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The Effects of Whole-Vault Cranioplasty versus Strip Craniectomy on Long-Term Neuropsychological Outcomes in Sagittal Craniosynostosis

Persing, John A. M.D.; Mayes, Linda M.D.; Bridgett, David Ph.D.; Hashim, Peter M.D.; Patel, Anup M.D.; Brooks, Eric B.A.; Yang, Jenny B.A.

Plastic and Reconstructive Surgery: July 2015 - Volume 136 - Issue 1 - p 115e–117e
doi: 10.1097/PRS.0000000000001341
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Yale University School of Medicine, New Haven, Conn.

Correspondence to Dr. Persing, Yale Plastic Surgery, Yale University School of Medicine, 330 Cedar Street, 3rd Floor, New Haven, Conn. 06520, john.persing@yale.edu

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Sir:

We wish to thank the authors for their commentary on our recently published articles related to the neuropsychological outcomes following variations in the type and timing of the surgery performed.1,2 As the authors state, this concept of improving long-term neuropsychological outcomes is of primary importance and the major impetus for surgery in infants with sagittal synostosis. The authors have raised the concern that the type of endoscopic craniectomy is not identical to that performed in some centers, therefore making the data presented not of use when determining the most appropriate surgical treatment. However, our group believes that this conclusion is not valid. Specifically, the comparison in our study was related to an analysis of the two general categories of surgical approaches as follows:

  1. Endoscopic approach with an associated strip craniectomy and reliance on a postoperative helmet to subsequently remodel the shape of the skull.
  2. Open approach with a whole-vault cranioplasty where skull bone is remodeled more completely, at the time of surgery, without any helmet therapy.

The question is, which general category of technique will result in better long-term neuropsychological outcomes? In terms of our analysis, the data strongly indicate better neuropsychological outcomes with the more comprehensive, immediate correction of the bony, skull deformities. This conclusion is supported by an adequately powered study, which uses well-developed measurement instruments that can appropriately assess intellectual function and other cognitive outcomes. The spring-assisted craniectomy has yet to be analyzed in humans, but the senior author (J.A.P.) previously showed experimentally in animals that it could expand the skull more readily compared with craniectomy alone.3 Conceptually, it is still to be determined as to whether it would be as effective as immediate and complete correction of the skull abnormality that occurs with the cranioplasty procedures. Regarding which procedures are performed most often in the United States, we used National Surgical Quality Improvement Program data to assess this issue, and it depends on where the procedures are performed.4 In larger medical centers, the open cranioplasty is performed significantly more often than endoscopic procedures; in smaller medical centers, the endoscopic procedure is more frequently used. Overall, the open cranioplasty procedures are performed more frequently than endoscopic craniectomy procedures for craniosynostosis in the United States.

Concerns were raised by the authors in relation to the methodology of how neuropsychological outcomes were examined. The authors indicate that our studies would be improved by preoperative valid assessments of intellectual function. We agree with this concept fully, but this type of analysis does not currently exist. Assessment of intelligence quotient cannot be performed during infancy. Other researchers, in an effort to use “something,” have relied on Bayley’s developmental tests and the associated developmental quotient. Unfortunately, the Bayley test and developmental quotient have only modest correlations with later intelligence quotient (parent intelligence quotient and educational level are typically better predictors). However, we are focusing in current studies on markers of neural function preoperatively by assessing stimulus-linked brain responses, using event-related potentials. Event-related potentials in infancy are reliably predictive (correlation coefficient, 0.81) of dyslexia and intellectual performance at 8 years of age.5,6 Some pilot studies have been published previously using this concept in a subset of similarly affected infants.7 In the current study (as the use of event-related potentials was not available to our group, when this project commenced), however, we took into account key factors related to children’s intelligence quotient, such as socioeconomic status and education level of the parents. There were no statistically significant differences between the patients with regard to either the endoscopic approach or the whole-vault cranioplasty approach in relation to these and other potential confounding factors.

