(780) Enlarged cavum septum pellucidum and small thymus as markers for 22q11.2 deletion syndrome

Retrospective cohort study of fetuses evaluated from 2016-2022. CSP and thymus are measured in all patients during anatomical ultrasound evaluation. The study group included fetuses with laboratory confirmation of 22q11.2DS. The control group included pregnancies with conotruncal heart disease/normal microarray as well as structurally normal fetuses with normal microarray. CSP and thymus measurements were classified as abnormal if they were > the 95^th or < the 5th percentile for gestational age, respectively. The groups were compared using analysis of variance or Kruskall-Wallis for continuous variables & Fisher’s exact test for categorical variables. Logistic regression was performed & a receiver operating characteristic curve was constructed.

Results:

We identified 47 fetuses with 22q11.2DS and compared them to 47 fetuses with conotruncal defects/normal microarray and 47 structurally normal fetuses with normal microarray. 41 (87%) fetuses with 22q11.2DS had conotruncal heart disease. 24 (51%) fetuses with 22q11.2DS had an enlarged CSP compared to 3 (6%) conotruncal/normal microarray fetuses & none of the structurally normal fetuses. 39 (83%) fetuses with 22q11.2DS had a hypoplastic or absent thymus compared to 4 (9%) of the conotruncal/normal microarray fetuses & none of the structurally normal fetuses (p < .001; p< .001). Logistic regression revealed that both enlarged CSP and hypoplastic/absent thymus were associated with 22q11.2DS. The area under the ROC curve was 0.94.

Conclusion:

Our data strongly suggest that enlarged CSP & hypoplastic/absent thymus can be used as markers for 22q11.2DS. These markers are associated with conotruncal defects in the setting of 22q 11.2DS but not normal controls or fetuses with conotruncal defects & normal microarray.