Dural arteriovenous fistulae at the lateral foramen magnum: A series of two microsurgical cases

Aim: To study specific vascular anatomy of dural arteriovenous fistulae (DAVFs) locating at the foramen magnum in patients admitted to our centre in the past year (2019-2020), and to evaluate effectiveness of microsurgical disconnection of DAVFs alone. Patients and Methods: Two male patients were included. Neuroimaging results obtained on admission, including computer tomography, digital subtraction angiography and magnetic resonance imaging of the brain, were studied and compared. Digital subtraction angiography with selective injection to the external carotid artery was particularly explored to trace main feeding arteries and draining veins of DAVFs. Results: Both patients had diffuse subarachnoid haemorrhage (SAH), particularly anterior to the medulla on initial computer tomography of the brain. Branches of the ascending pharyngeal artery were identified as main feeding arteries. Draining veins included anterior/posterior spinal veins and pterygopalatine venous plexus. Magnetic resonance imaging confirmed DAVFs at the level of foramen magnum to C1 vertebra. Complete occlusion was achieved with far-lateral microsurgical approach, with intra-operative indocyanine green injection confirming no filling of venous pouch. Post-operative follow-up digital subtraction angiography demonstrated no angiographic evidence of residual DAVFs or new haemorrhages. Conclusion: DAVFs at the foramen magnum could present as SAH. A combination of neuroimaging methods aid diagnosis and identification of underlying vascular anatomy. Satisfactory outcomes with complete occlusion were achieved with microsurgical approach alone.