The authors also questioned the rationale of removing only patients with low intelligence quotient, and not patients with high intelligence quotient in these studies. In neuropsychological studies of diverse issues, it is common to remove those with only low intelligence quotient, because low intelligence quotient is often associated with other neuropsychological problems, even in samples where low intelligence quotient is not attributable to any know neurologic issues. As such, we did not include patients suspected of having intellectual disability, which is, in part, defined by abnormally low intelligence quotient (2 SD or lower from published normative data) because it was impossible to know whether any neuropsychological difficulties the excluded patients experienced were related to the type of surgical intervention, versus having abnormally low intelligence quotient because of some unknown factor. In contrast, those with an intelligence quotient on the other end of the distribution (those who have above-average intelligence quotient) can have neuropsychological difficulties that may be unrelated to intelligence quotient. It also is important to point out that performance intelligence quotient between groups was not different. Only verbal and Full Scale Intelligence Quotient were different. Had performance intelligence quotient also been different between groups, we would have been much more concerned about some of the possibilities raised by the commentary. Finally, for all non–intelligence quotient–specific analyses, we took an important step to minimize the impact of intelligence quotient differences between groups in our findings. We statistically controlled for intelligence quotient in all such analyses (differences in word reading between groups are not likely related to any differences between groups in intelligence quotient, because we statistically controlled for intelligence quotient in this analysis). Because our findings suggest that age at the time of surgical intervention may affect intelligence quotient, and intelligence quotient in normative samples is related to performance on other types of neuropsychological measures (e.g., achievement measures), controlling for intelligence quotient statistically was a very conservative approach.

The authors also are concerned about grouping the two operative approaches together when examining the influence of age on the outcome of surgery. We understand and share this concern. To minimize the possibility that grouping the two operative approaches together would influence findings related to age of surgical intervention, we statistically controlled for type of surgical technique in these analyses.1 Thus, on the basis of our findings, it does appear that earlier surgical intervention, regardless of the type of intervention, may result in less risk of negative long-term neuropsychological outcomes.

Of course, we realize that no study is “perfect” and fully recognize that no study answers all questions for everyone. The limitations that we pointed to, and some of the potential limitations raised in the commentary, remain important to address in future studies. As such, we are committed to addressing limitations and further evaluating these questions from multiple angles, including genetics, neuroimaging, and long-term developmental studies to further improve the quality of care for patients undergoing surgical treatment for craniosynostosis. Nevertheless, our findings provide compelling evidence that timing of surgery and the type of surgical technique used may very well have implications for long-term neuropsychological outcomes in children with craniosynostosis. Moreover, the information we have provided is important for patients’ families to be cognizant of as they make informed decisions related to craniosynostosis surgery. As there is concern about when and how surgery should be performed in infants with sagittal synostosis, information about neuropsychological outcomes should be a part of the discussion with parents.

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DISCLOSURE

The authors have no financial interest to declare in relation to the content of this communication.

John A. Persing, M.D.

Linda Mayes, M.D.

David Bridgett, Ph.D.

Peter Hashim, M.D.

Anup Patel, M.D.

Eric Brooks, B.A.

Jenny Yang, B.A.

Yale University School of Medicine

New Haven, Conn.

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REFERENCES

1. Hashim P, Patel A, Yang J, et al. The effects of whole-vault cranioplasty versus strip craniectomy on long-term neuropsychological outcomes in sagittal craniosynostosis. Plast Reconstr Surg. 2014;134:491–501
2. Patel A, Hashim P, Yang J, et al. The impact of age at surgery on long-term neuropsychological outcomes in sagittal craniosynostosis. Plast Reconstr Surg. 2014;134:608e–617e
3. Persing JA, Babler WJ, Nagorsky MJ, Edgerton MT, Jane JA. Skull expansion in experimental craniosynostosis. Plast Reconstr Surg. 1986;78:594–603
4. Tuggle CT, Patel A, Broer N, Clune JE, Sosa JA, Persing JA. Craniosynostosis: Population-level predictors of surgical technique in 1,680 patientsPaper presented at: 14th International Society of Craniofacial Surgery Biennial CongressAugust 28–September 1, 2011Livingstone, Zambia
5. Leppänen PH, Hämäläinen JA, Guttorm TK, et al. Infant brain responses associated with reading-related skills before school and at school age. Neurophysiol Clin. 2012;42:35–41
6. Leppänen PH, Hämäläinen JA, Salminen HK, et al. Newborn brain event-related potentials revealing atypical processing of sound frequency and the subsequent association with later literacy skills in children with familial dyslexia. Cortex. 2010;46:1362–1376
7. Hashim PH, Brooks D, Persing JA, et al. Direct brain recordings reveal impaired neural function in infants with single-suture craniosynostosis: A future modality for guiding management? J Craniofac Surg. 2015;26:60–63
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