Surgical strategy for giant VS
VS is common intracranial tumor, which could be cured by total resection. The tumor should be removed as much as possible to prevent for the recurrence. On the other hand, the function of facial nerve is also very important for the quality of life. Total removal of giant VS is achievable at the technical level, but severe injury of facial nerve is sometimes inevitable even for those most experienced surgeons . For instance, if the facial nerve is severely compressed and closely adhered to the tumor, intact dissection of the facial nerve from the tumor is extremely difficult. When total removal of VS is contradictory to the preservation of the facial nerve, most doctors give preference to the preservation of facial nerve. In the current study, the anatomic reservation rate of the facial nerve was 96.0%. According to Madjid Samii et al., the anatomic reservation rate of the facial nerve for T4 grade VS was 97% [6, 7]. As a result, more effort will be needed for the protection of facial nerve in the future.
Definition of the resection extent of the VS
The resection extent of the VS is usually based on the subjective judgement of the surgeon during the operation and the diameter or volume of the residual tumor shown on the rechecked MRI after operation . In the current study, we adopted both the intraoperative finding and postoperative MRI results for the evaluation of the resection extent. Gross total removal (GTR) was defined by total resection of tumor under microscope and confirmed by postoperative brain MRI that no tumor remained. Near-total removal (NTR) meant that a thin section of tumor was remained during operation which could not be seen on the postoperative brain MRI. Subtotal removal (STR) meant that small part of tumor was remained during operation which could be seen on the postoperative brain MRI.
Indications for NTR or STR of giant VS
NTR or STR of VS should be considered in some situations. Firstly, if the facial outcome after dissection from the tumor could not be precisely and objectively evaluated during the surgery, NTR or STR may be sensible, because we could not identify the “critical point” that the facial nerve was permanently injured . On the other hand, the remained tumor was often stable or even shrink during the follow-up and could be effectively controlled by radiotherapy .
If the tumor was closely related to the facial nerve, brainstem, or vascular structures that dissection of the facial nerve was quite difficult or even impossible, total removal of the giant VS was not recommended. In some patients who were elderly or accompanied with other severe complications, whose hearing of the contralateral side was lost, or unexpected hemorrhage was intraoperatively encountered, total removal was also unadvisable [11, 12].
In the current study, total removal was not achieved in 10 cases. In two elderly patients who were accompanied with other diseases, the objectives of surgery were to relieve the brainstem compression and the severe trigeminal nerve due to tumor compression, so NTR and STR of tumor were performed. In one patient with evident brainstem edema, a thin layer of tumor adhered to the brainstem was remained during the operation. In one patient, the facial nerve is located right on the back of tumor; exposure of the ventral tumor was very difficult, so the total removal was not achieved. In another 6 cases, the tumor was closely related to the facial nerve; small part of tumor on the surface of facial nerve was remained. The postoperative brain MRI showed thin slice of tumor was remained in 6 patients (STR); in another 4 cases, the postoperative brain MRI could not reveal the residual tumor (NTR).
The postoperative treatment of the residual VS
The prognosis of residual VS including the tumor regrowth time, regrowth velocity, and whether need reoperation or other treatment has been reported in many researches. The recurrence rate is higher in patients who received STR or NTR, compared with those total removal was achieved. What’s more, the recurrence rate increased as the follow-up period extended. Carlson et al. reported that the recurrence rate was 22% after a follow-up of 3.5 years . Chen et al. reported the recurrence rate was 18% after 3.8 years of follow-up . Seol et al. reported that after a mean follow-up of 4.6 years, the residual VS regrew in 28% of patients , whereas there is also research reported that the VS could shrink in the early period after operation . Therefore, patients who received STR of VS should be closely followed after operation.
Many scholars suggest that radiotherapy should be conventionally arranged early after operation if the VS was not totally removed . Some others recommend that the radiotherapy should be performed only when regrowth of the residual VS was confirmed . In the current study, STR or NTR of the VS was performed in 10 patients, in view of the small volume of the residual tumor; none of them received radiotherapy. The treatment strategy will be depended on the growth tendency of the tumor during the close follow-up.