Morning Glory Disc Anomaly

A 3-year-old boy presents with left esotropia since infancy and poor vision in the left eye. On dilated fundoscopy, the left eye reveals the structure marked **A** — an enlarged, excavated, funnel-shaped optic disc with a central white glial tuft and approximately 20 retinal vessels emerging radially from the disc periphery like morning glory petals. MRI brain demonstrates a transsphenoidal basal encephalocele and bilateral supraclinoid internal carotid artery stenosis with basal collaterals. Which of the following is the most important systemic association that must be screened in all children with this optic disc anomaly?