Objective Filiform-like enlarged central canal without reasonable cause detected by magnetic resonance image(MRI) was studied and reported. Method 30 patients with an intramedullary filiform-like cavity(1～2 mm in diameter) were identified through MRI in our hospital from 2003 to 2005. Main causes of hydromyelia, such as anatomical factors of Chiari malformation, hydrocephalus, spinal cord malformation,tumor,trauma, and inflammation, were excluded among these patients. Results All the 30 patients had spine malformation, and most of them (21 of 30) were diagnosed as adolescent idiopathic scoliosis(AIS). The slightly clinical manifestations were identified but no obviously neurological damage and no changes were found in follow up, which meant no additional medical interference was needed. Conclusions The filiform-like cavity intramedullary in MRI image can be identified as the central of the spinal cord with slightly enlargement;however, this enlargement of spinal central canal was different from hydromyelia and no treatments were needed.