Reply: Very Low Prevalence of Intracranial Hypertension in Trigonocephaly

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We read with interest the letter by Dr. Rogers regarding our article on the prevalence of intracranial hypertension in trigonocephaly.1 This article describes the occurrence of intracranial hypertension, assessed through funduscopy, and its relation with the occipitofrontal head circumference curve in trigonocephaly patients. This study, which included 262 metopic synostosis patients, shows that intracranial hypertension (a positive funduscopic result) not only is rare preoperatively and postoperatively but also is related to stagnation of the occipitofrontal head circumference curve, as also shown in a previous article about syndromic craniosynostosis patients.2
Dr. Rogers raises two concerns with the methodology of the study, on which we are glad to comment. First, the accuracy of funduscopy in the detection of intracranial hypertension is questioned. As Tuite et al. have shown, the sensitivity of funduscopy in young children may be low.3 This may have resulted in an underestimation of the prevalence of intracranial hypertension in our series if the patients had been assessed by funduscopy alone. As stated in the Discussion section of the article, we would consider patients with a deflection of the occipitofrontal head circumference curve, but with a negative funduscopic examination, the ones most at risk for a false-negative funduscopic result. These patients underwent repeated funduscopy and were watched closely for other signs of intracranial hypertension, such as headaches in the morning. We feel that this approach adequately deals with the possible shortcomings of funduscopy in the screening for intracranial hypertension. In addition, comparable studies from our center have yielded significantly different results in patients with sagittal and syndromic craniosynostosis of the same age.2,4 This, combined with the large number of patients seen in our center, indicates a high level of expertise of our ophthalmologists and a true difference in prevalence of intracranial hypertension in trigonocephaly patients. We feel this cannot be explained by the possible low sensitivity of funduscopy.
The second issue raised by Dr. Rogers is the diagnostic criteria used to diagnose trigonocephaly, or metopic synostosis. The metopic suture is the first cranial suture to close, mostly within the first year of life. A physiologic closure can indeed occur in the first months of life, without a necessity to operate. True metopic synostosis originates at week 15 of gestation, resulting in a clear ridge in the midline.5 In contrast, when the metopic suture has closed at a later stage, some growth has occurred, resulting in a narrow, but not trigonocephalic, forehead with a tipping point bilaterally. This illustrates that the timing of closure is related to the severity of the trigonocephalic shape. We agree with Dr. Rogers that a closed metopic suture by itself is not a reason to operate. In our center, the indication for surgery is based on the following assessments: a radiographically confirmed closure of the metopic suture, retrusion of the lateral orbital rim, and obvious hypotelorism. The potential bias Dr. Rogers is suggesting is based on two assumptions: (1) within the patients that were included, there is a large group of mild trigonocephaly patients; and (2) mild trigonocephaly results in a lower risk of intracranial hypertension. In our eyes, these assumptions may not be accurate. Dr. Rogers advocates the use of radiographically based cranial measurements to standardize the diagnosis and suggests that the use of clinical parameters as mentioned above would lead to wide diagnostic and treatment variability. However, in an article by Anolik et al., it has been shown that these specific measurements relate closely to the expert decision of whether to operate or not.6 In other words, our clinical judgment would not differ from the computer-based decision of whether to operate or not.

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