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Transorbital optic nerve sheath ultrasonography in normal children
Chico!
Radiology
(1999) 54, 740-742
Transorbital J. BALLANTYNE*,
Optic Nerve Sheath Ultrasonography Normal Children A. S. HOLLMAN*, R. HAMILTON?, M. S. BRADNAMt, D. G. YOUNG*. G. N. DUTTONS
Departments
in
R. CARACHIS,
of *Radiology, tCIinica1 Physics. $Surgical Paediotrics and $Ophthalmology, Royal Hospital for Sick Children, Yorkhill, Gln.sgow. I/. K. Received: 26 January 1999 Accepted: 21 April 1999
AIM: Early diagnosis of acute intracranial hypertension is essential to enable prompt, optimal treatment. The optic nerve sheath diameter (ONSD) is increased in raised ICP and there has been recent interest in the use of ultrasound to diagnose and indirectly monitor raised ICP by ONSD measurement. The advantages of the technique include its non-invasiveness, wide availability, portability, low cost and the absence of ionizing radiation. This prospective study was designed to establish the range of normal values for ONSD in infants and children up to 15 years of age. PATIENTS AND METHODS: One hundred and two children attending the hospital for other reasons were recruited to the study. Three measurements of the ONSD were taken for each eye, 3 mm behind the optic nerve head using a 7 MHz sector probe. RESULTS: The range for ONSD was 2.1-4.3 mm, mean 3.08 (SD 0.36). There were no significant differences on ONSD measurement between boys and girls (P = 0.59) or between right and left eyes (P= 0.66). When the data were grouped and analysed, a correlation between increasing age and increasing ONSD was seen (r’=O.48), with the greatest increase occurring in the first 2 months of life. CONCLUSION: Using the technique described here, our results suggest that an ONSD of greater than 4 mm in infants lessthan 1 year, and 45 mm or greater in older children, should be regarded as abnormal. Ballantyne. J. et a/. (1999) C/in&l Radiology 54. 740-742. 0 1999 The Royal College of Radiologists Key words: optic nerve, ultrasound, orbit. paediatrics.
Early diagnosis of acute intracranial hypertension is essential to ensure prompt and effective treatment. Current methods for the diagnosis and monitoring of features of raised intracranial pressure (ICP) include clinical assessment, cranial computed tomography and magnetic resonance imaging. The most precise method of estimation and monitoring of intracranial pressure is by direct invasive measurement of intra-ventricular or subdural pressure. Neuroimaging requires transportation of the patient to the radiology department, and this can be problematic in critically ill patients in intensive care facilities. A non-invasive method of detecting raised ICP using transorbital sonography to evaluate the optic nerve sheath diameter (ONSD) has recently been reported [I]. Raised ICP results in widening of the ONSD, which was found to be maximal 3 mm behind the optic nerve head [2]. The advantages of transorbital sonography are that it is non-invasive, easily repeatable and portable. The aim of this prospective study is to establish the range of Correspondence to: Dr A. Hollman, Department of Radiology, Hospital for Sick Children, Yorkhill, Glasgow, G3 8SJ. U.K. 0009-9260/99/l
10740+03
$12.0010
Royal
normal values for optic nerve sheath diameter in infants and children up to I.5 years of age.
MATERIALS
AND METHODS
One hundred and two children attending the Royal Hospital for Sick Children for abdominal or hip ultrasound were recruited to the study. None suffered from neurological or ophthalmological disease. Approval to conduct this study was given by the local Research Ethics Committee. Written, informed consent was obtained from parents and. where appropriate, from the children. Transorbital optic nerve sheath ultrasound was carried out on an Acuson I28 XP IO system using a 7 MHz sector probe. The patients were examined in the supine position and, where appropriate, were asked to keep their eyes still and in a neutral position. The probe was placed gently on the closed upper eyelid using sterile coupling gel. Axial images were recorded of the orbit in the plane of the optic nerve and the diameter of the optic nerve sheath was measured in both eyes 3 mm behind the optic nerve head. Three measurements of each optic nerve sheath were performed. 0
1999 The Royal
College
of Radiologists
TRANSORBITAL
OPTIC NERVE SHEATH ULTRASONOCRAPHY
IN NORMAL
741
CHILDREN
Fig. I - Axial image of the orbit demonstrating the normal ultrasound appearance of measurement of an optic nerve sheath in a child.
