Acrania-Exencephaly-Anencephaly Sequence on Antenatal Scans

Acrania-Exencephaly-Anencephaly sequence is the progression from an absent cranial vault (acrania) showing relatively normal appearing exposed brain (exencephaly) to no recognisable brain parenchymal tissue (anencephaly). The study presents different cases of acrania, exencephaly and anencephaly along with their imaging features on Two Dimensional (2D) Ultrasonography (US) and additional benefits of using Three Dimensional (3D)/Four Dimensional (4D) ultrasonography to aid in the diagnosis. Over a span of one year, seven patients with abnormal foetuses were scanned during the first trimester or at 18-20 weeks of gestation using both 2D and 3D/4D volumetric probes. The International Society of Ultrasound in Obstetrics and Gynaecology (ISUOG) practice guidelines were adopted for appropriateness. Specific imaging features seen on 2D US helps early diagnosis and high detection rate of this rare type of Neural Tube Defect (NTD) malformation. A 3D/4D US can also detect foetal acrania, exencephaly and anencephaly as early as 2D scan and in addition can illustrate findings with different modes of reconstruction, which 2D US cannot. Hence, 3D/4D US may contribute to early detection of foetal acrania-exencephaly-anencephaly sequence.