the clinical and radiologic features of hydrocephalus seen in these patients.

3. Clinical features

This depends on the age at presentation and the time after the onset of symptoms or previous surgical intervention.

3.1 Neonates and infants

At birth, hydrocephalus is apparent in about 15% of neonates with myelomeningocele, with features such as macrocephaly with craniofacial disproportion, increasing head size, bulging anterior fontanelle, calvaria sutural diastasis, distended scalp veins, poor feeding, vomiting, sunsetting eyes, bradycardia, and recurrent apnea [1].

Patients who have had myelomeningocele repair may present with pseudomeningocele at the site of repair; CSF leak from the repair and lower brainstem compromise from the Chiari II malformation may cause stridor from vocal cord weakness, a weak high-pitched cry, swallowing difficulties, poor feeding, nasal regurgitation of feeds, weakness, and hypotonia [10].

Occipito-frontal circumference measurement is important because the patent fontanelles and calvarial sutures may mask overt signs of raised intracranial pressure due to increasing head size, though there may be significant pathology in the brain. When OFC crosses centiles or increases rapidly, surgical intervention is mostly indicated [11].

3.2 Post infancy

Beyond infancy, hydrocephalus typically presents with features of raised intracranial pressure such as headache, vomiting, and altered consciousness. They may also present with loss of developmental milestones, diplopia, unsteady gait, and impaired cognitive functions (Figure 1) [1].

Figure 1.

Clinical picture of an infant with macrocephaly, bulging anterior Fontanelle, craniofacial disproportion, and distended scalp veins.

4. Investigations

4.1 Trans Fontanelle ultrasound

Trans fontanelle ultrasound is useful in patients with open anterior fontanelle. It is easy to carry out, cheap, and widely available. It can assess ventricular size, evaluate other anatomic anomalies, and detect other pathologies such as intraventricular hemorrhage [11].

4.2 Brain magnetic resonance imaging (MRI)

It is a noninvasive, more accurate, and sensitive investigation modality; however, it is expensive and may not be readily available, particularly in low- and middle-income countries (Figures 2 and 3).

Figure 2.

Axial T2 weighted MRI, blue arrow shows enlarged frontal horn of lateral ventricle, red arrow shows enlarged third ventricle, and black arrow shows disproportionately large occipital horn of the lateral ventricle (colpocephaly).

Figure 3.

Sagittal T2 weighted MRI of a patient with Chiari II malformation, blue arrow shows enlarged lateral ventricle, white arrow shows enlarged Massa intermedia, red arrow shows aqueductal stenosis, yellow arrow shows small 4th ventricle, and green arrow shows inferiorly displaced cerebellar tonsil.

4.3 Brain computerized tomographic scan

It is a sensitive and widely available modality, but with exposure to radiation, there are concerns for the risk of tumors and adverse effects on cognition (Figure 4) [11].

Figure 4.

Axial non-contrast CT showing marked thinning/flattening of the cerebral cortex (blue arrow) and severe ventriculomegaly (red arrow).

5. Diagnosis

Based on clinical findings and supportive radiologic investigations.

5.1 Prenatal diagnosis

5.1.1 Fetal ultrasound

High-resolution fetal ultrasound may be used to diagnose hydrocephalus prenatally. It is a noninvasive, sensitive, readily affordable, and available investigation, but it is observer dependent [11].

5.1.2 Magnetic resonance imaging

Fetal magnetic resonance imaging (MRI) is a more accurate and noninvasive, but expensive investigation which may not be readily available and is subject to motion artifacts. It is very useful when fetal ultrasound is not conclusive and also provides accurate anatomic details about other anomalies of the brain and spinal cord that may be present [11].

6. Treatment

6.1 Nonoperative management

Asymptomatic patients with static or slowly increasing head size may be managed with routine clinic visits, to measure head circumference, monitor ventricular size with trans fontanelle ultrasound or MRI and assess for symptoms of hydrocephalus or associated Chiari II malformation [6].

6.2 Ventriculoperitoneal shunt (VPS) insertion

Shunts may be inserted simultaneously with the repair of myelomeningocele or after. There is no consensus on the timing of placement of shunts, but it has been reported that simultaneous repair of myelomeningocele and shunt insertion is not associated with increased risk of shunt complications [12, 13].

