Cowden syndrome (CS) is an autosomal dominant syndrome characterized by the development of hamartomas and an increased cancer risk. Most CS patients harbor mutations in the phosphatase and tensin homolog (PTEN) gene. We herein report a 70-year-old patient with CS who presented with lower extremity weakness caused by multiple thoracic dural arteriovenous fistulas (AVFs). Genetic testing revealed a truncated PTEN mutation (c.485_487delACAinsCC and p.D162Afs*5). Vascular malformations are common in CS, particularly in the extremities. However, spinal dural AVFs are extremely rare. Furthermore, in our case, the number of AVFs increased, and both lower limbs became flaccid four months after embolization. Therefore, we suggest that physicians carefully observe the changes in symptoms for prolonged periods after embolization.