Fluid Area Measurements in the Posterior Fossa at 11-13 Weeks in Normal Fetuses and Fetuses with Open Spina Bifida

Abstract

Objectives: To measure the area of the intracranial translucency (IT) (syn: 4th ventricle) and the future cisterna magna (CM) in normal fetuses and to compare with fetuses with open spina bifida. Patients: In the midsagittal plane of the face of 220 fetuses between 11 and 13 weeks' gestation, the areas of the IT and CM were measured and the sum, defined as the posterior fossa fluid (PFF) area was calculated. Reference ranges were constructed in relation to the crown-rump length. The study group consisted of 21 fetuses with open spina bifida and showed in all cases a single pocket of fluid in the posterior fossa. Fetuses with no fluid in the fossa were excluded. This PFF-area was measured and compared with the reference range of the IT-area and the PFF-area of normal fetuses and Z-scores were calculated. Results: In normal fetuses, a significant increase of the IT-, the CM- and the PFF-area was found as a sign of the expanding posterior fossa. The mean PFF-area increased from 8.55 to 29.72 mm² in the observation period. Fetuses with open spina bifida had reduced fluid in the posterior fossa with values ranging between 2.39 and 5.08 mm² and significantly lower Z-scores. Conclusions: Fetuses with open spina bifida have an abnormally small posterior fossa at 11-13 weeks' and in cases where the cerebrospinal fluid is still present, the fluid area in the midsagittal plane is reduced when compared to normal fetuses. Area fluid assessment can be an additional useful measurement in suspicious cases for open spina bifida in early gestation.

Intracranial translucency assessment at first trimester nuchal translucency ultrasound

“…These markers are sonographic representations of the anatomical changes that result from caudal displacement of the brain stem. In addition to the absence, 7,8,15,20 or reduced thickness of the IT, 13,14 other potential markers include obliteration of the cisterna magna, 9,10 increased anteroposterior diameter of the brain stem (BS), decreased brain stem to occipital bone diameter (BSOB) and an increased BS to BSOB ratio (BS/BSOB), 11,12,17,18 reduced posterior fossa fluid area 16 and simply an abnormal four-line view. 10,12,18 Other findings linked to early diagnosis of OSB at the nuchal scan, using views other than the mid sagittal view of the face, include small BPD, 21 small BPD to transverse abdominal diameter ratio 22 and reduced cerebral ventricular volume.…”

“…5 Over recent years, an abnormal posterior fossa on the mid-sagittal view of the face at the first trimester nuchal translucency scan, performed at 11-13+6 weeks' gestation, has been associated with the presence of OSB. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] The mid-sagittal view of the face has been routinely obtained in order to measure nuchal translucency (NT) thickness and assess the nasal bones as part of screening for chromosomal abnormalities.…”

Sonographic detection of central nervous system defects in the first trimester of pregnancy

“…To solve this issue, other posterior brain markers have been proposed . These include measurements of the cisterna magna , the brain stem and the brain stem occipital bone distance (BSOB), the posterior fossa fluid area, and the four‐line view (Figure ) . The anterior–posterior diameter of the cisterna magna can be measured in a mid‐sagittal view .…”

“…66 These include measurements of the cisterna magna, the brain stem and the brain stem occipital bone distance (BSOB), the posterior fossa fluid area, and the four-line view (Figure 3). 67,68 The anterior-posterior diameter of the cisterna magna can be measured in a midsagittal view. 69 Non-visualization of the cisterna magna, or a cisterna magna width below the fifth percentile, achieves sensitivity for OSB of 50% to 73%.…”

Maxillary gap at 11–13 weeks' gestation: marker of cleft lip and palate

“…In the last decade, widespread use of the 11–13‐week scan in screening for aneuploidies with measurement of fetal nuchal translucency (NT) thickness has resulted in many major fetal defects being diagnosed in the first trimester of pregnancy. This can be achieved by direct visualization of the fetal anatomy, for example in cases of anencephaly, exomphalos and megacystis, or by focused assessment of specific fetal structures triggered by the finding of indirect signs, for example increased NT in association with major cardiac defects and abnormal intracranial translucency (IT) in association with open spina bifida.…”