To the editor: Depending on the relationship between the tumor and the dura mater, dumbbell tumors can be divided into intradural-epidural (ID-ED) and epidural (ED) tumors. The surgical procedures and postoperative complications of both types are different. Nine cases of cervical dumbbell Schwannomas were treated at our hospital between June 2004 and August 2012. There were five cases of ED tumors and four cases of ID-ED tumors (Figure 1).

Although ED tumors often appear as huge ED masses, they seldom break through the root sleeves. ID-ED tumors originate from the subdural area. They grow along the nerve root to the outside of intervertebral foramen and break through the root sleeve into the epidural space. It is relatively difficult to distinguish ID-ED tumors from ED tumors. Accurate preoperative assessment of tumor types based on clinical and radiographic findings is therefore very important for successful surgery.

In our study, the mean duration of ED tumors was 23.4 months compared with 10.8 months for ID-ED tumors. This is because the root pain associated with ID-ED tumors draws earlier attention to the disease process. Even though ED tumor grows into very large masses, the resulting confinement of the dura mater only produces mild symptoms in most patients. Long tract signs were observed in three cases of ID-ED tumors, but were not apparent in any of the ED cases. Computer tomography examination revealed intervertebral foramen expansion in all patients. Destruction of the vertebral arch was observed in ED cases but not in ID-ED cases.

Edited by WANG Mou-yue and LIU Huan