For statistical analysis the ONSD data were grouped by age, and mean and standard deviation values were calculated. Regression analysis and analysis of variance (ANOVA) were used to compare groups.
o I 2
RESULTS
I 6
I 8
I 10
I 12
I 14
16
Age (years)
Transorbital optic nerve sonography was possible in all children. Figure I illustrates the normal appearances of the optic nerve sheath on ultrasonic examination. By inspection. the data are normally distributed, as are the data from male and female subjects and from right and left eyes. The range of values for ONSD is 2.1-4.3 mm (n = 612, mean 3.08. SD 0.36). There are no significant differences in ONSD between boys and girls (P = 0.59) or between right and left eyes (P = 0.66). Age Variation
I 4
OSND regression 2sd
in ONSD
Data were grouped to investigate changes with age (Table I). When the data are plotted a clear increase in ONSD over the first year of life is shown (Fig. 2). A logarithmic regression line shows a significant correlation (I? = 0.48) at the I% level. Global ANOVA suggests that the average ONSD differed between groups. Follow-up multiple comparisons based on Tukey’s approach indicated that this difference in ONSD was strongest between the O-2-month age group and the other groups. Table 1 - Mean ONSD by age Age
Number
Mean (mm)
SD (mm)
O-2 months 2-3 months 3-12 months l-2 years 2-3 years 3-4 years 4-5 years 5- 10 years IO-15 years
5 9 5 9 17 18 16 10 13
2.57 2.95 3.21 2.99 3.03 3.15 3.23 2.98 3.26
0.30 0.35 0.22 0.13 0.20 0.28 0.38 0.16 0.35
Fig. 2 - Optic nerve sheath diameter plotted in relation to age. Logarithmic regression line of ONSD with age. Logarithmic regression 2 two standard deviations illustrating 95% confidence interval.
Measurement
Variability
Any single measurement of ONSD was on average within 0.58 mm of the true mean (22 SD for all measurements, n =612). Repeating each ONSD measurement three times produced a mean measurement which was, on average, within 0.08 mm of the true mean (22 SD of the SD range from each set of three measurements, n = 204). DISCUSSION The examination and measurement of the optic nerve by sonographic means was pioneered by Ossoinig in the 1970s [3]. Subsequent studies have shown that the optic nerve sheath diameter increases in patients suffering from intracranial hypertension, with a subsequent return to normal values following successful surgical or medical treatment [4]. An increased ONSD has also been directly correlated to elevated cerebrospinal fluid pressure [5] and intracranial pressure [6]. Helmke and Hansen’s experimental study described maxima1 dilation of the optic nerve sheath 3 mm behind the optic nerve head [2] and confirmed the utility of the clinical application of optic nerve sheath ultrasonography in children in intensive care units with acutely raised ICP [l]. Our experience confirms this technique to be a quick, well-tolerated procedure that is readily mastered. This study has determined the normal age-related change in ONSD in children aged O-15 years. Maxima1 increase of the
742
.
CLINICAL
ONSD takes place during the first year of iife, in particular the first 2 months, with the rate of growth diminishing-over the next 14 years. These findings contrast with the results of Ossoinig [7], who found no age-related differences in the normal range of ONSD using an A-mode echographic technique. Helmke and Hansen [l] examined 51 control patients under the age of 18 years by B-mode scanning. They found the ONSD to be significantly lower for children under the age of 4 years than for older children. In contrast, Fig. 2 illustrates that an ONSD approaching the maximum is attained by the age of 2 years. The range of normal values for ONSD in children under 1 year is 2.1-4.0 mm and the range for children over 1 year of age is 2.4-4.3mm. The upper limit of the range of values for children aged 1-15 years is the same as. or close to, the upper limit of normal for ONSD values found in adult studies [8]. Our results suggest that an ONSD of greater than 4mm in infants under 1 year of age, and 4.5 mm or greater in older children, be regarded as abnormal.
