Background

Encephalocele is a neural tube defect (NTD) or brain disorder that causes part of the brain to protrude through a gap in the skull. The portion of the brain that protrudes through the gap in the skull is most often located on the back of the head (occipital region) and is typically covered by skin or a membrane. The gap in the skull is a result of the neural tube not completely closing during pregnancy. Surgery is necessary after birth to return the protruding part of the brain and membrane back into the skull. The symptoms of this condition vary depending on factors like the size and location of the protrusion. The most common symptoms are intellectual and growth delays, learning disabilities, vision impairment, and seizures. Some infants will go on to develop microcephaly. [1,2]

Although the specific causes are mostly unknown, folic acid supplementation before and in early pregnancy has been shown to decrease the risk of having a child with a NTD like encephalocele. [3]

Epidemiology

Alaska Birth Defects Registry (ABDR) registers birth defects as reported from health care providers using International Classification of Disease (ICD) billing codes. The use of these ICD codes can lead to misclassification of diagnosed conditions. Prior to this report, all prevalence estimates were based on the number of unique children reported to ABDR with an ICD code representing a specified condition regardless of case confirmation status.

The estimates in this report were derived by conducting medical record review and case confirmation of a random sample of cases of the condition reported to ABDR. The confirmation probability from the sample was used to develop informed estimates of the actual diagnosed defect prevalence. See Defect prevalence calculation.

For explanations of table columns see Column descriptions.

Prevalence

Encephalocele occurs in 0.95 (95% CI 0.87–1.04) out of every 10,000 live births in the United States. This results in about 340 babies diagnosed with encephalocele nationally each year.[5]

In Alaska, during 2007-2021, the prevalence of encephalocele was 0.8 per 10,000 live births.
Reports Defects Births Prevalence (95% CI)
30 12.2 162989 0.8 (0.4, 1.3)
Notes: 95% CI = 95% Confidence Interval

Trend

Prevalence per 10,000 births of encephalocele during 2007-2021 by three-year moving averages, with 95% confidence interval band and Poisson estimated fitted line.
The p-value test for trend detected a significant decrease in the number of live births with encephalocele during 2007-2021. See p-value estimate
Estimate Std. Error t value Pr(>|t|)
-0.14518 0.02314 -6.27301 0.00015
Notes: 95% CI = 95% Confidence Interval

Regional Distribution

Distribution of encephalocele in Alaska by Public Health Region of maternal residence at the time of birth. A description of regional breakdowns can be found here. Data suppressed for # of reports < 6.

Demographics

Some subgroups may be more at risk for having a baby with encephalocele. This section provides the descriptive epidemiology of specified maternal, birth, and child characteristics identified from the birth certificate.

Accompanying Diagnoses

The ten diagnoses most commonalty associated with encephalocele.

Technical notes

Column descriptions

# Reports: Unless otherwise noted, the number of unique reports of the defect received by ABDR during the specified birth year(s). Each report represents a unique child with the specified defect.

# Defects: The estimated true number of reports that are diagnosed defects based on medical record review and case confirmation.

# Births: The number of live births among Alaskan residents that occurred in Alaska during the specified birth year(s).

Prevalence (95% CI): The estimated diagnosed prevalence of the condition and corresponding 95% Confidence Interval. (For information on how the defect prevalence was estimated see below).

Defect prevalence calculation

The estimated defect prevalence was calculated using a Bayesian approach based on the reported prevalence, PPV and 1-NPV (see formula below).

Through medical records review and case confirmation of a random sample of reported cases, the defect prevalence is calculated as:

\[PPV (Positive Predictive Value) = p(defect|report)\] \[NPV (Negative Predictive Value) = p(\overline{defect}|\overline{report})\]

\[p(defect) \approx [p(report)\cdot PPV]+[p(\overline{report})\cdot (1-NPV)]\]

Defect prevalence estimates are a more accurate estimation of the actual diagnosed prevalance of birth defects compared to the reported prevalance estimates in Alaska. ABDR obtains reports from medical providers using International Classification of Disease (ICD) codes that are extracted from individual systems which when aggregated may not reflect true diagnostics. Caution should be used when interpreting and comparing the reported prevalence estimates with national estimates.

See Data analysis methods for more information.

P-value estimate

To evaluate the trend over time and account for under/over-dispersion we constructed a quasi-Poisson regression model. This model assumes the variance is a linear function of the mean and models the estimated number of annual defects by year with a natural log (ln) offset of the annual births. P-values < 0.05 are considered significant, which indicates that the predicted slope is significantly different from a slope of zero.

Data suppression

For region and demographic data tables, values are suppressed based on the number of reports received during the observation period. Counts less than 6 are suppressed (as indicated by ‘-’ in the table). For regions or demographics with only one cell count suppressed a second is suppressed to eliminate the ability to back-calculate the estimate.

References

[1] Centers for Disease Control and Prevention. Facts about Encephalocele https://www.cdc.gov/ncbddd/birthdefects/ encephalocele.html; 2016 [accessed 03.06.2017]

[2] National Organization for Rare Disorders. Encephalocele, https:// rarediseases.org/rare-diseases/encephalocele/; 2012 [accessed 03.06.2017]

[3] Centers for Disease Control and Prevention. Updated Estimates of Neural Tube Defects Prevented by Mandatory Folic Acid Fortification - United States, 1995-2011. MMWR Morb Mort Wkly Rep. 2015: 64(01); 1-5.

[4] Centers for Disease Control and Prevention, Birth Defects Data and Statistics, https://www.cdc.gov/ncbddd/birthdefects/data.html; 2016 [accessed 02.23.2017]

[5] Mai CT, Isenburg JL, Canfield MA, Meyer RE, Correa A, Alverson CJ, Lupo PJ, Riehle‐Colarusso T, Cho SJ, Aggarwal D, Kirby RS. National population‐based estimates for major birth defects, 2010–2014. Birth Defects Research. 2019; 111(18): 1420-1435

##Resources Centers for Disease Control and Prevention
National Birth Defects Prevention Network

Authorship

Maternal and Child Health (MCH) senior epidemiologist Dr. Jared Parrish, PhD conceived of the presented analysis. Alaska Birth Defects Registry program manager and epidemiologist Chris Barnett, MS MPH and Dr. Jared Parrish, PhD developed the theory and performed the computations. Research analysts Monica Mills and Jordyn Lord managed data collection and storage. All authors discussed the results and contributed to the final report.

Suggested Citation

State of Alaska Department of Health and Social Services, Division of Public Health, Section of Women’s, Children’s, and Family Health. Alaska Birth Defects Registry Condition Report: Encephalocele, Alaska, 2007-2021. Updated April 11, 2024. Available at: http://rpubs.com/AK_ABDR/Encephalocele

##Contact
Alaska Birth Defects Registry (ABDR)
3601 C Street, Suite 358
Anchorage, AK 99503
(907) 269-3400 phone
(907) 754-3529 fax

Updated: April 11, 2024
Code source: R:\ABDR\Analysis_New\ABDR_CASECONF\cond_reports\Published_reports\Targets_publications\Encephalocele_tar.Rmd