Diagnosis of foetal vein of galen aneurysmal malformation by ultrasound combined with magnetic resonance imaging: a case series

Foetal vein of Galen aneurysmal malformation (VGAM) is a very rare congenital malformation of the cerebral blood vessels, accounting for about 1% of foetal intracranial malformations [1]. These malformations form between the sixth and 11th week of gestation. Due to the fistula between the cerebral arteries and deep draining veins of the brain, the median prosencephalic vein, a precursor to the vein of Galen, becomes significantly enlarged and aneurysmal [2‐4]. The condition is mostly detected during late pregnancy in the third trimester, often combined with foetal brain injury and cardiac dysfunction, and the prognosis is poor [5]. Earlier diagnoses have also been reported [6, 7].

VGAM leads to a typical ultrasound sonogram [1, 3]. Magnetic resonance imaging (MRI) can show the development of the intracranial nervous system and brain parenchymal damage [8]. With a study of previous literatures, ultrasound or MRI examination was used to diagnose foetal VGAM. There were rarely reports of analysis and diagnosis of VGAM by ultrasound combined MRI. This study analysed the imaging characteristics and value in diagnosing VGAM by prenatal ultrasound and MRI among five foetuses at Gansu Maternal and Child Health Hospital.

The prenatal diagnosis of VGAM is usually made during the third trimester. Colour Doppler ultrasonography is most often used as the modality for exploring the foetus [11], demonstrating turbulent arterial and venous flow within a hypoechogenic structure located in the midline of the posterior part of the third ventricle [4, 11, 12]. However, foetal MRI has become superior to colour Doppler ultrasonography in the diagnosis of VGAM in recent years [13]. With the application of MRI in the foetus, VGAM can be more intuitively diagnosed and the situation of adjacent anatomy can be analysed, including the blood and cerebral ischaemic areas. In addition, MRI has high specificity and sensitivity in diagnosing brain VGAM and can accurately display the size and location of the VGAM and its relationship with adjacent brain tissue [14], so applying MRI in the diagnosis of VGAM is a valuable technique. The limitation of foetal MRI is that it cannot evaluate the blood-flow spectrum of arteriovenous fistula or foetal cardiac function, and the latter is closely related to prognosis [15]. The five cases in this study were first discovered during a routine ultrasound examination that clearly showed the internal blood flow of VGAM and the presence of arteriovenous leaks, indicating that ultrasound achieves a better sensitivity in detecting VGAM than MRI, with three-dimensional ultrasound being able to directly display the overall shapes of VGAM and the expansion of the straight sinus. In this study, all cases were found in the third trimester, which was consistent with the details of prior literature reports [11, 12].

The value of MRI and ultrasound in predicting the outcome of antenatally diagnosed VGAM has rarely been reported [16]. The cerebral shunt created by the aneurysm can increase the cardiac preload and lead to congestive heart failure. Intrauterine ultrasound signs of heart failure, such as cardiomegaly, tricuspid insufficiency, polyhydramnios, pericardial and pleural effusion, oedema and ascites carry a poor prognosis and indicate an intractable high-flow anomaly [17]. Among the three cases of heart failure diagnosed in this study, the heart function was assessed in detail by two-dimensional and colour Doppler through ultrasound. The authors thus believe that ultrasound has a clear advantage over MRI in evaluating foetal heart function.

The prognosis of VGAM depends upon two factors. First is the severity of heart failure, which is directly related to the number of arteriovenous shunts. This study shows that ultrasound can objectively reflect whether VGAM foetuses have heart failure and the degree of severity of the heart failure. In this study, smaller tumours are more prone to accompanying heart failure, while larger tumours are less likely to be paired with such. The main reason for this is that the straight sinus is more dilated when the tumour is smaller and, thus, most of the blood flow in the tumour passes through the tumour into the straight sinus. Important in this discussion, heart failure is caused by increased blood flow to the heart. When the tumour is large, arteriovenous leakage persists, the tumour expands and the straight sinus is not dilated. The blood flow in larger tumours does not flow well into the straight sinus, so such rarely causes heart failure. In this study, two cases of cardiac insufficiency were found by ultrasound, both of which showed an increased cardiothoracic ratio and straight sinus dilatations that were more obvious; another factor that determines the prognosis of VGAM is an increase in the internal venous pressure of VGAM, which causes the brain tissue surrounding VGAM to experience ischaemic changes. This study supports that MRI can clearly reveal changes in the brain tissue around the VGAM, which has advantages over ultrasound examination. This study further indicates that foetal heart failure is likely to be associated with smaller tumours, and changes in the brain tissue surrounding the foetal VGAM are likely to occur when the tumour is larger, both of which are responsible for the poor overall prognosis of the VGAM foetus. In summary, the authors believe that, when VGAM is suspected before birth, both ultrasound and MRI should be used for examination and evaluation to optimally benefit the overall prognosis of the foetus.

Previously, Deloison et al. [18] found that the prenatal diagnosis of VGAM with other abnormal foetal conditions has a poor prognosis, while isolated foetal VGAM often exhibits a better prognosis. In addition, because VGAM is typically found in the third trimester, if routine ultrasound examinations are not performed during the third trimester of pregnancy, cardiac insufficiency symptoms are often found only after the foetus is born. Therefore, when unexplained cardiac insufficiency occurs after birth, a detailed inspection should be conducted to determine whether this disease is at play. In this study, although all of the five cases continued to progress to birth, all infants died in the neonatal period after birth, which was consistent with the poor prognosis of the condition reported in the literature [19].

Recent studies have found that VGAM is often associated with aortic transition position, ventricular septal defect, atrioventricular septal defect and other cardiac structural abnormalities [18]. In this study, two cases presented with ventricular septal defect and one case demonstrated left superior vena cava, consistent with other findings in literature reports [19]. Interestingly, all of the five pregnant women involved in this study had high-risk factors or comorbidities, including in vitro fertilisation and premature membrane rupture in one each and complications during pregnancy, including hypertension during pregnancy, decreased thyroid function, and gestational diabetes, in the other three, suggesting that foetuses exposed to maternal high-risk factors or comorbidities are more likely to develop VGAM.

An advantage of this investigation is that the collected prenatal data include detailed foetal neurosonographic, echocardiographic and MRI measurements in all cases. Regarding the limitations of our study, the small size of the foetal population is of concern but attributed the rarity of VGAM and the fact that the condition is usually diagnosed postnatally. Second, as all infants in this study died during the neonatal period, no long-term clinical treatment or treatment effect evaluation could be performed.

Prenatal ultrasound is very important in the diagnosis of VGAM. When foetal intracranial midline cystic lesions are found, colour Doppler and pulse Doppler can be used to observe the nature, direction, and spectrum of blood flow and to distinguish arteries and veins while carefully observing indicators closely related with the prognosis of the foetus such as cardiac function status and damage to the nervous system. Next, three-dimensional ultrasound can be used to image the vascular structure, elucidating the relationship between the supplying artery and the dilated Galen vein; Finally, MRI may be applied to further judge the nerves’ phylogeny and extent of damage. The combined application of prenatal ultrasound and MRI can accurately diagnose VGAM and related complications early and provide a reference to the evaluation of foetal prognosis. Thus, we believe that three-dimensional colour Doppler rendering may be used effectively to assess the general architecture of the lesion and the straight sinus size, but volume calculation should be conducted on the basis of three-dimensional ultrasound and MRI. Based on this study, ultrasound combined with MRI can more accurately and comprehensively observe the pathological characteristics of VGAM, diagnose related complications early and determine its prognosis.