Predicting Shunt Outcome in Obstructive Hydrocephalus

In This Article

Abstract and Introduction

Abstract

Objective Despite significant advances in the medical field and shunt technology, shunt malfunction remains a nightmare of pediatric neurosurgeons. In this setting, the ability to preoperatively predict the probability of shunt malfunction is quite compelling. The authors have compared the preoperative radiological findings in obstructive hydrocephalus and the subsequent clinical course of the patient to determine any association with overall shunt outcome.

Methods This retrospective study included all pediatric patients (age < 18 years) who had undergone ventriculoperitoneal shunt insertion for obstructive hydrocephalus. Linear measurements were taken from pre- and postoperative CT or MRI studies to calculate different indices and ratios including Evans' index, frontal horn index (FHI), occipital horn index (OHI), frontooccipital horn ratio (FOHR), and frontooccipital horn index ratio (FOIR). Other morphological features such as bi- or triventriculomegaly, right-left ventricular symmetry, and periventricular lucency (PVL) were also noted. The primary clinical outcomes that were reviewed included the need for shunt revision, time interval to first shunt revision, frequency of shunt revisions, and revision-free survival.

Results A total of 121 patients were eligible for the analysis. Nearly half of the patients (47.9%) required shunt revision. The presence of PVL was associated with lower revision rates than those in others (39.4% vs 58.2%, p = 0.03). None of the preoperative radiological indices or ratios showed any correlation with shunt revision. Nearly half of the patients with shunt revision required early revision (< 90 days of primary surgery). The reduction in the FOHR was high in patients who required early shunt revision (20.16% in patients with early shunt revision vs 6.4% in patients with late shunt revision, p = 0.009). Nearly half of the patients (48.3%) requiring shunt revision ultimately needed more than one revision procedure. Greater occipital horn dilation on preoperative images was associated with a lower frequency of shunt revision, as dictated by a high OHI and a low FOIR in patients with a single shunt revision as compared with those in patients who required multiple shunt revisions (p = 0.029 and 0.009, respectively). The mean follow-up was 49.9 months. Age was a significant factor affecting shunt revision–free survival. Patients younger than 6 months of age had significantly less revision-free survival than the patients older than 6 months (median survival of 10.1 vs 94.1 months, p = 0.004).

Conclusions Preoperative radiological linear indices and ratios do not predict the likelihood of subsequent shunt malfunction. However, patients who required early shunt revision tended to have greater reductions in ventricular volumes on postoperative images. Therefore a greater reduction in ventricular volume is not actually desirable, and a ventricular volume high enough to reduce intracranial pressure is instead to be aimed at for long-term shunt compliance.

Introduction

Obstructive hydrocephalus is one of the most common diagnoses encountered in pediatric clinical practice. Mechanical shunting by placement of a ventriculoperitoneal (VP) shunt has traditionally been the treatment of choice in these patients. Recently, endoscopic procedures such as third ventriculostomy with or without choroid plexus cauterization have been considered as the first-line treatment or, at times, the first shunt failure. However, VP shunt insertion has continued to be the solely practiced method in many parts of the world, especially developing countries. Other forms of mechanical shunting such as with ventriculopleural, ventriculoatrial, and lumboperitoneal shunts are mostly reserved as a measure of last resort for difficult or complicated cases. Shunt malfunction in hydrocephalic pediatric patients has continued to be a large social and financial burden to the country with an average estimate of nearly 40% of patients requiring shunt revision within the first year itself.^[13,15,16] Despite significant advances in the medical field, shunt malfunction remains a nightmare of the pediatric neurosurgeon. Even programmable shunts, which were presumed to be an effective solution to shunt malfunction, do not reduce the shunt revision rate, as estimated in our previous study.^[13] In this setting, the ability to preoperatively predict the probability of shunt malfunction is an implicit desire of pediatric neurosurgeons. In this study, we compared the preoperative radiological findings in obstructive hydrocephalus with the subsequent clinical course of the patient to determine any associations with overall shunt outcome.

Table 1. Description of radiological linear indices and ratios
Indices & Ratios	Calculation Method	Formula*
Evans' index	Maximum frontal horn diameter divided by maximum cranial diameter in that plane	a/e
Frontal horn index (FHI)	Maximum frontal horn diameter divided by maximum cranial diameter at frontal horn level	a/b
Occipital horn index (OHI)	Maximum occipital horn diameter divided by maximum cranial diameter at occipital horn level	c/d
Frontooccipital horn ratio (FOHR)	(Maximum frontal horn diameter + maximum occipital horn diameter) divided by 2 × the biparietal diameter	(a + c)/2e
Frontooccipital horn index ratio (FOIR)	Frontal horn index divided by occipital horn index	(a/b)/(c/d) = ad/bc
Reduction FOHR (%)	Reduction in FOHR on postop images as a percentage of preop FOHR	[(preop FOHR – postop FOHR)/preop FOHR] × 100

*Refer to Fig. 1.

