Background <p>A spinal arteriovenous malformation is a rare condition caused by abnormal anastomoses in the spinal cord, in which blood flows from arteries to veins without capillary involvement. A congenital dermal sinus is a form of spinal dysraphism that results from aberrant development of ectodermal, mesodermal, and neuroectodermal tissues. We herein present the first reported case of an arteriovenous malformation with arteriovenous anastomosis adjacent to a congenital dermal sinus.</p> Case presentation <p>A 75-year-old Japanese man without underlying disease or trauma presented to a local hospital with a 4-month history of progressive bilateral lower limb paresthesia. Magnetic resonance imaging revealed the tip of the conus medullaris to be low at the L3/4 level, with hypersignal intensity of T2-weighted images in the spinal cord extending from the conus medullaris to T11. We diagnosed the lesion as a spinal arteriovenous malformation with congenital dermal sinus and surgically resected both structures. Postoperative radiological findings showed the disappearance of abnormal vascular shadows. The patient’s balance was stable, and he was able to walk independently.</p> Conclusion <p>We encountered a spinal arteriovenous malformation with abnormal anastomosis of the arteriovenous vein at a different site than previously reported. In the management of spinal arteriovenous malformations, confirmation of the patient’s cutaneous findings, appropriate history taking, and careful clinical and imaging examination may enable successful treatment.</p>