What's your Diagnosis of this Fetus?


Our patient presented at 30 weeks gestation for a routine prenatal ultrasound.

Our patient presented at 30 weeks gestation for a routine prenatal ultrasound.

History: This young woman came in for a routine ultrasound examination at 30 weeks gestational age. She had normal menstrual cycles before the pregnancy and did not have a history of major illness. This was her first pregnancy.

Family History: Our patient is one of 2 children.

Present Pregnancy: The patient gave a history of 30 weeks amenorrhea which corresponded with the age of the fetus on ultrasound scan. She had no history of abnormal bleeding per vagina (P/V) or spotting during the current pregnancy.

Clinical Examination: Her blood pressure was normal (BP: 128/ 82 mm. of Hg). All other vital signs were also normal.

On abdominal examination, she had mild tenderness and pain over the lower pelvis. The fundal height corresponded to the age of the fetus (30 weeks).

Imaging Studies: Our patient underwent transabdominal ultrasound imaging to study the viability of the pregnancy and to rule out any anomalies.

Image 1: Transverse section of fetal head
(Images open full size)

(Images courtesy of Dr. Anita Kaul, India)

 Image 2: Transverse section of fetal head

What are your findings? Add your comments and continue the B-mode ultrasound image discussion.

B-mode Ultrasound Image Discussion

The fetal head shows a midline, rounded cystic area seen posterior to the thalamus and midbrain. What are the causes of a cystic lesion which is so deeply seated and indeed apparently menacing for the fetus? Upon further observation there is a linear extension of the cystic lesion posteriorly. Could an arachnoid cyst cause such an ultrasound appearance?

Ultrasound imaging of the fetal heart also showed mild cardiomegaly. Can the above findings and the fetal cardiomegaly be related? What are the conditions where there is a cystic lesion in the fetal brain that may also be associated with fetal cardiomegaly?

Observse the lesion in the Power Doppler (image 3).

Image 3: Power Doppler image of the fetal brain

The Power Doppler image shows a striking appearance and is classical of a specific condition.

Image Discussion

There is a highly vascular lesion posterior to the thalamus and midbrain. This is in the location of the cystic area previously described, further it seems to drain posteriorly into a linear vessel. What are the diagnostic possibilities in this case?

Can these findings be produced by arachnoid cysts?

Arachnoid cysts are cystic lesions which are not vascular and they contain cerebrospinal fluid (CSF), therefore this cannot be an arachniod cyst.

Could this be a choroid plexus cyst?

Choroid cysts are found within the choroid plexus in the lateral ventricles. Our lesion is not in the correct location for a choroid cyst.

Are the findings consistent with a  porencephalic cyst?

Porencephalic cysts are the end result of intracranial hemorrhage and are not vascular on Doppler imaging. The answer again would be no, it is not a porencephalic cyst.

Is there a possibility of choroid papilloma?

Choroid papilloma tumors are relatively vascular but are almost always echogenic and not cystic.

The only remaining possibility is that this lesion is an enlarged vessel. The dilated vessel and draining vessel posterior to this have a striking appearance, almost like a “keyhole”. What vessel is found in this location and what is your diagnosis?

Add your opinions and continue to the final diagnosis.

Image 3 This is the vein of Galen and the straight sinus.

Final Diagnosis

Vein of Galen aneurysm or vein of Galen malformation


Vein of Galen malformation is a congenital anomaly that usually appears late in pregnancy. In this case the diagnosis was made in the 3rd trimester. Often 3rd trimester sonography is still not routinely performed in many centers, hence some cases are diagnosed only during the neonatal period when clinical symptoms arise. The usual presenting feature in post natal life is cardiac failure. It is for this reason that vein of Galen aneurysm or malformation should be suspected in cases of neonatal cardiac insufficiency.

The vein of Galen is located in the posterior part of the cerebrum and drains the anterior and central parts of the fetal brain. It drains into the straight sinus posteriorly. The vein of Galen aneurysmal malformation results from arteriovenous shunting of blood and is the most common arteriovenous malformation in the fetus. This anomaly may be associated with hydrocephalus resulting from obstruction of the CSF outflow. There are 5 variants of vein of Galen malfoimations described in the literature. If the vein of Galen aneurysm undergoes thrombosis, the sonographic appearance may change with an echogenic mass seen in this location.


Most fetuses develop cardiac insufficiency or intracranial hemorrhage immediately after birth. Quick intervention maybe the only hope for such neonates.

Differential Diagnosis

1) Arachnoid cyst  are not vascular
2) Porencephalic cysts are the result of intracranial hemorrhage and are not vascular.
3) Choroid plexus papilloma masses are located within the lateral or 3rd ventricles and are hyperechoic.
4) Choroid plexus cysts occur within the ventricles and are not vascular.


References:/>1) Callen, P. Ultrasonography in obstetrics and gynecology
2) Ruano, R., Benachi, A., Aubry, M., et al.“Perinatal Three-dimensional Color Power Doppler Ultrasonography of Vein of Galen Aneurysms” JUM., December 2003 22:1357-1362
3) Rumack, C.  Diagnostic Ultrasound
4) Suma, V.,  Marini, A., Saia, O., Rigobello, L.“Vein of Galen Malformation”. Sonoworld.com. 1991
5) Images fromUltrasound-images.comcourtesy of Dr. Anita Kaul, India

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