What does it indicate if the cisterna magna continues to enlarge in a fetus?

Question

Hello doctor,

At my 20-week scan, the cisterna magna measured 4 mm. I had another scan at 23 weeks to reassess a hypoplastic nasal bone, where cisterna magna measured 7.6 mm. I know the cutoff is 10 mm. At this rate, the CM length will exceed 10 mm in a few weeks. I have a low risk of NIPT. The baby's nasal bone is 3 mm on one side and 3.5 mm on the other. Also, there are no other ultrasound markers. Will the cisterna magna continue to grow?

Kindly advise.

Answer 1

Hello,

Welcome to icliniq.com.

I understand your concern.

I have reviewed your reports (attachment removed to protect the patient's identity).

Hypoplastic nasal bone increases the risk of chromosomal anomaly. The presence or absence of chromosomal anomalies can be confirmed by amniocentesis. The NIPT report is good and reassuring, but amniocentesis is the preferred method for confirmation. I suggest you consult a fetal medicine specialist. As you are already 23 plus weeks, it is important to consult at the earliest. Also, I suggest you repeat the scan.

Regarding the growth of the cisterna magna, if it continues to enlarge, it means there is an obstruction near the ventricles. Therefore, I suggest you go for fetal MRI (magnetic resonance imaging). It is a safe and noninvasive method that detects any obstructions near the ventricles of the brain. Otherwise, you can get a repeat ultrasound done by a fetal medicine specialist experienced in fetal neuroimaging. In most cases, hypoplastic nasal bone and 7.3 mm cisterna magna are normal findings.

I hope this helps.

Thank you.