Population Study (GKS-failuregroup): (Table 1)
Twenty-three consecutive patients who underwent salvage surgery for large VS after GKS failure were enrolled in this study, including 12 females and 11 males, with a mean age of 56 years (range 28-73). Every patient included in the study showed evidence of progressive tumor growth after GKS (mean tumor growth x 946 – range 126-5161). The mean delay between GKS and salvage surgery was 66 months (median 47 months). One patient included in the analysis had been operated on before the delay of 3 years after GKS (23months) because of worsening symptoms related to tumor growth. This patient had received a radiosurgical treatment for a Koos IV VS.
Clinical Features: (Table 1)
Before GKS treatment, 16 (70%) patients presented with serviceable hearing, including 6 (26%) G&R Class 1 and 10 (43%) Class 2. All of the patients previously treated with GKS experienced hearing loss related to tumor growth. At the time of salvage surgery, none of the patient presented with serviceable hearing anymore.
Ten (43%) patients reported balanced instability, 10 (43%) presented with tinnitus, 2 (9%) with vertigo, and cerebellar ataxia in 4 cases (17%). Three (13%) patients presented symptoms related to hydrocephalus treated by ventriculoperitoneal shunting before GKS treatment. Trigeminal neuropathy with facial hypoesthesia was present in 13 (57%) patients. Five (22%) patients suffered from trigeminal neuralgia. Two patients (9%) presented preoperative facial weakness (HB Grade II, III).
Radiological Features: (Table 1)
At the time of the first stage GKS treatment, 1 patient harbored a Koos Grade I VS (4% - VS volume 0.3cc), 7 Koos Grade 2 VS (30% - mean VS volume 1.6cc), 10 Koos Grade 3 VS (44% - mean VS volume 2.5cc) and 5 Koos Grade IV VS (22% - mean VS volume 6.0cc).
At the time of salvage surgery, all patients harbored a Koos IV VS. The mean VS extrameatal diameter was 26 mm (range 19-39 / median 25 mm); the mean VS volume was 10 cc (range 4-22 / median 8 cc). Four of the tumors (17%) displayed a cystic component. Two (9%) patients presented radiological hydrocephalus (Evans ratio > 0.3); none had received CSF shunting before tumor resection (but three patients had received VP shunting that were placed before radiation).
Surgical Features: (Figures 2&3 - Table 1)
Nine (39%) patients underwent surgery via a translabyrinthine and 14 (61%) via a retrosigmoid approach. The mean operative time was 338 min (150-720); the translabyrinthine mean operative time was 479 min (370-720) vs 251 min (150-350) in the retrosigmoid group.
The tumor consistency was soft and lipidized in 13 cases (57% - Figure 2), whereas indurated in 10 (43%). As described in the radiological study, 4 of the tumors (17%) displayed a cystic component. Post-GKS arachnoiditis had been reported in 20 cases (87% - Figure 3). The tumor was highly vascularized in 8 cases (35%). A severe adhesion to the brainstem or cranial nerves was reported in 8 patients (35% - Figure 3).
The overall mean postoperative tumor volume measured on the first postoperative MRI was .56 cc (range .08 - 1.50 / median .52 cc). Two patients (9%) underwent GTR, 9 underwent near total resection (39%), 9 (39%) subtotal resection, and 3 (13%) partial resection.
Histopathological findings:
The irradiated VSs were histologically similar to the genuine ones. The Antoni A (areas composed of Schwann cells that have a spindle cell morphology) and Antoni B patterns (loosely textured and microcystic areas) were both represented as follows: 2 (9%) tumors showed pure Antoni A pattern, 15 (65%) tumors presented pure Antoni B pattern, while 6 (26%) tumors exhibited both Antoni A & B patterns. As a comparison, 25% of the guenine VSs showed pure Antoni A pattern, 43% presented pure Antoni B pattern, while 32% exhibited both Antoni A & B patterns.
As a reminder, 2 tumors operated on after GKS-failure were diagnosed as MNSTs (Malignant Nerve Sheath Tumors). Both patients have been excluded from the analysis
(Figure 1).