RADIOLOGY
REFERENCES I Helme K. Hansen HC. Fundamentals of transorbital sonographic evaluation of optic nerve sheath expansion under intracranial hypertension. I. Experimental study. Pediatr Rndiol 1996:26:701-705. 2 Helmke K, Hansen HC. Fundamentals of transorbital sonomaohic I . evaluation of optic nerve sheath expansion under intracranial hypertension. II. Patient study. Pediorr Radio/ 1996;26:706-710. 3 Ossoinig KC. Standardised echography: basic principles. clinical applications and results. In: Dallow RL. Ophr/uh~ic U/rrasonograp/~~t Conpororive rechniqucs. International Ophthalmological Clinics 19. 1979;127-210. 4 Gangemi M. Cennamo G. Maiuri F. D’Andrea F. Echographic measurement of the optic nerve in patients with intracranial hypertension. Neurochirurgia 1987;30:53-55. 5 Galetta S, Byrne SF, Smith JL. Echographic correlation of optic nerve sheath size and cerebrospinal fluid pressure. J Clin Neuro-ophf/m/mo/ 1989;9:79-82. 6 Cennamo G. Gangemi M, Stella L. The correlation between endocranial pressure and optic nerve diameter: an ultrasonography study. In: Ossoinig KC. ed. Ophrholmic Echogrophp. 1987~603-606. 7 Ossoinig KC. Standardised echography of the optic nerve. In: Till P, ed. Ophrholrnic Echo.~rnnlw 13. 1993: 3-99. 8 Hinsen HC. Helike i. Kunze K. Optic nerve sheath enlargement in acute intracranial hypertension. Nelrro-oplrr/~o/r,~o/o~~ 1994; 1434.5354.
Radiology
(1999) 54, 740-742
Transorbital J. BALLANTYNE*,
Optic Nerve Sheath Ultrasonography Normal Children A. S. HOLLMAN*, R. HAMILTON?, M. S. BRADNAMt, D. G. YOUNG*. G. N. DUTTONS
Departments
in
R. CARACHIS,
of *Radiology, tCIinica1 Physics. $Surgical Paediotrics and $Ophthalmology, Royal Hospital for Sick Children, Yorkhill, Gln.sgow. I/. K. Received: 26 January 1999 Accepted: 21 April 1999
AIM: Early diagnosis of acute intracranial hypertension is essential to enable prompt, optimal treatment. The optic nerve sheath diameter (ONSD) is increased in raised ICP and there has been recent interest in the use of ultrasound to diagnose and indirectly monitor raised ICP by ONSD measurement. The advantages of the technique include its non-invasiveness, wide availability, portability, low cost and the absence of ionizing radiation. This prospective study was designed to establish the range of normal values for ONSD in infants and children up to 15 years of age. PATIENTS AND METHODS: One hundred and two children attending the hospital for other reasons were recruited to the study. Three measurements of the ONSD were taken for each eye, 3 mm behind the optic nerve head using a 7 MHz sector probe. RESULTS: The range for ONSD was 2.1-4.3 mm, mean 3.08 (SD 0.36). There were no significant differences on ONSD measurement between boys and girls (P = 0.59) or between right and left eyes (P= 0.66). When the data were grouped and analysed, a correlation between increasing age and increasing ONSD was seen (r’=O.48), with the greatest increase occurring in the first 2 months of life. CONCLUSION: Using the technique described here, our results suggest that an ONSD of greater than 4 mm in infants lessthan 1 year, and 45 mm or greater in older children, should be regarded as abnormal. Ballantyne. J. et a/. (1999) C/in&l Radiology 54. 740-742. 0 1999 The Royal College of Radiologists Key words: optic nerve, ultrasound, orbit. paediatrics.
