Remodeling of venous drainage after the treatment of dural sinus malformation with arteriovenous shunts in a neonate: a case report and literature review

Dural sinus malformations (DSMs) are rare congenital vascular diseases characterized by a giant venous pouch with or without arteriovenous shunts. We present a neonatal case of DSM that was diagnosed prenatally and treated via endovascular intervention in the early postnatal period. The patient presented with a large DSM involving the torcular Herophilion prenatal magnetic resonance imaging (MRI). Enlargement of the head circumference and respiratory failure rapidly progressed after birth. On the 5th day after birth, the neonate underwent endovascular occlusion via the umbilical artery. The arteriovenous shunt was occluded, and the reflux from the enlarged venous pouch to the dural sinus was decreased. No additional procedure other than ventriculoperitoneal shunting was required. The neonate’s development slowly caught up to normal parameters. Follow-up MRI demonstrated the successful development of the venous drainage system. DSMs are characterized by an abnormally dilated dural sinus, which can block the venous return and ultimately increase intracranial pressure and cerebral ischemia. Long-term follow-up indicates that an abnormally developed dural sinus can be reconstructed by appropriate and timely treatment.


Introduction
Dural sinus malformations (DSMs) are rare congenital vascular diseases characterized by a giant venous pouch with or without arteriovenous shunts (AV shunts). Torcular DSMs are associated with poor outcomes, severe neurological morbidity, or death [1,2]; thus, careful planning of treatment is required based on the natural course and pathological mechanism by multidisciplinary team. We present a case of DSM diagnosed prenatally and treated via endovascular intervention in the early postnatal period. Long-term followup magnetic resonance imaging (MRI) demonstrated the reconstruction of the venous drainage.

Case presentation
The ultrasound images of 26 weeks of gestation in a 39-yearold healthy woman revealed an intracranial cystic lesion. Fetal MRI at 33 weeks of pregnancy revealed a huge intracranial mass in the occipital region with partial thrombosis and an enlarged ventricle (Fig. 1), indicating DSM or vein of Galen malformation. A female newborn was delivered at 1 3 35 weeks of gestation via cesarean section with head circumference of 41 cm (+ 5.8 standard deviation). MRI on the 2nd day after birth indicated the DSM involving the torcular Herophili, 10 cm in diameter and compressing the brainstem, cerebellum, and cerebral hemisphere. Ultrasound showed multiple blood supplies into the enlarged sinus. Venous pouch included not only the torcular Herophili but also the superior sagittal sinus (SSS) and bilateral transverse sinus. In addition to rapidly increasing head circumference, respiratory failure and anemia had progressed. A multidisciplinary team involving neurosurgeon, neonatologist, and pediatric cardiologist decided to perform endovascular occlusion on the 5th day after birth.
The umbilical artery (UA) was secured with a 4-Fr umbilical catheter at birth. A 4-Fr short sheath was curved to fit to the elongation of the UA. A 4-Fr catheter was brought to the right common carotid artery demonstrating giant venous pouch and reflux to the SSS and superior orbital vein (SOV). Magic MP ® (Balt, Montorency, France) microcatheters were inserted into the feeders of the right occipital artery, and we injected 0.26 mL of 75% n-butyl-2-cyanoacrylate (NBCA). The feeder of the left posterior meningeal artery was embolized with 0.02 mL of 50% NBCA, whereas the feeder of the right subclavian artery was embolized with 0.1 mL 50% NBCA using Defrictor ® (Medico's Hirata, Osaka, Japan) microcatheter (Fig. 2). After embolization, reflux into SSS and SOV was markedly decreased. The ultrasound on postoperative day 1 indicated flow disappearance into the venous pouch, and MRI on day 7 showed thrombosis of the venous pouch.
Her development gradually caught up although was still delayed. She was able to cruise at 1 year and 9 months of age, articulate two-word sentences at 2 years and 4 months of age, and ambulate independently at 3 years of age.
Follow-up MRI revealed smaller venous pouch over time (Fig. 3).The transverse and sigmoid sinuses were not demonstrated before treatment; on follow-up magnetic resonance (MR) venography, a "normal" venous drainage system had developed (Fig. 4).

