A Case of Enlarged Intracranial Translucency in a Fetus with Blake's Pouch Cyst

Qualitative and quantitative study of fetal posterior fossa during the first trimester in a Chinese population

Background

To establish the normal reference ranges for parameters related to the fetal posterior fossa in the first trimester (11 ~ 13+6 weeks of gestation) and to analyze the relationship between them and crown-rump length (CRL) among the Chinese population.

Methods

Singleton pregnancies of 11 ~ 13⁺⁶ weeks (CRL:45 ~ 84 mm) with both parents from China were randomly selected from January 2021 to November 2021. The related parameters of the posterior fossa including cisterna magna (CM), intracranial translucency (IT), brain stem (BS), brain stem to the occipital bone (BSOB), and brain stem/brain stem to occipital bone (BS/BSOB) were evaluated and measured in nuchal translucency (NT) mid-sagittal section clearly by an experienced sonographer (operator 1). To assess the reproducibility of the measurements, we randomly selected 50 pregnant women. According to the blind method, operators 1 and 2 respectively screened and measured relevant parameters. In addition, operator 1 examined and measured relevant parameters again 2 h after the first.

Results

This study included 1663 fetuses. All fetuses can clearly show the three spaces of the fetal posterior fossa. The ICCs (95% CI) of intra-operator reproducibility of CM, IT, BS, BSOB, BS/BSOB were 0.981 (0.952 ~ 0.991, P < 0.001), 0.929 (0.866 ~ 0.961, P < 0.001), 0.970 (0.946 ~ 0.983, P < 0.001), 0.991 (0.974 ~ 0.996, P < 0.001), 0.939 (0.892 ~ 0.965, P < 0.001), respectively; The ICCs (95% CI) of inter-operator reproducibility 0.926 (0.860 ~ 0.960, P < 0.001), 0.810 (-0.083 ~ 0.940, P < 0.001), 0.820 (0.645 ~ 0.904, P < 0.001), 0.804 (0.656 ~ 0.888, P < 0.001), 0.772 (0.599 ~ 0.871, P < 0.001), respectively. There was a linear correlation between CRL and the parameters related to the posterior fossa (CM, IT, BS, BSOB, BS/BSOB). CM (mm) = -1.698 + 0.532 × CRL (cm) (r = 0.829, P < 0.001); IT (mm) = 0.701 + 0.179 × CRL (cm) (r = 0.548, P < 0.001); BS (mm) = 0.403 + 0.349 × CRL (cm) (r = 0.716, P < 0.001); BSOB (mm) = -0.277 + 0.719 × CRL (cm) (r = 0.829, P < 0.001); BS/BSOB = 0.747—0.021 × CRL (cm) (r = 0.196, P < 0.001).

Conclusions

Qualitative and quantitative assessment of the fetal posterior fossa structure was feasible in the first trimester. We constructed the normal reference ranges of CM, IT, BS, BSOB, and BS/BSOB. Furthermore, CM, IT, BS, and BSOB were positively correlated with CRL, but BS/BSOB was negatively correlated with CRL.

Blake's pouch cyst: Prenatal diagnosis and management

Objective:

This study aimed to present the characteristic features of 19 patients who were diagnosed as having Blake’s pouch cyst (BPC) at our center.

Materials and Methods:

Nineteen patients diagnosed as BPC between 2015 and 2019 were included in this retrospective study. Follow-up examinations were performed using ultrasonography (US) every three weeks up to 35 weeks of gestation. Prenatal magnetic resonance imaging (MRI) was performed at the time of diagnosis or during follow-up in 13 patients. MRI or transfontanellar US was performed to confirm the diagnosis of BPC after delivery. Karyotype results of eight patients were recorded.

Results:

Isolated BPC was observed in 9 (47%) patients, and associated anomalies were detected in 10 (53%) patients, including seven (36%) with the central nervous system and four (21%) with cardiac anomalies. Two fetuses had abnormal karyotype analysis as trisomy 21 and 13. The MRI report of eight patients was “differential diagnosis required for Dandy-Walker complex” and only in five (26%) patients, it was reported to be compatible with BPC. Spontaneous resolution was seen in four patients. Postnatal MRI was performed in five patients, and transfontanellar US in two patients, and all MRI and US results were consistent with BPC. During the neonatal period, abnormal neurologic development was observed in four (21%) patients, and one (5%) died.

Conclusion:

Although the prognosis of isolated BPC is very good with healthy neurologic development until advanced ages, death in the early neonatal period and abnormal neurologic development may be observed depending on the condition of the associated anomalies.

First-trimester cystic posterior fossa: reference ranges, associated findings, and pregnancy outcomes

OBJECTIVE

To report reference ranges for fetal cerebral posterior fossa measurements and to describe the sonographic findings, karyotype results, and pregnancy outcomes in fetuses presenting with cystic posterior fossa (CPF) in the first trimester of pregnancy.

METHODS

Two groups of patients undergoing first-trimester sonographic screening at 11-13 weeks' gestation were studied. The first (control group) consisted of 253 consecutive fetuses with normal posterior fossa, in which the brainstem (BS), fourth ventricle, cisterna magna, and BS-occipital bone (BS-OB) diameter were prospectively measured and the BS/BS-OB diameter ratio was calculated. The second (study group) consisted of 14 fetuses in which a CPF was detected. Information on sonographic findings, prenatal karyotype results, and pregnancy outcomes was obtained by reviewing ultrasound reports and medical records. The results from the two groups were then compared.

RESULTS

In the control group, the size of all posterior fossa structures increased and the BS/BS-OB diameter ratio slightly decreased as the pregnancy progressed. In the study group, the BS diameter did not differ significantly from the measurements obtained in the control group. However, the BS-OB diameter and the fourth ventricle were significantly larger (p < .05 and p < .001, respectively) in the study group than in the control group. Additionally, the cisterna magna was not identified in 13 of the 14 fetuses (93%) in the study group, in comparison to zero out of the 253 fetuses in the control group (p < .001). Finally, the BS/BS-OB diameter ratio was significantly smaller in the study group when compared with the control group (p < .05). Regarding pregnancy outcomes, 12 of the 14 (86%) affected pregnancies underwent elective termination (n = 11) or ended in an early intrauterine demise (n = 1) due to the associated chromosomal abnormalities or structural defects. The two fetuses with isolated CPF had a normal second-trimester scan and resulted in the delivery of healthy newborn infants.

CONCLUSIONS

The detection of a CPF in the first trimester is associated with a high rate of chromosomal and structural defects. By using normative data, early sonographic screening and detection of mildly and moderately abnormal cases is possible. Fetuses with isolated CPF require further study with a detailed second-trimester scan. This is essential in order to differentiate cases with poor and good perinatal outcomes. Finally, our data also demonstrate that the main sonographic tool when screening for CPF in the first trimester is the assessment of the fourth ventricle, which is significantly larger in abnormal cases as the result of the wide communication between the fourth ventricle and the cisterna magna.