Early diagnosis of acute intracranial hypertension is essential to ensure prompt and effective treatment. Current methods for the diagnosis and monitoring of features of raised intracranial pressure (ICP) include clinical assessment, cranial computed tomography and magnetic resonance imaging. The most precise method of estimation and monitoring of intracranial pressure is by direct invasive measurement of intra-ventricular or subdural pressure. Neuroimaging requires transportation of the patient to the radiology department, and this can be problematic in critically ill patients in intensive care facilities. A non-invasive method of detecting raised ICP using transorbital sonography to evaluate the optic nerve sheath diameter (ONSD) has recently been reported [I]. Raised ICP results in widening of the ONSD, which was found to be maximal 3 mm behind the optic nerve head [2]. The advantages of transorbital sonography are that it is non-invasive, easily repeatable and portable. The aim of this prospective study is to establish the range of Correspondence to: Dr A. Hollman, Department of Radiology, Hospital for Sick Children, Yorkhill, Glasgow, G3 8SJ. U.K. 0009-9260/99/l
10740+03
$12.0010
Royal
normal values for optic nerve sheath diameter in infants and children up to I.5 years of age.
MATERIALS
AND METHODS
One hundred and two children attending the Royal Hospital for Sick Children for abdominal or hip ultrasound were recruited to the study. None suffered from neurological or ophthalmological disease. Approval to conduct this study was given by the local Research Ethics Committee. Written, informed consent was obtained from parents and. where appropriate, from the children. Transorbital optic nerve sheath ultrasound was carried out on an Acuson I28 XP IO system using a 7 MHz sector probe. The patients were examined in the supine position and, where appropriate, were asked to keep their eyes still and in a neutral position. The probe was placed gently on the closed upper eyelid using sterile coupling gel. Axial images were recorded of the orbit in the plane of the optic nerve and the diameter of the optic nerve sheath was measured in both eyes 3 mm behind the optic nerve head. Three measurements of each optic nerve sheath were performed. 0
1999 The Royal
College
of Radiologists
TRANSORBITAL
OPTIC NERVE SHEATH ULTRASONOCRAPHY
IN NORMAL
741
CHILDREN
Fig. I - Axial image of the orbit demonstrating the normal ultrasound appearance of measurement of an optic nerve sheath in a child.
For statistical analysis the ONSD data were grouped by age, and mean and standard deviation values were calculated. Regression analysis and analysis of variance (ANOVA) were used to compare groups.
o I 2
RESULTS
I 6
I 8
I 10
I 12
I 14
16
Age (years)
Transorbital optic nerve sonography was possible in all children. Figure I illustrates the normal appearances of the optic nerve sheath on ultrasonic examination. By inspection. the data are normally distributed, as are the data from male and female subjects and from right and left eyes. The range of values for ONSD is 2.1-4.3 mm (n = 612, mean 3.08. SD 0.36). There are no significant differences in ONSD between boys and girls (P = 0.59) or between right and left eyes (P = 0.66). Age Variation
I 4
OSND regression 2sd
in ONSD
Data were grouped to investigate changes with age (Table I). When the data are plotted a clear increase in ONSD over the first year of life is shown (Fig. 2). A logarithmic regression line shows a significant correlation (I? = 0.48) at the I% level. Global ANOVA suggests that the average ONSD differed between groups. Follow-up multiple comparisons based on Tukey’s approach indicated that this difference in ONSD was strongest between the O-2-month age group and the other groups. Table 1 - Mean ONSD by age Age
Number
Mean (mm)
SD (mm)
O-2 months 2-3 months 3-12 months l-2 years 2-3 years 3-4 years 4-5 years 5- 10 years IO-15 years
5 9 5 9 17 18 16 10 13
2.57 2.95 3.21 2.99 3.03 3.15 3.23 2.98 3.26
0.30 0.35 0.22 0.13 0.20 0.28 0.38 0.16 0.35
Fig. 2 - Optic nerve sheath diameter plotted in relation to age. Logarithmic regression line of ONSD with age. Logarithmic regression 2 two standard deviations illustrating 95% confidence interval.