Discussion
In the present case, the torcular DSM with AV shunts was diagnosed prenatally. Prenatal diagnosis enabled the advance planning and treatment of the infant's condition. Embolization reduced the AV shunts, resulting in the shrinkage of the venous pouch and remodeling of the venous drainage.
DSM is a rare subtype of the pediatric dural arteriovenous fistula accounting for 1.9% of all intracranial arteriovenous malformations and 10% of pediatric arteriovenous fistulas [2][3][4]. DSM involving the torcular Herophili accounted for 46.6% of all DSM cases [2]. A poor natural history of DSM has been reported until recently. Barbosa et al. [2] found that 64.3% of untreated DSMs had poor neurological outcomes; especially, torcular DSM only had 28.6% chance of favorable outcome. However, with advancements in prenatal diagnosis and neuroendovascular interventions, the outcome has become more favorable. Ku et al. [5] reported 83.3% of favorable outcome in torcular DSM with treatment. Yang et al. [6] reviewed 99 cases of torcular DSM and found that torcular DSM diagnosed prenatally had 83% survival rate and 62% favorable outcome, whereas DSM diagnosed postnatally only had 59% survival rate and 29% favorable outcome.
Okudera et al. [7] demonstrated the anatomic and radiologic developments of the posterior fossa dural sinuses. During the embryogenic process, ballooning of the dural sinus begins from the transverse sinus at 4 months of gestation and then rapidly progresses to the torcular Herophili, superior petrosal sinus, and SSS. The ballooning of the sinus stops at approximately 7 months of gestation. The sinus shrinks to adult size at approximately 1 year after birth. DSM is considered to be a pathological progression of the ballooning of the dural sinus that persists after birth [7]. The possible mechanism of formation of arteriovenous shunts is associated with dural sinus thrombosis; nevertheless, the mechanism remains unclear.
The treatment of DSM is often via endovascular embolization. The transarterial embolization is often preferred because venous pouch often functions as normal venous drain [8]; thus, AV shunts must be reduced while preserving the patency of venous drainage [2]. If the venous pouch is not involved in normal venous drainage, coil embolization in the venous pouch can be effective [3,8]. The flow reduction of DSM could lead to thrombosis, venous pouch shrinking, and dural sinus remodeling. Anticoagulant therapy might be necessary if rapid thrombosis occurs in the sinus despite thrombosis having an important role in the regression of DSM [5].
Reconstruction of venous drainage after treatment has not been thoroughly investigated. In the present case, the transverse and straight sinuses gradually became visible on followup MR venography. Ku et al. [5] reported two cases treated during the neonatal period and normalized venous drainage. Liby et al. [9] reported a similar case. Despite the fact that the vascular abnormality is severe at birth, the observation of these cases suggests that the venous drainage system has the potential for remodeling with appropriate treatment at the optimal timing. To achieve such a favorable outcome, the intervention should be carefully planned by a multidisciplinary team.

Conclusion
DSM is a rare congenital vascular malformation that may have a better prognosis with prenatal diagnosis and optimal treatment. In this case, ultrasound and MRI were useful for in utero diagnosis, allowing for optimal and timely intervention. Treatment during the neonatal period can improve outcomes Fig. 4 Magnetic resonance (MR) venography demonstrating undetected posterior sagittal sinus, transverse to sigmoid sinuses, and jugular vein at 1 month of age (a). Follow-up MR venography clearly showing a normal venous drainage system, which improved gradually at 4 months (b), 1 year and 4 months (c), and 2 years and 4 months (d) of age and may encourage venous drainage remodeling deriving from the thrombosis in the venous pouch or normal transformation.