Iwao Yamakami

Transient expansion of vestibular schwannoma following stereotactic radiosurgery

OBJECT The authors prospectively analyzed volume changes in vestibular schwannomas (VSs) after stereotactic radiosurgery. METHODS One hundred consecutive patients with unilateral VS treated with Gamma Knife surgery (GKS) at Chiba Cardiovascular Center between 1998 and 2006 were analyzed in this study. For each lesion the Gd-enhanced volume was measured serially every 3 months in the 1st year, then every 6 months thereafter, using volumetric software. The frequency and degree of transient tumor expansion were documented and possible prognostic factors were analyzed. Concurrently, neurological deterioration involving trigeminal, facial, and cochlear nerve functions were also assessed. RESULTS The mean observation period was 65 months (range 25-100 months). There were 32 men and 68 women, whose mean age was 59.1 years (range 29-80 years). Tumor volumes at GKS averaged 2.7 cm3 (range 0.1-13.2 cm3), and the lesions were irradiated at the mean 52.2% isodose line for the tumor margin (range 50-67%), with a mean dose of 12.2 Gy (range 10.5-13 Gy) at the periphery. The tumor volume was increased by 23% at 3 months and 27% at 6 months. Tumors shrank to their initial size over a mean period of 12 months. The maximum volume increase was < 10% (no significant increase) in 26 patients, 10-30% in 23, 30-50% in 22, 50-100% in 16, and > 100% in 13. The peak tumor expansion averaged 47% (range 0-613%). A high-dose (> or = 3.5 Gy/min) treatment appears to be the greatest risk factor for transient tumor expansion, although the difference did not reach statistical significance. Transient facial palsy and facial dysesthesia correlated strongly with tumor expansion, but only half of the hearing loss was coincident with this phenomenon. CONCLUSIONS Transient expansion of VSs after GKS was found to be much more frequent than previously reported, strongly suggesting a correlation with deterioration of facial and trigeminal nerve functions.

Retrosigmoid removal of small acoustic neuroma: curative tumor removal with preservation of function

OBJECT Management of small acoustic neuromas (ANs) consists of 3 options: observation with imaging follow-up, radiosurgery, and/or tumor removal. The authors report the long-term outcomes and preservation of function after retrosigmoid tumor removal in 44 patients and clarify the management paradigm for small ANs. METHODS A total of 44 consecutively enrolled patients with small ANs and preserved hearing underwent retrosigmoid tumor removal in an attempt to preserve hearing and facial function by use of intraoperative auditory monitoring of auditory brainstem responses (ABRs) and cochlear nerve compound action potentials (CNAPs). All patients were younger than 70 years of age, had a small AN (purely intracanalicular/cerebellopontine angle tumor ≤ 15 mm), and had serviceable hearing preoperatively. According to the guidelines of the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology-Head and Neck Surgery Foundation, preoperative hearing levels of the 44 patients were as follows: Class A, 19 patients; Class B, 17; and Class C, 8. The surgical technique for curative tumor removal with preservation of hearing and facial function included sharp dissection and debulking of the tumor, reconstruction of the internal auditory canal, and wide removal of internal auditory canal dura. RESULTS For all patients, tumors were totally removed without incidence of facial palsy, death, or other complications. Total tumor removal was confirmed by the first postoperative Gd-enhanced MRI performed 12 months after surgery. Postoperative hearing levels were Class A, 5 patients; Class B, 21; Class C, 11; and Class D, 7. Postoperatively, serviceable (Class A, B, or C) and useful (Class A or B) levels of hearing were preserved for 84% and 72% of patients, respectively. Better preoperative hearing resulted in higher rates of postoperative hearing preservation (p = 0.01); preservation rates were 95% among patients with preoperative Class A hearing, 88% among Class B, and 50% among Class C. Reliable monitoring was more frequently provided by CNAPs than by ABRs (66% vs 32%, p < 0.01), and consistently reliable auditory monitoring was significantly associated with better rates of preservation of useful hearing. Long-term follow-up by MRI with Gd administration (81 ± 43 months [range 5-181 months]; median 7 years) showed no tumor recurrence, and although the preserved hearing declined minimally over the long-term postoperative follow-up period (from 39 ± 15 dB to 45 ± 11 dB in 5.1 ± 3.1 years), 80% of useful hearing and 100% of serviceable hearing remained at the same level. CONCLUSIONS As a result of a surgical technique that involved sharp dissection and internal auditory canal reconstruction with intraoperative auditory monitoring, retrosigmoid removal of small ANs can lead to successful curative tumor removal without long-term recurrence and with excellent functional outcome. Thus, the authors suggest that tumor removal should be the first-line management strategy for younger patients with small ANs and preserved hearing.

Life-Threatening Intracranial Hypotension after Skull Base Surgery with Lumbar Drainage.

Although lumbar drainage (LD) is widely used in skull base surgery (SBS), no cases with intracranial hypotension (IH) following LD-assisted SBS have been reported, and skull base surgeons lack awareness of this potentially life-threatening condition. We report two cases of IH after LD-assisted SBS, a spheno-orbital meningioma and an osteosarcoma in the orbit. Despite a minimal amount of cerebrospinal fluid (CSF) drainage and early LD removal, severe postural headache and even a deteriorating consciousness level were observed in the early postoperative course. Neuroimages demonstrated epidural fluid collections, severe midline shift, and tonsillar sag compatible with IH. Epidural blood patch (EBP) immediately and completely reversed the clinical and radiologic findings in both patients. IH should be included in the differential diagnosis of postural headache after LD-assisted SBS that can be managed successfully with EBP. Persistent leakage of CSF at the LD-inserted site leads to IH. Broad dural dissection and wide removal of bony structure may be involved in the midline shift. EBP should be performed soon after conservative management fails. Further reports will determine the risk factors for IH development following LD-assisted SBS.