Hydrocephalus in Africa: A surgical perspective
N. Bauman, Senior Surgical Resident, McMaster University Faculty of Medicine, Hamilton, ON,
Canada and D. Poenaru, Adjunct Professor of Surgery and Paediatrics, Queens’ University, Kingston, Canada, Hon. Professor of Surgery, Aga Khan University, Nairobi, Kenya, Medical Education and Research Director, AIC Kijabe Hospital, Kijabe.
Prof. D. Poenaru, P.O. Box 20, Kijabe 00220, Kenya, Email: MedEdDirokh@kijabe.net
Hydrocephalus is the excessive accumulation of cerebrospinal fluid (CSF) within the cranial vault due to excessive production or inadequate absorption. The management of hydrocephalus in developing nations is hindered by significant economic constraints and delays in treatment – most patients in fact do not present for at least seven months after the onset of clinical symptoms (1). CSF shunts are expensive and not always available, but can be used to treat hydrocephalus regardless of etiology. The management of hydrocephalus and the complications associated with its treatment require considerable surgical judgment and a life-long approach to patient follow-up.
The prevalence of hydrocephalus in developed nations is estimated as 0.9-1.2/1000 (2). No reliable estimate is available in the African literature, but its incidence is likely higher because of untreated/poorly treated neonatal meningitis and nutritional deficiencies.
Aetiology & pathophysiology
Cerebrospinal fluid (CSF) is produced predominantly by the choroid plexus of the four cerebral ventricles, at a rate of 20 ml/hour. It flows via the foramina of Luschka and Magendie into the subarachnoid space, and is absorbed by the arachnoid villi into the venous system via the superior sagittal sinus. Hydrocephalus has been categorized as communicating or noncommunicating: the former is due to failure of CSF absorption by the arachnoid villi, whereas the latter involves obstruction of CSF flow into the subarachnoid space. A small minority of cases exhibit excessive production of CSF — most commonly secondary to a choroid plexus papilloma.
In developed nations, hydrocephalus has historically been most commonly due to myelomeningocele, with the post-hemorrhagic hydrocephalus of prematurity becoming at least as common in recent years (2). Some reports have suggested that in central Africa the most common causes of hydrocephalus are —neural tube defects and congenital aqueductal stenosis (3). Similarly, in Zambia, the ratio of congenital to “postmeningitic” hydrocephalus has been reported to be 2:1 (4). In contrast, a well-documented prospective series in East Africa has shown the etiology of hydrocephalus to be 57% post-infectious, 29% non post-infectious, and myelomeningocele (Figure 1). Thus, neonatal meningitis /ventriculitis is likely the most common cause of hydrocephalus in East Africa (1).
Despite the prevalence of malaria in Africa and case reports of associated hydrocephalus, there is no clear relationship between its cerebral form and subsequent hydrocephalus (5). On the other hand the pathophysiology of hydrocephalus in the setting of myelomeningocele is multifactorial: it may be secondary to obstruction at the aqueduct, ventricular outlet, craniocervical junction, or arachnoid granulations.
The clinical presentation of hydrocephalus is characterized by signs and symptoms of increased intracranial pressure (ICP). Symptoms may include: headache, vomiting, failing vision, drowsiness, fatigue, deteriorating mental function, and enlarged head circumference. Signs include: wide tense fontanel, papilloedema, reduced visual acuity, failure of upward gaze (the sunsetting sign), general clumsiness, dyspraxic gait, and increasing head circumference. Older children will not present with increased head circumference, and often complain of the classic triad: headache, vomiting and lethargy (Table 1).
Click to view table 1
Clinical examination is the most readily available investigation for the diagnosis of increased ICP, shunt malfunction or infection. All shunts should be examined and manipulated, although pumping of the shunt is not a reliable test of malfunction. Nevertheless, classic teaching suggests that a reservoir that is difficult to depress (or refills instantaneously) may indicate distal obstruction whereas slow filling of the reservoir may indicate obstruction proximally (6).
