The thy-box for sonographic assessment of the fetal thymus: nomogram and review of the literature.
OBJECTIVE
To assess the feasibility and reproducibility of fetal thy-box visualization and to set normative data for the fetal thymus using this technique.


METHODS
We performed a cross-sectional observational study in pregnant women in their second trimester of pregnancy who attended the fetal medicine unit of the Hospital Gregorio Marañón from March 2011 to March 2013. Using thy-box sonography, which sets boundaries within the thymus, we assessed the feasibility of the thy-box and analyzed the factors related to its visualization. Measurements of the thy-box anteroposterior and transverse diameters were performed in healthy fetuses. Interobserver agreement was studied for both items. We set normative data for the thy-box diameters in singleton and twin pregnancies.


RESULTS
A total of 337 patients from 15 to 37 weeks were recruited after exclusion criteria. Thy-box feasibility was 74.2% (250 of 337). Nonfeasible cases were related to the fetal anterior spine and advanced gestational age. Assessment of the thy-box anteroposterior and transverse diameters was achievable in 250 fetuses. Interobserver agreement was good for feasibility and measurements (κ = 0.80). Linear growth of the thy-box in both diameters was observed in relation to gestational age during the second half of pregnancy. Thy-box diameters did not show significant differences according to the type of gestation, fetal sex, or chorionicity.


CONCLUSIONS
Thy-box diameters are achievable and reproducible by sonography in normal singleton and twin pregnancies during the second trimester; however, although feasible, the thy-box transverse diameter measurement is not reliable beyond 28 weeks. Further studies are needed to evaluate thy-box diameters in pathologic cases, especially conotruncal anomalies.
Fetal Medicine Unit, Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (M.M-C., F.G., C.B., L.O., R.P., J.A.D.L.-L.); and Department of Obstetrics and Gynecology, Hospital Central de la Defensa Gómez Ulla, Universidad de Alcalá de Henares, Madrid, Spain (C.B.).
Mar
M
Muñoz-Chápuli
Fetal Medicine Unit, Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (M.M-C., F.G., C.B., L.O., R.P., J.A.D.L.-L.); and Department of Obstetrics and Gynecology, Hospital Central de la Defensa Gómez Ulla, Universidad de Alcalá de Henares, Madrid, Spain (C.B.).
Francisco
F
Gámez
Fetal Medicine Unit, Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (M.M-C., F.G., C.B., L.O., R.P., J.A.D.L.-L.); and Department of Obstetrics and Gynecology, Hospital Central de la Defensa Gómez Ulla, Universidad de Alcalá de Henares, Madrid, Spain (C.B.).
Coral
C
Bravo
Fetal Medicine Unit, Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (M.M-C., F.G., C.B., L.O., R.P., J.A.D.L.-L.); and Department of Obstetrics and Gynecology, Hospital Central de la Defensa Gómez Ulla, Universidad de Alcalá de Henares, Madrid, Spain (C.B.).
Luis
L
Ortiz
Fetal Medicine Unit, Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (M.M-C., F.G., C.B., L.O., R.P., J.A.D.L.-L.); and Department of Obstetrics and Gynecology, Hospital Central de la Defensa Gómez Ulla, Universidad de Alcalá de Henares, Madrid, Spain (C.B.).
Ricardo
R
Pérez
Fetal Medicine Unit, Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (M.M-C., F.G., C.B., L.O., R.P., J.A.D.L.-L.); and Department of Obstetrics and Gynecology, Hospital Central de la Defensa Gómez Ulla, Universidad de Alcalá de Henares, Madrid, Spain (C.B.) jdeleonluis@yahoo.es.
Juan A
JA
De León-Luis
D000465:Algorithms; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D049451:Nomograms; D009929:Organ Size / Q000502:physiology; D010363:Pattern Recognition, Automated / Q000379:methods*; D011247:Pregnancy; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013950:Thymus Gland / Q000000981:diagnostic imaging* / Q000196:embryology*; D016216:Ultrasonography, Prenatal / Q000379:methods*
fetal thymus; nomogram; obstetric ultrasound; prenatal sonography; thy-box; thymus measurements