Measurement
Variability
Any single measurement of ONSD was on average within 0.58 mm of the true mean (22 SD for all measurements, n =612). Repeating each ONSD measurement three times produced a mean measurement which was, on average, within 0.08 mm of the true mean (22 SD of the SD range from each set of three measurements, n = 204). DISCUSSION The examination and measurement of the optic nerve by sonographic means was pioneered by Ossoinig in the 1970s [3]. Subsequent studies have shown that the optic nerve sheath diameter increases in patients suffering from intracranial hypertension, with a subsequent return to normal values following successful surgical or medical treatment [4]. An increased ONSD has also been directly correlated to elevated cerebrospinal fluid pressure [5] and intracranial pressure [6]. Helmke and Hansen’s experimental study described maxima1 dilation of the optic nerve sheath 3 mm behind the optic nerve head [2] and confirmed the utility of the clinical application of optic nerve sheath ultrasonography in children in intensive care units with acutely raised ICP [l]. Our experience confirms this technique to be a quick, well-tolerated procedure that is readily mastered. This study has determined the normal age-related change in ONSD in children aged O-15 years. Maxima1 increase of the
742
.
CLINICAL
ONSD takes place during the first year of iife, in particular the first 2 months, with the rate of growth diminishing-over the next 14 years. These findings contrast with the results of Ossoinig [7], who found no age-related differences in the normal range of ONSD using an A-mode echographic technique. Helmke and Hansen [l] examined 51 control patients under the age of 18 years by B-mode scanning. They found the ONSD to be significantly lower for children under the age of 4 years than for older children. In contrast, Fig. 2 illustrates that an ONSD approaching the maximum is attained by the age of 2 years. The range of normal values for ONSD in children under 1 year is 2.1-4.0 mm and the range for children over 1 year of age is 2.4-4.3mm. The upper limit of the range of values for children aged 1-15 years is the same as. or close to, the upper limit of normal for ONSD values found in adult studies [8]. Our results suggest that an ONSD of greater than 4mm in infants under 1 year of age, and 4.5 mm or greater in older children, be regarded as abnormal.
RADIOLOGY
REFERENCES I Helme K. Hansen HC. Fundamentals of transorbital sonographic evaluation of optic nerve sheath expansion under intracranial hypertension. I. Experimental study. Pediatr Rndiol 1996:26:701-705. 2 Helmke K, Hansen HC. Fundamentals of transorbital sonomaohic I . evaluation of optic nerve sheath expansion under intracranial hypertension. II. Patient study. Pediorr Radio/ 1996;26:706-710. 3 Ossoinig KC. Standardised echography: basic principles. clinical applications and results. In: Dallow RL. Ophr/uh~ic U/rrasonograp/~~t Conpororive rechniqucs. International Ophthalmological Clinics 19. 1979;127-210. 4 Gangemi M. Cennamo G. Maiuri F. D’Andrea F. Echographic measurement of the optic nerve in patients with intracranial hypertension. Neurochirurgia 1987;30:53-55. 5 Galetta S, Byrne SF, Smith JL. Echographic correlation of optic nerve sheath size and cerebrospinal fluid pressure. J Clin Neuro-ophf/m/mo/ 1989;9:79-82. 6 Cennamo G. Gangemi M, Stella L. The correlation between endocranial pressure and optic nerve diameter: an ultrasonography study. In: Ossoinig KC. ed. Ophrholmic Echogrophp. 1987~603-606. 7 Ossoinig KC. Standardised echography of the optic nerve. In: Till P, ed. Ophrholrnic Echo.~rnnlw 13. 1993: 3-99. 8 Hinsen HC. Helike i. Kunze K. Optic nerve sheath enlargement in acute intracranial hypertension. Nelrro-oplrr/~o/r,~o/o~~ 1994; 1434.5354.