The shunt has three parts: a ventricular catheter, a unidirectional valve that controls CSF drainage, and a peritoneal catheter that drains CSF into the peritoneal cavity. The VP shunt drains CSF from the ventricles to the peritoneal cavity. However, if the peritoneal cavity is not a viable option, the shunt may be inserted into the pleural cavity or right atrium of the heart [6]. The ventricular catheter may be inserted in a right frontal, parietal, or occipital region [14]. A shunt passer is tunneled subcutaneously between the abdominal and scalp incisions, the peritoneal catheter is passed from the cranial incision to the abdominal incision and the shunt passer is withdrawn, leaving the catheter in the subcutaneous space. The ventricular and peritoneal catheters are connected with a connector and secured to the pericranium. Distal flow of CSF is confirmed from the peritoneal catheter, which is subsequently inserted into the peritoneal cavity under direct vision or laparoscopically.

Complications of VP shunt insertion may range from 1 to 40% and include shunt extrusion, breakage, over drainage, obstruction, infection, and migration. Shunt infection rates of 2–9% have been reported in developed countries and 8.6–50% in developing countries [15].

6.3 Endoscopic third ventriculostomy with choroid plexus cauterization (ETV + CPC)

ETV + CPC is becoming an increasingly popular first-line treatment for hydrocephalus associated with myelomeningocele with a success rate as high as 76%. It has been reported that ETV alone has a low success rate (35%) among patients with myelomeningocele when compared with ETC + CPC (76%) [16, 17].

ETV success score was developed for predicting the success rate of ETV, and it is based on the age of the patient, etiology of hydrocephalus, and whether the patient has had a VPS inserted previously or not. It was proven that age > 6 months, etiology such as aqueductal stenosis and tectal tumors, as well as no previous shunt insertion, were factors that increase the success rate of ETV. Myelomeningocele, previous shunt insertion, and age < 6 months were predictive of low success rates. Benjamin Warf modified the ETV success score by adding choroid plexus cauterization and termed it Cure Children’s Hospital of Uganda (CCHU) ETV success score. He reported that choroid plexus cauterization significantly increased the success rates following ETV [18, 19].

The main attractions of this modality of treatment are the absence of a foreign body and its related complications, much lower risk of postoperative infection, and non-dependence on extracranial mechanical drainage system [11, 15].

ETV with CPC may be performed through a right frontal incision at the lateral corner of the anterior fontanelle, using a flexible or a rigid endoscope, which is maneuvered into the third ventricle. A ventriculocisternostomy is created in the floor of the third ventricle using a Bugby wire, to allow CSF flow into the prepontine and peri mesencephalic cisterns. Choroid plexus cauterization is done with a flexible endoscope whenever it is indicated, and if the septum pellucidum is intact, a septostomy is done to gain access to the contralateral ventricle [20]. It has been theorized that CPC decreases the secretion of CSF, enough to help the poorly developed CSF absorption mechanism to cope with the new flow of CSF through the stoma [21].

Complications of ETV + CPC include meningitis, CSF leakage, infections, subdural hygroma, and intraoperative hemorrhage (Figure 5) [22].

Figure 5.

(A) Endoscopic image of the floor of the 3rd ventricle with the tip of Bugby wire used to perforate the floor on right and the infundibular recess on left; left is anterior. (B) Basilar artery on right and VI cranial nerve on the left after passing endoscope through the third ventriculostomy into the prepontine cistern; clivus is anterior at left. (C) Distal intracisternal image of the right vertebral artery and junction of upper cervical spinal cord and lower medulla at the level of the foramen magnum; clivus is anterior at lower left. (D) Endoscopic image of endoscopic third ventriculostomy opening in floor of the third ventricle after withdrawing scope from prepontine cistern. (courtesy. Kahle KT, Kulkarni AV, Limbrick DD Jr., Warf BC. Hydrocephalus in children. Lancet. 2016 Feb 20;387(10020):788–99. Doi: 10.1016/S0140-6736(15)60694-8).

6.4 Treatment failure

Shunt failure has been defined as the need for any additional hydrocephalus-related surgery following the initial implantation of a shunt [23].

ETV failure has been defined by various authors as persistence or deterioration of clinical signs and symptoms of raised ICP after ETV, reappearance of symptoms of intracranial hypertension, repeated CSF diversion procedure, and death within 30 days of surgery. Most failures of ETV + CPC occur within 6 months of the primary surgery [22, 24].

Treatment failure can be managed by a repeat ETV + CPC or shunt insertion [24].

7. Conclusion

Hydrocephalus is a common association or complication of myelomeningocele, which may be present at birth or develop after the repair of myelomeningocele. In utero repair reduces its incidence postnatally. Prompt treatment with VP shunt or ETC + CPC is essential to improve the outcome of care.

Conflict of interest

None.