Discussed by Philippe Jeanty, MD, PhD

The rest of this fetus examination is normal. Here are several views of the head.

There is also a 2 MB video clip which shows more than just the pictures

Findings

The obvious finding was the large fluid collection in the head. The characteristics of that fluid collection are very important in identifying it:

1. It is in continuity with the ventricle
2. It extends all the way to the skull
3. It is located in the anterior middle third of the head
4. It bridges the midline

Aside from the observation of the abnormal finding, a few important normal findings were noteworthy. The brain has, aside from the fluid collection, a normal anatomy and in particular:

1. There is a well visible midline with normal interhemispheric fissure
2. The portion of the frontal horns of the lateral ventricle not affect by the fluid collection appears unremarkable
3. There is a band of normal cerebral tissue along the midline at the vertex.

Many responses focused solely on the fact that the fluid collection bridged the midline, a hallmark of alobar holoprosencephaly. However, in alobar holoprosencephaly there is no midline and no frontal horns.

Many also suggested porencephaly, which is correct, but I asked them to give the more specific term that describes this condition.

The findings are very typical of a condition called Schizencephaly, type II or "open-lip schizencephalyâ€. The current thought is that schizencephaly results from an ischemia in the territory of the middle cerebral artery. This does not necessarily mean an occlusion since patent middle cerebral arteries have been recognized in fetuses with schizencephaly. The ischemia may result from vasospasm (may be related to cocaine usage) or hypotension in the fetus.

The territory of the middle cerebral artery is affected but the band of cortex next to the midline is preserved since its vascularization arises from the anterior cerebral artery. 

In purple the territory that is infracted. Note the preserved band of cortex at the vertex. This has been nicknamed  the "basket handle" image.

References

Schizencephaly, type II

Ceccherini AF, Twining P, Variend S Schizencephaly: antenatal detection using ultrasound. Clin Radiol 1999 Sep;54(9):620-2

Patel AC, Cohen HL, Hotson GC US case of the day. Open-lip schizencephaly with an area of heterotopic gray matter and associated absence of the septa pellucida. Radiographics 1997 Jan-Feb;17(1):236-9

Pellicer A, Cabanas F, Perez-Higueras A, Garcia-Alix A, Quero J

Neural migration disorders studied by cerebral ultrasound and colour Doppler flow imaging. Arch Dis Child Fetal Neonatal Ed 1995 Sep;73(2):F55-61

Cerebral ultrasound and colour Doppler flow imaging (CDFI) were used to diagnose a wide spectrum of anomalies of cell migration (17 patients): presumed lissencephaly (n = 12); schizencephaly of both fused (n = 2) and open lips (n = 2); hemimegalencephaly (n = 1); and subependymal type grey matter heterotopia (n = 12). The patients with grey matter heterotopia had irregular ventricular margins (n = 10), periventricular hyperechogenic bands (n = 12), and/or periventricular hyperechogenic nodules (n = 7). Some patients had more than one type of migration disorder as well as other central nervous system malformations. Cerebral ultrasound diagnoses were confirmed by magnetic resonance imaging (MRI) or necropsy. It is concluded that colour Doppler flow imaging is a worthwhile addition to the assessment of brain surface anomalies.

Weissman A, Achiron R, Lipitz S, Blickstein I, Mashiach S The first-trimester growth-discordant twin: an ominous prenatal finding. Obstet Gynecol 1994 Jul;84(1):110-4

OBJECTIVE: To evaluate the clinical significance and the natural course of discordant twin growth found during the first trimester of pregnancy. METHODS: This was a retrospective survey between 1992-1993 of women presenting to the ultrasonographic unit with twin pregnancies in which considerable interfetal size variation was noted in the first trimester. Discordant embryonal growth was defined as a difference in crown-rump length corresponding to 5 or more days in the estimated gestational age. Only cases that presented with continued viability of both twins were reviewed. Cases were thoroughly followed by ultrasound examinations throughout pregnancy. Neonatal records provided the outcome data. RESULTS: Five cases with first-trimester discordant twin growth were identified. All had complications of major congenital anomalies in the smaller twin, ie, diaphragmatic hernia, ventriculomegaly, schizencephaly, critical aortic atresia, and sacral agenesis. CONCLUSIONS: The first-trimester growth-discordant twin is at increased risk for congenital anomalies. Meticulous sonographic search for congenital anomalies is indicated when inter-twin size variation is evident in the first trimester.

Suchet IB Schizencephaly: antenatal and postnatal assessment with colour-flow Doppler imaging. Can Assoc Radiol J 1994 Jun;45(3):193-200

Schizencephaly, a disorder of neuronal migration, is rarely discovered in utero. Three cases, detected in utero and followed through the early neonatal period, were assessed with colour-flow Doppler imaging in an attempt to determine whether the clefts were associated with any demonstrable vascular disturbance. The Doppler spectral wave-forms of the fetal and neonatal internal carotid and middle cerebral arteries were normal in two of the cases, whereas the right middle cerebral artery was persistently occluded in the third. Although Doppler imaging was not performed during the first trimester (when the defect occurs), these findings suggest that a vascular lesion, such as occlusion of the middle cerebral artery with or without complete recanalization, may result in the clefts seen in patients with schizencephaly. Two of the fetuses had been exposed to cocaine in the first trimester, and an association between cocaine-induced vasospasm and schizencephaly is suggested.

Komarniski CA, Cyr DR, Mack LA, Weinberger E Prenatal diagnosis of schizencephaly. J Ultrasound Med 1990 May;9(5):305-7

Klingensmith WC 3d, Cioffi-Ragan DT Schizencephaly: diagnosis and progression in utero. Radiology 1986 Jun;159(3):617-8

Schizencephaly is an unusual condition of obscure etiology. Most theories of pathogenesis postulate an in utero insult leading to maldevelopment rather than destruction of brain. The cause has most often been described as vascular or idiopathic dysgenesis. The authors report a case in which two in utero ultrasound (US) examinations performed at 31 and 36 menstrual weeks demonstrated progressive deterioration of the relatively narrow, symmetrical clefts connecting the lateral ventricles with the subarachnoid space into broad defects that corresponded to the entire distribution of the middle cerebral arteries. The findings in this case document progressive destruction of brain tissue in utero and are consistent with a vascular cause rather than a failure of formation of portions of the cerebral mantle.

Babcock DS Sonography of congenital malformations of the brain. Neuroradiology 1986;28(5-6):428-39

A variety of congenital malformations of the brain can be diagnosed by cranial sonography. Those which alter macroscopic morphology can be recognized, the findings are similar to those seen on computed tomography and pneumoencephalography. The findings in the Chiari II malformation, agenesis of the corpus callosum, the Dandy-Walker syndrome, holoprosencephaly, lissencephaly, schizencephaly, tuberous sclerosis, and arteriovenous malformations are described in this chapter.

DiPietro MA, Brody BA, Kuban K, Cole FS Schizencephaly: rare cerebral malformation demonstrated by sonography. AJNR Am J Neuroradiol 1984 Mar-Apr;5(2):196-8