Complications:
One patient (4%) presented postoperative meningitis which was cured under medical treatment. One (4%) postoperative hematoma had been treated by revision surgery and external ventricular drain. This patient retained postoperative permanent CN VI paralysis. No CSF leak occurred and no patient required CSF shunting.
Cranial Nerve Preservation:
Trigeminal nerve:
The patients who displayed a preoperative facial numbness were released from this symptom in 12 cases (92%) after surgery, whereas the other one have improved. None of the patients freed from this symptom before surgery have developed a postoperative facial hypoesthesia.
Cochlear nerve:
None of the patients presented with preoperative serviceable hearing; none reported recovery after surgery.
Facial nerve function: (Table 2)
Immediately after surgery, among the 21 patients with normal preoperative FN function, 19 (90%) retained a good FN function (HB Grades I & II), 1 (5%) displayed an intermediate FN function (HB Grade III), and 1 (5%) a poor FN function (cf. Table 2). No patient exhibited a delayed FN palsy.
At last follow-up examination, good HB Grade I & II FN function was observed in 20 patients (95%). Only one patient (5%) presented moderate deficit (HB Grade III). (cf. Table 2). Exposure keratitis occurred in 4 cases (17%). None of the patients secondarily treated by GKS presented FN deterioration in the long term.
Tumor Control:
The overall mean radiological follow-up was 74 months (range 12-175 / median 64 months). Thirteen patients (54%) were scanned for more than 5 years. Of the 21 patients who had undergone non-total resection of their VS, 11 (52%) had been allocated into a Wait-&-rescan policy and 10 (48%) underwent upfront GKS. The tumor control was achieved in 91% of cases. Two (9%) cases of regrowth were diagnosed during the follow-up period, respectively at 32 and 68 months. The 1-, 5- & 7-year tumor progression free survival (PFS) were 100% (n=23), 95% (n=18) & 85% (n=9), respectively.
During the follow-up period, 2 patients displayed pseudoprogression of their tumor remnants. The first one experienced a secondary regression to the postoperative tumor volume within 107 months, while the remnant of the second one remains >20% than the postoperative tumor volume at the time of analysis, and is therefore defined as regrowth.
Both patients harboring growing residues have been allocated under repeated MRI surveillance without additional treatment. None of the patient who received salvage surgery after a first-stage GKS required a second revision surgery.
Comparison to the genuine VSpopulation: (Figure 4 - Table 2, 3 & 4)
During the study period, 170 patients had undergone microsurgical resection for a large Koos IV VS. The GKS-failure and genuine VS groups differed in sex ratio, age and preoperative VS volume (p<.05) (cf Table 3).
The mean operative time was similar to the GKS-failure population (473 min – p=.93 and 265 min – p=.85, respectively after translabyrinthine and retrosigmoid approaches). The mean postoperative tumor residue was .62cc (median .41cc – p=.70). There was no difference in the occurrence of postoperative complications in the GKS-failure and genuine VS populations (p=.82).
At last follow-up examination, among the 160 patients with normal preoperative FN function, good FN function (HB Grade I & II) was observed in 134 patients (84%), moderate HB Grade III deficit in 25 (15%) of patients, while poor FN outcome were observed in one case (1%) (Table 2). Salvage surgery after GKS failure was not associated to early postoperative (p=.14), three months postoperative (p=.10), nor long-term (p=.25) impaired FN outcomes.
The overall mean radiological follow-up was 63 months (range 12-186 / median 55 months) in the genuine VS population (p=.34). Of the 155 patients who had undergone non-total resection of their VS, 89 (57%) had been allocated into a Wait-&-rescan policy and 66 (43%) underwent upfront GKS. The 1-, 5- & 7-year tumor progression free survival (PFS) were 97% (n=154), 81% (n=66) & 80% (n=49), respectively (Table 4). The tumor control was achieved in 83% of cases. Twenty-seven (17%) cases of regrowth were diagnosed during the FU period. Again, the GKS-failure population did not seem to be related to a higher rate of regrowth of the residues (p=.27 - Figure 4).