Venous varix enlargement after cerebrospinal fluid diversion in a neonate with pial arteriovenous fistula complicated with hydrocephalus. A case report

•Pial arteriovenous fistula (PAVF) presenting with hydrocephalus is rare.•Hydrocephalus due to PAVF should be treated by the obliteration of the fistula.•Transarterial embolization is safe and effective for the treatment of PAVF. Neonatal intracranial pial arteriovenous fistulas (AVFs) are rare vascular malformations. The pathophysiology of hydrocephalus in cases of pial AVF remains to be fully understood. Here, authors report a case of pial AVF with a large venous varix, which rapidly expanded after cerebrospinal fluid (CSF) diversion. A female neonate was born at full term following a normal pregnancy and delivery. A supracerebellar pial AVF with a large venous varix and the hydrocephalus due to complex mechanism were found on fetal imaging. She had no neurological deficits, but her head circumference was slightly larger than normal. The hydrocephalus was treated via CSF diversion, but this was followed by a remarkable expansion of the venous varix. Transarterial embolization of the AVF was subsequently performed, which resulted observable improvement of the hydrocephalus. Hydrocephalus complicating pial AVFs with a venous varix should not be treated by CSF diversion first. Instead, the initial step in the treatment should be obliteration of the AVFs. This restores the hydrodynamic balance between the CSF and intracranial venous system, resulting in the gradual improvement of the hydrocephalus.