OBGY Radiology


Case 20
Multiplanar MRI of fetus performed following an antenatal ultrasound of a 30 year old lady at 28 weeks gestation. What is the diagnosis.
Click here for bigger picture Click here for bigger picture Click here for bigger picture Click here for bigger picture
Fig 1 Fig 2 Fig 3 Fig 4
 
__________SCROLL FOR ANSWER__________














Imaging Finding

Multiplanar MRI of the foetus was subsequently performed on a GE -Echospeed 1.5 T MR, single shot fast spin echo (ssFSE) sequence, TE of 92, TR of 1370, Nex (no. of excitations) of 0.55, Field of view 38 x 26 cm and matrix 256 x 224. It showed a large S-shaped area of flow void along the course of the vein [Figure - 1]. The straight and transverse sinuses were also enlarged [Figure - 2].


Diagnosis

Vein of Galen aneurysmal malformation
There was no hyperintense signal within these dilated structures to suggest thrombosis. The rest of the brain parenchyma and ventricles were normal. No other abnormal tortuous vessels were found. MR venography was not done as the patient was unable to cooperate further.
Pregnancy continued uneventfully and the child was born at 35 weeks' gestation. Post-natal digital subtraction angiography [DSA] corroborated the findings [Figure - 5]. Glue embolisation was subsequently done, with successful obliteration of the malformation. However, the child died at 29 hours of age from intractable congestive heart failure.

Discussion

Vein of Galen aneurysmal malformations (VGAM) are rare congenital vascular malformations characterised by shunting of the arterial flow into an enlarged cerebral vein dorsal to the tectum. Most of these malformations present in early childhood, often causing congestive heart failure in the neonate.
VGAM is defined as an aneurysmal dilatation of the vein of Galen, with arterial input from one or more major intracranial arteries, either directly or via an interposed angiomatous malformation. Arteriovenous malformations arise when fistulas develop in positions where primitive vessels cross in the embryo, which is most prominent near the choroid plexus. Fistula formation in the deep midline region, therefore, results in a malformation consisting predominantly of the choroidal vessels drained by the deep venous system, of which the vein of Galen is the main channel.
Although VGAMs constitute only 1% of all cerebral vascular malformations, they comprise up to 30% of all paediatric vascular malformations. VGAM develops between the 6th and the 11th week of gestation, after the development of the circle of Willis. Other venous anomalies such as anomalous dural sinuses and sinus stenoses are commonly present in association with VGAM. A fully developed vein of Galen malformation may vary considerably in complexity from an aneurysmal dilatation fed by the branches of posterior choroidal or posterior cerebral vessels, to an extremely complex malformation fed by all major intracranial vessels. Antenatal MRI can show the malformation in three dimensions and depict the exact anatomy of the dilated channels and thrombosis if any. Magnetic resonance angiography (MRA) with 2D-TOF may be a useful additional technique for evaluating foetal VGAM.
Embolisation of the feeding arteries is the preferred therapeutic modality for a patient with severe cardiac failure. MRI is mandatory before endoarterial treatment, to assess the brain parenchyma. If there is severe parenchymal damage, endovascular treatment cannot compensate for the irreversible melting-brain process. MRI has a prognostic value, allowing the decision for therapeutic approach. Angiography is mandatory only at the time of endovascular treatment, while MRA and MRI have a role in follow-up.

Antenatal USG and Colour Doppler can make the diagnosis of VGAM; however, MRI can not only make the diagnosis but also evaluate any associated parenchymal damage and thrombosis to a better extent, because of excellent soft-tissue contrast and lack of interference by bony structures. In conclusion, MR imaging and MR angiography can indicate the major vessels of supply, tortuousity of accessible arteries, venous anatomy, and parenchymal / ventricular status even antenatally and aid in the management and follow-up of such lesions.

References
1. Jones BV, Ball WS, Tomsick TA, Millard J, Crone KR. Vein of Galen aneurysmal malformation: diagnosis and treatment of 13 children with extended clinical follow-up. AJNR Am J Neuroradiol 2002;23:1717-24. [PUBMED] [FULLTEXT]

2. Johnston IH, Whittle IR, Besser M, Morgan MK. Vein of Galen Malformation: Diagnosis and Management. Neurosurgery 1987;20:747-58. [PUBMED]

3. Kothari SS, Naik N, Juneja R, Saxena A. Aneurysm of the Vein of Galen in neonates: Report of Four Cases. Ind Heart J 2001;53:499-502.

4. Kurihara N, Tokieda K, Ikeda K, Mori K, et al. Prenatal MR findings in a case of aneurysm of the vein of Galen. Pediatr Radiol 2001;31:160-2. [PUBMED] [FULLTEXT]

5. Campi A, Rodesch G, Scotti G, Lasjaunias P. Aneurysmal malformation of the vein of Galen in three patients: clinical and radiological follow-up. Neuroradiology 1998; 40:816-



Dr Sona Pungavkar, MRI Centre, Nanavati Hospital, Mumbai.