Iatrogenic Impairment of Hearing During Surgery for Acoustic Neuroma

Isolated or combined labyrinthine, neural, and vascular damage account for failure to preserve hearing during removal of acoustic neuromas. However, the specific mechanisms of auditory impairment remain unclear unless surgical maneuvers can be related to peri- and postoperative hearing on the basis of intraoperative monitoring of auditory function.

Among the different auditory monitoring techniques, recording of cochlear nerve action potentials (CNAPs) from the intracranial portion of the nerve has proven particularly useful for identifying the mechanisms of iatrogenic auditory injury.

The present investigation analyzes intra- and postoperative auditory impairment in relation to surgical steps in a group of 38 subjects with acoustic neuroma (size ranging from 5 to 24 mm) undergoing removal via a retrosigmoid approach.

Coagulation close to the cochlear nerve, drilling of the internal auditory canal, and removal of the intrameatal portion of the acoustic neuroma have prove to be the most critical surgical steps in hearing preservation.

Changes were correlated with intra- and extrameatal tumor size, the relationship between the internal auditory canal and vestibule, and internal auditory canal enlargement, anatomic involvement of the cochlear nerve, preoperative auditory level, and ABR and ENG test findings.

Changes in CNAP morphology and latency are detailed, and mechanisms of injury are analyzed and discussed as a function of these variables.

     

Vestibular Neurectomy and Microvascular Decompression of the Cochlear Nerve in Meniere's Disease

Vestibular neurectomy (VN) results in a high success rate in the control of vertigo in Meniere's disease, although the subsequent fate of auditory function is fairly unpredictable. The present investigation reports the postoperative results obtained in a group of 30 subjects with a clinical diagnosis of Meniere's disease and vascular cross-compression of cranial nerve VIII. All subjects underwent VN using a retrosigmoid approach, and in half of them microvascular decompression (MVD) of the cochlear nerve with interposition of autogenous muscle was performed at the same time. All patients had complete relief from vertigo. Hearing was significantly improved in the VN-MVD group (46.7% of subjects). In this group tinnitus and aural fullness also improved significantly, with values of 62.6% and 66.6%, respectively.     

Preparation and local anaesthetic activity of benzotriazinone and benzoyltriazole derivatives

Two sets of benzotriazinone and benzoyltriazole derivatives were prepared and tested for local anaesthetic activity in comparison with lidocaine. Several of the prepared compounds exhibited a fairly good activity comparable or superior to that of lidocaine. The presence of a benzotriazinone or a benzoyltriazole moiety as an aromatic system was quite profitable for both the intensity and duration of activity. The acute toxicity in mice of the four most potent compounds of the series was also assessed. Compound 1b, which has an anaesthetic activity comparable to that of lidocaine, was also characterized by a more favourable therapeutic index. All compounds were tested in vitro to evaluate their negative chronotropic action in isolated rat right atria.     

Continuous retrograde monitoring of the facial nerve: preliminary experience during acoustic neuroma surgery

Continuous electromyographical (EMG) monitoring of the facial nerve is widely used during acoustic tumor surgery. Mechanical stimulation of the facial nerve is capable of eliciting synchronous and asynchronous EMG responses alerting the surgeon to damaging maneuvers performed on the nerve. Mechanical stimulation, however, elicits EMG responses only when the nerve has been injured by the underlying pathology or previous surgical maneuvers, and the technique is sensitive to administration of muscular blockers. In addition, EMG is unable to furnish quantitative information about the damage. The present paper illustrates an alternative technique for intraoperative facial nerve monitoring, that is, the recording of facial nerve antidromic potentials (FNAPs).Eleven subjects operated on by acoustic neuroma surgery via a retrosigmoid approach (tumor sizes ranging from 12 to 28 mm) participated in the investigation. Bipolar electrical stimulation of the marginalis mandibulae was performed to elicit FNAPs. Stimulus intensity ranged from 2 to 6 mA with a delivery rate of 7/second. A silver-wire electrode positioned on the proximal portion of the acoustic-facial bundle was used to record action potentials. Changes in latency and amplitude of FNAPs were analyzed as a function of the main surgical steps. FNAP monitoring provided quantitative real-time information about damaging maneuvers performed on the nerve and allowed prediction of postoperative facial function.     

Continuous retrograde monitoring of the facial nerve during cerebellopontine angle surgery: normative data

An alternative technique for the continuous monitoring of the facial nerve, monopolar recording of facial nerve antidromic potentials (FNAPs), on 10 subjects undergoing retrosigmoid vestibular neurectomy for Meniere's disease is described. To elicit FNAPs bipolar electrical stimulation of the marginalis mandibulae was performed. Stimulus intensity ranged from 0 to 10 mA with a delivery rate of 7/second. Antidromic potentials were recorded with a silver wire monopolar electrode positioned intracranially on the proximal portion (root entry zone) of the acoustic-facial bundle. Bipolar recordings with two silver electrodes were also performed from different nerves in the cerebellopontine angle to define the specific origin of the action potentials. FNAP. amplitude increased as a function of stimulus intensity. The average latency was 3.35 milliseconds (range 3.0 to 3.7 ms). Action potentials recorded intracranially during electrical stimulation of the marginal nerve originated specifically from the facial nerve. FNAP recording is therefore a promising technique for the continuous intraoperative monitoring of the facial nerve during cerebellopontine angle surgery.     

