A 34-year old primigravida woman was referred to our center for evaluation of a possible cystic hygroma.  The patient’s family history was negative for congenital anomalies.  Sonography revealed a 21-week fetus whose size was consistent with dates based on a prior ultrasound.  A large cystic structure measuring 79 x 87 mm arising from the left mandibular/auricular area was identified.  The walls were thickened.  There was glandular-appearing tissue with echogenic foci noted at the margins, which most likely represented calcifications.  The mass did not contain any septations.  Color flow Doppler did not reveal any blood flow within the mass.  At the level of the cervical spine, the midline soft tissue structures were displaced toward the right side.  The mass appeared separate from the thyroid or esophagus.  No dilatation of the esophagus was present.  Polyhydramnios was identified with an amniotic fluid index of 243 mm.

A follow up ultrasound examination was performed two weeks later and the mass had increased to 100 x 95 mm and the amniotic fluid index had increased to 316 mm.  An amniocentesis, amniotic fluid drainage and fetal neck mass aspiration were then performed. The karyotype revealed 46XY, male chromosome complement, 650 cc's of amniotic fluid was drained and 350 cc's of thick brown fluid was aspirated from the neck mass with a sample sent for cytology and chemistry.  The mass measured 133 mm after the drainage.  The post-procedure amniotic fluid index was 170 mm.

Aspiration needle in the cyst

Collapsed cyst

Within one week the mass had increased to its pre-drainage size and the amniotic fluid index had increased to 259 mm.  The patient was placed on Indomethacin for treatment of polyhydramnios.

At 25 weeks gestation a second amniotic fluid drainage was performed and 795 cc's of amniotic fluid was drained.    A shunt was placed into to neck mass and 445 cc's of fluid was aspirated from the cyst.  A pigtail catheter was inserted into the cyst to allow continuous drainage. 

Pigtail catheter inserted in the cyst 

Weekly ultrasound monitoring continued and by 29 weeks gestation a third amniotic fluid drainage of 840 cc's was performed.  The mass had again enlarged and 300 cc's of fluid was drained.  At 30 weeks 4 days gestation, a second shunt was placed in the mass since it had again enlarged, and the first shunt was assumed not to drain.  The mass measured 110 x 100 x 90 mm before the drainage and shunt placement, and 83 x 100 x 105 after the procedure.   A fourth amniotic fluid drainage of 1200 cc's was also performed.  Weekly ultrasound monitoring of amniotic fluid, mass size and Doppler of ductus arteriosus continued.  After one week the amniotic fluid index remained normal and the mass was unchanged in size.  One week later, the amniotic fluid index was normal, but the shunt was seen completely within the mass. 

At 33 weeks 5 days the patient was admitted to the hospital with preterm labor and spontaneous rupture of membranes.   Fetal lung maturity amniocentesis was negative.  Patient was placed on tocolytics for another week.  At 34 weeks 5 days a repeat lung maturity amniocentesis was performed and 600 cc's of fluid was drained from the mass.  Because the foam stability index was 48 (mature) and the fetus developed recurrent late heart rate decelerations, a cesarean section was performed and a 2.77 kg baby boy was delivered.

So the findings in this case is that of a large cystic mass with thick wall and internal nodules. We also know that some great amounts of fluid are produced in this mass since repeat drainage did not succeed in drying it out. Further the formation of fluid does not seem to affect the heart (no cardiac failure)

Many differential diagnosis have been suggested in this case including: 

• myoblastoma, sarcoma
• teratoma
• dermoid
• cephalocele
• heterotopic gastrointestinal cyst
• neurenteric cyst
• brachial cyst
• parathyroid/thyroid and salivary tumors
• epulis, ranula
• dacryocystocele
• gingival tumors
• sacrococcygeal tumor
• etc...

This case turned out to be a very rare case Cystic Heterotopic Brain Tissue, where the fluid is produce by choroid plexus like structures.