Comparing the sensitivity of linear and volumetric MRI measurements to detect changes in the size of vestibular schwannomas in patients with neurofibromatosis type 2 on bevacizumab treatment

Stereotactic Radiosurgery and Radiotherapy for Vestibular Schwannoma in NF2-Related Schwannomatosis

OBJECTIVES

To determine the long-term control rates and hearing outcomes for growing vestibular schwannoma in NF2-related schwannomatosis (NF2) treated with stereotactic radiosurgery (SRS) and fractionated radiotherapy (FRT).

METHODS

Retrospective review of all patients treated with SRS/FRT between 1986 and2021 from a tertiary NF2 unit. Overall tumor control was defined as: (1) growth control (growth failure was defined as growth in any dimension of 3 millimetres or more from baseline post-SRS/FRT), and (2) treatment control (no need for further intervention). Loss of serviceable hearing was defined as a drop in speech discrimination score below 50% after SRS/FRT.

RESULTS

There were 81 cases, with a mean duration of follow-up of 125 months. Overall control rate was 72% (58/81), with 80% (65/81) growth control and 74% (60/81) treatment control. There was a 5-year actuarial survival of 77% and 10-year survival of 71%. Forty-three percent (30/69) of cases did not have serviceable hearing at baseline. Of those remaining, 49% (19/39) preserved serviceable hearing during follow-up at a mean of 106 months. Actuarial survival for preservation of serviceable hearing at 5 and 10 years was 69% and 53%. There were poorer outcomes with increasing genetic severity, and with baseline tumor size >3 cm. No cases of SRS/FRT-related malignancy were identified at a mean follow-up of 10 years.

CONCLUSION

Stereotactic radiosurgery/fractionated radiotherapy are an effective option to treat growing vestibular schwannoma in patients with NF2 with the potential for hearing preservation in a proportion of patients.

LEVEL OF EVIDENCE

4-Case Series Laryngoscope, 134:2364-2371, 2024.

Prevalence and natural history of schwannomas in neurofibromatosis type 2 (NF2): the influence of pathogenic variants

This study explores the natural history of vestibular, trigeminal and lower cranial nerve schwannomas (VS, TS, LCNS) in patients with Neurofibromatosis type 2 (NF2), to understand how pathogenic variants (PVs) of the NF2 gene affect tumour burden and growth rate, via a retrospective analysis of a UK NF2 centre database and imaging. VS, TS and LCNS location and size were measured in accordance with a standardised protocol. PVs were categorised in accordance with the UK NF2 Genetic Severity Score (GSS). 153 patients (age 5-82) had 458 schwannomas, of which 362 were previously untreated comprising: 204 VS, 93 TS, and 65 LCNS (IX, X, XI). 322 schwannomas had sequential imaging allowing growth rate analysis with a mean follow-up of 45 months. VS were universally present, and bilateral in 146/153 cases. 65% of tumours grew >2 mm during the study period at mean rate 2.0 mm/year. Significant association was found between increasing GSS and growth rate. TS occurred in 66/153 patients (bilateral in 27/153); 31% of tumours showed growth (mean 1.8 mm/yr). Significant increase in tumour prevalence was noted with increasing GSS. LCNS were found in 47/153 patients (bilateral in 19/153); 27% of tumours showed growth (mean 1.9 mm/yr). The trend for increased prevalence with increasing GSS did not reach significance. VS growth rate was significantly influenced by GSS and they were much more likely to grow than TS and LCNS. TS prevalence also correlated with increasing GSS.

Imaging of the Vestibular Schwannoma: Diagnosis, Monitoring, and Treatment Planning

Appropriate imaging strategies for the detection, treatment planning, and posttreatment monitoring of vestibular schwannomas will be discussed. The typical and variant imaging appearances of vestibular schwannomas, as well as the imaging features that should prompt consideration of differential diagnoses, will be illustrated. Understanding the natural history of vestibular schwannomas, optimal measurement and definition of tumour growth helps the radiologist evaluate for the failure of conservative management and requirement for surgery or radiotherapy. In order to determine the success of conservative management, the radiologist is required to understand the natural history of vestibular schwannomas and how tumour growth is defined. Finally, the imaging features which help guide appropriate treatment with surgery or radiotherapy will be highlighted, and the expected posttreatment imaging changes will be described.

A Comparison of Repeatability and Usability of Semi-Automated Volume Segmentation Tools for Measurement of Vestibular Schwannomas

OBJECTIVE

Semi-automated volume segmentation tools (SAVST) offer a less time consuming technique compared with manual volume segmentation method. No data exists to suggest which of the available applications are optimal for use with vestibular schwannomas (VS). This study aims to compare repeatability and usability of three different SAVST for measurement of VS.

STUDY DESIGN

Experimental comparison of three SAVST.

SETTING

Tertiary skull base unit.