Table 2. Characteristics and outcomes of 121 patients with obstructive hydrocephalus
Parameter	Value
Median age (range)	6 mos (1 wk–17.8 yrs)
Sex
Male	68 (56.2%)
Female	53 (43.8%)
Race
White	54 (44.6%)
African American	65 (53.7%)
Other	2 (1.6%)
Diagnosis
Congenital hydrocephalus (w/spina bifida or other congenital anomalies)	38 (31.4%)
Aqueductal stenosis	30 (24.8%)
Posthemorrhagic	28 (23.1%)
Tumor	21 (17.4%)
Postmeningitis	1 (0.8%)
Posttraumatic	3 (2.5%)
Radiological findings
Hydrocephalus pattern
Biventricular	26 (21.5%)
Triventricular	95 (78.5%)
PVL
Present	66 (54.5%)
Absent	55 (45.4%)
Ventricular symmetry
Symmetric dilation	78 (64.5%)
Asymmetric dilation	43 (35.5%)
Shunt type
Medium-pressure shunt	65 (53.7%)
Low-pressure shunt	38 (31.4%)
Programmable shunt	18 (14.9%)
Shunt revision
Total no. of revisions	58 (47.9%)
Frequency of revision
Once	30 (24.8%)
Twice	17 (14%)
More than twice	11 (9.1%)
Interval from primary surgery
Early (w/in 3 mos)	28 (48.3%)
Late (after 3 mos)	30 (51.7%)
FU outcome
No complaints	103 (85.1%)
Associated morbidity (headache, blurring of vision, developmental delay, etc.)	15 (12.4%)
Death	3 (2.5%)

FU = follow-up.

Table 3. Factors affecting shunt revision in 58 patients with obstructive hydrocephalus
Factor	Shunt Revision			Revision Interval			Revision Frequency
Factor	Yes	No	p Value	Early (<3 mos)	Late (>3 mos)	p Value	Single	Multiple	p Value
Ventricular dilation			0.19			0.41			0.32
Biventricular	10	16		4	6		4	6
Triventricular	48	47		24	24		26	22
Ventricular symmetry			0.059			0.44			0.14
Symmetric	42	36		21	21		24	18
Asymmetric	16	27		7	9		6	10
PVL			0.03			0.51			0.29
Present	26	40		13	13		15	11
Absent	32	23		15	17		15	17
Diagnosis			0.09			0.20			0.38
Congenital	19	19		6	13		10	9
Aqueductal stenosis	19	11		11	8		7	12
Posthemorrhagic	13	15		8	5		8	5
Tumor	5	16		3	2		3	2
Other	2	2		0	2		2	0
Shunt type			0.33			0.14			0.68
Medium pressure	28	37		16	12		15	13
Low pressure	22	16		7	15		10	12
Programmable	8	10		5	3		5	3

Table 4. Relation of linear indices and ratios on pre- and postoperative images with the need for shunt revision
Linear Indices & Ratios	Shunt Revision		Univariate p Value	Multivariate p Value
Linear Indices & Ratios	Yes	No	Univariate p Value	Multivariate p Value
Preop
Evans' index	0.46 (0.01)	0.44 (0.01)	0.25	0.33
FHI	0.54 (0.01)	0.54 (0.02)	0.4	0.10
OHI	0.69 (0.01)	0.66 (0.02)	0.15	0.36
FOHR	0.56 (0.01)	0.53 (0.01)	0.18	0.97
FOIR	0.79 (0.02)	0.81 (0.02)	0.25	0.36
Postop
FOHR	0.48 (0.01)	0.47 (0.01)	0.38	0.21
FOHR reduction (%)	13 (2.65)	12.1 (2.23)	0.39	0.22

Values expressed as mean (standard error of the mean), unless indicated otherwise.

Table 5. Relation of linear indices and ratios on pre- and postoperative images with the interval of shunt revision
Linear Indices & Ratios	Shunt Revision Interval (from primary surgery)		Univariate p Value	Multivariate p Value
Linear Indices & Ratios	Early (<3 mos)	Late (>3 mos)	Univariate p Value	Multivariate p Value
Preop
Evans' index	0.48 (0.02)	0.44 (0.02)	0.08	0.41
FHI	0.57 (0.02)	0.52 (0.02)	0.07	0.66
OHI	0.71 (0.02)	0.67 (0.02)	0.12	0.83
FOHR	0.58 (0.02)	0.53 (0.02)	0.049	0.38
FOIR	0.81 (0.03)	0.77 (0.03)	0.20	0.39
Postop
FOHR	0.46 (0.02)	0.49 (0.02)	0.19	0.23
FOHR reduction (%)	20.16 (3.84)	6.4 (3.3)	0.009	0.037

Values expressed as mean (standard error of the mean), unless indicated otherwise.

Table 6. Relation of linear indices and ratios on pre- and postoperative images with the frequency of shunt revision
Linear Indices & Ratios	Shunt Revision Frequency		Univariate p Value	Multivariate p Value
Linear Indices & Ratios	Single	Multiple	Univariate p Value	Multivariate p Value
Preop
Evans' index	0.45 (0.02)	0.47 (0.02)	0.22	0.46
FHI	0.54 (0.02)	0.55 (0.02)	0.39	0.07
OHI	0.73 (0.02)	0.65 (0.02)	0.029	0.38
FOHR	0.57 (0.02)	0.54 (0.02)	0.24	0.98
FOIR	0.74 (0.02)	0.84 (0.03)	0.009	0.095
Postop
FOHR	0.47 (0.02)	0.48 (0.02)	0.25	0.98
FOHR reduction (%)	14.8 (3.9)	11.1 (3.6)	0.5	0.35

Values expressed as mean (standard error of the mean), unless indicated otherwise.

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Role of Radiological Parameters in Predicting Overall Shunt Outcome After Ventriculoperitoneal Shunt Insertion in Pediatric Patients With Obstructive Hydrocephalus

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