Is the alpha-beta ratio of prostate cancer really low? A prospective, non-randomized trial comparing standard and hyperfractionated conformal radiation therapy.

BACKGROUND AND PURPOSE: The objectives of the current study were to compare genito-urinary (GU) and gastro-intestinal (GI) toxicities as well as biochemical control (bRFS) in prostate cancer, utilizing conventional (2.0 Gy daily) (STD) or hyperfractionated (HFX) conformal irradiation (CRT). HFX (1.2 Gy BID) was chosen as a radiobiological method to try to reduce long term sequelae without compromising local control. PATIENTS AND METHODS: Three-hundred-and-seventy consecutive patients (pts) entered this prospective, non-randomized trial in the period January 1993-January 2003; 209 were treated with STD and 161 with HFX CRT. All were evaluable for acute toxicity analysis, 179 (STD) and 151 pts (HFX) being evaluable for late sequelae and bRFS analyses. Pt characteristics were not statistically different in the two groups. CRT consisted of a 4-field technique for prostate and/or pelvic nodes and a 5-field boost with rectal shielding. Median doses were 74 and 79.2 Gy for STD and HFX patients respectively, the latter dose being isoeffective for tumour control assuming alpha/beta=10 (EQD(2)=73.9 Gy). Median follow-up was 29.4 months (25.2 mos for STD; 37.7 mos for HFX; P<0.01). The two regimens were compared in terms of acute and late GU and GI toxicities and 5-year bRFS by univariate and multivariate analyses. RESULTS: Acute grade> or =2 GU toxicity was higher in the STD group (48.6% versus 37.3% in HFX, P=0.03), while no significant difference was found for acute GI toxicity. Late grade> or =2 GU and GI toxicities were lower in the HFX group (5-year actuarial rate: GU: 10.1% versus 20.3%, P=0.05; GI: 6.0% versus 10.6%, P=0.18). Five-year bRFS were 70% (+/-13.8%, 95% CI) and 82.6% (+/-7.2%) for STD and HFX, respectively (P=0.44); a trend favouring HFX was found in the subgroup of pts who did not receive hormonal therapy (5-year bRFS: 85.9%+/-12.4% versus 63.9%+/-23.8%, P=0.15). Multivariate analysis revealed only risk groups and age statistically related to bRFS but not fractionation regimen. Using the Nahum-Chapman TLCP model and prostate parameter set, which includes hypoxia, the TLCPs are approximately equal for the two regimens, whereas assuming alpha/beta=1.5 and no hypoxia we obtain 73% for the STD group but only 36% for the HFX group. CONCLUSIONS: As expected from radiobiological considerations, HFX reduces GI and GU late toxicities. Concerning early bRFS, our clinical findings suggest that HFX is no less effective than STD when delivering an isoeffective (alpha/beta=10) dose. Despite the relatively short follow-up, this result appears to be inconsistent with a low alpha/beta ratio for prostate cancer.     

Dose–volume and biological-model based comparison between helical tomotherapy and (inverse-planned) IMAT for prostate tumours

BACKGROUND AND PURPOSE: Helical tomotherapy (HT) and intensity-modulated arc therapy (IMAT) are two arc-based approaches to the delivery of intensity-modulated radiotherapy (IMRT). Through plan comparisons we have investigated the potential of IMAT, both with constant (conventional or IMAT-C) and variable (non-conventional or IMAT-NC, a theoretical exercise) dose-rate, to serve as an alternative to helical tomotherapy. MATERIALS AND METHODS: Six patients with prostate tumours treated by HT with a moderately hypo-fractionated protocol, involving a simultaneous integrated boost, were re-planned as IMAT treatments. A method for IMAT inverse-planning using a commercial module for static IMRT combined with a multi-leaf collimator (MLC) arc-sequencing was developed. IMAT plans were compared to HT plans in terms of dose statistics and radiobiological indices. RESULTS: Concerning the planning target volume (PTV), the mean doses for all PTVs were similar for HT and IMAT-C plans with minimum dose, target coverage, equivalent uniform dose (EUD) and tumour control probability (TCP) values being generally higher for HT; maximum dose and degree of heterogeneity were instead higher for IMAT-C. In relation to organs at risk, mean doses and normal tissue complication probability (NTCP) values were similar between the two modalities, except for the penile bulb where IMAT was significantly better. Re-normalizing all plans to the same rectal toxicity (NTCP=5%), the HT modality yielded higher TCP than IMAT-C but there was no significant difference between HT and IMAT-NC. The integral dose with HT was higher than that for IMAT. CONCLUSIONS: with regards to the plan analysis, the HT is superior to IMAT-C in terms of target coverage and dose homogeneity within the PTV. Introducing dose-rate variation during arc-rotation, not deliverable with current linac technology, the simulations result in comparable plan indices between (IMAT-NC) and HT.     

Moderately Hypofractionated Helical IMRT,FDG–PET/CT-guided,for Progressive Malignant Pleural Mesothelioma in Patients With Intact Lungs

Introduction

The objective of this study was to present the outcomes of moderately hypofractionated helical intensity-modulated radiation therapy (HT) with/without simultaneous integrated boost (SIB) on fluorodeoxyglucose-positron emission tomography (FDG-PET) positive areas (gross tumor volume [GTV]-PET) for patients with progressive malignant pleural mesothelioma (MPM) after previous treatments.