PATIENTS

Twenty-four patients with a unilateral VS imaged with T1-weighted Gadolinium enhanced MRI.

INTERVENTION

Repeated measurements made to determine intra and inter-observer agreement. This was repeated using three different SAVST.

MAIN OUTCOME MEASURES

1) Intra- and inter-observer intraclass correlation coefficients (ICC), repeatability coefficients (RC), and relative smallest detectable differences (%SDD).2) Usability as determined by the mean number of steps and time required per tumor measurement and the proportion of cases where manual editing was required.

RESULTS

Intra-observer ICCs were significantly better for SliceOmatic and OleaSphere than AW VolumeShare (0.998 versus 0.994, p < 0.05). Inter-observer ICCs were also better for SliceOmatic (0.994) and OleaSphere (0.989) compared with AW VolumeShare (0.976), however, this was only significant for SliceOmatic (p = 0.012). SliceOmatic had a poorer usability profile requiring more manual editing, time, and individual steps per measurement but its "watershed segmentation" algorithm was better at measuring cystic or heterogenous tumors.

CONCLUSIONS

This is the first study to compare three SAVST for measurement of VS. While SliceOmatic had the highest repeatability, Olea Sphere combined comparable repeatability with improved usability and a greater degree of automation and was, therefore, deemed optimal for use in routine clinical practice.

A comparison of semi-automated volumetric vs linear measurement of small vestibular schwannomas

Objective

Accurate and precise measurement of vestibular schwannoma (VS) size is key to clinical management decisions. Linear measurements are used in routine clinical practice but are prone to measurement error. This study aims to compare a semi-automated volume segmentation tool against standard linear method for measuring small VS. This study also examines whether oblique tumour orientation can contribute to linear measurement error.

Study design

Experimental comparison of observer agreement using two measurement techniques.

Setting

Tertiary skull base unit.

Participants

Twenty-four patients with unilateral sporadic small (< 15 mm maximum intracranial dimension) VS imaged with 1 mm-thickness T1-weighted Gadolinium enhanced MRI.

Main outcome measures

(1) Intra and inter-observer intraclass correlation coefficients (ICC), repeatability coefficients (RC), and relative smallest detectable difference (%SDD). (2) Mean change in maximum linear dimension following reformatting to correct for oblique orientation of VS.

Results

Intra-observer ICC was higher for semi-automated volumetric when compared with linear measurements, 0.998 (95% CI 0.994–0.999) vs 0.936 (95% CI 0.856–0.972), p < 0.0001. Inter-observer ICC was also higher for volumetric vs linear measurements, 0.989 (95% CI 0.975–0.995) vs 0.946 (95% CI 0.880–0.976), p = 0.0045. The intra-observer %SDD was similar for volumetric and linear measurements, 9.9% vs 11.8%. However, the inter-observer %SDD was greater for volumetric than linear measurements, 20.1% vs 10.6%. Following oblique reformatting to correct tumour angulation, the mean increase in size was 1.14 mm (p = 0.04).

Conclusion

Semi-automated volumetric measurements are more repeatable than linear measurements when measuring small VS and should be considered for use in clinical practice. Oblique orientation of VS may contribute to linear measurement error.

Volumetric analysis of olfactory neuroblastoma skull base laterality and implications on neck disease

OBJECTIVE

To determine if the laterality of primary tumors in patients with olfactory neuroblastoma (ONB) influenced the pattern and development of neck disease.

METHODS

Using a retrospective cohort study design from 1994 to 2015, the primary tumors of patients who either presented with or developed neck disease were volumetrically analyzed using iPlan software (version 3.0.0, BrainLAB, Feldkirchen, Germany) by two independent observers. Agreement of volume-derived sidedness was assessed with a kappa statistic, whereas agreement in volume-derived degree of tumor laterality was evaluated with an intraclass correlation coefficient. A one-sample t test was used to assess the difference in dominant percentage between the two observers.

RESULTS

Sixty-one patients with histological diagnosis and treatment of ONB at our institution were identified. Twenty-four patients exhibited neck involvement, 13 of whom could be volumetrically analyzed. Tumors that were greater than 75% eccentric to one side all exhibited contralateral disease, whereas the majority of unilateral neck disease was associated with relatively midline masses. Within the entire cohort, ipsilateral level 2 lymph nodes displayed the highest involvement (83%, 20 of 24), followed by ipsilateral level 1 (54%, 13 of 24), contralateral level 2 (46%, 11 of 24), contralateral level 1 (21%, 5 of 24), and ipsilateral level 3 (21%, 5 of 24).

CONCLUSION

Ipsilateral neck involvement frequently was observed; however, the degree of ONB primary site laterality did not appear to have implications on the development of contralateral neck disease. Therefore, when considering elective therapy to the neck, ONB laterality should not be used to justify unilateral neck treatment.

LEVEL OF EVIDENCE

4. Laryngoscope, 128:864-870, 2018.