Orphanet Journal of Rare Diseases | Foramen Magnum Stenosis and Cervicomedullary Decompression in Children with Achondroplasia: Impact on Growth

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This study reveals that children with achondroplasia who underwent cervicomedullary decompression (CMD) exhibited more pronounced growth delay at ages 4–6, suggesting that disease severity may be the primary factor affecting growth, rather than the surgery itself.

 

Literature Overview

The article titled 'Foramen magnum stenosis, cervicomedullary decompression, and growth in children with achondroplasia: a retrospective cohort study,' published in the Orphanet Journal of Rare Diseases, reviews and summarizes the impact of foramen magnum stenosis (FMS) and its surgical intervention—cervicomedullary decompression (CMD)—on early growth parameters in children with achondroplasia. Using a retrospective cohort design, the study systematically evaluated standardized growth data—including height, weight, head circumference, and BMI—in 87 children aged 4–6 years, and explored the association between FMS severity, assessed via MRI grading, and growth outcomes. Results showed that children who underwent CMD had significantly lower height standard deviation scores (H-SDS) compared to those without surgery, with the difference being more pronounced in males. The authors suggest this growth disparity is more likely attributable to underlying disease severity than to the surgical procedure itself. The study underscores the importance of early multidisciplinary assessment and provides new clinical evidence for understanding growth trajectories in achondroplasia.

Background Knowledge

Achondroplasia (ACH) is the most common form of skeletal dysplasia, caused by the p.Gly380Arg mutation in the FGFR3 gene, leading to impaired endochondral ossification. It is characterized by rhizomelic short stature, macrocephaly, and structural abnormalities at the craniocervical junction. A key complication is foramen magnum stenosis (FMS), which can compress the medulla and upper cervical spinal cord, leading to apnea, sudden death, or motor dysfunction. Although clinical guidelines recommend early neuroimaging, there remains debate on whether all children should undergo MRI. In practice, the decision to perform cervicomedullary decompression (CMD) often relies on symptoms or imaging findings. In recent years, CMD rates and the age at surgery have varied across centers, with associated perioperative risks. Notably, children with ACH naturally experience a decline in growth velocity; however, it remains unclear whether FMS or CMD further impacts growth trajectory. Most existing studies focus on neurological outcomes or surgical safety, lacking systematic comparisons of growth parameters. Therefore, investigating the relationship between CMD and long-term growth outcomes can help clarify the relative contributions of disease burden versus intervention, and optimize individualized management—particularly in balancing growth modulation with the timing of surgical intervention.

 

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Methods and Experiment

The study employed a retrospective cohort design, including 87 genetically confirmed children with achondroplasia (45 boys, 42 girls) aged 4–6 years, drawn from long-term follow-up records at the Pediatric Endocrinology Unit of the G. Gaslini Institute in Genoa, Italy. The primary exposure was whether the child underwent cervicomedullary decompression (CMD), and the primary outcome was height standard deviation score (H-SDS), along with other growth parameters (weight, head circumference, BMI, and sitting height). All growth metrics were converted to SDS values using ACH-specific reference standards established by Merker et al., while sitting height SDS was calculated using the Tanner method. FMS severity was blindly assessed via MRI using the Fornarino grading system, categorized from 0 to 4B. Statistical analysis used the Mann-Whitney U test to compare intergroup differences and built multivariable linear regression models adjusting for sex, Fornarino score, and age at surgery to assess the independent effect of CMD on H-SDS. Subgroup analyses were conducted by sex and age at surgery (<1 year vs. ≥1 year) to explore potential heterogeneity.

Key Findings and Insights

• At age 4–6, children with achondroplasia who underwent CMD had significantly lower H-SDS than non-surgical peers (p = 0.03), with the difference being statistically significant in males (p = 0.018)
• Multivariable regression analysis showed that CMD was an independent negative predictor of H-SDS (βAdj = −0.47; p = 0.027), indicating a significant association with growth delay
• The Fornarino score was significantly higher in the CMD group (p < 0.001), indicating more severe foramen magnum stenosis in surgical candidates
• Age at surgery (<1 year vs. ≥1 year) was not significantly associated with H-SDS, and growth parameter changes from pre-surgery to ages 4–6 remained stable, suggesting that growth differences likely stem from pre-existing disease severity
• Sitting height SDS did not differ significantly between groups, indicating that growth suppression primarily affects the lower limbs—consistent with the known limb-specific inhibitory effect of FGFR3 mutations
• No significant differences were observed in other growth parameters (weight, BMI, head circumference), and rates of comorbidities such as positive pressure ventilation and spinal deformities were similar, supporting that growth differences are indirectly linked to CMD rather than driven by other comorbidities

Implications and Future Directions

This study is the first to systematically assess the impact of CMD on growth in a relatively large cohort of children with achondroplasia. It finds that postoperative children exhibit poorer growth outcomes, but this is more likely due to greater underlying disease severity rather than direct surgical harm. These results challenge the simplistic causal assumption that growth delay is a consequence of surgical intervention, emphasizing that CMD should be viewed as a clinical marker of disease severity. The findings support current multidisciplinary management strategies—early identification of high-risk children and timely intervention—to prevent neurological complications.

Future research should include prospective, multicenter studies with denser growth monitoring and biomarker analysis to precisely elucidate the dynamic relationships among FMS, timing of CMD, and long-term growth trajectories. Additionally, with the advent of novel targeted therapies (e.g., vosoritide), investigating whether these treatments can improve growth outcomes in children with FMS—and how they interact with CMD—will be crucial. This study provides important evidence for developing individualized growth monitoring and intervention strategies.

 

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Conclusion

This study systematically analyzed growth outcomes in 87 children with achondroplasia at ages 4–6, finding that those who underwent cervicomedullary decompression (CMD) had significantly lower height standard deviation scores (H-SDS) than non-surgical peers, particularly among males. Multivariable analysis confirmed CMD as an independent negative predictor of H-SDS; however, further analysis showed that this growth disparity was unrelated to age at surgery, and growth trajectories from pre-surgery to early school age remained stable. Sitting height SDS did not differ significantly between groups, indicating that growth suppression primarily affects the lower limbs—consistent with the biological effects of FGFR3 mutations. Overall, growth delay associated with CMD likely reflects a more severe disease phenotype—including more pronounced foramen magnum stenosis and potential neurorespiratory comorbidities—rather than a direct surgical effect. The findings emphasize that CMD should be regarded as a clinical marker of disease severity, not as an independent cause of growth impairment. This supports early, comprehensive multidisciplinary evaluation of children with achondroplasia to identify high-risk individuals and optimize the timing of interventions. Future research should integrate emerging therapies to further explore ways to improve long-term growth outcomes in these children.

 

Daniela Fava, Alessia Angelelli, Caterina Tedesco, Mohamad Maghnie, and The Skeletal Dysplasia Multidisciplinary Team (GM-MOC). Foramen magnum stenosis, cervicomedullary decompression, and growth in children with achondroplasia: a retrospective cohort study. Orphanet Journal of Rare Diseases.