Cranial ultrasonography (US) is an essential diagnostic tool in developing countries: it can readily assess ventricular size with minimal training, and is relatively inexpensive. Depending on operator skill, the size of the fourth ventricle can be assessed on US as a proxy indication of the patency of the aqueduct. This may be particularly relevant in stratifying patients for treatment with prosthetic shunts versus endoscopic third ventriculostomy (ETV). Serial US imaging may be appropriate in patients with an equivocal presentation of increased ICP prior to subjecting them to shunt revision. All children with shunts should be followed up regularly, including baseline US within three months of surgery. Although acute changes from baseline may help in the subsequent diagnosis of shunt failure, up to a third of patients will not exhibit any evidence of ventriculomegaly (6).
Both computed tomography (CT) and magnetic resonance imaging (MRI) are excellent modalities, but their routine use is prohibited by cost in developing nations. Nevertheless, CT may be necessary in assessing the ventricular size in older children with closed fontanels noted. Evidence of increased ICP in children with closed fontanels can also be obtained through direct measurement of CSF pressure by lumbar puncture: the CSF column height is measured in a piece of intravenous (IV) tubing connected to the spinal needle via a 3-way stopcock.
Although rarely required, a “shuntogram” of the entire radiopaque shunt tract via a series of plain X- rays encompassing the skull, chest and abdomen is helpful when there is clinical suspicion of possible shunt migration or discontinuity (7).
Documentation of shunt infection or ventriculitis may require culturing of CSF samples from the ventricles (in the neonate) or from the shunt reservoir itself. There is a small but real risk of CSF contamination with each diagnostic tap. A value of 50-100 white cells/ mm3 is considered indicative of an infected CSF, as is elevated protein, decreased sugar, and naturally the presence of bacteria on Gram stain. A bloody tap may erroneously elevate the white cell number. Any febrile child with a shunt should be examined for the possibility of other common febrile illnesses, especially if they are beyond 6 months post-shunt insertion. Malaria, otitis media, and viral gastroenteritis should be excluded, in addition to the possibility of urinary tract infection particularly in those with spina bifida and bladder dysfunction (6).
The definitive management of hydrocephalus at present remains surgical. The diuretic acetazolamide has been shown to decrease CSF production in animal and human studies (8), but is of temporary benefit and should only be used in the palliative setting or in equivocal cases until a definitive diagnosis can be made. It has also been used in post-hemorrhagic hydrocephalus of the newborn as a temporizing maneuver to avoid shunting (9).
Ventriculo-peritoneal shunt: The most common surgical intervention to treat hydrocephalus is the insertion of a shunt through the skull and cortical mantle into the ventricle, with the distal catheter placed into a physiologic drainage basin, typically the peritoneal space (ventriculoperitoneal or VP shunt). Other sites for CSF diversion include the right atrium and the pleural space. The advantage of a CSF shunt is that it is beneficial in nearly all types of hydrocephalus— regardless of etiology.
CSF shunts usually contain three parts: a ventricular catheter, a valve, and a distal catheter. Most valves are designed to allow for sampling via needle puncture. The so-called “differential pressure valves” use the gradient between the ventricle and the tip of the distal catheter to effect flow. “Medium pressure” valves are those which drain CSF if the pressure gradient is >10 mm Hg, and are used most commonly. Although many different valve designs exist including “siphon limiting”, “flow limiting”, and “programmable” valves (whose settings can be changed using an external magnet) there is limited evidence for their benefit. A large randomized trial demonstrated no difference in time to first shunt failure in the treatment of children with newly diagnosed hydrocephalus when comparing a standard differential pressure valve compared to two other higher generation valves (10). Similarly, the use of an adjustable shunt was not shown to be of any benefit in terms of overall survival (11). Finally, and of most relevance to the developing world, there is good evidence from a prospective randomized controlled trial demonstrating that the Chhabra® shunt (made by Surgiwear in India) is equivalent to its common Western counterpart in incidence of shunt complications, despite it being almost 1/20 the cost (12). The Chhabra shunts are made available for free to qualifying centres through the International Federation of Spina Bifida and Hydrocephalus (www.ifglobal.org). In extreme situations, a piece of