Fc. Laing et al., SONOGRAPHY OF THE FETAL POSTERIOR-FOSSA - FALSE APPEARANCE OF MEGA-CISTERNA MAGNA AND DANDY-WALKER VARIANT, Radiology, 192(1), 1994, pp. 247-251
PURPOSE: To establish that incorrect scanning of the fetal posterior f
ossa may falsely create the appearance of a mega-cisterna magna (MCM)
or Dandy-Walker variant (DWV). MATERIALS AND METHODS: After routine so
nography, 100 consecutive fetuses (gestational age range, 25-40 weeks)
without abnormality underwent additional posterior fossa scanning in
an attempt to create the appearance of an MCM (anteroposterior diamete
r larger than 10 mm) or DWV. Sonograms were obtained in a plane inferi
or to or angled more coronally than the routine axial plane. RESULTS:
The posterior fossa was depicted in 93 fetuses. Pseudo-MCM occurred in
35 (38%) of 93 fetuses: 12 (30%) of 40 fetuses aged 25.0-29.9 weeks,
11 (50%) of 22 fetuses aged 30.0-34.9 weeks, and 12 (39%) of 31 fetuse
s aged 35.0-40.0 weeks. Pseudo-DWV occurred in 40 (43%) of 93 fetuses:
20 (50%) of 40 fetuses aged 25.0-29.9 weeks, 12 (55%) of 22 fetuses a
ged 30.0-34.9 weeks, and eight (26%) of 31 fetuses aged 35.0-40.0 week
s. CONCLUSIONS: Sonography of the posterior fossa in an angled semicor
onal plane should be avoided because it may create an appearance that
mimics an abnormality.