Keywords
obesity - ventriculoperitoneal shunt malfunction - hydrocephalus - intra-abdominal pressure
Palavras-chave
obesidade - derivação ventrículo-peritoneal - hidrocefalia - pressão intra-abdominal
Introduction
Hydrocephalus is a neurosurgical entity commonly encountered among the pediatric and adult populations. The ventriculoperitoneal shunt (VPS) is considered the standard treatment for several types of hydrocephali. However, these devices have high rates of complications and failures that require reoperation. Researches have shown that between 30% and 50% of VPSs will present some kind of malfunction in the first 12 months.[1]
[2] In addition, 41% of shunt procedures are related to system malfunction, while 7% are due to infectious complications.[1]
Cerebrospinal fluid (CSF) drainage through VPS is dependent on a differential pressure between the ventricles and the peritoneal cavity. In most cases, fluctuations in the intra-abdominal pressure (IAP) will not be of clinical significance. Occasionally, severe constipation, significant ascites and pregnancy may increase the IAP enough to induce high intracranial pressure in shunt-dependent patients.
Recent studies[3]
[4]
[5] have shown obesity as a possible variable associated to shunt malfunction. The associated mechanisms are increased IAP, catheter dystocia to the extraperitoneal space, and also as an independent factor that alters the CSF physiology. Since obesity is an endemic disease of the 21st century, its role in peritoneal shunt functionality needs to be addressed by more studies. We report the case of a peritoneal shunt that malfunctioned but did not show any evidence of malfunction in the revisions, except for the patient's morbid obesity.
Case Report
A 16-year-old girl was admitted to the emergency room with moderate to severe headache, nausea and vomiting. She was morbidly obese (body mass index [BMI]: 48), had a history of hydrocephalus secondary to myelomeningocele, and underwent a ventriculoperitoneal shunt surgery when she was 2 months old. When she was 3 months old, she was treated for ventriculitis with external ventricular drainage and antibiotics, followed by a new VPS. The patient had been asymptomatic since then.
Upon admission, a computed tomography (CT) scan showed a mild ventricular dilatation ([Fig. 1]) compared with her previous exam. The shunt trajectory image ([Fig. 2]) and abdominal ultrasound ruled out any mechanical malfunctions in the system. She was treated conservatively with symptomatic. After this episode, she presented four additional events, but a CT scan did not show any increase in the size of the ventricle. In view of the persistent symptoms, she underwent a shunt revision. The intraoperative finding was a proper distal CSF drainage after the catheter was removed from the abdominal cavity. Intra-abdominal adhesions were not identified. Two weeks after surgery, she returned with the same preoperative symptoms. A complete work-up once more ruled out system malfunction ([Fig. 1]). After discarding other possibilities that could be causing the system to malfunction, the patient's morbid obesity was considered, and we performed a ventriculoatrial shunt surgery ([Fig. 3]). During the postoperative period, she presented only with transient tachycardia. The patient was asymptomatic at the 6-month outpatient follow-up.
Fig. 1 Axial images of computed tomography (CT) scans of the head. (A, D) pre-operative axial image showing hydrocephalus and the parietal ventricular catheter; (B, E) post-ventriculoperitoneal shunt revision axial images; (C, F) post-ventriculoatrial shunt axial images.
Fig. 2 Head (A), thorax (B) and abdomen (C) radiographs ruled out any mechanical malfunctions of the shunt system.
Fig. 3 Anteroposterior (A) and lateral (B) radiographs showing catheter position at the right atrium.
Discussion
Childhood obesity is a serious medical condition that affects children and adolescents; it represents one of the most serious public health challenges of the 21st century.[4]
[6] Thus, a better understanding of the influence of obesity in the functioning of ventriculoperitoneal shunts, CSF physiology and intracranial pressure is mandatory.
Under normal conditions, the IAP is atmospheric (0 mm Hg) or slightly subatmospheric. After measuring the IAP with a transurethral catheter in 84 morbidly obese patients, Sugerman et al found that an increase in the sagittal abdominal diameter was associated with a significant increase in the IAP, positively correlating the BMI with the IAP.[6] In another study, the researchers found that for each 1 kg/mm2 increase in the normal BMI, there was a 0.07 mm Hg increase in the opening pressure in the abdominal pressure.[7] Therefore, it is estimated that obese patients may have an IAP between 8 mm Hg and 12 mm Hg.
Sahuquillo et al[3] published a series of sixty patients who underwent ventriculoperitoneal shunt surgery with an intraoperative measurement of the IAP by an intraperitoneal catheter. The values were correlated to the patient's BMI. In their sample, 30% of the patients had normal weight, 35% were moderately overweight, and 35% were obese. They showed that increases in the BMI positively correlate with increasing IAP values. This is especially relevant for the treatment of normal-pressure hydrocephalus, because a small increase in IAP may impair shunt functioning. Therefore, the researchers suggest that, in obese patients, the neurosurgeons should take the IAP into account when selecting the most adequate differential pressure valve to be implanted, and in which distal cavity to place the distal catheter to avoid shunt underdrainage induced by a high IAP.[3] In the present case report, we performed a ventriculoatrial shunt, which showed a good outcome during the follow-up.
Previous studies have already associated obesity with shunt malfunction, but, in these cases, the malfunctions were due to catheter migration and dystocia to the extra peritoneal cavity.[5]
[8]
[9]
New knowledge supports the association of overweightness not only with increased IAP, but also with high intracranial pressure (ICP). A recent study evaluated 62 subjects who underwent laparoscopic procedures to evaluate the relationship between a high ICP and obesity by measurements of the optic nerve sheet diameter (ONSD) with ocular ultrasonography.[4] There was a significant difference between obese and non-obese patients, with baseline ONSDs above the cut-off value for increased ICP, indicating chronic increases in ICP.[4]
Conclusion
Several differentials should be considered regarding the malfunction of a VPS. Obesity should not be neglected when determining the cavity in which to place the distal catheter to avoid unnecessary surgery and intermittent malfunction of the system.
